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Sample records for aligned nematic liquid

  1. Photoluminescence analysis of self induced planer alignment in azo dye dispersed nematic liquid crystal complex

    International Nuclear Information System (INIS)

    We have developed azo dye doped nematic liquid crystal complex for advanced photonic liquid crystal display technology aspects. Disperse orange azo dye self introduced planer alignment in the nematic liquid crystal without any surface anchoring treatment. Planer alignment was characterized by optical polarizing microscopy. The electro-optical switching response of dye disperse planer aligned nematic cell was investigated as a function of applied voltage with the help of photoluminescence spectrophotometer for the tuning of photoluminescence contrast

  2. Multiple alignment modes for nematic liquid crystals doped with alkylthiol-capped gold nanoparticles.

    Science.gov (United States)

    Qi, Hao; Hegmann, Torsten

    2009-08-01

    The ability of alkylthiol capped gold nanoparticles (Au NPs) to tune, alter, and reverse the alignment of nematic liquid crystals (LCs) has been investigated in detail. Adjusting the concentration of the suspended Au NPs in the nematic LC host, optimizing the sample preparation protocol, or providing different sample substrates (untreated glass slides, rubbed polyimide-coated LC test cell, or ITO-coated glass slides) results in several LC alignment scenarios (modes) including vertical alignment, planar alignment, and a thermally controlled alignment switch between these two alignment modes. The latter thermal switch between planar and homeotropic alignment was observed particularly for lower concentrations (i.e., around 1 to 2 wt %) of suspended NPs in the size regime of 1.5-2 nm and was found to be concentration-dependent and thermally reversible. Different scenarios are discussed that could explain these induced alignment modes. In one scenario, the NP-induced alignment is related to the temperature-dependent change of the order parameter, S, of the nematic phase (ordering in the bulk). In the second scenario, a change of the ordering of the nematic molecules around the NPs that reside at the interfaces is described. We also started to test spin coating as an alternative way of preparing nematic thin films with well-separated Au NPs on the substrate and found this to be a possible method for manufacturing of future NP-doped LC devices, as this method produced evenly distributed NPs on glass substrates. Together the presented findings continue to pave the way for LC display-related applications of Au NP-doped nematic LCs and provide insights for N-LC sensor applications. PMID:20355789

  3. Convection in a nematic liquid crystal with homeotropic alignment and heated from below

    Energy Technology Data Exchange (ETDEWEB)

    Ahlers, G. [Univ. of California, Santa Barbara, CA (United States)

    1995-12-31

    Experimental results for convection in a thin horizontal layer of a homeotropically aligned nematic liquid crystal heated from below and in a vertical magnetic field are presented. A subcritical Hopf bifurcation leads to the convecting state. There is quantitative agreement between the measured and the predicted bifurcation line as a function of magnetic field. The nonlinear state near the bifurcation is one of spatio-temporal chaos which seems to be the result of a zig-zag instability of the straight-roll state.

  4. Theoretical analysis of nanoparticle-induced homeotropic alignment in nematic liquid crystals

    CERN Document Server

    Choudhary, Amit; Li, Guoqiang

    2015-01-01

    A theoretical analysis of homeotropic alignment induced by nanoparticles (NPs) in a nematic liquid crystal (NLC) sample cell is presented. It is found that such alignment on the surface of a NP causes a change in the orientation of the molecular director near the surface, which in turn induces variations in the elastic constants and free energy. The induced NLC properties allow coupling between nearby NPs, mediated by the NLC molecules. The rotation of the coupled NPs close to the substrate tends to induce a long-range orientation of the NLC molecular director, leading to modification in the alignment at the interface of NLC and substrate which induces the orientation from homogeneous (planar) to homeotropic (vertical) in the bulk material.

  5. Nematic liquid crystalline alignment on graphitic carbon film surfaces and its electrooptical characteristics

    Science.gov (United States)

    Nakagaki, Takamitsu; Yamada, Kenji; Nakamura, Atsushi; Temmyo, Jiro; Kubono, Atsushi

    2015-09-01

    A graphitic carbon (g-C) film directly grown on a synthetic quartz glass substrate was applied to a liquid crystal (LC) device as an alignment layer combined with a transparent electrode for a demonstration of high performance. The as-grown g-C films showed a nanometer-size domain with 91.6% transmittance at 550 nm and with a sheet resistance of 5.9 kΩ/sq. The nanodomain of the g-C film surface was associated with a random orientation of the twisted nematic LC (4-pentyl-4‧-n-cyanobiphenyl, 5CB) molecules in an in-plane randomly parallel alignment that was analyzed by polarized optical microscopy (POM). We also demonstrated an LC display (LCD) in an in-plane random hybrid twisted nematic (IPR-HTN) configuration using the g-C films compared with a previously proposed configuration using a hydroxypropyl cellulose (HPC) sublayer and a TN configuration using a polyimide film with a rubbing treatment. It was found that the combined g-C alignment layer/electrode provides a low turn-on voltage, a fast response, and a wide viewing angle as an orientation sublayer and an electrode.

  6. Miscibility and alignment effects of mixed monolayer cyanobiphenyl liquid-crystal-capped gold nanoparticles in nematic cyanobiphenyl liquid crystal hosts.

    Science.gov (United States)

    Qi, Hao; Kinkead, Brandy; Marx, Vanessa M; Zhang, Huai R; Hegmann, Torsten

    2009-06-01

    Against the rule: Liquid crystal hosts (5CB and 8CB) are doped with different thiol decorated gold nanoparticles (see figure). The "simple" hexanethiol and dodecanethiol capped nanoparticles (Au1 and Au2) are more compatible to the nematic cyanobiphenyl liquid crystals than nanoparticles capped simultaneously with alkylthiols and a nematic cyanobiphenyl thiol (Au3 and Au4).This study focuses on the miscibility of liquid crystal (LC) decorated gold nanoparticles (NPs) in nematic LCs. To explore if LC functional groups on the gold NP corona improve the compatibility (miscibility) with structurally related LC hosts, we examined mixtures of two LC hosts, 5CB and 8CB, doped at 5 wt % with different types of gold NPs. Four alkanethiol-capped NPs were synthesized; two homogeneously coated with alkanethiols (Au1 with C(6)H(13)SH and Au2 with C(12)H(25)SH), and two that were additionally capped at a different ratio with a mesogenic cyanobiphenyl end-functionalized alkanethiol HS10OCB (C(6)H(13)SH + HS10OCB for Au3 and C(12)H(25)SH + HS10OCB for Au4). Investigating these mixtures in the bulk for settling of the NPs, and in thin films using polarized optical microscopy (POM) between untreated glass slides as well as POM studies and electro-optic tests in planar ITO/polyimide test cells, reveal that the alkanethiol capped NPs Au1 and Au2 are more compatible with the two polar cyanobiphenyl hosts in comparison to the NPs decorated with the cyanobiphenyl moieties. All NPs induce homeotropic alignment in 5CB and 8CB between untreated glass slides, with Au1 and Au2 showing characteristic birefringent stripes, and Au3 and A4 exhibiting clear signs of aggregation. In rubbed polyimide cells, however, Au3 and Au4 fail to induce homeotropic alignment and show clear signs of macroscopic aggregation. PMID:19334026

  7. Effects of polymers on the rotational viscosities of nematic liquid crystals and dynamics of field alignment

    International Nuclear Information System (INIS)

    Many of the important physical phenomena exhibited by the nematic phase, such as its unusual flow properties and its responses to the electric and the magnetic fields, can be discussed regarding it as a continous medium. The Leslie-Erickson dynamic theory has the six dissipative coefficients from continuum model of liquid crystal. Parodi showed that only five of them are independent, when Onsagar's reciprocal relations are used. One of these, which has no counterpart in the isotropic liquids, is the rotational viscosity co-efficient, γ1. The main objective of this project is to study the rotational viscosities of selected micellar nematic systems and the effect of dissolved polymers in micellar and thermotropic liqud crystals. We used rotating magnetic field method which allows one to determine γ1 and the anisotropic magnetic susceptibility, χa. For the ionic surfactant liquid crystals of SDS and KL systems used in this study, the rotational viscosity exhibited an extraordinary drop after reaching the highest values γ1 as the temperature was lowered. This behavior is not observed in normal liquid crystals. But this phenomena can be attributed to the existence of nematic biaxial phase below the rod-like nematic Nc phase. The pretransitional increase in γ1 near the disk-like nematic to smectic-A phase transition of the pure CsPFO/H2O systems are better understood with the help of mean-field models of W.L. McMillan. He predicted a critical exponent ν = 1/2 for the divergence of γ1. The polymer (PEO, molecular weight = 105) dissolved in CsPFO/H2O system (which has 0.6% critical polymer concentration), suppressed the nematic to lamellar smectic phase transition in concentrated polymer solutions (0.75% and higher). In dilute polymer solutions with lower than 0.3% polyethylene-oxide, a linear increase of γ1 is observed, which agrees with Brochard theory

  8. The effect of initial alignment on the optical properties of Fe3O4 nanoparticles doped in nematic liquid crystals

    International Nuclear Information System (INIS)

    Recently the nonlinear effects of the different materials doped liquid crystals are more interesting. In all previous works, nonlinearity of samples with the homeotropic alignment is investigated because of the larger component of the refractive index in this direction. Here, there are spherical Fe3O4 nanoparticles that have both parallel and perpendicular components. We were looking for the effect of initial alignment on the nonlinearity of pure and doped nematic liquid crystals (NLCs). The experimental results emphasize, even the same compositional percentage of nanoparticles prepared by two different alignment configurations are showing different results when dispersed in the same NLCs. Comparing nonlinear studies, the magnitude of nonlinear refraction index, n2 and nonlinear absorption coefficient, β increase 102 and 101 times, respectively, in homeotropic alignment samples and the sign of these parameters is changed rather than homogeneous ones

  9. Nematic liquid crystal bridges

    Science.gov (United States)

    Doss, Susannah; Ellis, Perry; Vallamkondu, Jayalakshmi; Danemiller, Edward; Vernon, Mark; Fernandez-Nieves, Alberto

    We study the effects of confining a nematic liquid crystal between two parallel glass plates with homeotropic boundary conditions for the director at all bounding surfaces. We find that the free surface of the nematic bridge is a surface of constant mean curvature. In addition, by changing the distance between the plates and the contact angle with the glass plates, we transition between loops and hedgehogs that can be either radial or hyperbolic.

  10. Titanium dioxide surface modification via ion-beam bombardment for vertical alignment of nematic liquid crystal.

    Science.gov (United States)

    Na, Hyun-Jae; Lee, Jin-Woo; Lee, Won-Kyu; Lim, Ji-Hun; Park, Hong-Gyu; Kim, Byoung-Yong; Hwang, Jeong-Yeon; Han, Jeong-Min; Seo, Dae-Shik

    2010-04-15

    We introduce the characteristics of the titanium dioxide (TiO(2)) inorganic film deposited by rf magnetron sputtering for liquid crystal display applications. The TiO(2) films demonstrated vertical alignment (VA) of the liquid crystals (LCs) obtained by using ion-beam (IB) bombardment. As observed by using x-ray photoelectron spectroscopy, the chemical structure of the TiO(2) was changed by IB bombardment, altering the Ti-O bonding of the Ti 2p spectra to lower intensity levels. Breaking Ti-O bonding by IB bombardment created pretilt angles between the TiO(2) film and LC molecules. The better voltage-transmittance characteristics of the VA LCDs based on TiO(2) film were measured and compared with the same characteristics of polyimide film. PMID:20410949

  11. Twist viscosities and flow alignment of biaxial nematic liquid crystal phases of a soft ellipsoid-string fluid studied by molecular dynamics simulation.

    Science.gov (United States)

    Sarman, Sten; Laaksonen, Aatto

    2012-09-14

    We have calculated the twist viscosity and the alignment angle between the director and the stream lines in shear flow of a liquid crystal model system, which forms biaxial nematic liquid crystals, as functions of the density, from the Green-Kubo relations by equilibrium molecular dynamics simulation and by a nonequilibrium molecular dynamics algorithm, where a torque conjugate to the director angular velocity is applied to rotate the director. The model system consists of a soft ellipsoid-string fluid where the ellipsoids interact according a repulsive version of the Gay-Berne potential. Four different length-to-width-to-breadth ratios have been studied. On compression, this system forms discotic or calamitic uniaxial nematic phases depending on the dimensions of the molecules, and on further compression a biaxial nematic phase is formed. In the uniaxial nematic phase there is one twist viscosity and one alignment angle. In the biaxial nematic phase there are three twist viscosities and three alignment angles corresponding to the rotation around the various directors and the different alignments of the directors relative to the stream lines, respectively. It is found that the smallest twist viscosity arises by rotation around the director formed by the long axes, the second smallest one arises by rotation around the director formed by the normals of the broadsides, and the largest one by rotation around the remaining director. The first twist viscosity is rather independent of the density whereas the last two ones increase strongly with density. One finds that there is one stable director alignment relative to the streamlines, namely where the director formed by the long axes is almost parallel to the stream lines and where the director formed by the normals of the broadsides is almost parallel to the shear plane. The relative magnitudes of the components of the twist viscosities span a fairly wide interval so this model should be useful for parameterisation

  12. Macroscopic dynamics of polar nematic liquid crystals.

    Science.gov (United States)

    Brand, Helmut R; Pleiner, Harald; Ziebert, Falko

    2006-08-01

    We present the macroscopic equations for polar nematic liquid crystals. We consider the case where one has both, the usual nematic director, n[over ] , characterizing quadrupolar order as well as the macroscopic polarization, P , representing polar order, but where their directions coincide and are rigidly coupled. In this case one has to choose P as the independent macroscopic variable. Such equations are expected to be relevant in connection with nematic phases with unusual properties found recently in compounds composed of banana-shaped molecules. Among the effects predicted, which are absent in conventional nematic liquid crystals showing only quadrupolar order, are pyro-electricity and its analogs for density and for concentration in mixtures as well as a flow alignment behavior, which is more complex than in usual low molecular weight nematics. We also discuss the formation of defect structures expected in such systems. PMID:17025458

  13. Dendronized polyimides bearing long-chain alkyl groups and their application for vertically aligned nematic liquid crystal displays.

    Science.gov (United States)

    Tsuda, Yusuke; Min, Jae; Kuwahara, Renpei

    2009-11-01

    Polyimides having dendritic side chains were investigated. The terphenylene diamine monomer having a first-generation monodendron, 3,4,5-tris(n-dodecyloxy)-benzoate and the monomer having a second-generation monodendron, 3,4,5-tris[-3',4',5'-tri(n-dodecyloxy)benzyloxy]benzoate were successfully synthesized and the corresponding soluble dendritic polyimides were obtained by polycondensation with conventional tetracarboxylic dianhydride monomers such as benzophenone tertracarboxylic dianhydride (BTDA). The two-step polymerizations in NMP that is a general method for the synthesis of soluble polyimides is difficult; however, the expected dendritic polyimides can be obtained in aromatic polar solvents such as m-cresol and pyridine. The solubility of these dendoronized polyimides is characteristic; soluble in common organic solvents such as dichloromethane, chloroform, toluene and THF. These dendronized polyimides exhibited high glass transition temperatures and good thermal stability in both air and under nitrogen. Their application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs). PMID:20087476

  14. Dendronized Polyimides Bearing Long-Chain Alkyl Groups and Their Application for Vertically Aligned Nematic Liquid Crystal Displays

    Directory of Open Access Journals (Sweden)

    Yusuke Tsuda

    2009-11-01

    Full Text Available Polyimides having dendritic side chains were investigated. The terphenylene diamine monomer having a first-generation monodendron, 3,4,5-tris(n-dodecyloxy-benzoate and the monomer having a second-generation monodendron, 3,4,5-tris[-3’,4’,5’-tri(n-dodecyloxybenzyloxy]benzoate were successfully synthesized and the corresponding soluble dendritic polyimides were obtained by polycondensation with conventional tetracarboxylic dianhydride monomers such as benzophenone tertracarboxylic dianhydride (BTDA. The two-step polymerizations in NMP that is a general method for the synthesis of soluble polyimides is difficult; however, the expected dendritic polyimides can be obtained in aromatic polar solvents such as m-cresol and pyridine. The solubility of these dendoronized polyimides is characteristic; soluble in common organic solvents such as dichloromethane, chloroform, toluene and THF. These dendronized polyimides exhibited high glass transition temperatures and good thermal stability in both air and under nitrogen. Their application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs.

  15. Photo-alignment of low-molecular mass nematic liquid crystals on photochemically bifunctional chalcone-epoxy film by irradiation of a linearly polarized UV light

    International Nuclear Information System (INIS)

    Photocrosslinkable chalcone-epoxy compound comprising 1,3-bis-(4-hydroxy-phenyl)-propenone was synthesized for fabricating the photo-alignment layer of liquid crystals. Chalcone group was introduced into the main chain unit of the epoxy oligomer. We observed a photodimerization behavior and an optical anisotropy of this material by irradiation of a linearly polarized UV(LP-UV) light. With a trace amount of cationic photo initiator (TRS-HFA), polymerization of epoxy groups was also conducted at the similar wavelength range used for photodimerization . Linearly polarized UV irradiation on the chalcone-epoxy films with cationic photoinitiator induced optical anisotropy of the film and the resultant film can be used for alignment layers for low molecular weight nematic liquid crystals

  16. Pretilt Angles of Vertically Aligned Nematic Liquid Crystal (NLC) with the Application of Copolymers Possessing Chalconyl and Cholesteryl Moieties

    Science.gov (United States)

    Hwang, Jeoung-Yeon; Seo, Dae-Shik; Son, Jong Ho; Suh, Dong Hack

    2000-11-01

    We performed the synthesis of a new copoly (M4Ch-ChMA), copoly ((4-methacryloyloxy) chalcone-cholestery methacrylate), with chalconyl and cholesteryl moiety characteristics for photoalignment materials. Good thermal stabilities of the synthesized copolymers are confirmed by thermogravimetric analysis (TGA) measurement. The pretilt angles of the nematic liquid crystal (NLC) are reduced as UV exposure time is increased on the copolymer surfaces. A pretilt angle of 81° in NLC was observed with UV exposure of 3 min on the copolymer-3 surface. The NLCs pretilt angle is attributed to increased chalcone with increasing the UV exposure time.

  17. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide

    Science.gov (United States)

    Akbari, Abozar; Sheath, Phillip; Martin, Samuel T.; Shinde, Dhanraj B.; Shaibani, Mahdokht; Banerjee, Parama Chakraborty; Tkacz, Rachel; Bhattacharyya, Dibakar; Majumder, Mainak

    2016-03-01

    Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm2) in 90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30-40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71+/-5 l m-2 hr-1 bar-1 for 150+/-15 nm thick membranes).

  18. Electro-optical properties of a nematic liquid crystal aligned with a mixture of nanofibres and polyimide

    Science.gov (United States)

    Lee, Hyojin; Kim, Hyungmin; Yang, Seungbin; Hwang, Jiyong; Lee, Ji-Hoon; Choi, Jonghyun

    2014-08-01

    We examined the electro-optical properties of a nematic liquid crystal sample whose substrates were coated with a mixture of nanofibres (NFs) and polyimide (PI). The samples coated with a NF-PI mixture showed a faster turn-off time than the sample coated with pure PI. We found that the elastic constant and the order parameter of the NF-PI samples were greater than those of the pure PI sample, thus inducing the reduction in turn-off time. The NF-PI mixture-coated surface showed a more homogeneous striped surface topology along the rubbing direction compared to the pure PI surface. The uniform topological anisotropy of the surface seems to be related to the increase in the elastic constant and the order parameter of the NF-PI mixture sample.

  19. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide

    Science.gov (United States)

    Akbari, Abozar; Sheath, Phillip; Martin, Samuel T.; Shinde, Dhanraj B.; Shaibani, Mahdokht; Banerjee, Parama Chakraborty; Tkacz, Rachel; Bhattacharyya, Dibakar; Majumder, Mainak

    2016-01-01

    Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm2) in 90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30–40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71±5 l m−2 hr−1 bar−1 for 150±15 nm thick membranes). PMID:26947916

  20. Measurement of anchoring coefficient of homeotropically aligned nematic liquid crystal using a polarizing optical microscope in reflective mode

    Directory of Open Access Journals (Sweden)

    Sang-In Baek

    2015-09-01

    Full Text Available Although the homeotropic alignment of liquid crystals is widely used in LCD TVs, no easy method exists to measure its anchoring coefficient. In this study, we propose an easy and convenient measurement technique in which a polarizing optical microscope is used in the reflective mode with an objective lens having a low depth of focus. All measurements focus on the reflection of light near the interface between the liquid crystal and alignment layer. The change in the reflected light is measured by applying an electric field. We model the response of the director of the liquid crystal to the electric field and, thus, the change in reflectance. By adjusting the extrapolation length in the calculation, we match the experimental and calculated results and obtain the anchoring coefficient. In our experiment, the extrapolation lengths were 0.31 ± 0.04 μm, 0.32 ± 0.08 μm, and 0.23 ± 0.05 μm for lecithin, AL-64168, and SE-5662, respectively.

  1. Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

    Directory of Open Access Journals (Sweden)

    Vasily F. Shabanov

    2013-08-01

    Full Text Available Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.

  2. Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

    OpenAIRE

    Vasily F. Shabanov; Parshin, Alexander M.; Victor Y. Zyryanov; Gunyakov, Vladimir A.

    2013-01-01

    Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with ...

  3. Anomalous light transmission by nematic liquid crystal cells

    Science.gov (United States)

    Konshina, E. A.; Fedorov, M. A.; Ivanova, N. L.; Amosova, L. P.

    2008-01-01

    Light transmission through nematic liquid crystal (NLC) cells with a planar alignment and various boundary conditions has been studied as a function of the bias voltage in the regimes of maximum transmittance and complete extinction. The phenomenon of anomalous light leakage in the regime of complete extinction has been observed in the NLC sells with alignment layers of amorphous hydrogenated carbon (a-C:H) and poly(vinyl alcohol) (PVA), in which an anisotropy was induced by rubbing the electrode surface (for a-C:H) and the alignment layer (for PVA). The anomalous transmission is caused by the deformation of nematic molecules, which are situated near the surface, in the direction perpendicular to the direction of rubbing. The magnitude of anomalous transmission increases with the bias voltage. This behavior is explained by the anisotropy of the surface anchoring energy of nematic molecules at the interface.

  4. Electro-osmosis in nematic liquid crystals

    Science.gov (United States)

    Tovkach, O. M.; Calderer, M. Carme; Golovaty, Dmitry; Lavrentovich, Oleg; Walkington, Noel J.

    2016-07-01

    We derive a mathematical model of a nematic electrolyte based on a variational formulation of nematodynamics. We verify the model by comparing its predictions to the results of the experiments on the substrate-controlled liquid-crystal-enabled electrokinetics. In the experiments, a nematic liquid crystal confined to a thin planar cell with surface-patterned anchoring conditions exhibits electro-osmotic flows along the "guiding rails" imposed by the spatially varying director. Extending our previous work, we consider a general setup which incorporates dielectric anisotropy of the liquid-crystalline matrix and the full set of nematic viscosities.

  5. Dielectrophoretic manipulation of the mixture of isotropic and nematic liquid

    Science.gov (United States)

    Kim, Soo-Dong; Lee, Bomi; Kang, Shin-Woong; Song, Jang-Kun

    2015-08-01

    In various applications involving liquid crystals, the manipulation of the nanoscale molecular assembly and microscale director alignment is highly useful. Here we show that a nematic-isotropic mixture, a unique bi-liquid system, has potential for the fabrication of microstructures having an ordered phase within a disordered phase, or vice versa. The volume expansion and shrinkage, migration, splitting, mergence and elongation of one phase within the other are easily accomplished via thermal treatment and dielectrophoretic manipulation. This is particularly achievable when one phase is suspended in the middle. In that case, a highly biased ordered-phase preference of surfaces, that is, the nematic-philic nature of a polyimide layer and the nematic-phobic nature of a self-assembled monolayer of chlorosilane derivatives, is used. Further, by combining this approach with photopolymerization, the patterned microstructure is solidified as a patterned polymer film having both isotropic and anisotropic molecular arrangements simultaneously, or as a template with a morphological variation.

  6. Photorefractivity in polymer-stabilized nematic liquid crystals

    Science.gov (United States)

    Wiederrecht, Gary P.; Wasielewski, Michael R.

    1998-10-01

    Polymer-stabilized liquid crystals, consisting of low concentrations of a polymeric electron acceptor, are shown to exhibit significantly enhanced photorefractive properties. The charge generation and transport properties of these composite systems are strongly modified from nematic liquid crystals doped with electron donors and acceptors. The new composites are produced by polymerizing a small quantity of a 1,4:5,8-naphthalenediimide electron acceptor functionalized with an acrylate group in an aligned nematic liquid crystal. Photopolymerization creates an anisotropic gel-like medium in which the liquid crystal is free to reorient in the presence of a space charge field, while maintaining charge trapping sites in the polymerized regions of the material. The presence of these trapping sites results in the observation of longer lived, higher resolution holographic gratings in the polymer-stabilized liquid crystals than observed in nematic liquid crystals alone. These gratings display Bragg regime diffraction. Asymmetric beam coupling, photo-conductivity, and four-wave mixing experiments are performed to characterize the photophysics of these novel materials.

  7. Improvement of the relaxation time and the order parameter of nematic liquid crystal using a hybrid alignment mixture of carbon nanotube and polyimide

    International Nuclear Information System (INIS)

    We examined the electrooptical properties of a nematic liquid crystal (LC) sample whose substrates were coated with a mixture of carbon nanotube (CNT) and polyimide (PI). The relaxation time of the sample coated with 1.5 wt. % CNT mixture was about 35% reduced compared to the pure polyimide sample. The elastic constant and the order parameter of the CNT-mixture sample were increased and the fast relaxation of LC could be approximated to the mean-field theory. We found the CNT-mixed polyimide formed more smooth surface than the pure PI from atomic force microscopy images, indicating the increased order parameter is related to the smooth surface topology of the CNT-polyimide mixture

  8. Improvement of the relaxation time and the order parameter of nematic liquid crystal using a hybrid alignment mixture of carbon nanotube and polyimide

    Science.gov (United States)

    Lee, Hyojin; Yang, Seungbin; Lee, Ji-Hoon; Soo Park, Young

    2014-05-01

    We examined the electrooptical properties of a nematic liquid crystal (LC) sample whose substrates were coated with a mixture of carbon nanotube (CNT) and polyimide (PI). The relaxation time of the sample coated with 1.5 wt. % CNT mixture was about 35% reduced compared to the pure polyimide sample. The elastic constant and the order parameter of the CNT-mixture sample were increased and the fast relaxation of LC could be approximated to the mean-field theory. We found the CNT-mixed polyimide formed more smooth surface than the pure PI from atomic force microscopy images, indicating the increased order parameter is related to the smooth surface topology of the CNT-polyimide mixture.

  9. Improvement of the relaxation time and the order parameter of nematic liquid crystal using a hybrid alignment mixture of carbon nanotube and polyimide

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyojin; Yang, Seungbin; Lee, Ji-Hoon, E-mail: jihoonlee@jbnu.ac.kr [Advanced Electronics and Information Research Center, Division of Electronic Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of); Soo Park, Young, E-mail: irony@kctech.re.kr [Department of Polymer-Nano Science and Technology, Chonbuk National University, Jeonju, Jeonbuk, 561-756 (Korea, Republic of); Korea Institute of Carbon Convergence Technology, Banryong-ro, Jeonju, Jeonbuk 561-844 (Korea, Republic of)

    2014-05-12

    We examined the electrooptical properties of a nematic liquid crystal (LC) sample whose substrates were coated with a mixture of carbon nanotube (CNT) and polyimide (PI). The relaxation time of the sample coated with 1.5 wt. % CNT mixture was about 35% reduced compared to the pure polyimide sample. The elastic constant and the order parameter of the CNT-mixture sample were increased and the fast relaxation of LC could be approximated to the mean-field theory. We found the CNT-mixed polyimide formed more smooth surface than the pure PI from atomic force microscopy images, indicating the increased order parameter is related to the smooth surface topology of the CNT-polyimide mixture.

  10. A theory of the nematic liquid crystals

    International Nuclear Information System (INIS)

    A theory of the nematic phase of liquid crystals is presented, taking explicit account of the geometry of the molecule. The three broad peaks of the neutron scattering structure factor are explained. Expressions of the order parameters (average value of Psub(2L)) are given and they can be extracted by comparison with scattering experiments. (author)

  11. Stochastic rotation dynamics for nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kuang-Wu, E-mail: jeff.lee@ds.mpg.de; Mazza, Marco G., E-mail: marco.mazza@ds.mpg.de [Max Planck Institute for Dynamics and Self-Organization, Am Faßberg 17, 37077 Göttingen (Germany)

    2015-04-28

    We introduce a new mesoscopic model for nematic liquid crystals (LCs). We extend the particle-based stochastic rotation dynamics method, which reproduces the Navier-Stokes equation, to anisotropic fluids by including a simplified Ericksen-Leslie formulation of nematodynamics. We verify the applicability of this hybrid model by studying the equilibrium isotropic-nematic phase transition and nonequilibrium problems, such as the dynamics of topological defects and the rheology of sheared LCs. Our simulation results show that this hybrid model captures many essential aspects of LC physics at the mesoscopic scale, while preserving microscopic thermal fluctuations.

  12. Influence of shear flow on the Fréedericksz transition in nematic liquid crystals.

    Science.gov (United States)

    Makarov, D V; Zakhlevnykh, A N

    2006-10-01

    Within the framework of Ericksen-Leslie continuum theory we analyze the influence of shear flow on the magnetic-field-induced Fréedericksz transition in nematic liquid crystal with rodlike molecules. We consider three basic orientational configurations of a nematic planar layer in the uniform magnetic field. Conditions of rigid director coupling on the boundaries of the layer and constant shear flow gradient inside the layer are used. We exhibit some flow aligning effects for nematic liquid crystals with various ratio of rotary viscosities and investigate how unequal elastic constants (elastic anisotropy) alter the magnetic Fréedericksz transition in sheared nematics. Our calculations predict that surface boundary effects in nematic films and magnetic field action lead to existence of stationary flow regimes in the so-called nonflow aligning nematics, otherwise, surface and magnetic forces extend the range of viscous coefficient values corresponding to the flow aligning regimes. We show that imposing of shear flow on the Fréedericksz transition leads to a threshold behavior or to a "smoothing" of the transition. It depends on the orientation of the nematic layer in magnetic field and magnitudes of rotary viscous coefficients. PMID:17155081

  13. Drifting Abnormal Rolls in Electroconvection of Hybrid Aligned Nematic

    OpenAIRE

    Delev, V. A.; Krekhov, A. P.

    2001-01-01

    We report experimental and theoretical results on the conductive regime of electroconvection in hybrid aligned nematics. The drifting oblique/normal rolls below/above the Lifshitz frequency are observed at the onset of electroconvection under a.c. voltage. The experimental data on the threshold voltage, wavelength, oblique angle and drift period of the rolls as function of a.c. frequency are in good agreement with the results of linear stability analysis. The transition from drifting oblique ...

  14. In situ laser-imprinted surface realignment of a nematic liquid crystal.

    Science.gov (United States)

    Mirri, Giorgio; Škarabot, Miha; Muševič, Igor

    2015-05-01

    We present a new method for the in-plane realignment of nematic liquid crystals in already fully assembled cells with uni-directionally rubbed polyimide as an aligning layer. We use nematic liquid crystals (NLCs) with a relatively high nematic-isotropic transition temperature and we focus the IR laser beam of the laser tweezers selectively onto one or the other of the inner interfaces. The heat generated by the IR absorption locally melts the liquid crystal and creates an isotropic island with well-defined molecular anchoring at the nematic-isotropic interface. By scanning the laser beam along a pre-defined line, the moving isotropic-nematic interface leaves behind a well oriented LC domain, with LC molecules aligned at 45° to the rubbing direction. If we in addition move the sample with respect to this scanning line, we would be able to selectively realign micro-domains of the liquid crystal with respect to the original alignment induced by the PI rubbing. The realignment can be performed independently on each LC-glass interface, thereby producing predefined domains with customized and controllable alignment within an otherwise uniformly aligned cell. PMID:25790268

  15. Rheology of a Twist-bend Nematic Liquid Crystal

    Science.gov (United States)

    Salili, Seyyed Muhammad; Kim, Chanjoong; Sprunt, Samuel; Gleeson, James; Parri, Owain; Jakli, Antal; Kim Lab Team; Merck Lab Team

    2015-03-01

    First detailed flow shear alignment studies and rheological measurements in the twist-bend nematic (Ntb) liquid crystalline phase of odd numbered flexible dimer molecules is presented. It is found that the Ntb phase is strongly shear-thinning. At shear stresses below 1 Pa the apparent viscosity of the Ntb phase is 1000 times larger than in the nematic phase. At stresses above 10 Pa the Ntb viscosity drops by two orders of magnitude and the material exhibits Newtonian fluid behavior. The results are consistent with the behavior of a system with pseudo-layer structure with layer spacing determined by the heliconical pitch. From the measurements of dynamic modulus we estimate the compression modulus of the pseudo-layers to be B ~ 2 kPa this value is discussed within the context of a simple theoretical model based upon a coarse-grained elastic free energy. www.jakligroup.com.

  16. Study of two dimensional nematic liquid crystal reorientations and anchoring effects

    OpenAIRE

    S Shoarinejad; MA Shahzamanian

    2010-01-01

    In this paper, the director distribution is calculated for a nematic liquid crystal, in the cell with different surface anchoring conditions and external fields. The effects of finite and infinite surface anchoring on molecular orientations for one dimensional geometry are discussed. In these situations, the planar alignment is considered. Then, in a two dimensional geometry the planar and homotropic anchoring conditions are assumed for wall- interfaces of confined nematic, and the reorientat...

  17. Surface-assisted unidirectional orientation of ZnO nanorods hybridized with nematic liquid crystals.

    Science.gov (United States)

    Kubo, Shoichi; Taguchi, Rei; Hadano, Shingo; Narita, Mamiko; Watanabe, Osamu; Iyoda, Tomokazu; Nakagawa, Masaru

    2014-01-22

    Inorganic semiconductor nanorods are regarded as the primary components of optical and electrical nanoscale devices. In this paper, we demonstrate the unidirectional alignment of monolayered and dispersed ZnO nanorods on a rubbed polyimide alignment layer, which was achieved by a conventional liquid crystal alignment technique. The outermost surfaces of the ZnO nanorods (average diameter 7 nm; length 50 nm) were modified by polymerization initiator moieties, and nematic liquid crystalline (LC) methacrylate polymers were grown by atom transfer radical polymerization. By regulating the densities of the polymerization initiator moieties, we successfully hybridized LC-polymer-grafted ZnO nanorods and small nematic LC molecules. The LC-polymer-modified ZnO nanorods were hierarchically aligned on the substrate via cooperative molecular interactions among the liquid crystal mesogens, which induced molecular orientation on the rubbed polyimide alignment layer. PMID:24299205

  18. Charge transfer reactions in nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wiederrecht, G.P. [Argonne National Lab., IL (United States). Chemistry Div.; Wasielewski, M.R. [Argonne National Lab., IL (United States). Chemistry Div.]|[Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Galili, T.; Levanon, H. [Hebrew Univ. of Jerusalem (Israel). Dept. of Physical Chemistry

    1998-07-01

    Ultrafast transient absorption studies of intramolecular photoinduced charge separation and thermal charge recombination were carried out on a molecule consisting of a 4-(N-pyrrolidino)naphthalene-1,8-imide donor (PNI) covalently attached to a pyromellitimide acceptor (PI) dissolved in the liquid crystal 4{prime}-(n-pentyl)-4-cyanobiphenyl (5CB). The temperature dependencies of the charge separation and recombination rates were obtained at temperatures above the nematic-isotropic phase transition of 5CB, where ordered microdomains exist and scattering of visible light by these domains is absent. The authors show that excited state charge separation is dominated by molecular reorientation of 5CB perpendicular to the director within the liquid crystal microdomains. They also show that charge recombination is adiabatic and is controlled by the comparatively slow collective reorientation of the liquid crystal microdomains relative to the orientation of PNI{sup +}-PI{sup {minus}}. They also report the results of time resolved electron paramagnetic resonance (TREPR) studies of photoinduced charge separation in a series of supramolecular compounds dissolved in oriented liquid crystal solvents. These studies permit the determination of the radical pair energy levels as the solvent reorganization energy increases from the low temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal.

  19. Free surface dynamics of nematic liquid crystal

    Science.gov (United States)

    Cummings, Linda; Kondic, Lou; Lam, Michael; Lin, Te-Sheng

    2014-11-01

    Spreading thin films of nematic liquid crystal (NLC) are known to behave very differently to those of isotropic fluids. The polar interactions of the rod-like molecules with each other, and the interactions with the underlying substrate, can lead to intricate patterns and instabilities that are not yet fully understood. The physics of a system even as simple as a film of NLC spreading slowly over a surface (inclined or horizontal) are remarkably complex: the outcome depends strongly on the details of the NLC's behavior at both the substrate and the free surface (so-called ``anchoring'' effects). We will present a dynamic flow model that takes careful account of such nematic-substrate and nematic-free surface interactions. We will present model simulations for several different flow scenarios that indicate the variety of behavior that can emerge. Spreading over a horizontal substrate may exhibit a range of unstable behavior. Flow down an incline also exhibits intriguing instabilities: in addition to the usual transverse fingering, instabilities can be manifested behind the flowing front in a manner reminiscent of Newtonian flow down an inverted substrate. NSF DMS-1211713.

  20. Carbon Nanoparticles in Nematic Liquid Crystals

    Institute of Scientific and Technical Information of China (English)

    S.Eren San; Mustafa Okutan; O(g)uz K(o)ysal; Yusuf Yer-li

    2008-01-01

    Fullerene G60,C70,single-walled and multi-walled carbon nanotubes and graphene sheets are doped to nematic liquid crystal(LC)host in the same percentage.Planar samples of these mixtures are prepared and our measurements constitute an optimization basis for possible applications.Fullerene balls are found to be the best compatible material for optical aims and reorientation of LC molecules,while the carbon nanotubes experience some reorientation possibility in LC media and graphene layers are good barriers to preserve reorientation.

  1. Thermal diode made by nematic liquid crystal

    Science.gov (United States)

    Melo, Djair; Fernandes, Ivna; Moraes, Fernando; Fumeron, Sébastien; Pereira, Erms

    2016-09-01

    This work investigates how a thermal diode can be designed from a nematic liquid crystal confined inside a cylindrical capillary. In the case of homeotropic anchoring, a defect structure called escaped radial disclination arises. The asymmetry of such structure causes thermal rectification rates up to 3.5% at room temperature, comparable to thermal diodes made from carbon nanotubes. Sensitivity of the system with respect to the heat power supply, the geometry of the capillary tube and the molecular anchoring angle is also discussed.

  2. Isotropization of nematic liquid crystals by TMDSC

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wei; Dadmun, M.; Zhang, Ge; Boller, A.; Wunderlich, B. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry]|[Oak Ridge National Lab., TN (United States)

    1997-12-01

    Temperature-modulated differential scanning calorimetry (TMDSC) and traditional DSC are used to study the transition between the nematic liquid crystalline state and the isotropic liquid for two small molecules [4,4{prime}-azoxyanisole and N,N`-bis(4-n-octyloxybenzal)-1,4-phenylenediamine] and one macromolecule (4,4{prime}-dihydroxy-{alpha}-methylstilbene copolymerized with a 1:1 molar mixture of 1,7-dibromoheptane and 1,9-dibromononane). The DSC measurements with 4,4{prime}-azoxyanisole were used for temperature calibration with varying heating and cooling rates. Quasi-isothermal TMDSC with small temperature amplitude and standard TMDSC with underlying heating and cooling rates were utilized to analyze the breadth of the transitions. It could be verified that the isotropization transition of a nematic liquid crystal is, indeed, reversible for all three molecules. The nature of the transition changes, however, from relatively sharp, for small, rigid molecules, to about three kelvins wide for the small molecule with flexible ends, to as broad as 20 K for the macromolecule. It was also demonstrated that quantitative heats of fusion of sharp transitions can be extracted from TMDSC, but only from the time-domain heat-flow signal.

  3. Nonlinear flow behaviors of nematic liquid crystals in complex geometries

    Science.gov (United States)

    Araki, Takeaki

    2013-02-01

    We study nematic liquid crystals flowing in a regular-shaped porous medium by means of lattice Boltzmann simulations. With strong anchoring, the director field cannot align uniformly and topological defects are stably formed with a large number of possible configurations. In a quiescent state, each configuration is arrested since the energy barriers between possible configurations are higher than the thermal energy. If the flow speed is slow enough, the defect pattern is not changed from the initial quiescent configuration. Above a critical flow speed, the defect pattern transforms to a new stable configuration. In a regular-shaped porous matrix, there remain regularly aligned disclination loops. This regular pattern is maintained even after the flow is stopped.

  4. Hard Spherocylinders of Two Different Lengths as a Model System of a Nematic Liquid Crystal on an Anisotropic Substrate

    Science.gov (United States)

    Koda, Tomonori; Hyodo, Yosuke; Momoi, Yuichi; Kwak, Musun; Kang, Dongwoo; Choi, Youngseok; Nishioka, Akihiro; Haba, Osamu; Yonetake, Koichiro

    2016-02-01

    In this article, we describe the effects of an anisotropic substrate on the alignment of a nematic liquid crystal. We examine how the substrate affects the alignment of a nematic liquid crystal by Monte Carlo simulation. The liquid crystal on a substrate was described by the phase separation of liquid crystal molecules and substrate molecules, both of which were modeled by hard particles. We used hard rods to represent both the liquid crystal and the substrate. The length of the hard rods representing the substrate was adjusted to represent the degree of substrate anisotropy. The results show that the nematic alignment could either be reinforced or weakened, depending on the length of the substrate rods. Mean field theory is used to analyze the simulation results. We confirmed that the distance over which the substrate affects the bulk liquid crystal is about 3 nm for the present hard-rod-based model.

  5. Shape-controlled orientation and assembly of colloids with sharp edges in nematic liquid crystals.

    Science.gov (United States)

    Beller, Daniel A; Gharbi, Mohamed A; Liu, Iris B

    2015-02-14

    The assembly of colloids in nematic liquid crystals via topological defects has been extensively studied for spherical particles, and investigations of other colloid shapes have revealed a wide array of new assembly behaviors. We show, using Landau-de Gennes numerical modeling, that nematic defect configurations and colloidal assembly can be strongly influenced by fine details of colloid shape, in particular the presence of sharp edges. For cylinder, microbullet, and cube colloid geometries, we obtain the particles' equilibrium alignment directions and effective pair interaction potentials as a function of simple shape parameters. We find that defects pin at sharp edges, and that the colloid consequently orients at an oblique angle relative to the far-field nematic director that depends on the colloid's shape. This shape-dependent alignment, which we confirm in experimental measurements, raises the possibility of selecting self-assembly outcomes for colloids in liquid crystals by tuning particle geometry. PMID:25523158

  6. Adsorption phenomena and anchoring energy in nematic liquid crystals

    CERN Document Server

    Barbero, Giovanni

    2005-01-01

    Despite the large quantity of phenomenological information concerning the bulk properties of nematic phase liquid crystals, little is understood about the origin of the surface energy, particularly the surface, interfacial, and anchoring properties of liquid crystals that affect the performance of liquid crystal devices. Self-contained and unique, Adsorption Phenomena and Anchoring Energy in Nematic Liquid Crystals provides an account of new and established results spanning three decades of research into the problems of anchoring energy and adsorption phenomena in liquid crystals.The book contains a detailed discussion of the origin and possible sources of anchoring energy in nematic liquid crystals, emphasizing the dielectric contribution to the anchoring energy in particular. Beginning with fundamental surface and anchoring properties of liquid crystals and the definition of the nematic phase, the authors explain how selective ion adsorption, dielectric energy density, thickness dependence, and bias voltage...

  7. Instability of a Biaxial Nematic Liquid Crystal Formed by Homeotropic Anchoring on Surface Grooves

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhi-Dong; XUAN Li

    2011-01-01

    A method used to treat the elastic distortion of a uniaxial nematic liquid crystal induced by homogeneous anchoring on the surface grooves is generalized to biaxial nematic liquid crystals under the homeotropic anchoring condition.Employing some approximations for the elastic constants,we obtain an additional term in the elastic energy per unit area which depends on the angle between the minor director at infinity and the direction of the grooves,with a period of π/2.This leads to instability on the surface grooves so that two states with crossed minor directors are energetically indistinguishable.Our theoretical study explains why the homeotropic alignment method developed for uniaxial liquid crystals loses efficacy for biaxial nematics.In most liquid crystal devices,the liquid crystals are sandwiched between two substrates coated with alignment layers.In the absence of externally applied fields,the orientation of the liquid crystal in the cell is determined by the anchoring condition of the alignment layer.[1-3] One usually distinguishes three main types of liquid crystalline director alignment near solid walls:homeotropic,homogeneous (or planar) and tilted orientations.Here we study the first of these and consider the biaxial nematic phase,which was observed in lyotropic systems as early as 1980[4] and has been confirmed by deuterium NMR spectroscopy.%A method used to treat the elastic distortion of a uniaxial nematic liquid crystal induced by homogeneous anchoring on the surface grooves is generalized to biaxial nematic liquid crystals under the homeotropic anchoring condition. Employing some approximations for the elastic constants, we obtain an additional term in the elastic energy per unit area which depends on the angle between the minor director at infinity and the direction of the grooves, with a period of π/2. This leads to instability on the surface grooves so that two states with crossed minor directors are energetically indistinguishable. Our

  8. Homeotropic alignment of lyotropic chromonic liquid crystals using noncovalent interactions.

    Science.gov (United States)

    Jeong, Joonwoo; Han, Ganghee; Johnson, A T Charlie; Collings, Peter J; Lubensky, Tom C; Yodh, Arjun G

    2014-03-18

    We report on the homeotropic alignment of lyotropic chromonic liquid crystals (LCLCs). Homeotropic anchoring of LCLCs is difficult to achieve, and this challenge has limited development of applications for LCLCs. In this work, homeotropic alignment is achieved using noncovalent interactions between the LCLC molecules and various alignment layers including graphene, parylene films, poly(methyl methacrylate) films, and fluoropolymer films. The LCLC molecules are unique in that they self-assemble via noncovalent interactions in water into elongated aggregates which, in turn, form nematic and columnar liquid crystal (LC) phases. Here we exploit these same noncovalent interactions to induce homeotropic anchoring of the nematic LCLC. Homeotropic alignment is confirmed by polarized optical microscopy and conoscopy. We also report on novel transient stripe textures that occur when an initial flow-induced planar alignment transforms into the equilibrium homeotropic alignment required by boundary conditions. An understanding of this behavior could be important for switching applications. PMID:24559290

  9. Light-scattering study of a polymer nematic liquid crystal

    Science.gov (United States)

    Taratuta, Victor G.; Hurd, Alan J.; Meyer, Robert B.

    1985-07-01

    We study the relaxation of thermally excited orientation fluctuations in a polymer nematic liquid crystal using photon correlation spectroscopy. The material studied is poly-γ-benzyl glutamate at a concentration just above the isotropic to nematic transition point. The relaxation rates of elastic deformation modes exhibit large anisotropies. Quantitative measurements of ratios of Frank elastic constants and Leslie viscosities are described.

  10. Director orientation of nematic liquid crystal using orientated nanofibers obtained by electrospinning

    Science.gov (United States)

    Toan, Duong Quoc; Ozaki, Ryotaro; Moritake, Hiroshi

    2014-01-01

    Nanofibers with diameters less than 1000 nm assembled by electrospinning and with a large surface area per unit mass have been attracting considerable attention and are expected to affect the orientation of liquid crystals (LCs). Firstly, to determine the orientated nanofibers on an indium-tin-oxide (ITO) glass surface, the spectral analysis technique of using fast Fourier transform is applied. Optical observation is performed to confirm the orientation of LC molecules in a twisted nematic LC cell. Finally, optical measurement of an LC cell is carried out to estimate the threshold voltage of the LC in two types of twisted nematic LC cell: one with rubbed polyimide and the other with orientated nanofibers as the alignment layer. A twisted nematic LC is oriented in the cell using orientated nanofibers as the alignment layer and the threshold voltage of this cell agrees with that of the conventional polyimide rubbed cell.

  11. Spatiotemporal complexity of electroconvection patterns in nematic liquid crystals

    Science.gov (United States)

    Krekhov, Alexei; Dressel, Bernd; Pesch, Werner; Delev, Vladimir; Batyrshin, Eduard

    2015-12-01

    We investigate a number of complex patterns driven by the electroconvection instability in a planarly aligned layer of a nematic liquid crystal. They are traced back to various secondary instabilities of the ideal roll patterns bifurcating at onset of convection, whereby the basic nematohydrodynamic equations are solved by common Galerkin expansion methods. Alternatively these equations are systematically approximated by a set of coupled amplitude equations. They describe slow modulations of the convection roll amplitudes, which are coupled to a flow field component with finite vorticity perpendicular to the layer and to a quasihomogeneous in-plane rotation of the director. It is demonstrated that the Galerkin stability diagram of the convection rolls is well reproduced by the corresponding one based on the amplitude equations. The main purpose of the paper is, however, to demonstrate that their direct numerical simulations match surprisingly well new experiments, which serves as a convincing test of our theoretical approach.

  12. Carbon Nanotube Liquid Crystals: Nematic Droplets and Coarsening Dynamics

    Science.gov (United States)

    Behabtu, Natnael; Senyuk, Bohdan; Smalyukh, Ivan; Pasquali, Matteo

    2012-02-01

    On a fundamental basis, carbon nanotubes (CNTs) offer a new model molecule to explore the dynamics and phases of rigid rods and test theories. Their large aspect ratio (100 to 100,000) and persistence length (˜ 100 microns) allow exploring the physics of nematic phases with high Frank elastic constant. Moreover, understanding of CNT liquid crystals is key to their rational processing into ordered materials such as fibers. Here we report the formation of elongated nematic droplets of CNTs in chlorosulfonic acid. In nematic droplets, a continuous transition from a homogeneous to bipolar nematic director field is expected theoretically, as a function of droplet volume; yet, experimental determination of such transition has been elusive. We show that CNT nematic droplets display such transition. We study the coarsening dynamics of positive and negative nematic droplets and observe that two or more droplets merge by matching their nematic director. Merging scenarios that lead to defect formation are not observed. Negative tactoids (isotropic phase in liquid crystalline continuum) merge through attractive forces induced by the nematic director distortion with quadrupolar symmetry.

  13. Liquid crystallinity driven highly aligned large graphene oxide composites

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kyung Eun; Oh, Jung Jae; Yun, Taeyeong [Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon 305-701 (Korea, Republic of); Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of); Kim, Sang Ouk, E-mail: sangouk.kim@kaist.ac.kr [Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon 305-701 (Korea, Republic of); Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of)

    2015-04-15

    Graphene is an emerging graphitic carbon materials, consisting of sp{sup 2} hybridized two dimensinal honeycomb structure. It has been widely studied to incorporate graphene with polymer to utilize unique property of graphene and reinforce electrical, mechanical and thermal property of polymer. In composite materials, orientation control of graphene significantly influences the property of composite. Until now, a few method has been developed for orientation control of graphene within polymer matrix. Here, we demonstrate facile fabrication of high aligned large graphene oxide (LGO) composites in polydimethylsiloxane (PDMS) matrix exploiting liquid crystallinity. Liquid crystalline aqueous dispersion of LGO is parallel oriented within flat confinement geometry. Freeze-drying of the aligned LGO dispersion and subsequent infiltration with PDMS produce highly aligned LGO/PDMS composites. Owing to the large shape anisotropy of LGO, liquid crystalline alignment occurred at low concentration of 2 mg/ml in aqueous dispersion, which leads to the 0.2 wt% LGO loaded composites. - Graphical abstract: Liquid crystalline LGO aqueous dispersions are spontaneous parallel aligned between geometric confinement for highly aligned LGO/polymer composite fabrication. - Highlights: • A simple fabrication method for highly aligned LGO/PDMS composites is proposed. • LGO aqueous dispersion shows nematic liquid crystalline phase at 0.8 mg/ml. • In nematic phase, LGO flakes are highly aligned by geometric confinement. • Infiltration of PDMS into freeze-dried LGO allows highly aligned LGO/PDMS composites.

  14. Liquid crystallinity driven highly aligned large graphene oxide composites

    International Nuclear Information System (INIS)

    Graphene is an emerging graphitic carbon materials, consisting of sp2 hybridized two dimensinal honeycomb structure. It has been widely studied to incorporate graphene with polymer to utilize unique property of graphene and reinforce electrical, mechanical and thermal property of polymer. In composite materials, orientation control of graphene significantly influences the property of composite. Until now, a few method has been developed for orientation control of graphene within polymer matrix. Here, we demonstrate facile fabrication of high aligned large graphene oxide (LGO) composites in polydimethylsiloxane (PDMS) matrix exploiting liquid crystallinity. Liquid crystalline aqueous dispersion of LGO is parallel oriented within flat confinement geometry. Freeze-drying of the aligned LGO dispersion and subsequent infiltration with PDMS produce highly aligned LGO/PDMS composites. Owing to the large shape anisotropy of LGO, liquid crystalline alignment occurred at low concentration of 2 mg/ml in aqueous dispersion, which leads to the 0.2 wt% LGO loaded composites. - Graphical abstract: Liquid crystalline LGO aqueous dispersions are spontaneous parallel aligned between geometric confinement for highly aligned LGO/polymer composite fabrication. - Highlights: • A simple fabrication method for highly aligned LGO/PDMS composites is proposed. • LGO aqueous dispersion shows nematic liquid crystalline phase at 0.8 mg/ml. • In nematic phase, LGO flakes are highly aligned by geometric confinement. • Infiltration of PDMS into freeze-dried LGO allows highly aligned LGO/PDMS composites

  15. Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogens with a Nematic-Nematic Transition and a Negative Elastic Constant

    Science.gov (United States)

    Panov, V. P.; Nagaraj, M.; Vij, J. K.; Panarin, Yu. P.; Kohlmeier, A.; Tamba, M. G.; Lewis, R. A.; Mehl, G. H.

    2010-10-01

    Hydrocarbon linked mesogenic dimers are found to exhibit an additional nematic phase below the conventional uniaxial nematic phase as confirmed by x-ray diffraction. The phase produces unusual periodic stripe domains in planar cells. The stripes are found to be parallel to the rubbing direction (in rubbed cells) with a well-defined period equal to double the cell gap. The stripes appear without external electromagnetic field, temperature or thickness gradients, rubbing or hybrid alignment treatments. Simple modeling proposes a negative sign for at least one of the two elastic constants: splay and twist, as a necessary condition for the observed pattern.

  16. Liquid Crystal Microlens Using Nanoparticle-Induced Vertical Alignment

    Directory of Open Access Journals (Sweden)

    Shug-June Hwang

    2015-01-01

    Full Text Available The nanoparticle-induced vertical alignment (NIVA of the nematic liquid crystals (LC is applied to achieve an adaptive flat LC microlens with hybrid-aligned nematic (HAN mode by dropping polyhedral oligomeric silsesquioxane (POSS nanoparticle solution on a homogeneous alignment layer. The vertical alignment induced by the POSS nanoparticles resulted in the formation of a hybrid-aligned LC layer with concentric nonuniform distribution of the refractive index in the planar LC cell, which subsequently played the role of the lens, even in the absence of any applied voltages. The dimensions of the concentric HAN structure significantly depend on the volume of the microdroplet and the POSS concentration. The focus effect of this flat microlens was observed while electrically controlling its focal length using the applied voltages from −50 mm to −90 mm.

  17. Thermal and optical study of semiconducting CNTs-doped nematic liquid crystalline material

    Science.gov (United States)

    Vimal, T.; Singh, D. P.; Gupta, S. K.; Pandey, S.; Agrahari, K.; Manohar, R.

    2016-06-01

    We report the thermal and spectroscopic analysis of the carbon nanotubes (CNTs)-doped nematic liquid crystal (NLC) material. The CNTs have been oriented in the p-ethoxybenzylidene p-butylaniline NLC. The thermal study of the CNTs doped nematic mixtures shows a significant decrease in the isotropic to nematic phase transition temperature. However higher doping concentration of CNTs has led to the further increase in transition temperature. The UV-Visible spectroscopy has been attempted on the CNTs/NLC mixtures at room temperature. The investigated NLC present one absorption band corresponding to π-π* electronic transition. A red shift of λmax with the increasing concentration of CNTs in the mixture has been observed. The band gap of NLC has been found to decrease after the doping of CNTs. The absorbance was measured for the UV light, polarized parallel and perpendicular to the LC director in the planar aligned cell.

  18. Regular and chaotic states in a local map description of sheared nematic liquid crystals.

    Science.gov (United States)

    Kamil, S M; Sinha, Sudeshna; Menon, Gautam I

    2008-07-01

    We propose and study a local map capable of describing the full variety of dynamical states, ranging from regular to chaotic, obtained when a nematic liquid crystal is subjected to a steady shear flow. The map is formulated in terms of a quaternion parametrization of rotations of the local frame described by the axes of the nematic director, subdirector, and the joint normal to these, with two additional scalars describing the strength of ordering. Our model yields kayaking, wagging, tumbling, aligned, and coexistence states, accommodated in a phase diagram which closely resembles phase diagrams obtained using representations of the dynamics which are based on ordinary differential equations. We also study the behavior of the map under periodic perturbations of the shear rate. Such a map can serve as a building block for the construction of lattice models of the complex spatiotemporal states predicted for sheared nematics. PMID:18763972

  19. Stability in the memory state of the silica nanoparticle-doped hybrid aligned nematic device

    Science.gov (United States)

    Huang, Chi-Yen; Chen, Jian-Hong; Hsieh, Chia-Ting; Song, Heng-Cheng; Wang, Yu-Wu; Horng, Lance; Tian, Ching-Jui; Hwang, Shug-June

    2011-01-01

    We investigate the stability in the memory state of the silica nanoparticle doped hybrid aligned nematic (SN-HAN) cell. The mixed polyimide (PI)-coated planar substrate provides the SN-HAN cell with a stable memory state. The mixed PI comprises the homogeneous PI and small amounts of the homeotropic PI (H-PI). The tiny H-PI dopant decreases the surface energy, increases the roughness of the planar substrate, and increases the pretilt angle of the liquid crystals (LCs). When the pretilt angle is high, the relaxation torque that rewinds the LCs from the electrically addressed homeotropic state to the originally HAN state is too small to break the formed aggregated silica networks, which stabilize the LCs at the electrically addressed homeotropic state. Consequently, the memory state of the SN-HAN cell is stable when the pretilt angle of the LCs is high.

  20. A continuum model for nematic alignment of self-propelled particles

    OpenAIRE

    Degond, Pierre; Manhart, Angelika; Yu, Hui

    2015-01-01

    A continuum model for a population of self-propelled particles interacting through nematic alignment is derived from an individual-based model. The methodology consists of introducing a hydrodynamic scaling of the corresponding mean-field kinetic equation. The resulting perturbation problem is solved thanks to the concept of generalized collision invariants. It yields a hyperbolic but non-conservative system of equations for the nematic mean direction of the flow and the densities of particle...

  1. Smectic-A Order at the Surface of a Nematic Liquid Crystal

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage; Christensen, Finn Erland; Pershan, P. S.

    1982-01-01

    A novel geometry in which it is possible to do x-ray diffraction from a horizontal surface of fluids is applied to liquid crystals. A large-diameter drop of octyloxycyanobiphenyl (8OCB) on a glass plate treated for homeotropic alignment yields perfect alignment of the smectic-A layers at the top...... surface over an area of several square millimeters. The surface in the bulk nematic as well as in the isotropic phase was found to consist of smectic-A layers with a penetration depth equal to the longitudinal smectic-A correlation length ξ∥∼(T-TNA)-ν∥ determined previously....

  2. Polarization converting textures of nematic liquid crystal in glass cavities

    Science.gov (United States)

    Wang, Xiahui; Xu, Miao; Ren, Hongwen

    2014-01-01

    When a nematic liquid crystal (LC) is filled in a glass cavity, the LC molecules present azimuthal orientations in the cavity. If the surface of the cavity is coated with a homeotropic polyimide, then the LC molecules exhibit radial orientations. By treating the LC on one side of the cavity with homogeneous alignment, the former orientations change to a twisted-azimuthal texture, while the latter orientations change to a twisted-radial texture. Both textures are verified experimentally, and they can convert a linearly polarization light to an azimuthal and/or radial polarization light, depending on the polarization direction of the incident light. In contrast to previous approaches, various LC textures can be easily formed in a cavity, and the fabrication procedure is simple. Since the LC texture is confined in a cavity, an array pattern of the texture can be obtained, if the employed substrate has multiple cavities. A LC with twisted-azimuthal and/or twisted-radial textures in a cavity array has potential applications in phase modulation, polarization compensating, sharp focus, and material processing.

  3. Molecular engineering of discotic nematic liquid crystals

    Indian Academy of Sciences (India)

    Sandeep Kumar

    2003-08-01

    Connecting two columnar phase forming discotic mesogens via a short rigid spacer leads to the formation of a -conjugated discotic dimer showing discotic nematic (D) phase. Attaching branched-alkyl chains directly to the core in hexaalkynylbenzene resulted in the stabilisation of D phase at ambient temperature. Pentalkynylbenzene derivatives possessing a combination of normal-and branched-alkoxy chains display a very broad D phase which is stable well below and above the room temperature.

  4. Dynamic-Mechanical Analysis of Monodomain Nematic Liquid Crystalline Elastomers

    Science.gov (United States)

    Hotta, Atsushi; Terentjev, Eugene

    2003-03-01

    Dynamic-mechanical analysis was performed in the glassy, nematic and isotropic states of several monodomain nematic liquid crystalline elastomers (LCE) which differ in their degrees of anisotropy and internal microstructure. It was found that the type of network crosslinker makes a significant difference in the equilibrium properties of these elastomers, in particular, in their effective anisotropy. In spite of these differences, the observed dynamic-mechanical behaviour was very similar. The fact that there is a consistently high and wide loss over the whole nematic region, where storage modulus G' behaves non-monotonically, is most likely an indicator of the fact that the dynamic-mechanical response is not linear. Master curves have been built between the glassy state and the nematic-isotropic phase transition, where the modulus reaches a low-level soft plateau. Above the nematic-isotropic transition temperature Tni, the modulus rises substantially, since internal relaxation is no longer able to reduce the elastic response - and further time-temperature superposition fails. The dynamics of these elastomers are dominated by power laws, which was confirmed by the successful procedure of the master curve inversion (time-frequency inversion) to describe the static stress relaxation. Interestingly, it was found that mechanical properties characterized by power laws (in time) of stress relaxation match very well with the dynamic properties, where power laws (in frequency) were also observed in the dynamic modulus in the appropriate range of temperatures. The work demonstrates the potential for the use of nematic liquid crystalline elastomers in many acoustic and vibration damping applications.

  5. Biaxial nematic liquid crystals theory, simulation and experiment

    CERN Document Server

    Luckhurst, Geoffrey R

    2015-01-01

    Liquid Crystals are a state of matter that have properties between those of conventional liquid and those of a solid crystal. Thermotropic liquid crystals react to changes in temperature or, in some cases, pressure. The reaction of lyotropic liquid crystals, which are used in the manufacture of soaps and detergents, depends on the type of solvent they are mixed with. Since the accidental discovery of the chiral nematic (ordered) phase in 1888 many liquid crystal phases have been found, sometimes by chance and sometimes by design. The existence of one such phase was predicted by Freiser in 197

  6. Droplet Breakup of the Nematic Liquid Crystal MBBA

    CERN Document Server

    Nachman, Benjamin

    2012-01-01

    Droplet breakup is a well studied phenomena in Newtonian fluids. One property of this behavior is that, independent of initial conditions, the minimum radius exhibits power law scaling with the time left to breakup tau. Because they have additional structure and shear dependent viscosity, liquid crystals pose an interesting complication to such studies. Here, we investigate the breakup of a synthetic nematic liquid crystal known as MBBA. We determine the phase of the solution by using a cross polarizer setup in situ with the liquid bridge breakup apparatus. Consistent with previous studies of scaling behavior in viscous-inertial fluid breakup, when MBBA is in the isotropic phase, the minimum radius decreases as tau^{1.03 \\pm 0.04}. In the nematic phase however, we observe very different thinning behavior. Our measurements of the thinning profile are consistent with two interpretations. In the first interpretation, the breakup is universal and consists of two different regimes. The first regime is characterize...

  7. Co-dispersion of plasmonic nanorods in thermotropic nematic liquid crystals

    Science.gov (United States)

    Sheetah, Ghadah; Liu, Qinkun; Smalukh, Ivan

    Colloidal dispersions of plasmonic metal nanoparticles in liquid crystals promise the capability of pre-engineering tunable optical properties of mesostructured metal-dielectric composites. Recently, concentrated dispersions of anisotropic gold, silver, and metal alloy nanoparticles in nematic hosts have been achieved and successfully controlled by low-voltage fields. However, to enable versatile designs of material behavior of the composites, simultaneous co-dispersion of anisotropic particles with different shapes, alignment properties, and compositions are often needed. We achieve such co-dispersions and explore their switching characteristics in response to external stimuli like light and electric fields. We demonstrated that spectral characteristics of co-dispersions of multiple types of anisotropic nanoparticles in a common nematic host provides unprecedented variety of electrically- and optically-tunable material behavior, with a host of potential practical applications in electro-optic devices and displays Ghadah acknowledges support from the King Faisal University (KFU) graduate fellowship.

  8. Robustness of the periodic and chaotic orientational behavior of tumbling nematic liquid crystals.

    Science.gov (United States)

    Heidenreich, Sebastian; Ilg, Patrick; Hess, Siegfried

    2006-06-01

    The dynamical behavior of molecular alignment strongly affects physical properties of nematic liquid crystals. A theoretical description can be made by a nonlinear relaxation equation of the order parameter and leads to the prediction that rather complex even chaotic orientational behavior occur. Here the influence of fluctuating shear rates on the orientational dynamics especially on chaotic solutions is discussed. With the help of phase portraits and time evolution diagrams, we investigated the influence of different fluctuation strengths on the flow aligned, isotropic, and periodic solutions. To explore the effect of fluctuations on the chaotic behavior, we calculated the largest Lyapunov exponent for different fluctuation strengths. We found in all cases that small fluctuations of the shear rate do not affect the basic features of the dynamics of tumbling nematics. Furthermore, we present an amended potential modeling the isotropic to nematic transition and discuss the equivalence and difference to the commonly used Landau-de Gennes potential. In contrast to the Landau-de Gennes potential, our potential has the advantage to restrict the order parameter to physically admissible values. In the case of extensional flow, we show that the amended potential leads for increasing extensional rate to a better agreement with experimental results. PMID:16906852

  9. Robustness of the periodic and chaotic orientational behavior of tumbling nematic liquid crystals

    International Nuclear Information System (INIS)

    The dynamical behavior of molecular alignment strongly affects physical properties of nematic liquid crystals. A theoretical description can be made by a nonlinear relaxation equation of the order parameter and leads to the prediction that rather complex even chaotic orientational behavior occur. Here the influence of fluctuating shear rates on the orientational dynamics especially on chaotic solutions is discussed. With the help of phase portraits and time evolution diagrams, we investigated the influence of different fluctuation strengths on the flow aligned, isotropic, and periodic solutions. To explore the effect of fluctuations on the chaotic behavior, we calculated the largest Lyapunov exponent for different fluctuation strengths. We found in all cases that small fluctuations of the shear rate do not affect the basic features of the dynamics of tumbling nematics. Furthermore, we present an amended potential modeling the isotropic to nematic transition and discuss the equivalence and difference to the commonly used Landau-de Gennes potential. In contrast to the Landau-de Gennes potential, our potential has the advantage to restrict the order parameter to physically admissible values. In the case of extensional flow, we show that the amended potential leads for increasing extensional rate to a better agreement with experimental results

  10. Two-Dimensional Spatial Solitons in Nematic Liquid Crystals

    Institute of Scientific and Technical Information of China (English)

    ZHONG Wei-Ping; YANG Zheng-Ping; XIE Rui-Hua; Milivoj Be-lie; Goong Chen

    2009-01-01

    We study the propagation of spatial solitons in nematic liquid crystals, using the self-similar method.Analytical solutions in the form of self-similar solitons are obtained exactly.We confirm the stability of these solutions by direct numerical simulation, and find that the stable spatial solitons can exist in various forms, such as Gaussian solitons, radially symmetric solitons, multipoIe solitons, and soliton vortices.

  11. Surface induced structures in nematic liquid crystal colloids

    OpenAIRE

    Chernyshuk, S. B.; Tovkach, O. M.; Lev, B. I.

    2014-01-01

    We predict theoretically the existence of a class of colloidal structures in nematic liquid crystal (NLC) cells, which are induced by surface patterns on the plates of the cell (like cells with UV-irradiated polyimide surfaces using micron size masks). These bulk structures arise from non-zero boundary conditions for the director distortions at the confining surfaces. In particular, we demonstrate that quadrupole spherical particles (like spheres with boojums or Saturn-ring director configura...

  12. Spinodal dewetting of a nematic liquid crystal film

    Science.gov (United States)

    Braun; Yokoyama

    2000-08-01

    We discuss spinodal dewetting of a nematic film destabilized by Van der Waals forces, focusing on the case of non-antagonistic anchoring conditions. Using physical parameters pertinent to low-molecular-weight thermotropic liquid crystals, we predict a small damping effect. In the presence of an antagonistic applied magnetic field, the anchoring conditions become more significant, and can influence the shape and dynamics of the unstable modes. PMID:11088786

  13. Nematic Liquid Crystal Spatial Light Modulators for Laser Beam Steering

    OpenAIRE

    Hällstig, Emil

    2004-01-01

    Laser beam control is important in many applications. Phase modulating spatial light modulators (SLMs) can be used to electronically alter the phase distribution of an optical wave-front and thus change the direction and shape of a laser beam. Physical constraints set limitations to the SLM and an ideal phase distribution can usually not be realised. In order to understand how such components can be used for non-mechanical beam control three nematic liquid crystal (NLC) SLMs have been thoroug...

  14. General elastic interaction in nematic liquid crystals colloids

    OpenAIRE

    Chernyshuk, S. B.; Lev, B. I.

    2009-01-01

    The new free energy functional that describes general elastic interaction between colloidal particles and nematic liquid crystal has been proposed. It generalizes results of the paper \\cite{lupe} on the case of arbitrary orientation of colloidal particles and is valid for arbitrary surface anchoring strength. Formal analogies and differences between electric particles and colloidal particles in LC are found. It is first time shown that spur of the quadrupole moment tensor is different from ze...

  15. Chaotic orientational behavior of a nematic liquid crystal subjected to a steady shear flow.

    Science.gov (United States)

    Rienäcker, Götz; Kröger, Martin; Hess, Siegfried

    2002-10-01

    Based on a relaxation equation for the second rank alignment tensor characterizing the molecular orientation in liquid crystals, we report on a number of symmetry-breaking transient states and simple periodic and irregular, chaotic out-of-plane orbits under steady flow. Both an intermittency route and a period-doubling route to chaos are found for this five-dimensional dynamic system in a certain range of parameters (shear rate, tumbling parameter at isotropic-nematic coexistence, and reduced temperature). A link to the corresponding rheochaotic states, present in complex fluids, is made. PMID:12443167

  16. Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

    Science.gov (United States)

    Tartan, Chloe C.; Salter, Patrick S.; Booth, Martin J.; Morris, Stephen M.; Elston, Steve J.

    2016-05-01

    Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10-100 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.

  17. Elastic Properties of Nematic Liquid Crystals Formed by Living and Migrating Cells

    CERN Document Server

    Kemkemer, R; Kaufmann, D; Gruler, H; Kemkemer, Ralf; Kling, Dieter; Kaufmann, Dieter; Gruler, Hans

    1998-01-01

    In culture migrating and interacting amoeboid cells can form nematic liquid crystal phases. A polar nematic liquid crystal is formed if the interaction has a polar symmetry. One type of white blood cells (granulocytes) form clusters where the cells are oriented towards the center. The core of such an orientational defect (disclination) is either a granulocyte forced to be in an isotropic state or another cell type like a monocyte. An apolar nematic liquid crystal is formed if the interaction has an apolar symmetry. Different cell types like human melanocytes (=pigment cells of the skin), human fibroblasts (=connective tissue cells), human osteoblasts (=bone cells), human adipocytes (= fat cells) etc., form an apolar nematic liquid crystal. The orientational elastic energy is derived and the orientational defects (disclination) of nematic liquid crystals are investigated. The existence of half-numbered disclinations show that the nematic phase has an apolar symmetry. The density- and order parameter dependence...

  18. Homeotropic orientation of a nematic liquid crystal by bent-core molecules adsorbed on its surface

    Science.gov (United States)

    Hwang, Jiyong; Yang, Seungbin; Lee, Hyojin; Kim, Jongyoon; Lee, Ji-Hoon; Kang, Shin-Woong; Choi, E.-Joon

    2015-06-01

    We reported the promotion of a homeotropic alignment of a nematic liquid crystal (NLC) by bent-core liquid-crystal (BLC) Molecules adsorbed its surface. The BLC was mixed at various concentrations with the NLC, and the mixtures were injected into an empty cell with a cell gap of 13 μm. Although the pure NLC showed a heterogeneous orientation, the BLC-NLC mixture was gradually transformed to a homeotropic alignment with increasing concentration of the BLC. We investigated the surface topography of the samples by using an atomic force microscopy (AFM) and found that the BLC molecules were segregated into a polyimide (PI) surface and formed protrusion domains with diameters of 50-100 nm. The BLC protrusions might promote the homeotropic orientation of the NLC molecules.

  19. Orientational fluctuation study in nematic liquid crystals by high speed micrograph

    Science.gov (United States)

    Yoon, Beom-Jin; Park, Min Sang; Park, Jung O.; Srinivasarao, Mohan

    2009-03-01

    The orientational fluctuations in uniaxial and biaxial nematic liquid crystals were investigated with a polarized microscope and a high speed TV camera. Liquid crystals usually have fluctuations with respect to their director, even when the molecular axes tend to be aligned to each other. These fluctuations are sufficiently slow and large, have long wave length and increase with temperature. Herein, we describe our study on fluctuation dynamics by direct observations in real space, while it has been typically done by the photon scattering in reciprocal space. The twinkling of liquid crystals due to orientational fluctuations was observed with a high speed camera up to 500 frames/sec. The time correlation function of the intensity was computed via 2D spatial Fourier transform of each image and then the relaxation frequency was estimated from it. The elastic constant to the viscosity ratio was computed from the relaxation frequency. This approach provides facile route to analyze fluctuation dynamics in liquid crystals.

  20. Transitions through critical temperatures in nematic liquid crystals

    KAUST Repository

    Majumdar, Apala

    2013-08-06

    We obtain estimates for critical nematic liquid crystal (LC) temperatures under the action of a slowly varying temperature-dependent control variable. We show that biaxiality has a negligible effect within our model and that these delay estimates are well described by a purely uniaxial model. The static theory predicts two critical temperatures: the supercooling temperature below which the isotropic phase loses stability and the superheating temperature above which the ordered nematic states do not exist. In contrast to the static problem, the isotropic phase exhibits a memory effect below the supercooling temperature in the dynamic framework. This delayed loss of stability is independent of the rate of change of temperature and depends purely on the initial value of the temperature. We also show how our results can be used to improve estimates for LC material constants. © 2013 American Physical Society.

  1. Advection of nematic liquid crystals by chaotic flow

    CERN Document Server

    O'Naraigh, Lennon

    2016-01-01

    Consideration is given to the effects of inhomogeneous shear flow (both regular and chaotic) on nematic liquid crystals in a planar two-dimensional geometry. The Landau-de Gennes equation coupled to an externally-prescribed flow field is the basis for the study: this is solved numerically in a periodic spatial domain. The focus is on a limiting case where the advection is passive, such that variations in the liquid-crystal properties do not feed back into the equation of motion for the uid velocity. The numerical simulations demonstrate that the coarsening of the liquid-crystal domains is arrested by the ow. The nature of the arrest is different depending on whether the flow is regular or chaotic. For the specific case where tumbling is important, the flow has a strong effect on the the liquid-crystal morphology: this provides a mechanism for controlling the shape of the liquid-crystal domains.

  2. Nematic Director Reorientation at Solid and Liquid Interfaces under Flow: SAXS Studies in a Microfluidic Device

    OpenAIRE

    Silva, Bruno F. B.; Zepeda-Rosales, Miguel; Venkateswaran, Neeraja; Fletcher, Bretton J.; Carter, Lester G.; MATSUI, Tsutomu; Weiss, Thomas M.; Han, Jun; Li, Youli; Olsson, Ulf; Safinya, Cyrus R.

    2014-01-01

    In this work we investigate the interplay between flow and boundary condition effects on the orientation field of a thermotropic nematic liquid crystal under flow and confinement in a microfluidic device. Two types of experiments were performed using synchrotron small-angle X-ray-scattering (SAXS). In the first, a nematic liquid crystal flows through a square-channel cross section at varying flow rates, while the nematic director orientation projected onto the velocity/velocity gradient plane...

  3. Non-equilibrium nature of two-dimensional isotropic and nematic coexistence in amyloid fibrils at liquid interfaces

    Science.gov (United States)

    Jordens, Sophia; Isa, Lucio; Usov, Ivan; Mezzenga, Raffaele

    2013-05-01

    Two-dimensional alignment of shape-anisotropic colloids is ubiquitous in nature, ranging from interfacial virus assembly to amyloid plaque formation. The principles governing two-dimensional self-assembly have therefore long been studied, both theoretically and experimentally, leading, however, to diverging fundamental interpretations on the nature of the two-dimensional isotropic-nematic phase transition. Here we employ single-molecule atomic force microscopy, cryogenic scanning electron microscopy and passive probe particle tracking to study the adsorption and liquid crystalline ordering of semiflexible β-lactoglobulin fibrils at liquid interfaces. Fibrillar rigidity changes on increasing interfacial density, with a maximum caused by alignment and a subsequent decrease stemming from crowding and domain bending. Coexistence of nematic and isotropic regions is resolved and quantified by a length scale-dependent order parameter S2D(d). The nematic surface fraction increases with interfacial fibril density, but depends, for a fixed interfacial density, on the initial bulk concentration, ascribing the observed two-dimensional isotropic-nematic coexistence to non-equilibrium phenomena.

  4. Nematic quantum liquid crystals of bosons in frustrated lattices

    Science.gov (United States)

    Zhu, Guanyu; Koch, Jens; Martin, Ivar

    2016-04-01

    The problem of interacting bosons in frustrated lattices is an intricate one due to the absence of a unique minimum in the single-particle dispersion where macroscopic number of bosons can condense. Here, we consider a family of tight-binding models with macroscopically degenerate lowest energy bands, separated from other bands by a gap. We predict the formation of exotic states that spontaneously break rotational symmetry at relatively low filling. These states belong to three nematic phases: Wigner crystal, supersolid, and superfluid. The Wigner crystal phase is established exactly at low filling. Supersolid and superfluid phases, at larger filling, are obtained by making use of a projection onto the flat band, construction of an appropriate Wannier basis, and subsequent mean-field treatment. The nematic superfluid that we predict is uniform in real space but has an anisotropic momentum distribution, providing a novel scenario for Bose condensation with an additional nematic order. Our findings open up a promising direction of studying microscopic quantum liquid crystalline phases of bosons.

  5. Flexoelectricity in an oxadiazole bent-core nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, S., E-mail: Sarabjot.Kaur@manchester.ac.uk; Panov, V. P.; Gleeson, H. F. [School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); Greco, C.; Ferrarini, A. [Department of Chemical Sciences, University of Padua, Padua I-35131 (Italy); Görtz, V. [Department of Chemistry, University of York, York YO10 5DD (United Kingdom); Department of Chemistry, University of Lancaster, Lancaster LA1 4YB (United Kingdom); Goodby, J. W. [Department of Chemistry, University of York, York YO10 5DD (United Kingdom)

    2014-12-01

    We have determined experimentally the magnitude of the difference in the splay and bend flexoelectric coefficients, |e{sub 1} − e{sub 3}|, of an oxadiazole bent-core liquid crystal by measuring the critical voltage for the formation of flexodomains together with their wave number. The coefficient |e{sub 1} − e{sub 3}| is found to be a factor of 2–3 times higher than in most conventional calamitic nematic liquid crystals, varying from 8 pCm{sup −1} to 20 pCm{sup −1} across the ∼60 K—wide nematic regime. We have also calculated the individual flexoelectric coefficients e{sub 1} and e{sub 3}, with the dipolar and quadrupolar contributions of the bent-core liquid crystal by combining density functional theory calculations with a molecular field approach and atomistic modelling. Interestingly, the magnitude of the bend flexoelectric coefficient is found to be rather small, in contrast to common expectations for bent-core molecules. The calculations are in excellent agreement with the experimental values, offering an insight into how molecular parameters contribute to the flexoelectric coefficients and illustrating a huge potential for the prediction of flexoelectric behaviour in bent-core liquid crystals.

  6. Dispersion and Excluded Volume Interactions in Nematic Liquid Crystals.

    Science.gov (United States)

    Poliks, Mark David

    1988-12-01

    The effectiveness of the potential of mean torque in accounting for solute orientation is explored. It is described by repulsive (excluded volume) and attractive forces (dispersion) and is tested using rigid, semi-flexible and flexible solutes dissolved in nematic phases. For rigid molecules (benzenes and anthracene) the attractive short range potential gave the best results. For anthracene the results indicated that the potential can discriminate between solute/solvent interactions. For wholly aliphatic solvents the excluded volume forces gave excellent agreement, as did the attractive forces for the aromatic solvents. For the semi-flexible molecule, biphenyl, quadrupole splittings were simulated using the internal torsion angle as a parameter. The values of this angle were predicted to vary systematically with temperature. Using crystallographic and idealized structural data as the starting points for the calculation, the structure of PAA in the nematic phase was estimated. Both the internal angle and the aromatic proton valence angles were determined. Flexible, "siamese-twin" liquid crystals having an internal per-deuterated spacer consisting of ten methylenes were studied. They differed only in the length of the aliphatic tails (5105, 101010). The quadrupole splittings of both twins dissolved in the nematic phase of BCH-S1131 were identical. Quantitative simulations of the splittings using standard RIS geometry and excluded volume forces were successful. In the bulk nematic phase the order parameter of 5105 was greater than 101010. The difference was interpreted as a dilution effect of the mesogenic cores by aliphatic tails. Simulations indicated the conformation of the spacer is highly extended. As parameterized the required strength of the mean field is a strong function of the molecular dimensions, suggesting that the current description still is incomplete.

  7. Determination of azimuthal anchoring strength in twisted nematic liquid crystal cells using heterodyne polarimeter.

    Science.gov (United States)

    Yu, Tsung-Chih; Lo, Yu-Lung; Huang, Rei-Rong

    2010-09-27

    Two external-field-free methods are presented for measuring the azimuthal anchoring strength in twisted nematic liquid crystal (TNLC) cells. For asymmetrical TNLC samples, the twist angle is derived from the phase of the detected signal in a phase-sensitive heterodyne polarimeter and is then used to calculate the weak anchoring strength directly. The measurement resolution which is found to be about 0.01 μJ/m(2) makes the present method sensitive enough for the LC-based bio-sensing application. Using the proposed method, the weak azimuthal anchoring strength of a composite liquid crystal mixture (40% LCT-061153 + 60% MJO-42761) in contact with a plasma-alignment layer is found to be 7.19 μJ/m(2). For symmetrical TNLC samples, the liquid crystals are injected into a wedge cell, and the two-dimensional distributions of the twist angle and cell gap are extracted from the detected phase distribution using a genetic algorithm (GA). The azimuthal anchoring strength is then obtained by applying a fitting technique to the twist angle vs. cell gap curve. Utilizing the proposed approach, it is shown that the strong anchoring strength between a rubbed polyimide (PI) alignment layer and E7 liquid crystal is around 160 μJ/m(2) while that between a rubbed PI alignment layer and MLC-7023 liquid crystal is approximately 32 μJ/m(2). PMID:20941014

  8. Polarization converters based on axially symmetric twisted nematic liquid crystal.

    Science.gov (United States)

    Ko, Shih-Wei; Ting, Chi-Lun; Fuh, Andy Y-G; Lin, Tsung-Hsien

    2010-02-15

    An axially symmetric twisted nematic liquid crystal (ASTNLC) device, based on axially symmetric photoalignment, was demonstrated. Such an ASTNLC device can convert axial (azimuthal) to azimuthal (axial) polarization. The optical properties of the ASTNLC device are analyzed and found to agree with simulation results. The ASTNLC device with a specific device can be adopted as an arbitrary axial symmetric polarization converter or waveplate for axially, azimuthally or vertically polarized light. A design for converting linear polarized light to axially symmetric circular polarized light is also demonstrated. PMID:20389369

  9. Singularities and nonuniqueness in cylindrical flow of nematic liquid crystals

    OpenAIRE

    Van Hout, R.; Vilucchi, E

    2001-01-01

    The subject of this paper is the behavior of the director field of a nematic liquid crystal in flow through a tube with circular cross-section. Both the flow and the director field are assumed to have cylindrical symmetry. The requirement of finite Frank-Oseen energy forces ``admissible" director fields to be axially directed at the location of the symmetry axis. Thus, the angle between the axis and the director field at the location of the axis amounts to $k\\pi$, $k$ being an ...

  10. Role of Molecular Structure on X-ray Diffraction in Thermotropic Uniaxial and Biaxial Nematic Liquid Crystal Phases

    Energy Technology Data Exchange (ETDEWEB)

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra; (Kent); (Platypus)

    2009-08-27

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  11. Quasielastic Light Scattering Measurements of the Anisotropic Mechanical Properties of a Polymer Nematic Liquid Crystal.

    Science.gov (United States)

    Taratuta, Victor Gregory

    An experimental investigation of macroscopic mechanical properties of a polymer nematic liquid crystal was conducted on nematic solutions formed from rigid or semiflexible main chain polymers that are fully extended in a solution. The particular system under investigation is a poly-(gamma) -benzyl glutamate (PBG) which belongs to a class of synthetic polypeptides. Quasielastic Rayleigh light scattering on well aligned nematic single crystals of PBG was used to measure the elastic constants and the anisotropic viscosities as a function of concentration. The elastic constants are measured from the intensity of the scattered light which is determined by the amplitude of thermally excited director fluctuations. That amplitude depends on the energy of the fluctuation which is proportional to the appropriate elastic constant. The viscosities associated with the elastic deformation modes are computed from the characteristic relaxation times of the fluctuations by measuring their temporal autocorrelation function. The splay and bend elastic constants were found to be very similar in magnitude; both showed a linear dependence on concentration. The twist elastic constant was much smaller than either splay or bend and showed only a weak concentration dependence. Four out of five independent Leslie viscosities were measured (except the elongational flow viscosity (alpha)(,1)). The viscosities were found to exhibit very large anisotropies. Different types of viscosities showed distinctly different patterns of concentration dependence. (gamma)(,1) and (eta)(,c) were quadratic in concentration, (eta)(,a) was linear in concentration, and (eta)(,b) did not show any strong concentration dependence. The viscosity data indicate that even at a moderate length to diameter ratio studied (L/D - 30), the PBG approaches a behavior predicted for a system composed of infinitely long molecular chains. The concentration dependence data for the elastic constants and the anisotropic viscosities

  12. Tetratic, triatic and nematic liquid crystals on a complex plane

    Science.gov (United States)

    Manyuhina, Oksana; Bowick, Mark

    Liquid crystals are elastic materials able to resolve geometric and topological frustration by creating disclinations, discontinuities in their continuous orientation field. The strength and the nature of disclinations depend on the symmetry of elements forming liquid crystal phase. Several examples of confined nematic (director field), triatic (Y-field) and tetratic (cross-field) liquid crystals will be considered to show that their ground state contains topological defects. Next, we analyze shape variation of the boundary, enclosing different defect textures. We argue that topological defects can capture essential features of macroscopic shape and relate it to microscopic order, providing a natural way to connect different length scales and to account for large deformations in soft and biological systems. Soft Matter Program of Syracuse University.

  13. Substrate-induced gliding in a nematic liquid crystal layer

    Science.gov (United States)

    Mema, E.; Kondic, L.; Cummings, L. J.

    2015-12-01

    We consider the interaction between nematic liquid crystals (NLCs) and polymer substrates. Such substrates can interact with NLCs, exhibiting a phenomenon known as director gliding: the preferred orientation of the NLC molecules at the interface changes on time scales that are slow relative to the elastic relaxation time scale of the NLC. We present two models for gliding, inspired by experiments that investigate the interaction between the NLC and a polymer substrate. These models, though simple, lead to nontrivial results, including loss of bistability under gliding. Perhaps surprisingly, we find that externally imposed switching between the steady states of a bistable system may reverse the effect of gliding, preventing loss of bistability if switching is sufficiently frequent. Our findings may be of relevance to a variety of technological applications involving liquid crystal devices, and particularly to a new generation of flexible liquid crystal displays that implement polymeric substrates.

  14. Alignment of liquid crystal on a polyimide surface exposed to an Ar ion beam

    International Nuclear Information System (INIS)

    In this paper properties of nematic liquid crystals aligned on polyimide surfaces exposed to a low-energy Ar ion beam are investigated. We studied how the pretilt angle of a liquid crystal cell is affected by ion-beam conditions, such as the energy of the incident ions, the angle of incidence, and the exposure time. X-ray photoelectron spectroscopy data indicate that ion-beam exposure changes the chemical bonding states of the polyimide surface, which may be one of the main causes of anisotropic liquid crystal alignment. We also found that twisted-nematic cells fabricated by the ion-beam alignment method have the voltage holding time enough for application to thin-film-transistor liquid crystal displays

  15. Investigation into the temperature dependence of isotropic- nematic phase transition of Gay- Berne liquid crystals

    OpenAIRE

    A Avazpour; S M Hekmatzadeh

    2014-01-01

    Density functional approach was used to study the isotropic- nematic (I-N) transition and calculate the values of freezing parameters of the Gay- Berne liquid crystal model. New direct and pair correlation functions of a molecular fluid with Gay- Berne pair potential were used. These new functions were used in density functional theory as input to calculate the isotropic- nematic transition densities for elongation at various reduced temperatures. It was observed that the isotropic- nematic...

  16. Smectic-A Order at the Surface of a Nematic Liquid Crystal: Synchrotron X-Ray Diffraction

    OpenAIRE

    Als-Nielsen, J.; Christensen, F.; Pershan, Peter S.

    1982-01-01

    A novel geometry in which it is possible to do x-ray diffraction from a horizontal surface of fluids is applied to liquid crystals. A large-diameter drop of octyloxycyanobiphenyl (8OCB) on a glass plate treated for homeotropic alignment yields perfect alignment of the smectic-A layers at the top surface over an area of several square millimeters. The surface in the bulk nematic as well as in the isotropic phase was found to consist of smectic-A layers with a penetration depth equal to the lon...

  17. Light-controlled topological charge in a nematic liquid crystal

    Science.gov (United States)

    Nikkhou, Maryam; Škarabot, Miha; Čopar, Simon; Ravnik, Miha; Žumer, Slobodan; Muševič, Igor

    2015-02-01

    Creating, imaging, and transforming the topological charge in a superconductor, a superfluid, a system of cold atoms, or a soft ferromagnet is a difficult--if not impossible--task because of the shortness of the length scales and lack of control. The length scale and softness of defects in liquid crystals allow the easy observation of charges, but it is difficult to control charge creation. Here we demonstrate full control over the creation, manipulation and analysis of topological charges that are pinned to a microfibre in a nematic liquid crystal. Oppositely charged pairs are created through the Kibble-Zurek mechanism by applying a laser-induced local temperature quench in the presence of symmetry-breaking boundaries. The pairs are long-lived, oppositely charged rings or points that either attract and annihilate, or form a long-lived, charge-neutral loop made of two segments with a fractional topological charge.

  18. New theories for smectic and nematic liquid crystalline polymers

    International Nuclear Information System (INIS)

    A summary of results from new statistical-physics theories for both backbone and side-chain liquid crystalline polymers (LCPs) and for mixtures with LCPs is presented. Thermodynamic and molecular ordering properties (including odd-even effects) have been calculated as a function of pressure, density, temperature, and molecule chemical structures (including degree of polymerization and the following properties of the chemical structures of the repeat units: lengths and shapes, intra-chain rotation energies, dipole moments, site-site polarizabilities and Lennard-Jones potentials, etc.) in nematic and multiple smectic-A LC phases and in the isotropic liquid phase. These theories can also be applied to combined LCPs. Since these theories have no ad hoc or arbitrarily adjustable parameters, these theories have been used to design new LCPs and new solvents and to predict and explain properties

  19. Zenithal alignment of liquid crystal on homeotropic polyimide film irradiated by ion beam

    OpenAIRE

    Choi, Yoonseuk; Yoon, Tae-Hoon; Kwon, Jin Hyuk; Yi, Jonghoon; Gwag, Jin Seog

    2012-01-01

    We investigate the pretilt characteristics of a nematic liquid crystal [LC] in terms of ion beam exposure conditions on the homeotropic polyimide alignment layer. The pretilt angle of LCs in the case of high-energy ion beam treatment was decreased considerably almost the same to that of the homogenous alignment layer though we used homeotropic polyimide film at first. Increasing irradiating energy, we could control the pretilt from 90° to 1° with several steps. We believe that this is because...

  20. Rheological properties of a reentrant nematic liquid crystal.

    Science.gov (United States)

    Ananthaiah, J; Rajeswari, M; Sastry, V S S; Dabrowski, R; Dhara, Surajit

    2012-07-01

    We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (N(R)) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-N(R) phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-N(R) phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density. PMID:23005440

  1. Rheological properties of a reentrant nematic liquid crystal

    Science.gov (United States)

    Ananthaiah, J.; Rajeswari, M.; Sastry, V. S. S.; Dabrowski, R.; Dhara, Surajit

    2012-07-01

    We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (NR) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-NR phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-NR phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density.

  2. Fast switching from isotropic liquids to nematic liquid crystals: rotaxanes as smart fluids.

    Science.gov (United States)

    He, Hao; Sevick, Edith M; Williams, David R M

    2015-11-28

    We examine a solution of rod-like piston-rotaxanes, which can switch their length by external excitation (for example optically) from a short state of length L to a long state of length qL. We show that this solution can exhibit a number of different behaviours. In particular it can rapidly switch from an isotropic to a nematic liquid crystalline state. There is a minimum ratio q* = 1.13 for which transitions from a pure isotropic state to a pure nematic state are possible. We present a phase-switching diagram, which gives the six possible behaviours for this system. It turns out that a large fraction of the phase switching diagram is occupied by the transition from a pure isotropic to a pure nematic state. PMID:26419821

  3. Solitons and defects in nematic liquid crystals under a simple shear flow and in a static external magnetic field

    Institute of Scientific and Technical Information of China (English)

    Luo Kai-Fu; Jiang Xiu-Li; Yang Yu-Liang

    2008-01-01

    Under a simple shear flow and in a static external magnetic field, the production of defects in the director-aligning regime of nematic liquid crystals has been investigated in terms of the Leslie-Ericksen theory. The equation of motion of the nematic director, which conforms to the driven over-damped sine-Gordon equation, has a soliton solution of the amplitude π. We show that the stationary state with the director uniformly oriented at a Leslie angle is only a metastable state and the potential, which governs the motion of the director, has a number of stable stationary states. For a strong magnetic field, the higher energy barrier between the stable and unstable states leads the director to be locked along the magnetic field direction. However, at the appropriate shear rate and magnetic field the defects, which appear as a stable solitary solution, can be nucleated from a uniformly aligned nematic liquid crystal. We have calculated the stationary travelling velocity of the solitary waves and the distance between a pair of defects.

  4. Breakup of partially wetting nanoscale nematic liquid films

    Science.gov (United States)

    Lam, Michael; Linda Cummings Collaboration; Lou Kondic Collaboration; Te-Sheng Lin Collaboration

    2015-11-01

    The breakup of nematic liquid crystals (NLCs) films with thicknesses less than a micrometer is studied. Particular attention is paid to the interplay between the bulk elasticity and the anchoring (boundary) conditions at the substrate and free surface. Within the framework of the long wave approximation, a fourth order nonlinear partial differential equation (PDE) is derived for the free surface height. Numerical simulations of a perturbed flat film show that, depending on the initial average thickness of the film, satellite droplets form and persist on time scales much longer than dewetting. Formulating the model in terms of an effective disjoining pressure (elastic response and van der Waals interaction), simulations further suggest that satellite droplets form when the initial average film thickness corresponds to a positive effective disjoining pressure. Our results may shed light on the so-called ''forbidden film thicknesses'' seen in experiments. Supported by NSF grant DMS-1211713.

  5. Dielectric Anisotropy of Gold Nanoparticle Colloids in Nematic Liquid Crystals

    Science.gov (United States)

    Visco, Angelo; Foust, Jon; Mahmood, Rizwan

    We present electrical and optical studies of hexanethiol-treated gold nanoparticle (GNPs) colloids in 4-cyano-4 '-pentyl-biphenyl (5CB) liquid crystals. Preliminary data analysis suggests an unusual behavior of sudden drop and then rise in the dielectric anisotropy at a critical concentration of 0.0862% by wt. GNPs and a sudden rise and then drop in the nematic to isotropic transition temperature. Above the critical concentration the data level off to within the uncertainty of the experimental errors. This colloidal system will help us to understand the interaction and the effects of nanoparticles on the self-assembly of LC molecules and the manner in which these particles organize in LC. This study is important for further developments in nanotechnology, sharp and fast display panels, and within the medical field.

  6. Hydrodynamics of defects in nematic liquid crystal films

    International Nuclear Information System (INIS)

    In this thesis I propose a new theory to deal with the presence of a macroscopic density of defects or disclinations in two-dimensional systems of uniaxial nematic liquid crystal. The static part of the Abelian-Higgs model is the basis for a gauge covariant form of the Frank free energy for distortions in nematics, where the gauge field models the screening due to the presence of the defects. Certain results for vortices in the Abelian-Higgs model are reformulated for use in my theory. The model suggests disclinations with an isotropic core region. The covariant Frank free energy is used to derive a new form of the Ericksen-Leslie equations describing the hydrodynamics off nematics. These equations are set up according to the concept of thermodynamic fluxes and forces. Detailed analytic results are derived for the case where the dynamics is due to director reorientations, but no liquid flow. The hydrodynamic equations are reduced to dynamic equations for disclination points assuming a quasi-static motion in moduli space. The static form of the disclinations is based on solutions in the Bogomol'nyi limit, their quasi-static motion is induced through a deviation from this limit. The resulting equations are valid for a configuration containing disclinations with winding numbers of the same sign. These general equations require a, specific ansatz to yield further results. I consider two regimes, for defects close together and far apart from one another. A set of disclinations with winding numbers of the same sign which are close to one another, i.e. with overlapping cores, can result from disintegration of a larger disclination, and they repel one another. The results for this case predict how the disintegration could occur. The interaction of disclinations, with winding numbers of the same sign, which are far apart from one another is repulsive and decreases exponentially with the distances between them. Two such disclinations move on a straight line where their

  7. Liquid crystal alignment on excimer laser irradiated polyimide

    International Nuclear Information System (INIS)

    Grating and photoinduced anisotropic modifications are made to polyimide layers to promote homogeneous and pretilted nematic liquid crystal alignment. Gratings are etched into the polyimide by irradiating a phase mask of period 1.1 μm with the output from a KrF excimer laser of wavelength 248 nm with fluences above the threshold required for ablation. Grating depths from 10 to 190 nm have been achieved using a simple pulse from the laser, and the liquid crystal azimuthal anchoring energy is determined as a function of the grating depth. Values up to 1.3 x 10-5 Jm-2 are found. Discrepancies are found when comparisons are made between experimental data and a theory based upon elastic strain energy minimisation. A modified theory taking finite polar anchoring into account shows better agreement. Polarised excimer laser radiation at normal incidence is used to induce an anisotropy which gives rise to homogeneous liquid crystal alignment. The strength of the azimuthal anchoring energy is similar to that produced by grating alignment. Spectroscopic analysis reveals that the alignment originates from the stronger depletion of polyimide chains parallel to the exposure polarisation direction. The dependence of beam fluence and exposure time on the anchoring energy is measured, and the degradation mechanism of the polyimide is investigated as a function of the exposure. We find that oxidative degradation takes place. We also use these techniques to identify the chemical composition of the polyimide material. Pretilted liquid crystal alignment has also been achieved, with pretilt angles up to 3.7 deg. A tilted polymer distribution is generated by oblique exposure of the polyimide to an elliptically polarised beam. We measure the liquid crystal pretilt angle as a function of the angle of incidence, and exposure time and present a theoretical analysis of the polyimide chain azimuthal distribution which agrees with the experimental results. Finally, a simple and novel technique

  8. Shape changing nonlocal molecular deformations in a nematic liquid crystal system

    Directory of Open Access Journals (Sweden)

    L. Kavitha

    2015-10-01

    Full Text Available The nature of nonlinear molecular deformations in a homeotropically aligned nematic liquid crystal (NLC is presented. We start from the basic dynamical equation for the director axis of a NLC with elastic deformation and mapped onto a integro-differential perturbed Nonlinear Schrödinger equation which includes the nonlocal term. By invoking the modified extended tangent hyperbolic function method aided with symbolic computation, we obtain a series of solitary wave solutions. Under the influence of the nonlocality induced by the reorientation nonlinearity due to fluctuations in the molecular orientation, the solitary wave exhibits shape changing property for different choices of parameters. This intriguing property as a result of the relation between the coherence of the solitary deformation and the nonlocality reveals a strong need for a deeper understanding in the theory of self-localization in NLC systems.

  9. Influences of surface and flexoelectric polarization on the effective anchoring energy in nematic liquid crystal

    Science.gov (United States)

    Guan, Rong-Hua; Ye, Wen-Jiang; Xing, Hong-Yu

    2015-10-01

    The physical effects on surface and flexoelectric polarization in a weak anchoring nematic liquid crystal cell are investigated systematically. We derive the analytic expressions of two effective anchoring energies for lower and upper substrates respectively as well as their effective anchoring strengths and corresponding tilt angles of effective easy direction. All of these quantities are relevant to the magnitudes of both two polarizations and the applied voltage U. Based on these expressions, the variations of effective anchoring strength and the tilt angle with the applied voltage are calculated for the fixed values of two polarizations. For an original weak anchoring hybrid aligned nematic cell, it may be equivalent to a planar cell for a small value of U and has a threshold voltage. The variation of reduced threshold voltage with reduced surface polarization strength is also calculated. The role of surface polarization is important without the adsorptive ions considered. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274088, 11374087, and11304074), the Natural Science Foundation of Hebei Province, China (Grant No. A2014202123), the Research Project of Hebei Provincial Education Department, China (Grant No. QN2014130), and the Key Subject Construction Project of Hebei Provincial University, China.

  10. Effect of confining walls on the interaction between particles in a nematic liquid crystal

    International Nuclear Information System (INIS)

    We investigate theoretically how the confining walls of a nematic cell affect the interaction of particles mediated by the elastic deformation of a nematic liquid crystal. We consider the case where strong homeotropic or planar anchoring is imposed on the flat parallel walls so that the director on the wall surfaces is fixed and uniform alignment is achieved in the bulk. This set-up is more realistic experimentally than any other previous theoretical studies concerning the elastic-deformation-mediated interactions that assume an infinite medium. When the anchoring on the particle surfaces is weak, an exact expression of the interaction between two particles can be obtained. The two-body interaction can be regarded as the interaction between one particle and an infinite array of 'mirror images' of the other particle. We also obtain the 'self-energy' of one particle, the interaction of a particle with confining walls, which is interpreted along the same way as the interaction of one particle with its mirror images. We show that the walls play a different role in homeotropic and planar cells, which is attributed to the difference in the symmetry of the cells. We also present the landscapes of the interaction energy when one particle is fixed and demonstrate that the interaction is sensitively dependent on the fixed particle as well as the interparticle distance

  11. Optical security devices using nonuniform schlieren texture of UV-curable nematic liquid crystal.

    Science.gov (United States)

    Nakayama, Keizo; Ohtsubo, Junji

    2016-02-10

    We proposed and quantitatively evaluated an optical security device that provides nonuniform or random patterns of schlieren texture in nematic liquid crystal as unique identification information with a design by employing computer image processing and normalized cross correlation. Using the same photomask as the first author's university logo, the written patterns, which were composed of polymerized isotropic areas and polymerized nematic areas, were stable among different cells. Judging from the maximum correlation coefficient of 0.09, the patterns of the schlieren texture were unique in different cells. These results indicate that photocurable nematic liquid crystal materials have the potential to be applied to security devices for anticounterfeiting measures. PMID:26906368

  12. Dielectrophoretic manipulation of the mixture of isotropic and nematic liquid

    OpenAIRE

    Kim, Soo-Dong; Lee, Bomi; Kang, Shin-Woong; Song, Jang-Kun

    2015-01-01

    In various applications involving liquid crystals, the manipulation of the nanoscale molecular assembly and microscale director alignment is highly useful. Here we show that a nematic–isotropic mixture, a unique bi-liquid system, has potential for the fabrication of microstructures having an ordered phase within a disordered phase, or vice versa. The volume expansion and shrinkage, migration, splitting, mergence and elongation of one phase within the other are easily accomplished via thermal ...

  13. Extremely sensitive light-induced reorientation in nondoped nematic liquid crystal cells due to photoelectric activation of the interface

    International Nuclear Information System (INIS)

    We report an investigation of the extremely sensitive molecular reorientation in pure nematic liquid crystal film induced by the combined application of low dc electric field (less than 0.1 V/μm) and very low intensity optical irradiation (few mW/cm2). The effect is observed in planar cells of well-known commercial nematic mixture (E7) aligned with rubbed polyvinyl alcohol layers, which exhibit photorefractive-like effect. We analyze the dependence of the photoinduced changes in birefringence upon the applied dc voltage and the light intensity. According to our results we believe that the effect is due to photoinduced recombination of the opposite charged carriers accumulated near the interface. In the low dc voltage regime (a few volts) the voltage mainly drops on the electric double layers at the interfaces as a consequence of dc field collected charge carriers from liquid crystalline and polymeric films to the border surfaces. Irradiation with appropriate wavelength reduces the interfacial charges density, because of photoinduced carrier injection and recombination processes, and consequently, induces a relocation of the electric field from the surface to the liquid crystal bulk. The light-induced additional electric field component in the nematic film results in a lowering of the Freedericksz threshold or an enhanced molecular reorientation

  14. Elementary statistical models for nematic transitions in liquid-crystalline systems

    Science.gov (United States)

    Liarte, Danilo B.; Salinas, Silvio R.

    2014-03-01

    We introduce a simple Maier-Saupe-Zwanzig (MSZ) model to describe the well-known first-order nematic-isotropic transition in liquid-crystalline systems. We then use the MSZ model, with the addition of disorder degrees of freedom, to investigate the stability of a biaxial nematic phase in a mixture of rods and disks. There is a biaxial nematic structure if we consider a fixed distribution of rods and disks. For a thermalized distribution of shapes, however, this biaxial structure becomes thermodynamically unstable. We then resort to a formalism that accounts for two sets of relaxation times, and show that a small departure from complete thermalization is enough to recover a stable biaxial structure. As another application of the MSZ model, we report an investigation of some properties of nematic elastomers. We point out the possibility of continuous nematic transitions, and reproduce a characteristic stress-strain response, with a plateau that indicates a polydomain-monodomain transition.

  15. Generation of harmonics and supercontinuum in nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Nyushkov, B N; Trashkeev, S I; Klementyev, Vasilii M; Pivtsov, V S; Kobtsev, Sergey M

    2013-02-28

    Nonlinear optical properties of nematic liquid crystals (NLC) have been investigated. A technique for efficient laser frequency conversion in a microscopic NLC volume deposited on an optical fibre end face is experimentally demonstrated. An efficient design of a compact NLC-based IR frequency converter with a fibre input and achromatic collimator is proposed and implemented. Simultaneous generation of the second and third harmonics is obtained for the first time under pumping NLC by a 1.56-mm femtosecond fibre laser. The second-harmonic generation efficiency is measured to be about 1 %, while the efficiency of third-harmonic generation is several tenths of percent. A strong polarisation dependence of the third-harmonic generation efficiency is revealed. When pumping NLC by a cw laser, generation of spectral supercontinua (covering the visible and near-IR spectral ranges) is observed. The nonlinear effects revealed can be due to the light-induced change in the orientational order in liquid crystals, which breaks the initial symmetry and leads to formation of disclination structures. The NLC optical nonlinearity is believed to be of mixed orientationalelectronic nature as a whole. (laser optics 2012)

  16. Synthesis of novel aromatic polyimides containing bulky side chain for vertical alignment liquid crystals

    Institute of Scientific and Technical Information of China (English)

    Jian Wang; Ying Han Wang

    2008-01-01

    In this study, a novel 4-(4-octyloxybenzoyloxy)biphenyl-3',5'-diaminobenzoate and polyimides based on it were synthesized. The polyimide with mesogenic unit side chain exhibited excellent vertical alignment for nematic liquid crystal (LC). The pretilt angles of LCs above 89° were kept after the rubbing process with 220 mm rubbing strength. The polyimide films as the alignment layer were baked at 120℃ for 12 h, the vertical alignment of LCs was still uniform and stable. Meanwhile, the UV-vis spectra of the novel polyimide films showed the high transparency in a visible wave length.

  17. Investigation into the temperature dependence of isotropic- nematic phase transition of Gay- Berne liquid crystals

    Directory of Open Access Journals (Sweden)

    A Avazpour

    2014-12-01

    Full Text Available Density functional approach was used to study the isotropic- nematic (I-N transition and calculate the values of freezing parameters of the Gay- Berne liquid crystal model. New direct and pair correlation functions of a molecular fluid with Gay- Berne pair potential were used. These new functions were used in density functional theory as input to calculate the isotropic- nematic transition densities for elongation at various reduced temperatures. It was observed that the isotropic- nematic transition densities increase as the temperature increases. It was found that the new direct correlation function is suitable to study the isotropic- nematic transition of Gay- Berne liquids. Comparison to other works showed qualitative agreement

  18. Direct mapping of local director field of nematic liquid crystals at the nanoscale.

    Science.gov (United States)

    Xia, Yu; Serra, Francesca; Kamien, Randall D; Stebe, Kathleen J; Yang, Shu

    2015-12-15

    Liquid crystals (LCs), owing to their anisotropy in molecular ordering, are of wide interest in both the display industry and soft matter as a route to more sophisticated optical objects, to direct phase separation, and to facilitate colloidal assemblies. However, it remains challenging to directly probe the molecular-scale organization of nonglassy nematic LC molecules without altering the LC directors. We design and synthesize a new type of nematic liquid crystal monomer (LCM) system with strong dipole-dipole interactions, resulting in a stable nematic phase and strong homeotropic anchoring on silica surfaces. Upon photopolymerization, the director field can be faithfully "locked," allowing for direct visualization of the LC director field and defect structures by scanning electron microscopy (SEM) in real space with 100-nm resolution. Using this technique, we study the nematic textures in more complex LC/colloidal systems and calculate the extrapolation length of the LCM. PMID:26621729

  19. A NEW METHOD TO ALIGN LIQUID CRYSTAL MOLECULES BY LINEAR PHOTO-POLYMERIZATION FOR LIQUID CRYSTAL DISPLAY

    Institute of Scientific and Technical Information of China (English)

    LIANG ZHAO-YAN; FANG KUN; XUAN LI; HUANG XI-MIN; DING BAO-QUAN; LU RAN; ZHAO YING-YING

    2000-01-01

    A new technique to uniformly align liquid crystal molecules is presented.The technique is based on producing an anisotropic surface on the glass substrate coated with photo-polymers by photo-polymerization of linear polarized UVlight.The orientation of liquid crystal molecules is governed by the direction of the polarized vector of UV-light.Using this method,we have studied the photo-polymer PSi-CM aligning LC 6710A molecules.The liquid crystal microscopic texture between crossed polarizers,optical retardation from liquid crystal layers and electro-optical properties of twisted nematic liquid crystal display cell are obtained,which was prepared with one side -photo-alignment and the other siderebbed substrate.

  20. Stability of the Melting Hedgehog in the Landau-de Gennes Theory of Nematic Liquid Crystals

    Science.gov (United States)

    Ignat, Radu; Nguyen, Luc; Slastikov, Valeriy; Zarnescu, Arghir

    2015-02-01

    We investigate stability properties of the radially symmetric solution corresponding to the vortex defect (the so called "melting hedgehog") in the framework of the Landau-de Gennes model of nematic liquid crystals. We prove local stability of the melting hedgehog under arbitrary Q-tensor valued perturbations in the temperature regime near the critical supercooling temperature. As a consequence of our method, we also rediscover the loss of stability of the vortex defect in the deep nematic regime.

  1. Internal Rotations and Stress Tensor Symmetry in Theories of Nematic Liquids and Solids

    OpenAIRE

    Leonov, A. I.; Volkov, V. S.

    2002-01-01

    The paper analyses kinematics and dynamics of internal rotations with spin and their effects on the constitutive relations for uniaxial (nematic) liquids and for weakly elastic nematic solids. It is shown that neglecting the internal rotational inertia terms and effects of director gradient made the stress symmetric. This not only highly simplifies the theories but also allows calculating all the kinematic variables of internal rotations without any additional constants, other than those pres...

  2. Anchoring energy enhancement and pretilt angle control of liquid crystal alignment on polymerized surfaces

    Science.gov (United States)

    Weng, Libo; Liao, Pei-Chun; Lin, Chen-Chun; Ting, Tien-Lun; Hsu, Wen-Hao; Su, Jenn-Jia; Chien, Liang-Chy

    2015-09-01

    We demonstrate enhanced surface anchoring energy and control of pretilt angle in a nematic liquid crystal cell with vertical alignment and polymerized surfaces (PS-VA). The polymerized surfaces are formed by ultraviolet (UV) irradiation-induced phase separation of a minute amount of a reactive monomer in the vertical-aligned nematic liquid crystal. By introducing a bias voltage during UV curing, surface-localized polymer protrusions with a dimension of 100nm and a field-induced pretilt angle are observed. Experimental evidences and theoretical analyses validate that PS-VA has increased surface anchoring strength by two folds and pretilt angle has been changed from 89° to 86° compared to those of a VA cell. The enabling PS-VA cell technique with excel electro-optical properties such as very good dark state, high optical contrast, and fast rise and decay times may lead to development of a wide range of applications.

  3. Anchoring energy enhancement and pretilt angle control of liquid crystal alignment on polymerized surfaces

    Directory of Open Access Journals (Sweden)

    Libo Weng

    2015-09-01

    Full Text Available We demonstrate enhanced surface anchoring energy and control of pretilt angle in a nematic liquid crystal cell with vertical alignment and polymerized surfaces (PS-VA. The polymerized surfaces are formed by ultraviolet (UV irradiation-induced phase separation of a minute amount of a reactive monomer in the vertical-aligned nematic liquid crystal. By introducing a bias voltage during UV curing, surface-localized polymer protrusions with a dimension of 100nm and a field-induced pretilt angle are observed. Experimental evidences and theoretical analyses validate that PS-VA has increased surface anchoring strength by two folds and pretilt angle has been changed from 89° to 86° compared to those of a VA cell. The enabling PS-VA cell technique with excel electro-optical properties such as very good dark state, high optical contrast, and fast rise and decay times may lead to development of a wide range of applications.

  4. Anomalous swimming behavior of bacteria in nematic liquid crystals

    Science.gov (United States)

    Sokolov, Andrey; Zhou, Shuang; Lavrentovich, Oleg; Aranson, Igor

    2015-03-01

    Flagellated bacteria stop swimming in isotropic media of viscosity higher than 0.06kgm-1s-1. However, Bacillus Subtilis slows down by only about 30% in a nematic chromonic liquid crystal (CLC, 14wt% DSCG in water), where the anisotropic viscosity can be as high as 6kgm-1s-1. The bacteria velocity (Vb) is linear with the flagella rotation frequency. The phase velocity of the flagella Vf ~ 2Vb in LC, as compared to Vf ~ 10Vb in water. The flow generated by the bacteria is localized along the bacterial body axis, decaying slowly over tens of micrometers along, but rapidly over a few micrometers across this axis. The concentrated flow grants the bacteria new ability to carry cargo particles in LC, ability not seen in their habitat isotropic media. We attribute these anomalous features to the anisotropy of viscosity of the CLC, namely, the viscosities of splay and twist is hundreds times higher than that of bend deformation, which provides extra boost of swimming efficiency and enables the bacteria swim at considerable speed in a viscous medium. Our findings can potentially lead to applications such as particle transportation in microfluidic devices. A.S and I.A are supported by the US DOE, Office of Science, BES, Materials Science and Engineering Division. S.Z. and O.D.L are supported by NSF DMR 1104850, DMS-1434185.

  5. On a non-isothermal model for nematic liquid crystals

    International Nuclear Information System (INIS)

    A model describing the evolution of a liquid crystal substance in the nematic phase is investigated in terms of three basic state variables: the absolute temperature thetav, the velocity field u and the director field d, representing preferred orientation of molecules in a neighbourhood of any point of a reference domain. The time evolution of the velocity field is governed by the incompressible Navier–Stokes system, with a non-isotropic stress tensor depending on the gradients of the velocity and of the director field d, where the transport (viscosity) coefficients vary with temperature. The dynamics of d is described by means of a parabolic equation of Ginzburg–Landau type, with a suitable penalization term to relax the constraint |d| = 1. The system is supplemented by a heat equation, where the heat flux is given by a variant of Fourier's law, depending also on the director field d. The proposed model is shown to be compatible with first and second laws of thermodynamics, and the existence of global-in-time weak solutions for the resulting PDE system is established, without any essential restriction on the size of the data

  6. Dielectric Properties of Nematic Liquid Crystal Modified with Diamond Nanoparticles

    International Nuclear Information System (INIS)

    In the present study, the influence of diamond nanoparticles (DNPs) on dielectric properties of nematic liquid crystal (LC) E7 from Merck has been considered. It is established that the insertion of DNPs leads to an increase in the dielectric constant ε' as well as to a significant change in the electric conductivity σ of the LC. The growth of ε' with the concentration of DNPs, CDNP, is mainly caused by a contribution of the DNP permittivity to the effective permittivity of the composite. The character of the σ(CDNP) curves depends on the ionic purity of LC E7: for the samples based on pure E7, an increase of the electric conductivity with the concentration of DNPs is detected, whereas the reverse trend is observed for the samples containing impure E7. This behavior is attributed to the competitive adsorption and desorption of ions on/from the surface of DNPs and the ion transfer along the percolation network of these particles.

  7. Liquid crystal anchoring transitions on aligning substrates processed by plasma beam

    OpenAIRE

    Yaroshchuk, Oleg V.; Kiselev, Alexei D.; Kravchuk, Ruslan M.

    2007-01-01

    We observe a sequence of the anchoring transitions in nematic liquid crystals (NLC) sandwiched between the hydrophobic polyimide substrates treated with the plasma beam. There is a pronounced continuous transition from homeotropic to low tilted (nearly planar) alignment with the easy axis parallel to the incidence plane of the plasma beam (the zenithal transition) that takes place as the exposure dose increases. In NLC with positive dielectric anisotropy, a further increase in the exposure do...

  8. Determination of the flexoelectric coefficient (e1-e3) in nematic liquid crystal by using fully leaky optical-guided mode

    Science.gov (United States)

    Zheng, Guili; Zhang, Hui; Ye, Wenjiang; Zhang, Zhidong; Song, Hong-wei; Xuan, Li

    2016-02-01

    Fully leaky optical-guided mode was employed to determine the difference in the splay and bend flexoelectric coefficient (e1-e3) in negative nematic liquid crystal MS-N01300-000. The experimental curves of reflectivity versus internal angle (angle of incident light to the liquid crystal) were obtained when a laser beam passed through the hybrid-aligned nematic in-plane switching liquid crystal cell; the cell was embedded in pyramid-coupled waveguide with different alternating current (AC) and direct current (DC) voltages. The curves of the applied DC with voltage similar to that of AC shift to the left or the right. Experimental results were then compared with theoretical results derived from elastic continuum theory and multi-layer optical theory of liquid crystals. The approximate value of the flexoelectric coefficient (e1-e3) of MS-N01300-000 is 9.0 × 10-11 C/m.

  9. Lattice Boltzmann Simulation of 3D Nematic Liquid Crystal near Phase Transition

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun; TAO Rui-Bao

    2002-01-01

    Phase transition between nematic and isotropic liquid crystal is a very weak first order phase transition.We avoid to use the normal Landau-de Gennes's free energy that reduces a strong first order transition, and set up adata base of free energy calculated by means of Tao-Sheng Lin's extended molecular field theory that can explain theexperiments of the equilibrium properties of nematic liquid crystal very well. Then we use the free energy method oflattice Boltzmann developed by Oxford group to study the phase decomposition, pattern formation in the flow of theliquid crystal near transition temperature.

  10. Control on the anomalous interactions of Airy beams in nematic liquid crystals.

    Science.gov (United States)

    Shen, Ming; Li, Wei; Lee, Ray-Kuang

    2016-04-18

    We reveal a controllable manipulation of anomalous interactions between Airy beams in nonlocal nematic liquid crystals numerically. With the help of an in-phase fundamental Gaussian beam, attraction between in-phase Airy beams can be suppressed or become a repulsive one to each other; whereas the attraction can be strengthened when the Gaussian beam is out-of-phase. In contrast to the repulsive interaction in local media, stationary bound states of breathing Airy soliton pairs are found in nematic liquid crystals. PMID:27137288

  11. Vitrified chiral-nematic liquid crystalline films for selective reflection and circular polarization

    Energy Technology Data Exchange (ETDEWEB)

    Katsis, D.; Chen, P.H.M.; Mastrangelo, J.C.; Chen, S.H. [Univ. of Rochester, NY (United States); Blanton, T.N. [Eastman Kodak Co., Rochester, NY (United States)

    1999-06-01

    Nematic and left-handed chiral-nematic liquid crystals comprising methoxybiphenylbenzoate and (S)-(-)-1-phenylethylamine pendants to a cyclohexane core were synthesized and characterized. Although pristine samples were found to be polycrystalline, thermal quenching following heating to and annealing at elevated temperatures permitted the molecular orders characteristic of liquid crystalline mesomorphism to be frozen in the glassy state. Left at room temperature for 6 months, the vitrified liquid crystalline films showed no evidence of recrystallization. An orientational order parameter of 0.65 was determined with linear dichroism of a vitrified nematic film doped with Exalite 428 at a mole fraction of 0.0025. Birefringence dispersion of a blank vitrified nematic film was determined using a phase-difference method complemented by Abbe refractometry. A series of vitrified chiral-nematic films were prepared to demonstrate selective reflection and circular polarization with a spectral region tunable from blue to the infrared region by varying the chemical composition. The experimentally measured circular polarization spectra were found to agree with the Good-Karali theory in which all four system parameters were determined a priori: optical birefringence, average refractive index, selective reflection wavelength, and film thickness.

  12. Anisotropic mechanical properties of a polymer nematic liquid crystal

    Science.gov (United States)

    Taratuta, Victor G.; Lonberg, Franklin; Meyer, Robert B.

    1988-03-01

    A concentration dependence of elastic and viscous properties of nematic poly-γ-benzyl glutamate (PBG) was studied experimentally. The splay and bend constants are similar in magnitude, both linear in concentration. The twist constant is much smaller and constant. Viscosities exhibit large anisotropies. γ1 and ηc are roughly quadratic in concentration, ηa is linear, while ηb is constant. The data are self-consistently interpreted in terms of the theoretical models for nematics of semi flexible chains rather than those of rigid rods.

  13. The inherent dynamics of isotropic- and nematic-phase liquid crystals

    Science.gov (United States)

    Frechette, Layne; Stratt, Richard M.

    2016-06-01

    The geodesic (shortest) pathways through the potential energy landscape of a liquid can be thought of as defining what its dynamics would be if thermal noise were removed, revealing what we have called the "inherent dynamics" of the liquid. We show how these inherent paths can be located for a model liquid crystal former, showing, in the process, how the molecular mechanisms of translation and reorientation compare in the isotropic and nematic phases of these systems. These mechanisms turn out to favor the preservation of local orientational order even under macroscopically isotropic conditions (a finding consistent with the experimental observation of pseudonematic domains in these cases), but disfavor the maintenance of macroscopic orientational order, even in the nematic phase. While the most efficient nematic pathways that maintain nematic order are indeed shorter than those that do not, it is apparently difficult for the system to locate these paths, suggesting that molecular motion in liquid-crystal formers is dynamically frustrated, and reinforcing the sense that there are strong analogies between liquid crystals and supercooled liquids.

  14. Dielectric and electro-optic measurements of nematic liquid crystals doped with carbon nanotubes

    Science.gov (United States)

    Peterson, Matthew; Georgiev, Georgi; Atherton, Timothy; Cebe, Peggy

    We studied the effects of carbon nanotubes (CNTs) on the dielectric and electro-optic properties of nematic 5CB liquid crystals (LCs). Samples containing 0.01%, 0.10% and 1.00% CNTs by weight were prepared. Anti- parallel rubbed cells with a nominal thickness of 10 μm were prepared using indium tin oxide coated glass cells and a polyimide alignment layer. The capacitance and dissipation factor were measured using an Agilent 4284A precision LCR meter. From these measurements, the complex dielectric permittivity was determined as a function of frequency. Analysis of the low frequency regime (f <1000 Hz) indicates that 5CB samples containing CNTs have a higher conductance than neat samples. The Fréedericksz transition critical voltage was noted by a sharp increase in capacitance after an initial plateau. Numerical simulations of CNT-facilitated switching show that polarization induced on the nanotubes from capacitive effects can significantly reduce the critical voltage in DC electric fields, in agreement with experimental results. Measurements of the critical voltage over a range of frequencies will also be presented. Research was supported by the National Science Foundation, DMR1206010.

  15. Nonisothermal nematic liquid crystal flows with the Ball-Majumdar free energy

    Czech Academy of Sciences Publication Activity Database

    Feireisl, Eduard; Schimperna, G.; Rocca, E.; Zarnescu, A.

    2015-01-01

    Roč. 194, č. 5 (2015), s. 1269-1299. ISSN 0373-3114 EU Projects: European Commission(XE) 320078 - MATHEF Keywords : nematic liquid crystal * Ball-Majumdar free theory * nonisothermal model * existence theorem Subject RIV: BA - General Mathematics Impact factor: 1.065, year: 2014 http://link.springer.com/article/10.1007%2Fs10231-014-0419-1

  16. Surface charge and interactions of 20-nm nanocolloids in a nematic liquid crystal

    Science.gov (United States)

    Ryzhkova, A. V.; Škarabot, M.; Muševič, I.

    2015-04-01

    We studied real-time motion of individual 20-nm silica nanoparticles in a thin layer of a nematic liquid crystal using a dark-field optical videomicroscopy. By tracking the positions of individual nanoparticles we observed that particle pair interactions are not only mediated by strong thermal fluctuations of the nematic liquid crystal, but also with a repulsive force of electric origin. We determined the total electric charge of silanated silica particles in the nematic liquid crystal 5CB by observing the electric-force-driven drift. Surprisingly, the surface electric charge density depends on colloidal size and is ˜4.5 ×10-3C/m2 for 20-nm nanocolloids, and two orders of magnitude lower, i.e., ˜2.3 ×10-5C/m2 , for 1 -μ m colloids. We conclude that electrostatic repulsion between like-charged particles prevents the formation of permanent colloidal assemblies of nanometer size. We also observed strong attraction of 20-nm silica nanoparticles to confining polyimide surfaces and larger clusters, which gradually results in complete expulsion of nanoparticles from the nematic liquid crystal to the surfaces of the confining cell.

  17. A new method for solid surface topographical studies using nematic liquid crystals

    Science.gov (United States)

    Baber, N.; Strugalski, Z.

    1984-03-01

    A new simple method has been developed to investigate the topography of a wide range of solid surfaces using nematic liquid crystals. Polarizing microscopy is employed. The usefulness of the method for detecting weak mechanical effects has been demonstrated. An application in criminology is foreseen.

  18. Monotonicity of a Key Function Arised in Studies of Nematic Liquid Crystal Polymers

    Directory of Open Access Journals (Sweden)

    Hongyun Wang

    2007-01-01

    Full Text Available We revisit a key function arised in studies of nematic liquid crystal polymers. Previously, it was conjectured that the function is strictly decreasing and the conjecture was numerically confirmed. Here we prove the conjecture analytically. More specifically, we write the derivative of the function into two parts and prove that each part is strictly negative.

  19. Simulation of Nematic Free Surfaces

    Science.gov (United States)

    de Miguel, Enrique; Martín del Río, Elvira

    Molecular dynamics and Monte Carlo methods are applied to study the liquid free surfaces in model liquid crystals. The simulation results suggest that the attractive interactions promote parallel alignment of the molecules at the nematic free surface in the Gay-Berne model, in agreement with theoretical predictions. A change in the orientation from planar to homeotropic is observed and explained in terms of a competing effect between attractive and repulsive interactions. Finally, the simulation results give clear evidence that the hard-core repulsions favor homeotropic orientation at the nematic free surface, in agreement with most theories.

  20. Influence of the bias-voltage on the anchoring energy for nematic liquid crystals

    OpenAIRE

    Barbero, Giovanni

    2004-01-01

    The influence of the bias-voltage on the anisotropic part of the nematic surface energy is analyzed. The experimental data show a strong dependence of the anchoring strength on the bias-voltage when the electrodes of the nematic cell are covered with WO3. The observed dependence can be interpreted taking into account the ions dissolved in the liquid crystal. We propose a model in which the effect of the bias-voltage is to collect the ions near the electrodes, in a surface layer whose thicknes...

  1. Feedback control of flow alignment in sheared liquid crystals

    Science.gov (United States)

    Strehober, David A.; Schöll, Eckehard; Klapp, Sabine H. L.

    2013-12-01

    Based on a continuum theory, we investigate the manipulation of the nonequilibrium behavior of a sheared liquid crystal via closed-loop feedback control. Our goal is to stabilize a specific dynamical state, that is, the stationary "flow alignment," under conditions where the uncontrolled system displays oscillatory director dynamics with in-plane symmetry. To this end we employ time-delayed feedback control (TDFC), where the equation of motion for the ith component qi(t) of the order parameter tensor is supplemented by a control term involving the difference qi(t)-qi(t-τ). In this diagonal scheme, τ is the delay time. We demonstrate that the TDFC method successfully stabilizes flow alignment for suitable values of the control strength K and τ; these values are determined by solving an exact eigenvalue equation. Moreover, our results show that only small values of K are needed when the system is sheared from an isotropic equilibrium state, contrary to the case where the equilibrium state is nematic.

  2. Dynamics of ordered colloidal particle monolayers at nematic liquid crystal interfaces.

    Science.gov (United States)

    Wei, Wei-Shao; Gharbi, Mohamed Amine; Lohr, Matthew A; Still, Tim; Gratale, Matthew D; Lubensky, T C; Stebe, Kathleen J; Yodh, A G

    2016-05-25

    We prepare two-dimensional crystalline packings of colloidal particles on surfaces of the nematic liquid crystal (NLC) 5CB, and we investigate the diffusion and vibrational phonon modes of these particles using video microscopy. Short-time particle diffusion at the air-NLC interface is well described by a Stokes-Einstein model with viscosity similar to that of 5CB. Crystal phonon modes, measured by particle displacement covariance techniques, are demonstrated to depend on the elastic constants of 5CB through interparticle forces produced by LC defects that extend from the interface into the underlying bulk material. The displacement correlations permit characterization of transverse and longitudinal sound velocities of the crystal packings, as well as the particle interactions produced by the LC defects. All behaviors are studied in the nematic phase as a function of increasing temperature up to the nematic-isotropic transition. PMID:27109759

  3. Molecular theory of nematic liquid crystals viewed as effect of collective excitation in ferromagnetic systems

    Institute of Scientific and Technical Information of China (English)

    Liu Jian-Jun; Shen Man; Liu Xiao-Jing; Yang Guo-Chen

    2006-01-01

    We develop a microscopic theory of the nematic phase with consideration of the effect of the collective excitation on properties of nematic liquid crystals. The model is based on the Heisenberg's exchange model of the ferromagnetic materials. Since the orientation of the molecular long axis and the angular momentum of the molecule rotating around its long axis have the same direction, operators can be introduced to research the nematic liquid crystals. Using the lattice model and the Holstein-Primakoff transformation, the Hamiltonian of the system can be obtained, which has the same form as that of the ferromagnetic substance. The relation between the order parameter and reduced temperature can be gotten. It is in good agreement with the experimental results in the low temperature region, the accordance is better than that of the molecular field theory and the computer simulation. In high temperature region close to the transition point, by considering the effect of the higher-order terms in the Hamiltonian, theoretical prediction is in better agreement with the experiment. That indicates the many-body effect is important to nematic liquid crystals.

  4. Nematic quantum phase transition of composite Fermi liquids in half-filled Landau levels and their geometric response

    Science.gov (United States)

    You, Yizhi; Cho, Gil Young; Fradkin, Eduardo

    2016-05-01

    We present a theory of the isotropic-nematic quantum phase transition in the composite Fermi liquid arising in half-filled Landau levels. We show that the quantum phase transition between the isotropic and the nematic phase is triggered by an attractive quadrupolar interaction between electrons, as in the case of conventional Fermi liquids. We derive the theory of the nematic state and of the phase transition. This theory is based on the flux attachment procedure, which maps an electron liquid in half-filled Landau levels into the composite Fermi liquid close to a nematic transition. We show that the local fluctuations of the nematic order parameters act as an effective dynamical metric interplaying with the underlying Chern-Simons gauge fields associated with the flux attachment. Both the fluctuations of the Chern-Simons gauge field and the nematic order parameter can destroy the composite fermion quasiparticles and drive the system into a non-Fermi liquid state. The effective-field theory for the isotropic-nematic phase transition is shown to have z =3 dynamical exponent due to the Landau damping of the dense Fermi system. We show that there is a Berry-phase-type term that governs the effective dynamics of the nematic order parameter fluctuations, which can be interpreted as a nonuniversal "Hall viscosity" of the dynamical metric. We also show that the effective-field theory of this compressible fluid has a Wen-Zee-type term. Both terms originate from the time-reversal breaking fluctuation of the Chern-Simons gauge fields. We present a perturbative (one-loop) computation of the Hall viscosity and also show that this term is also obtained by a Ward identity. We show that the topological excitation of the nematic fluid, the disclination, carries an electric charge. We show that a resonance observed in radio-frequency conductivity experiments can be interpreted as a Goldstone nematic mode gapped by lattice effects.

  5. Ferromagnetic nanoparticles suspensions in twisted nematic

    Science.gov (United States)

    Cîrtoaje, Cristina; Petrescu, Emil; Stan, Cristina; Creangă, Dorina

    2016-05-01

    Ferromagnetic nanoparticles insertions in nematic liquid crystals (NLC) in twisted configuration are studied and a theoretical model is proposed to explain the results. Experimental observation revealed that nanoparticles tend to overcrowd in long strings parallel to the rubbing direction of the alignment substrate of the LC cell. Their behavior under external field was studied and their interaction with their nematic host is described using elastic continuum theory.

  6. Random lasing in dye doped nematic liquid crystals: the role of confinement geometry

    Science.gov (United States)

    Strangi, G.; Ferjani, S.; Barna, V.; De Luca, A.; Versace, C.; Scaramuzza, N.; Bartolino, R.

    2007-05-01

    The first experimental evidence of random laser action in a partially ordered, dye doped nematic liquid crystal with long-range dielectric tensor fluctuations is reported. Above a given pump power the fluorescence curve collapses and discrete sharp peaks emerge above the residual spontaneous emission spectrum. The spectral linewidth of these emission peaks is narrow banded, typically around 0.5nm. The unexpected surviving of interference effects in recurrent multiple scattering of the emitted photons provide the required optical feedback for lasing in nematic liquid crystalline materials. Light waves coherent backscattering in orientationally ordered nematics manifests a weak localization, strongly supporting the diffusive laser action phenomenon in the presence of a gain medium. Unlike distributed feedback mirror-less laser, this system can be considered as a cavity-less microlaser where the disorder unexpectedly plays the most important role, behaving as randomly distributed feedback laser. The far field spatial distribution of the emission intensity shows a huge number of bright tiny spots spatially overlapped and the intensity of each pulse strongly fluctuates in time and space. Here, we report the main characteristics of this novel systems for various confinement geometries and under different conditions. A brief presentation of boundary-less systems such as free standing and freely suspended dye doped nematic films and droplets is also introduced, revealing unique emission features because of the complete absence of confining borders.

  7. Polarization axis-selective realignment of a photoreactive liquid crystalline composite with homogeneous alignment

    Science.gov (United States)

    Sasaki, Tomoyuki; Shoho, Takashi; Goto, Kohei; Sakamoto, Moritsugu; Noda, Kohei; Kawatsuki, Nobuhiro; Ono, Hiroshi

    2016-06-01

    We investigated the photoalignment properties of a liquid crystalline composite. The composite consisted of a low molecular weight nematic liquid crystal (LC) and a photoreactive liquid crystalline polymer containing 4-(4-methoxycinnamoyloxy)biphenyl side groups. Homogeneously aligned LC composite cells were fabricated using rubbed substrates and were then exposed to a linearly polarized (LP) ultraviolet (UV) laser beam. The alignment states of the LC composites were characterized using a LP visible laser beam. The LC composite in the cell was realigned by LP UV exposure and subsequent annealing. The direction of the realignment could be controlled by the polarization direction of the LP UV beam. The relationship between the realignment direction and the rubbing strength of the substrates was also investigated. A large realignment was induced in the LC composite cell when the azimuthal anchoring strength of the rubbed substrates was relatively weak.

  8. Symmetric and nematic Z2 quantum spin liquids: applications to the J1-J2 Heisenberg model

    Science.gov (United States)

    Jiang, Yifan; Yang, Fan; Yao, Hong

    2013-03-01

    We classify symmetric and nematic Z2 quantum spin liquid states on the square lattice by analyzing bosonic PSG. We then compute the energies of various symmetric and nematic Z2 spin liquid states for the J1-J2 square Heisenberg model by doing variational Monte Carlo simulations. The connections of our variational Monte Carlo studies with the recent DMRG results on the same model will also be discussed.

  9. Multi-particle collision dynamics algorithm for nematic fluids.

    Science.gov (United States)

    Shendruk, Tyler N; Yeomans, Julia M

    2015-07-01

    Research on transport, self-assembly and defect dynamics within confined, flowing liquid crystals requires versatile and computationally efficient mesoscopic algorithms to account for fluctuating nematohydrodynamic interactions. We present a multi-particle collision dynamics (MPCD) based algorithm to simulate liquid-crystal hydrodynamic and director fields in two and three dimensions. The nematic-MPCD method is shown to successfully reproduce the features of a nematic liquid crystal, including a nematic-isotropic phase transition with hysteresis in 3D, defect dynamics, isotropic Frank elastic coefficients, tumbling and shear alignment regimes and boundary condition-dependent order parameter fields. PMID:26035731

  10. Effects of added silica nanoparticles on the nematic liquid crystal phase formation in beidellite suspensions.

    Science.gov (United States)

    Landman, Jasper; Paineau, Erwan; Davidson, Patrick; Bihannic, Isabelle; Michot, Laurent J; Philippe, Adrian-Marie; Petukhov, Andrei V; Lekkerkerker, Henk N W

    2014-05-01

    In this article, we present a study of the liquid crystal phase behavior of mixed suspensions of the natural smectite clay mineral beidellite and nonadsorbing colloidal silica particles. While virtually all smectite clays dispersed in water form gels at very low concentrations, beidellite displays a first order isotropic-nematic phase transition before gel formation (J. Phys. Chem. B, 2009, 113, 15858-15869). The addition of silica nanospheres shifts the concentrations of the coexisting isotropic and nematic phases to slightly higher values while at the same time markedly accelerating the phase separation process. Furthermore, beidellite suspensions at volume fractions above the isotropic-nematic phase separation, trapped in a kinetically arrested gel state, liquefy on the addition of silica nanospheres and proceed to isotropic-nematic phase separation. Using small-angle X-ray scattering (SAXS), we probe the structural changes caused by the addition of the silica nanospheres, and we relate the modification of the phase transition kinetics to the change of the rheological properties. PMID:24758198

  11. Molecular dynamics simulations of Gay-Berne nematic liquid crystal: Elastic properties from direct correlation functions

    International Nuclear Information System (INIS)

    We report NVT and NPT molecular dynamics simulations of a Gay-Berne nematic liquid crystal using generalization of recently proposed algorithm by Toxvaerd [Phys. Rev. E47, 343, 1993]. On the basis of these simulations the Oseen-Zoher-Frank elastic constants K11, K22 and K33 as well as the surface constants K13 and K24 have been calculated within the framework of the direct correlation function approach of Lipkin et al. [J. Chem. Phys. 82, 472 (1985)]. The angular coefficients of the direct pair correlation function, which enter the final formulas, have been determined from the computer simulation data for the pair correlation function of the nematic by combining the Ornstein-Zernike relation and the Wienier-Hopf factorization scheme. The unoriented nematic approximation has been assumed when constructing the reference, isotropic state of Lipkin et al. By an extensive study of the model over a wide range of temperatures, densities and pressures a very detailed information has been provided about elastic behaviour of the Gay-Berne nematic. Interestingly, it is found that the results for the surface elastic constants are qualitatively different than those obtained with the help of analytical approximations for the isotropic, direct pair correlation function. For example, the values of the surface elastic constants are negative and an order of magnitude smaller than the bulk elasticity. (author). 30 refs, 9 figs

  12. Microsecond-range optical shutter for unpolarized light with chiral nematic liquid crystal

    Directory of Open Access Journals (Sweden)

    Mohammad Mohammadimasoudi

    2015-04-01

    Full Text Available A fast electro-optic shutter is fabricated and demonstrated. The device works independently of the polarization state of the incoming light beam. Modulation between 3% transmission and 60% transmission is obtained within a wavelength range of 50 nm with a response time of 20 μs. The device consists of two partly polymerized chiral nematic liquid crystal layers separated by a half wave plate. The transmission modulation is due to a 50 nm wavelength shift of the photonic band gap of the chiral liquid crystal realized by applying an electric field over a mixture of photo-polymerized LC and non-reactive nematic LC containing a chiral dopant. The shutter features high reflectivity in the photonic band gap. We investigate the influence of the amplitude of the applied voltage on the width and the depth of the reflection band.

  13. Microsecond-range optical shutter for unpolarized light with chiral nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Mohammadimasoudi, Mohammad, E-mail: Mohammad.Mohammadimasoudi@elis.ugent.be; Neyts, Kristiaan; Beeckman, Jeroen [Electronics and Information Systems Department, Ghent University, St. Pietersnieuwstraat 41, 9000 Gent (Belgium); Center for Nano- and Bio-photonics, Ghent University, St. Pietersnieuwstraat 41, 9000 Gent (Belgium); Shin, Jungsoon; Lee, Keechang [Samsung Advanced Institute of Technology, 130 Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do, 443-803 (Korea, Republic of)

    2015-04-15

    A fast electro-optic shutter is fabricated and demonstrated. The device works independently of the polarization state of the incoming light beam. Modulation between 3% transmission and 60% transmission is obtained within a wavelength range of 50 nm with a response time of 20 μs. The device consists of two partly polymerized chiral nematic liquid crystal layers separated by a half wave plate. The transmission modulation is due to a 50 nm wavelength shift of the photonic band gap of the chiral liquid crystal realized by applying an electric field over a mixture of photo-polymerized LC and non-reactive nematic LC containing a chiral dopant. The shutter features high reflectivity in the photonic band gap. We investigate the influence of the amplitude of the applied voltage on the width and the depth of the reflection band.

  14. Hydrodynamics of defects in the Abelian-Higgs model: An application to nematic liquid crystals

    International Nuclear Information System (INIS)

    The Abelian-Higgs model is the basis for a gauge covariant form of the distortion free energy for nematic liquid crystals. This is used to derive a new form of the Ericksen-Leslie equations incorporating the dynamics of disclinations in nematic films. The zero liquid flow case is treated in detail for simplicity. The equations are reduced to dynamic equations for disclination points in moduli space for a small deviation from the Bogomol'nyi limit. We are able to derive analytically the dynamics of disclinations with winding numbers of the same sign. A set of such disclinations close to one another, i.e., with overlapping cores, can result from the disintegration of a larger disclination, and they repel one another. For a pair of such dis- clinations far apart from one another we find that they move on a straight line where their separation increases logarithmically over time

  15. Landau–De Gennes Theory of Nematic Liquid Crystals: the Oseen–Frank Limit and Beyond

    KAUST Repository

    Majumdar, Apala

    2009-07-07

    We study global minimizers of a continuum Landau-De Gennes energy functional for nematic liquid crystals, in three-dimensional domains, subject to uniaxial boundary conditions. We analyze the physically relevant limit of small elastic constant and show that global minimizers converge strongly, in W1,2, to a global minimizer predicted by the Oseen-Frank theory for uniaxial nematic liquid crystals with constant order parameter. Moreover, the convergence is uniform in the interior of the domain, away from the singularities of the limiting Oseen-Frank global minimizer. We obtain results on the rate of convergence of the eigenvalues and the regularity of the eigenvectors of the Landau-De Gennes global minimizer. We also study the interplay between biaxiality and uniaxiality in Landau-De Gennes global energy minimizers and obtain estimates for various related quantities such as the biaxiality parameter and the size of admissible strongly biaxial regions. © Springer-Verlag (2009).

  16. COMPENSATION EFFECT OF POLYIMIDE THIN FILMS ON NORMALLY WHITE TWISTED NEMATIC LIQUID CRYSTAL DISPLAYS

    Institute of Scientific and Technical Information of China (English)

    LI Baozhong; HE Tianbai; DING Mengxian

    1997-01-01

    The disadvantages of Normally White Twisted Nematic Liquid Crystal Display (NW-TN-LCD) were discussed. The reason that the negative birefringent polyimide thin films were used to compensate NW-TN-LCD to decrease off-axis leakage, improve contrast ratios and enlarge viewing angles' was explained in this paper. A certain polyimide thin film was taken as an example to show compensation effect on NW-TN-LCD.

  17. Phase Behavior of Mixtures of Low Molecular Weight Nematic Liquid Crystals and Photochemically Crosslinked Polyacrylates

    OpenAIRE

    BEDJAOUI, Lamia; N. BERRIAH; K. BOUDRAA; Bouchaour, T.; MASCHKE, Ulrich

    2010-01-01

    The present work deals with theoretical and experimental studies to explore some physical properties of composite materials made of crosslinked poly(nbutylacrylate) networks and low molecular weight nematic liquid crystals (LCs). The chemically crosslinked polymers were obtained by exposure to UV radiation of initial solutions composed of a reactive monomer, n-butylacrylate, a small amount of a crosslinking agent, hexanedioldiacrylate, and a photoinitiator. To obtain different ...

  18. Pseudo-casimir structural force drives spinodal dewetting in nematic liquid crystals

    Science.gov (United States)

    Ziherl; Podgornik; Zumer

    2000-02-01

    We analyze theoretically the fluctuation-induced force in thin nematic films subject to competing surface interactions, and we find that the force is attractive at small distances and repulsive otherwise. The results provide a consistent interpretation of a recent study of spinodal dewetting of 5CB on a silicon wafer [F. Vandenbrouck et al., Phys. Rev. Lett. 82, 2693 (1999)], implying that this experiment can be regarded as the first observation of the pseudo-Casimir effect in liquid crystals. PMID:11017485

  19. Spin-charge interplay in electronic liquid crystals: fluctuating spin stripe driven by charge nematic

    OpenAIRE

    Sun, Kai; Lawler, Michael J.; Kim, Eun-Ah

    2009-01-01

    We study the interplay between charge and spin ordering in electronic liquid crystalline states with a particular emphasis on fluctuating spin stripe phenomena observed in recent neutron scattering experiments\\cite{Hinkov2008, Haug2009}. Based on a phenomenological model, we propose that charge nematic ordering is indeed behind the formation of temperature dependent incommensurate inelastic peaks near wavevector $(\\pi,\\pi)$ in the dynamic structure factor of YBa$_2$Cu$_3$O$_{6+y}$. We strengt...

  20. Design of twisted-nematic liquid crystal displays for holographic data storage

    OpenAIRE

    Fernández Varó, Elena; Márquez Ruiz, Andrés; Pérez Molina, Manuel; Fuentes Rosillo, Rosa; García Llopis, Celia; Francés Monllor, Jorge; Pascual Villalobos, Inmaculada

    2010-01-01

    This work describes an ideal design of a nematic liquid crystal display (TN-LCD) that allows obtaining the best configuration of a hybrid ternary modulation to be applied in holographic data storage. With this purpose, the thickness of a real LCD was modified in order to change the birefringence versus gray level. With these new birefringences, simulations for different configurations were made to design an LCD having a HTM as close as possible to the ideal one.

  1. Long-time Behavior for Nonlinear Hydrodynamic System Modeling the Nematic Liquid Crystal Flows

    OpenAIRE

    Wu, Hao

    2009-01-01

    We study a simplified system of the original Ericksen--Leslie equations for the flow of nematic liquid crystals. This is a coupled non-parabolic dissipative dynamic system. We show the convergence of global classical solutions to single steady states as time goes to infinity (uniqueness of asymptotic limit) by using the \\L ojasiewicz--Simon approach. Moreover, we provide an estimate on the convergence rate. Finally, we discuss some possible extensions of the results to certain generalized pro...

  2. Long-time dynamics of the nonhomogeneous incompressible flow of nematic liquid crystals

    OpenAIRE

    Hu, Xianpeng; Wu, Hao

    2012-01-01

    We study the long-time behavior of global strong solutions to a hydrodynamic system for nonhomogeneous incompressible nematic liquid crystal flows driven by two types of external forces in a smooth bounded domain in $\\mathbb{R}^2$. For arbitrary large regular initial data with the initial density being away from vacuum, we prove the decay of the velocity field for both cases. Furthermore, for the case with asymptotically autonomous external force, we can prove the convergence of the density f...

  3. ON THE SATURATION BEHAVIOUR OF TWISTED NEMATIC LIQUID CRYSTAL CELLS WITH A NONZERO PRETILT ANGLE

    Institute of Scientific and Technical Information of China (English)

    ZHANG ZHI-DONG; YU HUI; LI LI

    2001-01-01

    Equations are obtained for the surface tilt angle and the twist angle of the director in a twisted nematic liquid crystal cell under a high magnetic field. Under a zero pretilt angle, the two equations reduce to those obtained by Sugimura et al.[2,3] This fact has also been demonstrated numerically. With finite field strength and nonzero pretilt angle, no saturation transition exists.

  4. Unconventional non-Fermi liquid state caused by nematic criticality in cuprates

    Science.gov (United States)

    Wang, Jing-Rong; Liu, Guo-Zhu; Zhang, Chang-Jin

    2016-07-01

    At the nematic quantum critical point that exists in the {d}{x2-{y}2}-wave superconducting dome of cuprates, the massless nodal fermions interact strongly with the quantum critical fluctuation of nematic order. We study this problem by means of the renormalization group approach and show that, the fermion damping rate | {Im}{{{Σ }}}R(ω )| vanishes more rapidly than the energy ω and the quasiparticle residue {Z}f\\to 0 in the limit ω \\to 0. The nodal fermions thus constitute an unconventional non-Fermi liquid that represents an even weaker violation of Fermi liquid theory than a marginal Fermi liquid. We also investigate the interplay of quantum nematic critical fluctuation and gauge-potential-like disorder, and find that the effective disorder strength flows to the strong coupling regime at low energies. Therefore, even an arbitrarily weak disorder can drive the system to become a disorder controlled diffusive state. Based on these theoretical results, we are able to understand a number of interesting experimental facts observed in curpate superconductors.

  5. Liquid Crystal Alignment on Solution Derived Zinc Oxide Films via Ion Beam Irradiation.

    Science.gov (United States)

    Park, Hong-Gyu; Han, Jae-Jun; Seo, Dae-Shik

    2016-03-01

    A 75-nm-thick ZnO film was deposited by a sol-gel method on indium-tin oxide (ITO)-coated glass. This film served as a liquid crystal (LC) alignment layer. We report the fabrication and characteristics of this film after ion-beam (IB) irradiation. Uniform LC alignment was achieved at an IB incident energy above 2400 eV. The IB-treated ZnO surface was analyzed by X-ray photoelectron spectroscopy (XPS), monitoring the intensity of the Zn 2p and O 1s peaks as a function of IB-irradiation energy density. The electro-optical (EO) characteristics of a twisted nematic-liquid crystal display (TN-LCD) were comparable to rubbed polyimide. PMID:27455726

  6. Modeling Textural Processes during Self-Assembly of Plant-Based Chiral-Nematic Liquid Crystals

    Directory of Open Access Journals (Sweden)

    Yogesh K. Murugesan

    2010-12-01

    Full Text Available Biological liquid crystalline polymers are found in cellulosic, chitin, and DNA based natural materials. Chiral nematic liquid crystalline orientational order is observed frozen-in in the solid state in plant cell walls and is known as a liquid crystal analogue characterized by a helicoidal plywood architecture. The emergence of the plywood architecture by directed chiral nematic liquid crystalline self assembly has been postulated as the mechanism that leads to optimal cellulose fibril organization. In natural systems, tissue growth and development takes place in the presence of inclusions and secondary phases leaving behind characteristic defects and textures, which provide a unique testing ground for the validity of the liquid crystal self-assembly postulate. In this work, a mathematical model, based on the Landau-de Gennes theory of liquid crystals, is used to simulate defect textures arising in the domain of self assembly, due to presence of secondary phases representing plant cells, lumens and pit canals. It is shown that the obtained defect patterns observed in some plant cell walls are those expected from a truly liquid crystalline phase. The analysis reveals the nature and magnitude of the viscoelastic material parameters that lead to observed patterns in plant-based helicoids through directed self-assembly. In addition, the results provide new guidance to develop biomimetic plywoods for structural and functional applications.

  7. Time history of laser pulse polarization transformation as a tool of the isotropic-nematic phase transition in liquid crystals

    Science.gov (United States)

    Makarov, Vladimir A.; Il'inova, Tamara M.; Marchenko, Tatiana B.; Shkurinov, Aleksandr P.; Zolot'ko, Alexander S.

    2003-06-01

    We theoretically investigate in the aberrationless approximation the self-action of the elliptically polarized Gaussian pulse during its propagation in a thin dish with a nematic liquid crystal in the isotropic phase. Quadrature formulas are obtained to describe the time history of the intensity, the elliptisity degree and the rotation angle of the polarization ellipse of the output radiation at the different points of the beam cross-section. They are expressed in terms of the parameters describing two, essential near the temperature of the isotropic-nematic phase transition, mechanisms of the spatial nonlocality of the nonlinear medium optical response, and in terms of the other parameters, which describe the nematic liquid crystal and the elliptically polarized incident pulse. The former mechanism is specified by the medium heating due to light absorption; the latter is determined by the fluctuations of the nematic liquid crystal order parameter tensor near the temperature of the isotropic-nematic phase transition. It is shown that for some values of temperature and of the nematic liquid crystal parameters the elliptical polarization of the incident pulse, which is constant at the entry of the thin dish, transforms into the linear or another different elliptical one at the exit and keeps this new state up to the pulse tail. The dependence of the ellipticity degree on time becomes significantly nonmonotonic and changes its sign in some cases. The nonlocality of the nonlinear medium optical response weakens these transformations.

  8. Aligned Carbon Nanotube Thin Films from Liquid Crystal Polyelectrolyte Inks.

    Science.gov (United States)

    Tune, Daniel D; Blanch, Adam J; Shearer, Cameron J; Moore, Katherine E; Pfohl, Moritz; Shapter, Joseph G; Flavel, Benjamin S

    2015-11-25

    Single walled carbon nanotube thin films are fabricated by solution shearing from high concentration sodium nanotubide polyelectrolyte inks. The solutions are produced by simple stirring of the nanotubes with elemental sodium in dimethylacetamide, and the nanotubes are thus not subject to any sonication-induced damage. At such elevated concentrations (∼4 mg mL(-1)), the solutions exist in the liquid crystal phase and during deposition this order is transferred to the films, which are well aligned in the direction of shear with a 2D nematic order parameter of ∼0.7 determined by polarized absorption measurements. Compared to similarly formed films made from superacids, the polyelectrolyte films contain smaller bundles and a much narrower distribution of bundle diameters. After p-doping with an organic oxidizer, the films exhibit a very high DC electrical to optical conductivity ratio of σ(DC)/σ(OP) ∼ 35, corresponding to a calculated DC conductivity of over 7000 S cm(-1). When very thin (T550 ∼ 96%), smooth (RMS roughness, R(q) ∼ 2.2 nm), and highly aligned films made via this new route are used as the front electrodes of carbon nanotube-silicon solar cells, the power conversion efficiency is almost an order of magnitude greater than that obtained when using the much rougher (R(q) ∼ 20-30 nm) and less conductive (peak σ(DC)/σ(OP) ∼ 2.5) films formed by common vacuum filtration of the same starting material, and having the same transmittance. PMID:26511159

  9. Domain Walls and Anchoring Transitions Mimicking Nematic Biaxiality in the Oxadiazole Bent-Core Liquid Crystal C7

    OpenAIRE

    Kim, Young-Ki; Cukrov, Greta; Xiang, Jie; Shin, Sung-Tae; Lavrentovich, Oleg D.

    2015-01-01

    We investigate the origin of secondary disclinations that were recently described as a new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. With an assortment of optical techniques such as polarizing optical microscopy, LC PolScope, and fluorescence confocal polarizing microscopy, we demonstrate that the secondary disclinations represent non-singular domain walls formed in an uniaxial nematic during the surface anchoring transition, in which surfa...

  10. Calculating the dielectric anisotropy of nematic liquid crystals: a reinvestigation of the Maier-Meier theory

    Institute of Scientific and Technical Information of China (English)

    Zhang Ran; He Jun; Peng Zeng-Hui; Xuan Li

    2009-01-01

    This paper investigates the average dielectric permittivity (-ε) in the Maier-Meier theory for calculating the dielectric anisotropy (△ε) of nematic liquid crystals. For the reason that e of nematics has the same expression as the dielectric permittivity of the isotropic state, the Onsager equation for isotropic dielectric was used to calculate it. The computed -ε shows reasonable agreement with the results of the numerical methods used in the literature. Molecular parameters, such as the polarizability and its anisotropy, the dipole moment and its angle with the molecular long axis,were taken from semi-empirical quantum chemistry (MOCPAC/AM1) modeling. The calculated values of Ae according to the Maier-Meier equation are in good agreement with the experimental results for the investigated compounds having different core structures and polar substituents.

  11. Weak Anchoring and Surface Elasticity Effects in Electroosmotic Flow of Nematic Liquid Crystals Through Narrow Confinements

    CERN Document Server

    Poddar, Antarip; Chakraborty, Suman

    2016-01-01

    Advent of nematic liquid crystals flows have attracted renewed attention in view of microfluidic transport phenomena. Among various transport processes, electroosmosis stands as one of the efficient flow actuation method through narrow confinement. In the present study, we explore the electrically actuated flow of a nematic fluid with ionic inclusions taking into account the influences from surface induced elastic and electrical double layer phenomena. Influence of surface effects on the flow characteristics is known to get augmented in micro-confined environment and must be properly addressed. Towards this, we devise the coupled flow governing equations from fundamental free energy analysis considering the contributions from first and second-order elastic, dielectric, flexoelectric, ionic and entropic energies. We have further considered weak anchoring surface conditions with second order elasticity which helps us to more accurately capture the director deformations along the boundaries. The present study fo...

  12. Generalized nematohydrodynamic boundary conditions with application to bistable twisted nematic liquid-crystal displays

    KAUST Repository

    Fang, Angbo

    2008-12-08

    Parallel to the highly successful Ericksen-Leslie hydrodynamic theory for the bulk behavior of nematic liquid crystals (NLCs), we derive a set of coupled hydrodynamic boundary conditions to describe the NLC dynamics near NLC-solid interfaces. In our boundary conditions, translational flux (flow slippage) and rotational flux (surface director relaxation) are coupled according to the Onsager variational principle of least energy dissipation. The application of our boundary conditions to the truly bistable π -twist NLC cell reveals a complete picture of the dynamic switching processes. It is found that the thus far overlooked translation-rotation dissipative coupling at solid surfaces can accelerate surface director relaxation and enhance the flow rate. This can be utilized to improve the performance of electro-optical nematic devices by lowering the required switching voltages and reducing the switching times. © 2008 The American Physical Society.

  13. Orientational behavior of a nematic liquid crystal filled with inorganic oxide nanoparticles

    International Nuclear Information System (INIS)

    We report the results of dielectric spectroscopy, Fourier transformed infrared spectroscopy (FTIR) and atomic force microscopy (AFM) studies performed on the nematic liquid crystal (LC) mixture Merck ZLI-1132 filled with TiO2 (rutile and anatase) and SiO2 nanoparticles. The observed static dielectric permittivities are interpreted in terms of orientation of the LC with respect to the measuring electric field. Adding of SiO2 particles mainly induces a statistical orientation of LC molecules, whereas TiO2 particles promote the perpendicular orientation. The dynamics of LC molecules in all systems is very similar. The reason for the slightly faster reorientation observed in the mixtures may be connected with a disturbed nematic order near the surface of solid particles

  14. Calculating the dielectric anisotropy of nematic liquid crystals: a reinvestigation of the Maier–Meier theory

    International Nuclear Information System (INIS)

    This paper investigates the average dielectric permittivity (ε-bar ) in the Maier–Meier theory for calculating the dielectric anisotropy (Δε) of nematic liquid crystals. For the reason that ε-bar of nematics has the same expression as the dielectric permittivity of the isotropic state, the Onsager equation for isotropic dielectric was used to calculate it. The computed ε-bar shows reasonable agreement with the results of the numerical methods used in the literature. Molecular parameters, such as the polarizability and its anisotropy, the dipole moment and its angle with the molecular long axis, were taken from semi-empirical quantum chemistry (MOCPAC/AM1) modeling. The calculated values of Δε according to the Maier–Meier equation are in good agreement with the experimental results for the investigated compounds having different core structures and polar substituents. (condensed matter: structure, thermal and mechanical properties)

  15. Generalized nematohydrodynamic boundary conditions with application to bistable twisted nematic liquid-crystal displays.

    Science.gov (United States)

    Fang, Angbo; Qian, Tiezheng; Sheng, Ping

    2008-12-01

    Parallel to the highly successful Ericksen-Leslie hydrodynamic theory for the bulk behavior of nematic liquid crystals (NLCs), we derive a set of coupled hydrodynamic boundary conditions to describe the NLC dynamics near NLC-solid interfaces. In our boundary conditions, translational flux (flow slippage) and rotational flux (surface director relaxation) are coupled according to the Onsager variational principle of least energy dissipation. The application of our boundary conditions to the truly bistable pi -twist NLC cell reveals a complete picture of the dynamic switching processes. It is found that the thus far overlooked translation-rotation dissipative coupling at solid surfaces can accelerate surface director relaxation and enhance the flow rate. This can be utilized to improve the performance of electro-optical nematic devices by lowering the required switching voltages and reducing the switching times. PMID:19256854

  16. Optical properties of planar nematic liquid crystals samples which are parallel oriented by nanofibers

    Science.gov (United States)

    Yusuf, Yusril; Kusumasari, Ervanggis Minggar; Ula, Nur Mufidatul; Jahidah, Khannah; Triyana, Kuwat; Sosiati, Harini; Harsojo

    2016-04-01

    Optical properties of two nematic liquid crystals, i.e., 4-methoxybenzylidene-4-butylaniline (MBBA) and 4-cyano-4'-pentylbiphenyl (5 CB) which are parallel oriented by nanofibers has been successfully performed. Planar samples of liquid crystals were made using polyvinyl alcohol (PVA) nanofiber from electrospinning process. Electrospinning method was modified using copper (Cu) as gap collector. These planar samples area are 15 mm x 25 mm. Optical characteristic of these samples were studied by using optical polarizing microscope. The optical intensity changes by a rotationof crossed polarizers is observed. The sinusoidal intensity change was observedin these samples as such as in the planar sample prepared by the rubbing method.

  17. Spectral properties of BChl c in nematic liquid crystals. II: Aggregated form of dye

    Science.gov (United States)

    Dudkowiak, A.; Francke, C.; Amesz, J.; Planner, A.; Frackowiak, D.

    1996-11-01

    The orientation properties of aggregated bacteriochlorophyll c in a nematic liquid crystal matrix have been studied by means of polarized steady-state and time-resolved spectroscopy. The pigment introduced to the model system was predominantly in tetrameric (or hexameric) form with absorption maxima located at about 670 and 710 nm. Two tetramers with long-wavelength maxima at 704 and 722 nm could be distinguished. They exhibited different orientations in liquid crystal and different yields of fluorescence. Both tetramers exhibited delayed luminescence in the μs time region.

  18. All-optical modulation in dye-doped nematic liquid crystal photonic bandgap fibers

    DEFF Research Database (Denmark)

    Alkeskjold, Thomas Tanggaard; Lægsgaard, Jesper; Bjarklev, Anders Overgaard;

    2004-01-01

    Photonic crystal fibers (PCFs) have attracted significant attention during the last years and much research has been devoted to develop fiber designs for various applications, hereunder tunable fiber devices. Recently, thermally and electrically tunable PCF devices based on liquid crystals (LCs......) have been demonstrated. However, optical tuning of the LC PCF has until now not been demonstrated. Here we demonstrate an all-optical modulator, which utilizes a pulsed 532nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid...

  19. Blazed vector grating liquid crystal cells with photocrosslinkable polymeric alignment films fabricated by one-step polarizer rotation method

    Science.gov (United States)

    Kawai, Kotaro; Kuzuwata, Mitsuru; Sasaki, Tomoyuki; Noda, Kohei; Kawatsuki, Nobuhiro; Ono, Hiroshi

    2014-12-01

    Blazed vector grating liquid crystal (LC) cells, in which the directors of low-molar-mass LCs are antisymmetrically distributed, were fabricated by one-step exposure of an empty glass cell inner-coated with a photocrosslinkable polymer LC (PCLC) to UV light. By adopting a LC cell structure, twisted nematic (TN) and homogeneous (HOMO) alignments were obtained in the blazed vector grating LC cells. Moreover, the diffraction efficiency of the blazed vector grating LC cells was greatly improved by increasing the thickness of the device in comparison with that of a blazed vector grating with a thin film structure obtained in our previous study. In addition, the diffraction efficiency and polarization states of ±1st-order diffracted beams from the resultant blazed vector grating LC cells were controlled by designing a blazed pattern in the alignment films, and these diffraction properties were well explained on the basis of Jones calculus and the elastic continuum theory of nematic LCs.

  20. Density-functional theory of surfacelike elasticity of nematic liquid crystals

    Science.gov (United States)

    Yokoyama, Hiroshi

    1997-03-01

    Based on the density-functional theory, we show that the splay-bend surfacelike bulk elastic constant K13 is an artifact of the phenomenological as well as the gradient expansion construction of the curvature elastic free energy of nematic liquid crystals, while the saddle-splay constant K24 is real and approximately obeys an extended Nehring-Saupe relation K24 >=(K11 -K22 )/2, with K11 and K22 being the splay and twist Frank constants, respectively. The result K13 =0 automatically resolves the Oldano-Barbero pathology, which inevitably accompanies a nonzero K13 , and gives a concrete rationale for the conventional approaches in the continuum theory disregarding the surfacelike elasticity. The source of an apparently nonzero K13 in previous microscopic theories is discussed in detail and is demonstrated to be a result of an inconsistent use of a nonlocal-to-local mapping of the elastic free-energy functional at the boundary. The absence of K13 can be regarded as a type of Cauchy relation in the nematic continuum theory in the sense that it is not directly rooted in any of the macroscopic symmetries existing in the nematic phase, but is a general consequence of the particular algebraic form of the nonlocal free-energy term from which K13 derives; its linearity in the distortion amplitude and the symmetry of the relevant direct correlation function with respect to the permutation of a molecular pair leads always to the vanishing K13 . In this respect, K13 =0 applies not only to nematic liquid crystals but also to a more general class of phases such as cholesteric liquid crystals, whose structure can be viewed as a weak modulation of a translationally invariant phase. We finally consider the elastic description of nematic liquid crystals in the presence of real interfaces. The present formulation allows a straightforward decomposition of the elastic excess free energy into the bulk contribution and the interfacial excess in the Gibbs sense. The bulk part yields the

  1. Spectral properties of bacteriochlorophyll c in nematic liquid crystal. Part 1. Monomeric forms of dye

    Science.gov (United States)

    Dudkowiak, A.; Francke, C.; Amesz, J.; Planner, A.; Hanyz, I.; Fraçkowiak, D.

    1996-02-01

    The spectroscopic features of bacteriochlorophyll c and bacteriopheophytin c in a nematic liquid crystal matrix have been investigated. Absorption, circular dichroism, fluorescence and time resolved delayed luminescence spectra have been measured. The pigment is introduced to the liquid crystal from a dry and from a hydrated chloroform solution. In both cases the pigment is in the monomeric form. Hydration of the solvent and the presence or absence of the central Mg atom affect the interaction of the pigment molecules with the liquid crystal matrix, changing the fluorescence anisotropy. A model for the bacteriochlorophyll c orientation in the liquid crystal is proposed and the averaged angles between the transition moments and the liquid crystal orientation axis are determined. A slow process (in the microsecond range) of radiative deactivation of energy absorbed by the pigments is observed. This delayed emission could be due to pigment ionization and delayed charge recombination and/or thermal activation from the triplet to the excited singlet state.

  2. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

    Energy Technology Data Exchange (ETDEWEB)

    Armas-Pérez, Julio C.; Londono-Hurtado, Alejandro [Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Guzmán, Orlando [Departamento de Física, Universidad Autónoma Metropolitana, Iztapalapa, DF 09340, México (Mexico); Hernández-Ortiz, Juan P. [Departamento de Materiales y Minerales, Universidad Nacional de Colombia, Sede Medellín, Medellín (Colombia); Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Pablo, Juan J. de, E-mail: depablo@uchicago.edu [Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2015-07-28

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

  3. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields.

    Energy Technology Data Exchange (ETDEWEB)

    Armas-Perez, Julio C.; Londono-Hurtado, Alejandro; Guzman, Orlando; Hernandez-Ortiz, Juan P.; de Pablo, Juan J.

    2015-07-27

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

  4. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

    International Nuclear Information System (INIS)

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate

  5. Symmetry breaking in nematic liquid crystals: analogy with cosmology and magnetism

    International Nuclear Information System (INIS)

    Universal behavior related to continuous symmetry breaking in nematic liquid crystals is studied using Brownian molecular dynamics. A three-dimensional lattice system of rod-like objects interacting via the Lebwohl–Lasher interaction is considered. We test the applicability of predictions originally derived in cosmology and magnetism. In the first part we focus on coarsening dynamics following the temperature driven isotropic–nematic phase transition for different quench rates. The behavior in the early coarsening regime supports predictions made originally by Kibble in cosmology. For fast enough quenches, symmetry breaking and causality give rise to a dense tangle of defects. When the degree of orientational ordering is large enough, well defined protodomains characterized by a single average domain length are formed. With time subcritical domains gradually vanish and supercritical domains grow with time, exhibiting a universal scaling law. In the second part of the paper we study the impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase. We demonstrate that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry–Ma theorem prediction only for the appropriate history of systems. (paper)

  6. Field-driven dynamics of microcapillaries filled with nematic liquid crystal

    Science.gov (United States)

    Fu, Fred; Khayyatzadeh, Pouya; Abukhdeir, Nasser M.

    Polymer-dispersed liquid crystal (PDLC) composites have long been a focus of study for their unique electro-optical properties and the feasibility of manufacturing them on a large scale, resulting in applications such as switchable windows. LC domains within PDLCs are typically spheroidal, as opposed to rectangular in LCD technology, and thus exhibit substantially different behaviour in the presence of an external field. In this work, continuum simulations were performed in order to capture the complex formation and electric field-driven switching dynamics of approximations of PDLC domains. A simplified elliptic cylinder (microcapillary) geometry is used and the effects of varying aspect ratio, surface anchoring, and external field strength were studied using the Landau-de Gennes model. The observed nematic formation and reorientation dynamics were found to be governed by the presence and motion of defects within the domain. Aspect ratio was found to strongly influence domain texture by providing regions of high curvature to which defects are attracted. Simulations also predict the presence of a geometry-controlled transition from nematic order enhanced by an external field (low aspect ratio) to nematic order frustrated by an external field (high aspect ratio). This work was made possible by the Natural Sciences and Engineering Research Council of Canada and Compute Ontario.

  7. Surface Dipole Control of Liquid Crystal Alignment.

    Science.gov (United States)

    Schwartz, Jeffrey J; Mendoza, Alexandra M; Wattanatorn, Natcha; Zhao, Yuxi; Nguyen, Vinh T; Spokoyny, Alexander M; Mirkin, Chad A; Baše, Tomáš; Weiss, Paul S

    2016-05-11

    Detailed understanding and control of the intermolecular forces that govern molecular assembly are necessary to engineer structure and function at the nanoscale. Liquid crystal (LC) assembly is exceptionally sensitive to surface properties, capable of transducing nanoscale intermolecular interactions into a macroscopic optical readout. Self-assembled monolayers (SAMs) modify surface interactions and are known to influence LC alignment. Here, we exploit the different dipole magnitudes and orientations of carboranethiol and -dithiol positional isomers to deconvolve the influence of SAM-LC dipolar coupling from variations in molecular geometry, tilt, and order. Director orientations and anchoring energies are measured for LC cells employing various carboranethiol and -dithiol isomer alignment layers. The normal component of the molecular dipole in the SAM, toward or away from the underlying substrate, was found to determine the in-plane LC director orientation relative to the anisotropy axis of the surface. By using LC alignment as a probe of interaction strength, we elucidate the role of dipolar coupling of molecular monolayers to their environment in determining molecular orientations. We apply this understanding to advance the engineering of molecular interactions at the nanoscale. PMID:27090503

  8. Macroscopic biaxiality and electric-field-induced rotation of the minor director in the nematic phase of a bent-core liquid crystal

    Science.gov (United States)

    Nagaraj, Mamatha; Merkel, K.; Vij, J. K.; Kocot, A.

    2010-09-01

    Biaxiality in the nematic phase has been investigated for the bent-core liquid-crystal para-heptylbenzoate diester, using polarised IR spectroscopy. Anisotropic fluctuations of the nematic director are discussed in terms of the self-assembly of the chiral conformers. The ordering of the minor director for the homeotropicaly aligned sample is found to depend on the rubbing of the substrates of the cell and the amplitude of in-plane electric field. On increasing the in-plane electric field, the rotation of the minor director in the plane of the substrate is observed with an angle of approximately 45°, where initially the minor director is shown to lie along the rubbing direction. It is also shown that on the average the long axis of the molecules is normal to the substrate with surface treatment, with and without rubbing. The electric in-plane field combined with rubbing is shown to induce biaxial order in the nematic phase of a material with negative dielectic anisotropy for the first time.

  9. New developments in nanoparticle-liquid crystal composites: from magic-sized semiconductor nanoclusters to alignment pattern formation via nanoparticle stenciling

    Science.gov (United States)

    Mirzaei, Javad; Sawatzky, Ryan; Sharma, Anshul; Urbanski, Martin; Yu, Kui; Kitzerow, Heinz-S.; Hegmann, Torsten

    2012-03-01

    We here report on the alignment and electro-optic properties of nematic liquid crystals (LCs) either containing nanoscale particles as additives or featuring particles patterned on substrates. The investigated nematic LCs or LC dispersions are doped or in contact with magic-sized semiconductor CdSe nanocrystals (MSNCs) or silane- and alkylthiol monolayercapped gold nanoparticles. Three single-sized CdSe quantum dots capped with myristic acid exhibiting bright bandgap photoluminescence (PL) at λmax ~ 463 nm were tested as additives. Two of the quantum dots only vary in the amount of defects as indicated by different bandgap and deep trap PL. The third MSNC sample is compositionally different, doped with Zn. These MSNCs with almost identical sizes were doped at different concentrations (1-5 wt%) into the nematic phase of the 2-phenylpyrimidine-based LC1. Only the Zn-doped MSNCs showed the formation of birefringent stripes surrounded by areas of homeotropic alignment between plain glass slides at all concentrations as observed for many other nanoparticle-doped nematic LCs reported earlier by our group. In polyimide-coated glass slides favoring planar orientation of the nematic director, planar alignment was observed. Similarly, siloxane-coated gold nanoparticle additives with narrow size distribution, but larger size, show homeotropic alignment between plain glass and planar alignment in rubbed polyimide-coated cells. Surprisingly then, we succeeded in creating alignment patterns using smaller, ~2 nm alkylthiol-capped gold nanoparticles using a process called stenciling that allowed us to generate patterns of homeotropic alignment in a continuum of planar alignment of the nematic LC. Finally, electro-optic investigations on some of these samples revealed that only the Zn-doped magic-sized MSNCs significantly lower the dielectric anisotropy as well as the splay elastic constant of the nematic host, despite identical size and surface functionality of the three used

  10. Determination of the flexoelectric coefficient (e1–e3 in nematic liquid crystal by using fully leaky optical-guided mode

    Directory of Open Access Journals (Sweden)

    Guili Zheng

    2016-02-01

    Full Text Available Fully leaky optical-guided mode was employed to determine the difference in the splay and bend flexoelectric coefficient (e1–e3 in negative nematic liquid crystal MS-N01300-000. The experimental curves of reflectivity versus internal angle (angle of incident light to the liquid crystal were obtained when a laser beam passed through the hybrid-aligned nematic in-plane switching liquid crystal cell; the cell was embedded in pyramid-coupled waveguide with different alternating current (AC and direct current (DC voltages. The curves of the applied DC with voltage similar to that of AC shift to the left or the right. Experimental results were then compared with theoretical results derived from elastic continuum theory and multi-layer optical theory of liquid crystals. The approximate value of the flexoelectric coefficient (e1–e3 of MS-N01300-000 is 9.0 × 10−11 C/m.

  11. Molecular simulation of model liquid crystals in a strong aligning field

    Science.gov (United States)

    de Miguel, Enrique; Blas, Felipe J.; Martín Del Río, Elvira

    We report a computer simulation study of systems of perfectly aligned molecules interacting through the Gay-Berne (GB) potential model for two different values of the molecular anisotropy parameter κ, namely 3 and 4.4. The models are appropriate to gauge the effects of strong aligning fields on the thermodynamics and structural properties of thermotropic liquid crystals. According to our results, one of the main effects of the external field is to increase the range of stability of the smectic A phase, which indicates the existence of a strong coupling between orientational and translational order. For the κ = 3 GB model the smectic phase, which is not stable in the absence of the field, is promoted when the molecules are constrained to be parallel. According to the simulation results, the smectic A-nematic transition is, in general, continuous; however, this transition appears to be first order at low pressure for the κ = 4.4 GB fluid model.

  12. Zenithal alignment of liquid crystal on homeotropic polyimide film irradiated by ion beam

    Science.gov (United States)

    Choi, Yoonseuk; Yoon, Tae-Hoon; Kwon, Jin Hyuk; Yi, Jonghoon; Gwag, Jin Seog

    2012-01-01

    We investigate the pretilt characteristics of a nematic liquid crystal [LC] in terms of ion beam exposure conditions on the homeotropic polyimide alignment layer. The pretilt angle of LCs in the case of high-energy ion beam treatment was decreased considerably almost the same to that of the homogenous alignment layer though we used homeotropic polyimide film at first. Increasing irradiating energy, we could control the pretilt from 90° to 1° with several steps. We believe that this is because the side chain with hydrophobicity in the used polyimide is broken by ion beam exposure. To confirm it, contact angle measurement was carried out. With this result, we can easily control the LC pretilt in the pixel with appropriate exposure conditions which is critical to achieve excellent electrooptic characteristics and good image quality.

  13. Brownian motion of particles in nematic fluids

    Science.gov (United States)

    Yao, Xuxia; Nayani, Karthik; Park, Jung; Srinivasarao, Mohan

    2011-03-01

    We studied the brownian motion of both charged and neutral polystyrene particles in two nematic fluids, a thermotropic liquid crystal, E7, and a lyotropic chromonic liquid crystal, Sunset Yellow FCF (SSY). Homogeneous planar alignment of E7 was easliy achieved by using rubbed polyimide film coated on the glass. For SSY planar mondomain, we used the capillary method recently developed in our lab. By tracking a single particle, the direction dependent diffussion coefficients and Stokes drag were measured in the nematic phase and isotropic phase for both systems.

  14. Imaging in natural light with nematic liquid crystals (Presentation Recording)

    Science.gov (United States)

    Galstian, Tigran V.

    2015-10-01

    Nametic liquid crystals (NLC) are most commonly used liquid crystal (LC) materials in various light modulators [1], displays [2] and lenses [3]. However those materials have a fundamental limitation: they are polarization sensitive since the refractive index modulation here is achieved by the electric field induced reorientation of their local anisotropy axis. Thus, the standard imaging optical systems (used in consumer electronic products and dealing with natural light sources [4]) have to use double NLC structures in a cross oriented way and in rather requiring geometrical conditions. We describe a simple but very efficient optical device that allows the dynamic focusing of unpolarized light using a single NLC layer. The operation principle of the proposed device is based on the combination of an electrically variable "single layer lens" with two fixed optical elements for light reflection and 90° polarization flip. Such an approach is made possible thanks to the close integration of thin film wave plate and mirror. Preliminary experimental studies of the obtained electrically variable mirror show very promising results. Several standard camera geometries, using the double layer approach, and possible new geometries, using the reflective approach, will be described. References 1. Gordon D. Love, Wave-front correction and production of Zernike modes with a liquid-crystal spatial light modulator, Applied Optics, Vol. 36, Issue 7, pp. 1517-1524 (1997). 2. P. Yeh and C. Gu, Optics of Liquid Crystal Displays, Wiley, 1999. 3. T. Galstian, Smart Mini-Cameras, CRC Press, Taylor and Francis group, 2013. 4. www.lensvector.com

  15. Lensing effects in a nematic liquid crystal with topological defects.

    Science.gov (United States)

    Sátiro, C; Moraes, F

    2006-06-01

    Light traveling through a liquid crystal with disclinations perceives a geometrical background which causes lensing effects similar to the ones predicted for cosmic objects like global monopoles and cosmic strings. In this paper we explore the effective geometry as perceived by light in such media. The comparison between both systems suggests that experiments can be done in the laboratory to simulate optical properties, like gravitational lensing, of cosmic objects. PMID:16775663

  16. Dipole solitons in highly nonlocal nematic liquid crystals: finite size effects

    International Nuclear Information System (INIS)

    We investigate numerically dipole solitons in highly nonlocal three-dimensional uniaxial nematic liquid crystals in the presence of an externally applied bias voltage. Using the modified Petviashvili method, we calculate shape-invariant dipole profiles. We study the influence of boundary conditions and finite size effects on the dipole solitons obtained. We show that the solitons found in one transverse dimension may differ dramatically from solitons of the same family, but found in two transverse dimensions. We report the existence of crystal thicknesses for which a specific dipole soliton from a given family of dipole solitons achieves minimal power and maximal width. (paper)

  17. Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals

    OpenAIRE

    Wang, Xiang; Pu, Shengli; Ji, Hongzhu; YU, GUOJUN

    2012-01-01

    Ferronematic materials composed of 4-cyano-4′-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (Δn) and figure of merit of optical properties (Q = Δn/α, where α is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to ...

  18. Symmetry of uniaxial global Landau-de Gennes minimizers in the theory of nematic liquid crystals

    CERN Document Server

    Henao, Duvan

    2011-01-01

    We study uniaxial energy-minimizers within the Landau-de Gennes theory for nematic liquid crystals on a three-dimensional spherical droplet subject to homeotropic boundary conditions. We work in the low-temperature regime and show that uniaxial energy-minimizers necessarily have the structure of the well-studied radial-hedgehog solution in the low-temperature limit. An immediate consequence of this result is that Landau-de Gennes energy minimizers cannot be purely uniaxial for sufficiently low temperatures.

  19. Electrical Properties of Zn-Phthalocyanine and Poly (3-hexylthiophene Doped Nematic Liquid Crystal

    Directory of Open Access Journals (Sweden)

    Y. Karakuş

    2011-01-01

    Full Text Available An E7 coded nematic liquid crystal was doped with zinc phthalocyanine and poly (3-hexylthiophene. A variety of properties including relaxation time, absorption coefficient, and critical frequency of this doped system were investigated using impedance spectroscopy. The doped systems displayed increased absorption coefficients in the range 0.22–0.55 and relaxation times from 5.05×10−7 s to 3.59×10−6 s with a decrease in the critical frequency from 3.54 MHz to 2.048 MHz.

  20. Electrically Rotatable Polarizer Using One-Dimensional Photonic Crystal with a Nematic Liquid Crystal Defect Layer

    Directory of Open Access Journals (Sweden)

    Ryotaro Ozaki

    2015-09-01

    Full Text Available Polarization characteristics of defect mode peaks in a one-dimensional (1D photonic crystal (PC with a nematic liquid crystal (NLC defect layer have been investigated. Two different polarized defect modes are observed in a stop band. One group of defect modes is polarized along the long molecular axis of the NLC, whereas another group is polarized along its short axis. Polarizations of the defect modes can be tuned by field-induced in-plane reorientation of the NLC in the defect layer. The polarization properties of the 1D PC with the NLC defect layer is also investigated by the finite difference time domain (FDTD simulation.

  1. Spatial Light Interference Microscopy (SLIM) using twisted-nematic liquid-crystal modulation

    OpenAIRE

    Nguyen, Tan H.; Popescu, Gabriel

    2013-01-01

    We report the use of a twisted nematic liquid-crystal spatial light modulator (TNLC-SLM) for quantitative phase imaging. The experimental setup is a new implementation of the SLIM principle, which is a phase shifting, white light method for quantitative phase imaging. The approach is based on switching between the phase and amplitude modulation modes of the SLM. Our system is able to deliver a 0.99 nm spatial and 1.33 nm temporal pathlength sensitivity while retaining the optical transverse r...

  2. Long-time dynamics of the nonhomogeneous incompressible flow of nematic liquid crystals

    CERN Document Server

    Hu, Xianpeng

    2012-01-01

    We study the long-time behavior of global strong solutions to a hydrodynamic system for nonhomogeneous incompressible nematic liquid crystal flows driven by two types of external forces in a smooth bounded domain in $\\mathbb{R}^2$. For arbitrary large regular initial data with the initial density being away from vacuum, we prove the decay of the velocity field for both cases. Furthermore, for the case with asymptotically autonomous external force, we can prove the convergence of the density function and the director vector as time goes to infinity. Estimates on convergence rate are also provided.

  3. Nematic Liquid Crystal Systems and Magneto-Hydrodynamics System:The Properties of Their Solutions

    OpenAIRE

    Dai, Mimi

    2012-01-01

    We study a simplified system for the flow of Nematic Liquid Crystals (LCD) in the cases of non-constant density and constant density with certain initial and boundary conditions. This is a coupled non-parabolic dissipative dynamic system. For the system with non-constant density in the whole space $\\mathbb{R}^3$, we establish the global existence of weak solutions. For the system with non-constant density on a bounded domain in two dimensional and three dimensional cases, we establish the reg...

  4. OPTICAL FREQUENCY-LOCKING OF A NEMATIC LIQUID CRYSTAL IN A FABRY-PEROT INTERFEROMETER

    OpenAIRE

    Wang, P.-Y.; Dai, J.-H.; Zhang, H.-J.

    1988-01-01

    The light-induced frequency-locking of a nematic liquid crystal in a Fabry-Perot interferometer with a periodic optical drive are studied. The frequency lockings with winding numbers 1/1, 1/2, 113, 1/4, and so on are easily observed by varying the driving amplitude Ɗ and frequency ω. Frequency lockings between the above mentioned winding numbers can only be observed occasionally due to the effect of noise. All the winding numbers of the frequency lockings belong to the Farey tree. Quasiperiod...

  5. Gel formation in a mixture of a block copolymer and a nematic liquid crystal.

    Science.gov (United States)

    Khazimullin, Maxim; Müller, Thomas; Messlinger, Stephan; Rehberg, Ingo; Schöpf, Wolfgang; Krekhov, Alexei; Pettau, Robin; Kreger, Klaus; Schmidt, Hans-Werner

    2011-08-01

    The viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state at about 3%. In the gel state, the system does not flow, exhibits a polydomain structure on a microscopic level, and strongly scatters light. Below the gelation point, the system is homogeneous and behaves like a usual nematic, so the continuum theory of liquid crystals can be applied for interpreting the experimental data. Using the dynamic Fréedericksz transition technique, the dependence of the splay elastic constant and the rotational viscosity on the polymer concentration have been obtained. Comparing the dynamic behavior of block copolymer solutions with the respective homopolymer solutions reveals that, above a mass concentration of 1%, self-assembling of the block copolymer chain segments in clusters occurred, resulting in a gel state at higher concentrations. The effective cluster size is estimated as a function of the concentration, and a scaling-law behavior near the sol-gel transition is confirmed. This technique may serve as an alternative method for determining the gelation point. PMID:21929007

  6. Gel formation in a mixture of a block copolymer and a nematic liquid crystal

    Science.gov (United States)

    Khazimullin, Maxim; Müller, Thomas; Messlinger, Stephan; Rehberg, Ingo; Schöpf, Wolfgang; Krekhov, Alexei; Pettau, Robin; Kreger, Klaus; Schmidt, Hans-Werner

    2011-08-01

    The viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state at about 3%. In the gel state, the system does not flow, exhibits a polydomain structure on a microscopic level, and strongly scatters light. Below the gelation point, the system is homogeneous and behaves like a usual nematic, so the continuum theory of liquid crystals can be applied for interpreting the experimental data. Using the dynamic Fréedericksz transition technique, the dependence of the splay elastic constant and the rotational viscosity on the polymer concentration have been obtained. Comparing the dynamic behavior of block copolymer solutions with the respective homopolymer solutions reveals that, above a mass concentration of 1%, self-assembling of the block copolymer chain segments in clusters occurred, resulting in a gel state at higher concentrations. The effective cluster size is estimated as a function of the concentration, and a scaling-law behavior near the sol-gel transition is confirmed. This technique may serve as an alternative method for determining the gelation point.

  7. Serrin blow-up criterion for strong solutions to the 3-D compressible nematic liquid crystal flows with vacuum

    OpenAIRE

    Qiao Liu

    2013-01-01

    In this article, we extend the well-known Serrin's blow-up criterion for solutions of the 3-D incompressible Navier-Stokes equations to the 3-D compressible nematic liquid crystal flows where the initial vacuum is allowed. It is proved that for the initial-boundary value problem of the 3-D compressible nematic liquid crystal flows in a bounded domain, the strong solution exists globally if the velocity satisfies the Serrin's condition and $L^1(0,T;L^{infty})$-norm of the gradient of th...

  8. Serrin blow-up criterion for strong solutions to the 3-D compressible nematic liquid crystal flows with vacuum

    Directory of Open Access Journals (Sweden)

    Qiao Liu

    2013-04-01

    Full Text Available In this article, we extend the well-known Serrin's blow-up criterion for solutions of the 3-D incompressible Navier-Stokes equations to the 3-D compressible nematic liquid crystal flows where the initial vacuum is allowed. It is proved that for the initial-boundary value problem of the 3-D compressible nematic liquid crystal flows in a bounded domain, the strong solution exists globally if the velocity satisfies the Serrin's condition and $L^1(0,T;L^{infty}$-norm of the gradient of the velocity is bounded.

  9. Fabrication of twisted nematic structure and vector grating cells by one-step exposure on photocrosslinkable polymer liquid crystals.

    Science.gov (United States)

    Kuzuwata, Mitsuru; Sasaki, Tomoyuki; Kawatsuki, Nobuhiro; Ono, Hiroshi

    2012-03-15

    We present a simple yet efficient method to automatically fabricate the twisted nematic structure by one-step exposure on an empty glass cell coated with photocrosslinkable polymer liquid crystal (PCLC) films. The resultant photoalignment directions of two substrates can be orthogonal to each other by controlling the difference between the exposure energy for upper and lower PCLC films and the twisted nematic (TN) structure can be automatically fabricated. The vector grating liquid crystalline cell with TN structure was also fabricated by means of a developed method, and the diffraction properties were well explained by the theoretical calculation on the basis of Jones calculus. PMID:22446243

  10. The role of defects and boundary and volume inhomogeneities in the field-induced director reorientation in nematic liquid crystals confined between parallel plates

    International Nuclear Information System (INIS)

    A deep understanding of the director dynamics in nematic liquid crystals confined between parallel plates is important for display technology as well as for basic science. Some aspects of this dynamics are still not clear, in spite of intense research and significant progress in the last thirty years. When a strong magnetic (or electric, with some precautions) field is applied to a well aligned nematic sample, depending on the angle between the director and the field one usually observes either a homogeneous or a spatially periodic (inhomogeneous) director reorientation to the new equilibrium position, parallel to the field, as shown by NMR observations well supported by the Leslie-Ericksen theory [A.F. Martins, P. Esnault and F. Volino, Phys. Rev. Lett. 57, 1745 (1986)]. These are collective modes (observed simultaneously over the whole sample) and the spatially periodic one originates in the long wavelength thermal fluctuations of the director orientation in equilibrium. Recent experiments [G.R. Luckhurst, A. Sugimura, B.A. Timimi and H. Zimmermann, Liquid Crystals 32, 1389 (2005)] have shown that in some practical cases the director reorientation in thin nematic samples confined between two parallel plates does not follows any of those two pictures. We focus on such experiments and present 2D computer simulations of the director dynamics in the presence of topological defects or boundary or volume inhomogeneities in the sample. Deuterium NMR spectra directly computed from the numerical results show good agreement with the experimental data. We propose that in addition to the above mentioned collective modes, a qualitatively different mode of reorientation, that we may call progressive mode, exists and may dominate the director reorientation in thin samples of low molecular mass liquid crystals

  11. Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals

    Science.gov (United States)

    Wang, Xiang; Pu, Shengli; Ji, Hongzhu; Yu, Guojun

    2012-05-01

    Ferronematic materials composed of 4-cyano-4'-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (Δ n) and figure of merit of optical properties ( Q = Δ n/α, where α is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to evaluate their optical properties. Similar magnetic-field- and magnetic-particle-concentration-dependent properties of birefringence and figure of merit of optical properties were obtained for the pure magnetic fluids and the ferronematic materials. For the ferronematic materials, the values of Q increase with the volume fractions of nematic liquid crystal under certain fixed field strength and are larger than those of their corresponding pure magnetic fluids at high field region. In addition, the enhancement of Q value increases monotonously with the magnetic field and becomes remarkable when the applied magnetic field is beyond 50 mT. The maximum relative enhanced value of Q R exceeds 6.8% in our experiments. The results of this work may conduce to extend the pragmatic applications of nanostructured magnetic fluids in optical field.

  12. Light-induced dynamics in nematic liquid crystals-a fascinating world of complex nonlinear phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Demeter, Gabor [Research Institute for Particle and Nuclear Physics, Konkoly Thege Miklos ut 29-33, H-1121 Budapest (Hungary)]. E-mail: gdemeter@rmki.kfki.hu; Krimer, Dmitry O. [Theoretische Physik, Universitaet Tuebingen, 72076 Tuebingen (Germany)]. E-mail: Dmitry.Krimer@uni-tuebingen.de

    2007-08-15

    Intense laser light traversing a thin layer of nematic liquid crystal is an example of a simple, easy to realise physical system, that shows very complex behaviour. Light can turn the optical axis of this uniaxial medium while propagating through it, and the dynamical behaviour that results ranges from simple orientational instabilities, through low-dimensional chaotic behaviour, to spatiotemporal pattern formation. In this paper, we review recent advances in the theoretical description of the complex phenomena that light can induce in nematic liquid crystals. We discuss the various approximations made in the models, their range of applicability, and contrast their results with experimental observations. In particular, we discuss the achievements of the plane wave approximation in various geometries, and examine how the numerous bifurcation scenarios calculated from the models can be used to interpret observations. We treat with special emphasis the results achieved in the description of the strongly nonlinear regime, where experiments have revealed interesting bifurcations and chaotic behaviour. We also discuss the mostly open problems of transverse pattern formation and the effects that can be attributed to the finite cross-section of the laser beam.

  13. Study on laser action from UV-curable chiral nematic liquid crystals

    International Nuclear Information System (INIS)

    This paper describes the study on laser action from UV-curable chiral nematic liquid crystals (CLCs) doped with a fluorescent dye before and after photopolymerization of CLC host. When an optically active agent without crosslinkable moiety was doped in a UV-curable nematic liquid crystal, the laser action from the CLC cell was quite different before and after photopolymerization. Before the polymerization, optically pumping of dye-doped CLC cells with a linearly polarized laser beam gave rise to the laser emission with circular polarization at the band edge of CLC reflection as a consequence of the internal distributed feedback effect. Successively, photopolymerization of the CLC with 365 nm light brought about the thorough disappearance of the CLC reflection band probably due to the phase separation leading to the emergence of amplified spontaneous emission of fluorescent dye by optically pumping. In contrast, the dye-doped CLC cell including a crosslinkable agent with a cholesteryl residue enabled the mirrorless laser action after photopolymerization. This is because the selective reflection band of CLC host was retained by the planar structure of cholesteric polymer network

  14. Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals.

    Science.gov (United States)

    Wang, Xiang; Pu, Shengli; Ji, Hongzhu; Yu, Guojun

    2012-01-01

    Ferronematic materials composed of 4-cyano-4'-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (Δn) and figure of merit of optical properties (Q = Δn/α, where α is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to evaluate their optical properties. Similar magnetic-field- and magnetic-particle-concentration-dependent properties of birefringence and figure of merit of optical properties were obtained for the pure magnetic fluids and the ferronematic materials. For the ferronematic materials, the values of Q increase with the volume fractions of nematic liquid crystal under certain fixed field strength and are larger than those of their corresponding pure magnetic fluids at high field region. In addition, the enhancement of Q value increases monotonously with the magnetic field and becomes remarkable when the applied magnetic field is beyond 50 mT. The maximum relative enhanced value of QR exceeds 6.8% in our experiments. The results of this work may conduce to extend the pragmatic applications of nanostructured magnetic fluids in optical field. PMID:22587542

  15. Quick measurement of electrorheological effect for small amounts of nematic liquid crystal

    International Nuclear Information System (INIS)

    A quick measurement method of effective viscosity, employing damped oscillation between two parallel plates, was proposed to examine the electrorheological (ER) effect for small amounts of nematic liquid crystal (LC). To demonstrate the validity of the method, the viscosity measurements were conducted for ordinary liquids [polyalphaolefins (PAOs)] and a nematic LC [4-pentyl-4′-cyanobiphenyl (5CB)] by using a newly developed apparatus that embodied the measurement principle. The viscosity measurements for PAOs showed that when the film thickness is in the submillimeter range (e.g. 0.2 mm), this method provides reliable values of the effective viscosity. The viscosity measurement for 5CB showed that this method evaluates the ER effect with a few dozen cubic millimeters of the sample (e.g. 16 mm3) under the application of a voltage (e.g. 0 to 300 V). It was confirmed that the effective viscosities of 5CB measured at various conditions were scaled to a single master curve as a function of the applied voltage, effective velocity and film thickness. (paper)

  16. Toroidal Nematics

    Science.gov (United States)

    Fernandez-Nieves, Alberto

    We will discuss how nematic liquid crystals organize inside toroidal droplets. When the director is parallel to the bounding surface, we find spontaneous reflection symmetry breaking, which we attribute to the role played by saddle-splay contributions to the Frank free energy. When the director is perpendicular to the bounding surface, we find that the structure is reminiscent of the escape radial configuration seen in cylinders, but with a central doubly-twisted organization, which we attribute to the geometry of the torus. We will end by presenting recent experiments with active nematics on the toroidal surface. In this case, topology and activity both affect the structure and dynamics of the material.

  17. The Landau-de Gennes theory of nematic liquid crystals: Uniaxiality versus Biaxiality

    KAUST Repository

    Majumdar, Apala

    2011-12-01

    We study small energy solutions within the Landau-de Gennes theory for nematic liquid crystals, subject to Dirichlet boundary conditions. We consider two-dimensional and three-dimensional domains separately. In the two-dimensional case, we establish the equivalence of the Landau-de Gennes and Ginzburg-Landau theory. In the three-dimensional case, we give a new definition of the defect set based on the normalized energy. In the threedimensional uniaxial case, we demonstrate the equivalence between the defect set and the isotropic set and prove the C 1,α-convergence of uniaxial small energy solutions to a limiting harmonic map, away from the defect set, for some 0 < a < 1, in the vanishing core limit. Generalizations for biaxial small energy solutions are also discussed, which include physically relevant estimates for the solution and its scalar order parameters. This work is motivated by the study of defects in liquid crystalline systems and their applications.

  18. Physical methods for measuring the viscosity coefficients of nematic liquid crystals

    International Nuclear Information System (INIS)

    Methods for measuring the viscosity coefficients of the best known type of anisotropic fluid, nematic liquid crystals (NLCs), are reviewed. The hydrodynamic Leslie - Ericksen - Parodi theory is described in brief, which predicts five independent viscosity coefficients for a NLC. The feature that distinguishes NLCs from isotropic liquids is the rotational viscosity, due to energy dissipation caused by NLC reorientation. The shear flow method, methods based on ultrasonic wave propagation and absorption in an anisotropic medium, and the rotating magnetic field technique are described in detail, as well as methods that involve analyzing the Freedericksz transition dynamics (LC reorientation in an electric or magnetic field) and those using light scattering from the thermal fluctuations of the NLC director. In each case, the accuracy of the method is evaluated, its complexity assessed, and the amount of material needed for measurement estimated. (reviews of topical problems)

  19. Physical methods for measuring the viscosity coefficients of nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Belyaev, Viktor V [Central R and D ' Cometa' , Moscow (Russian Federation)

    2001-03-31

    Methods for measuring the viscosity coefficients of the best known type of anisotropic fluid, nematic liquid crystals (NLCs), are reviewed. The hydrodynamic Leslie - Ericksen - Parodi theory is described in brief, which predicts five independent viscosity coefficients for a NLC. The feature that distinguishes NLCs from isotropic liquids is the rotational viscosity, due to energy dissipation caused by NLC reorientation. The shear flow method, methods based on ultrasonic wave propagation and absorption in an anisotropic medium, and the rotating magnetic field technique are described in detail, as well as methods that involve analyzing the Freedericksz transition dynamics (LC reorientation in an electric or magnetic field) and those using light scattering from the thermal fluctuations of the NLC director. In each case, the accuracy of the method is evaluated, its complexity assessed, and the amount of material needed for measurement estimated. (reviews of topical problems)

  20. Thermal switching of the reflection in chiral nematic mesoporous organosilica films infiltrated with liquid crystals.

    Science.gov (United States)

    Giese, Michael; De Witt, Joanna C; Shopsowitz, Kevin E; Manning, Alan P; Dong, Ronald Y; Michal, Carl A; Hamad, Wadood Y; MacLachlan, Mark J

    2013-08-14

    Materials that undergo stimulus-induced optical changes are important for many new technologies. In this paper, we describe a new free-standing silica-based composite film that exhibits reversible thermochromic reflection, induced by a liquid crystalline guest in the pores of iridescent mesoporous films. We demonstrate that selective reflection from the novel mesoporous organosilica material with chiral nematic organization can be reversibly switched by thermal cycling of the 8CB guest between its isotropic and liquid crystalline states, which was proven by solid-state NMR experiments. The switching of the optical properties of the chiral solid-state host by stimulus-induced transitions of the guest opens the possibility of applications for these novel materials in sensors and displays. PMID:23859140

  1. A random laser made of nematic liquid crystal doped with a laser dye

    Science.gov (United States)

    Sznitko, L.; Kaliciak, K.; Adamow, A.; Mysliwiec, J.

    2016-06-01

    We report on random laser emission obtained in 5CB and E7 nematic liquid crystal (LC) mixtures doped with 1% weight to weight ratio of DCM laser dye. The LC cell was used as asymmetric planar waveguide were emission was collected from the edge of the sample. Variable stripe length method was utilized to estimate the gain and the losses coefficients. Both systems have shown the threshold energy fluence in order of several mJ/cm2. In both cases above Fredericks potential, significant increase of emission intensity was observed due to the increase of light scattering on liquid crystalline domains. Moreover the use of fifth order of diffraction grating covered with thin alumina film resulted in strong multimode and directional laser emission.

  2. Temperature-driven anchoring transition in nematic liquid crystals interacting with Langmuir-Blodgett films

    International Nuclear Information System (INIS)

    Surface treatment with an azo-compound (p,p'-hexyloxy-cyano-azobenzol) is used to influence the orientation of nematic liquid crystals (NLC). The azo-compound is deposited as Z-type Langmuir-Blodgett (LB) films 1, 3 or 5 monolayers thick upon fused quartz or glass slides. Sandwich-type liquid crystal cells have been prepared with NLC MBBA and the orientation have been studied in polarized light. Non homogeneous NLC orientation over the cell has been observed. Pulsating transitions from homeotropic to conically tilted orientation and from planar to homeotropic orientation take place under local UV illumination. The orientation switching is attributed to local heating by the IR light component. It is concluded that the LB films produce weak NLC anchoring and decrease substantially the surface melting transition temperature. In mixed azo-DPPA LB films a surprising wetting to non-wetting transition has been observed. 2 figs., 8 refs

  3. Photosensitive soft matter: mixtures of nematic liquid crystal with azo molecules

    International Nuclear Information System (INIS)

    Photosensitive soft matter based upon guest-host liquid crystal systems was prepared by mixing azobenzene-containing mesogens with the nematic liquid crystal 4-butyl-cyclohexane carboxylic acid 4-pentyloxy-phenyl ester (CM80). Binary mixtures of the host CM80 with three azo-bonded compounds as UV-active dopants (guests) at a relatively small concentration of 1~wt.% were characterized by thermo-optical, dielectric, spectral and flexoelectric measurements. The study aimed to determine the mechanisms that result in variations of material parameters caused by light-driven molecular conformation change of the azo-dye guest molecules (the transition from rod-shaped trans isomers to bent-shaped cis isomers)

  4. Investigation of the liquid crystal alignment layer: effect on electrical properties

    OpenAIRE

    Asma Abderrahmen et al

    2008-01-01

    We investigate the electrical behavior of a symmetric liquid crystal (LC) cell: elecrode-silane-LC-silane-electrode. The silane (chlorodimethyloctadecyl-silane) layer induces a homeotropic orientation of the nematic liquid crystal (NLC) molecules. The wettability technique is used to detect the change of the surface energy of the electrode upon cleaning and silane layer deposition. We report on the dynamic impedance measurements of the nematic liquid crystal cell. It is found that the silane ...

  5. The director and molecular dynamics of the field-induced alignment of a Gay-Berne nematic phase: An isothermal-isobaric nonequilibrium molecular dynamics simulation study

    Science.gov (United States)

    Luckhurst, Geoffrey R.; Satoh, Katsuhiko

    2010-05-01

    Isothermal-isobaric molecular dynamics simulations have been performed for the generic Gay-Berne (GB) mesogen, GB(4.4, 20.0, 1, 1), to investigate director and molecular rotational motion during the field-induced alignment of a nematic. The alignment process for the director is discussed within the context of a hydrodynamic analysis based on the Ericksen-Leslie theory and this is found to predict the simulated behavior well. The dependence of the relaxation time for the alignment on the field strength is also in good accord with the theory. The rotational viscosity coefficient estimated from the simulation is smaller than that typically observed for real nematics and the possible reasons for this are discussed. However, the simulation results are found to follow not only the theory but also the experiments, at least qualitatively. No significant variation in the local and long-range structure of the nematic phase is found during the field-induced alignment process. In addition, we have explored the molecular dynamics in the nematic phase in the presence of the field using the first- and second-rank time autocorrelation functions. More importantly we are able to show that the director relaxation time is longer than that for molecular rotation. It is also possible to use the two orientational correlation times to explore the relationship between the rotational viscosity coefficient and the rotational diffusion constant. The diffusion constants determined from the orientational correlation times, based on the short-time expansion of the autocorrelation functions, are found to be significantly different. In consequence it is not possible to test, unambiguously, the relationship between the rotational viscosity coefficient and the rotational diffusion constant. However, it would seem that the second-rank rotational correlation time provides the most reliable route to the rotational viscosity coefficient.

  6. Detection of a new 'nematic-like' phase in liquid crystal-amphiphile mixture by differential scanning calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Dan, Kaustabh, E-mail: kaustabhdan@gmail.com; Roy, Madhusudan, E-mail: kaustabhdan@gmail.com; Datta, Alokmay, E-mail: kaustabhdan@gmail.com [Surface Physics and Materials Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar Block, Sector 1, Kolkata-700064 (India)

    2014-04-24

    Differential Scanning Calorimetry (DSC) studies on phase transitions of the pure liquid crystalline material N-4-methoxybenzylidene-4-butylaniline (MBBA) and mixtures of MBBA and the amphiphile Stearic Acid (StA) show significant changes in the behavior of mixture from pure MBBA, as regards the nematic-isotropic (N-I) transition temperature (T{sub c}) and other thermodynamic parameters like enthalpy, specific heat and activation energy with concentration of StA. In particular, the convexity of the Arrhenius plot in pure MBBA vanishes with StA concentration pointing to the formation of a new, perhaps 'nematic-like', phase in the mixtures.

  7. Dynamics of colloidal particles in electrohydrodynamic convection of nematic liquid crystal.

    Science.gov (United States)

    Takahashi, Kentaro; Kimura, Yasuyuki

    2014-07-01

    We have studied the dynamics of micrometer-sized colloidal particles in electrohydrodynamic convection of nematic liquid crystal. Above the onset voltage of electroconvection, the parallel array of convection rolls appears to be perpendicular to the nematic field at first. The particles are forced to rotate by convection flow and are trapped within a single roll in this voltage regime. A slow glide motion along the roll axis is also observed. The frequency of rotational motion and the glide velocity increase with the applied voltage. Under a much larger voltage where the roll axis temporally fluctuates, the particles occasionally hop to the neighbor rolls. In this voltage regime, the motion of the particles becomes two-dimensional. The motion perpendicular to the roll axis exhibits diffusion behavior at a long time period. The effective diffusion constant is 10(3)-10(4) times larger than the molecular one. The observed behavior is compared with the result obtained by a simple stochastic model for the transport of the particles in convection. The enhancement of diffusion can be quantitatively described well by the rotation frequency in a roll, the width of the roll, and the hopping probability to the neighbor rolls. PMID:25122319

  8. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    International Nuclear Information System (INIS)

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  9. Annihilation dynamics of topological monopoles on a fiber in nematic liquid crystals

    Science.gov (United States)

    Nikkhou, M.; Škarabot, M.; Muševič, I.

    2016-06-01

    We use the laser tweezers to create isolated pairs of topological point defects in a form of radial and hyperbolic hedgehogs, located close and attracted to a thin fiber with perpendicular surface orientation of nematic liquid crystal molecules in a thin planar nematic cell. We study the time evolution of the interaction between the two monopoles by monitoring their movement and reconstructing their trajectories and velocities. We find that there is a crossover in the pair interaction force between the radial and hyperbolic hedgehog. At small separation d , the elastic force between the opposite monopoles results in an increase of the attractive force with respect to the far field, and their relative velocity v scales as a v (d ) ∝d-2 ±0.2 power law. At large separations, the two oppositely charged monopoles can either attract or repel with constant interaction force. We explain this strange far-field behavior by the experimental inaccuracy in setting the fiber exactly perpendicular to the cell director.

  10. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Bhargavi, R.; Nair, Geetha G., E-mail: geeraj88@gmail.com, E-mail: skpras@gmail.com; Krishna Prasad, S., E-mail: geeraj88@gmail.com, E-mail: skpras@gmail.com [Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore 560013 (India); Majumdar, R.; Bag, Braja G. [Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore (W) 721 102 (India)

    2014-10-21

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  11. Dynamics of colloidal particles in electrohydrodynamic convection of nematic liquid crystal

    Science.gov (United States)

    Takahashi, Kentaro; Kimura, Yasuyuki

    2014-07-01

    We have studied the dynamics of micrometer-sized colloidal particles in electrohydrodynamic convection of nematic liquid crystal. Above the onset voltage of electroconvection, the parallel array of convection rolls appears to be perpendicular to the nematic field at first. The particles are forced to rotate by convection flow and are trapped within a single roll in this voltage regime. A slow glide motion along the roll axis is also observed. The frequency of rotational motion and the glide velocity increase with the applied voltage. Under a much larger voltage where the roll axis temporally fluctuates, the particles occasionally hop to the neighbor rolls. In this voltage regime, the motion of the particles becomes two-dimensional. The motion perpendicular to the roll axis exhibits diffusion behavior at a long time period. The effective diffusion constant is 103-104 times larger than the molecular one. The observed behavior is compared with the result obtained by a simple stochastic model for the transport of the particles in convection. The enhancement of diffusion can be quantitatively described well by the rotation frequency in a roll, the width of the roll, and the hopping probability to the neighbor rolls.

  12. Temperature dependences of the electrooptical properties of rodlike nematic liquid crystals doped with hockey-stick-shaped liquid crystals

    Science.gov (United States)

    Yeo, Sunggu; Srivastava, Anoop Kumar; Lee, Hyojin; Lee, Ji-Hoon; Choi, E.-Joon

    2016-01-01

    We investigated the temperature dependences of the dielectric anisotropy, birefringence, order parameter, splay elastic constant, and rotational viscosity of rodlike nematic liquid crystals (RLCs) doped with hockey-stick-shaped liquid crystals (HLCs). Although the order parameter of the HLC-RLC mixtures was similar to that of the pure RLC, the dielectric anisotropy and the birefringence of the mixtures were decreased or increased depending on the structure of the HLC molecule. In addition, the activation energies of the mixtures were different, which implies that the intramolecular structure of the HLC molecule had more influence on the electrooptical properties of the HLC-RLC binary mixtures than the inter-molecular interaction between the HLC and the RLC molecules.

  13. Novel cell parameter determination of a twisted-nematic liquid crystal display

    Institute of Scientific and Technical Information of China (English)

    Huang Xia; Jing Hai; Fu Guo-Zhu

    2008-01-01

    In this paper a novel method is proposed to determine the cell parameters including the twist angle, optic retardation and rubbing direction of twisted-nematic liquid crystal displays (TNLCD) by rotating the TNLCD. It is a single-wavelength method. Because using subtraction equation of transmittance as curve fitting equation, the influence of the light from environment and the absorption by polarizer, the sample of TNLCD and analyser on the transmittance is eliminated. Accurate results can also be obtained in imperfect darkness. By large numbers of experiments, we found that not only the experimental setup is quite simple and can be easily adopted to be carried out, but also the results are accurate.

  14. MOLECULAR FIELD THEORY FOR NEMATIC LIQUID CRYSTAL POLYMER COMPRISING FLEXIBLE SPACER

    Institute of Scientific and Technical Information of China (English)

    WANG Xiaogong; LIU Deshan; ZHOU Qixiang

    1993-01-01

    Based on the new model and concept of intramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes account of orientational correlation among all mesogens in a polymer chain and the relationship between the intramolecular orientation and spatial orientation of the mesogens. The free energy, temperature and entropy of the nematic-isotropic transition were determined with the theory and compared with experiments in current work. It was found that many unique transition properties of the MC-LCPs comprising flexible spacer are correctly predicted by the theory and the agreement of the theory with the experiments is impressive.

  15. Electrically Controlled Plasmonic Lasing Resonances with Silver Nanoparticles Embedded in Amplifying Nematic Liquid Crystals

    CERN Document Server

    Wang, Chin

    2014-01-01

    We demonstrate an electrically controlled coherent random lasing with silver nano-particles dispersed in a dye-doped nematic liquid crystal (NLC), in which external electric field dependent emission intensity and frequency-splitting are recorded. A modified rate equation model is proposed to interpret the observed coherent lasing, which is a manifestation of double enhancements, caused by the plasmon-polariton near-fields of Ag particles, on the population inversion of laser dye molecules and the optical energy density of lasing modes. The noticeable quenching of lasing resonances in a weak applied field is due to the dynamic light scattering by irregular director fluctuations of the NLC host, which wash out the coherent interference among different particle palsmon-polariton fields. This provides a proof to support that the present lasing resonances are very sensitive to the dielectric perturbations in the host medium and thus are likely associated with some coupled plasmonic oscillations of metal nanopartic...

  16. Nematic liquid crystals in a spatially step-wise magnetic field

    Science.gov (United States)

    Napoli, Gaetano; Scaraggi, Michele

    2016-01-01

    We study the molecular reorientation induced by a textured external field in a nematic liquid crystal (nLC). In particular, we consider an infinitely wide cell with strong planar anchoring boundary conditions, subjected to a spatially periodic piecewise magnetic field. In the framework of the Frank's continuum theory, we use the perturbation analysis to study in detail the field-induced splay-bend Fréedericksz transition. A numerical approach, based on the finite differences method, is instead employed to solve the fully nonlinear equations. At high field strengths, an analytic approach allows us to draw the bulk profile of the director in terms of elliptic integrals. Finally, through the application of the Bruggeman texture hydrodynamics theory, we qualitatively discuss on the LCs piecewise director configuration under sliding interfaces, which can be adopted to actively regulate friction. Our study opens the pathway for the application of highly controlled nLC texturing for tribotronics.

  17. Symmetry of Uniaxial Global Landau--de Gennes Minimizers in the Theory of Nematic Liquid Crystals

    KAUST Repository

    Henao, Duvan

    2012-01-01

    We extend the recent radial symmetry results by Pisante [J. Funct. Anal., 260 (2011), pp. 892-905] and Millot and Pisante [J. Eur. Math. Soc. (JEMS), 12 (2010), pp. 1069- 1096] (who show that the equivariant solutions are the only entire solutions of the three-dimensional Ginzburg-Landau equations in superconductivity theory) to the Landau-de Gennes framework in the theory of nematic liquid crystals. In the low temperature limit, we obtain a characterization of global Landau-de Gennes minimizers, in the restricted class of uniaxial tensors, in terms of the well-known radial-hedgehog solution. We use this characterization to prove that global Landau-de Gennes minimizers cannot be purely uniaxial for sufficiently low temperatures. Copyright © by SIAM.

  18. Controlling pitch length of chiral monomer-doped nematic/cholesteric liquid crystals using photopolymerization

    International Nuclear Information System (INIS)

    This work presents a simple approach to control the pitch length of chiral monomer-doped nematic/cholesteric liquid crystals (CM-NLCs/CM-CLCs) using photopolymerization. Illuminating CM-NLCs/CM-CLCs with unpolarized UV light causes the diffusion and polymerization of CM, and then increases/decreases the pitch length by reducing the concentration of the CM in the bulk. It should be noted that the pitch length change is irreversible in either red- or blue-shift. The key to control the pitch length of CM-NLCs/CM-CLCs is the competition between the right- and left-hand chiral dopants in the sample. CM-NLCs and CM-CLCs are used to study the red- and blue-shifts, respectively. The properties of cobweb-like polymer layers are also discussed.

  19. Controlling pitch length of chiral monomer-doped nematic/cholesteric liquid crystals using photopolymerization

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Cheng-Kai; Fuh, Andy Ying-Guey; Cheng, Ko-Ting [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Chen, Yuan-Di, E-mail: chengkt@mail.ncku.edu.t [Institute of Electro-optical Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan (China)

    2010-12-22

    This work presents a simple approach to control the pitch length of chiral monomer-doped nematic/cholesteric liquid crystals (CM-NLCs/CM-CLCs) using photopolymerization. Illuminating CM-NLCs/CM-CLCs with unpolarized UV light causes the diffusion and polymerization of CM, and then increases/decreases the pitch length by reducing the concentration of the CM in the bulk. It should be noted that the pitch length change is irreversible in either red- or blue-shift. The key to control the pitch length of CM-NLCs/CM-CLCs is the competition between the right- and left-hand chiral dopants in the sample. CM-NLCs and CM-CLCs are used to study the red- and blue-shifts, respectively. The properties of cobweb-like polymer layers are also discussed.

  20. Extensional flow of nematic liquid crystal with an applied electric field

    KAUST Repository

    CUMMINGS, L. J.

    2013-10-17

    Systematic asymptotic methods are used to formulate a model for the extensional flow of a thin sheet of nematic liquid crystal. With no external body forces applied, the model is found to be equivalent to the so-called Trouton model for Newtonian sheets (and fibres), albeit with a modified \\'Trouton ratio\\'. However, with a symmetry-breaking electric field gradient applied, behaviour deviates from the Newtonian case, and the sheet can undergo finite-time breakup if a suitable destabilizing field is applied. Some simple exact solutions are presented to illustrate the results in certain idealized limits, as well as sample numerical results to the full model equations. Copyright © Cambridge University Press 2013.

  1. Pairing instabilities of a Non-Fermi liquid in the presence of nematic and gauge fluctuations

    Science.gov (United States)

    Mesaros, Andrej; Lawler, Michael J.; Kim, Eun-Ah

    2015-03-01

    In the absence of Fermi-liquid starting point, instabilities of non-Fermi liquids are theoretically challenging problems. Here we note that a non-Fermi liquid state occurring at ν = 1 / 2 may be a promising concrete case for theoretical investigation of the issue for two reasons. Firstly, exotic ordered states observed in half-filled Landau levels, namely the FQH state at ν = 5 / 2 which is most likely best described as a paired state, and the quantum Hall nematic state at ν = 9 / 2 , present a compelling possibility that the non-Fermi liquid state with gauge fluctuations at ν = 1 / 2 is close to instabilities towards these ordered states. Secondly, a recent theoretical progress [Metlitski et al., arXiv:1403.3694] offers a scheme for a controlled renormalization group study of the problem. We will discuss competition between the two fluctuations in promoting or suppressing a superconducting instability, based on the phase diagram we obtain from a renormalization group calculation. This research was supported by NSF through CAREER Grant DMR-0955822.

  2. Superconductivity from a confinement transition out of a fractionalized Fermi liquid with Z2 topological and Ising-nematic orders

    Science.gov (United States)

    Chatterjee, Shubhayu; Qi, Yang; Sachdev, Subir; Steinberg, Julia

    2016-07-01

    The Schwinger boson theory of the frustrated square lattice antiferromagnet yields a stable, gapped Z2 spin liquid ground state with time-reversal symmetry, incommensurate spin correlations, and long-range Ising-nematic order. We obtain an equivalent description of this state using fermionic spinons (the fermionic spinons can be considered to be bound states of the bosonic spinons and the visons). Upon doping, the Z2 spin liquid can lead to a fractionalized Fermi liquid (FL*) with small Fermi pockets of electronlike quasiparticles, while preserving the Z2 topological and Ising-nematic orders. We describe a Higgs transition out of this deconfined metallic state into a confining superconducting state which is almost always of the Fulde-Ferrell-Larkin-Ovchinnikov type, with spatial modulation of the superconducting order.

  3. Polyimide photo-alignment layers for inclined homeotropic alignment of liquid crystal molecules

    International Nuclear Information System (INIS)

    We have succeeded in realizing an inclined homeotropic alignment of liquid crystal (LC) molecules by using photo-aligned films of a polyimide containing azobenzene in the backbone structure. To induce such an LC alignment, a side chain structure was introduced into the backbone structure. The LC pretilt angle, measured from the surface normal, could be controlled up to 1.75o by varying the light exposure in oblique angle irradiation with unpolarized light. Its thermal stability was examined by annealing the LC cell at 100 deg. C. No change was observed in the pretilt angle even after annealing for 36 h, indicative of its excellent thermal stability. Since photo-alignment has patterning capability, the photo-aligned polyimide film is expected as a promising alignment film for multi-domain vertical alignment mode LC displays

  4. Conformational fluctuations affect protein alignment in dilute liquid crystal media

    DEFF Research Database (Denmark)

    Louhivuori, M.; Otten, R.; Lindorff-Larsen, Kresten;

    2006-01-01

    The discovery of dilute liquid crystalline media to align biological macromolecules has opened many new possibilities to study protein and nucleic acid structures by NMR spectroscopy. We inspect the basic alignment phenomenon for an ensemble of protein conformations to deduce relative contributions...

  5. Wetting of liquid-crystal surfaces and induced smectic layering at a nematic-liquid interface: an x-ray reflectivity study.

    Science.gov (United States)

    Fukuto, Masafumi; Gang, Oleg; Alvine, Kyle J; Ocko, Benjamin M; Pershan, Peter S

    2008-03-01

    We report the results of a synchrotron x-ray reflectivity study of bulk liquid-crystal surfaces that are coated by thin wetting films of an immiscible liquid. The liquid-crystal subphase consisted of the nematic or isotropic phase of 4-octyl- 4;{'} -cyanobiphenyl (8CB), and the wetting film was formed by the fluorocarbon perfluoromethylcyclohexane (PFMC), a volatile liquid. The thickness of the wetting film was controlled by the temperature difference DeltaT(micro) between the sample and a reservoir of bulk PFMC, contained within the sealed sample cell. Phase information on the interfacial electron density profiles has been extracted from the interference between the scattering from the PFMC-vapor interface and the surface-induced smectic order of the 8CB subphase. The liquid-crystal side of the nematic-liquid (8CB-PFMC) interface is characterized by a density oscillation whose period corresponds to the smectic layer spacing and whose amplitude decays exponentially toward the underlying nematic subphase. The decay length xi of the smectic amplitude is independent of the PFMC film thickness but increases as the nematic-smectic- A transition temperature T(NA) is approached, in agreement with the longitudinal correlation length xi(parallel) proportional, variant(T-T(NA))(-0.7} for the smectic fluctuations in the bulk nematic. The results indicate that the homeotropic orientation of the 8CB molecules is preferred at the 8CB-PFMC interface and that the observed temperature dependence of the smectic layer growth is consistent with the critical adsorption mechanism. The observed DeltaT(micro) dependence of the PFMC film thickness, L proportional, variant(DeltaT(micro))(-1/3) , implies that PFMC completely wets the 8CB surface and is dominated by the nonretarded dispersion interactions between hydro- and fluorocarbons. The complete wetting behavior of PFMC is nearly independent of the degree of interfacial smectic order in the subphase. PMID:18517395

  6. X-ray diffraction study of thermotropic liquid crystalline polyesters and diester model compounds

    Science.gov (United States)

    Chin, H. H.; Azaroff, L. V.; Griffin, A. C.

    1987-10-01

    Two nematic liquid crystalline polyesters were examined by X-ray diffraction following quenching from the nematic temperature in a magnetic field of 15 tesla. It was not possible to quench an aligned nematic glass; instead a polycrystalline phase showing some preferred orientation or an unoriented nematic melt yielded monodomain nematic diffraction patterns with one resembling that of a fiber (crystalline) photograph while the other showed good nematic alignment which could be enhanced slightly by annealing. A series of Siamese-twin diester model compounds also examined at their respective nematic temperatures in a magnetic field of compounds also were examined at their crystalline phase at room temperature. All displayed well-aligned nematic monodomains above the crystallization point.

  7. Light-control of liquid crystal alignment from vertical to planar

    Science.gov (United States)

    Ata Alla, Rasha; Hegde, Gurumurthy; Komitov, Lachezar

    2013-06-01

    Continuous or discontinuous transition from vertical to planar alignment was found in nematic cells, containing polyimide alignment layer exposed to linear polarized UV light, depending on whether the alignment layer was mechanically rubbed or not prior the illumination. The polyimide material is designed originally to promote vertical alignment when deposited onto the inner cell substrates' surface. The mechanism behind these observations is complicated. It includes inclination of the alkyl side chains of the polyimide alignment layer towards the rubbing direction and the bond breaking process due to UV illumination which are considered as the key factors for occurrence of such alignment transition.

  8. Interactions of carbon nanotubes in a nematic liquid crystal. I. Theory

    Science.gov (United States)

    Galerne, Yves

    2016-04-01

    Elongated and rodlike objects such as carbon nanotubes (CNTs) are studied when immersed in a nematic liquid crystal. Their interaction energy in a uniform nematic field depends on their orientation relative to the director n , and its minimum determines if they stabilize parallel or perpendicular to n . Using free energy calculations, we deduce the orientation at equilibrium that they choose in a uniform director field n or when they are in contact with a splay-bend disclination line. Naturally, the CNT orientations also depend on the anchoring conditions at their surface. Essentially, three types of anchorings are considered, planar, homeotropic, and Janus anchorings in the cases of weak and strong anchoring strengths. In the presence of a splay-bend disclination line, they are attracted toward it and ultimately, they get out of the colloidal dispersion to stick on it. Their orientation relative to the line is found to be parallel or perpendicular to it, again depending on the anchoring conditions. When a sufficient number of particles are deposited on a disclination line, we finally obtain a micro- or nanonecklace in the shape of a thin thread or of a bottle brush, according to the CNTs being oriented parallel or perpendicular to the disclination line, respectively. The system exhibits a rich versatility even if up to now the weak anchorings appear to be difficult to control. As discussed in the associated experimental paper, these necklaces could be a step toward interesting applications for realizing nanowires self-connected in three dimensions to predesignated electrodes. This method could provide a way to increase the number of transistors that may be connected together on a small volume.

  9. Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal

    OpenAIRE

    F. De Vita; Hegde, M.; Portale, G.; Bras, W.; Ferrero, C.; Samulski, E.T.; Francescangeli, O.; Dingemans, T.

    2016-01-01

    We report the structural characterization of the nematic phase of 2,6-biphenyl naphthalene (PPNPP). This lath-like all-aromatic mesogen provides a valuable benchmark for classical theories of nematic order. PPNPP exhibits a very high temperature nematic phase (417–489 °C) above an enantiotropic smectic A phase. X-ray diffraction reveals a surprisingly strong tendency towards molecular layering in the nematic phase, indicative of “normal cybotaxis” (i.e. SmA-like stratification within clusters...

  10. Hierarchical Organization in Liquid Crystal-in-Liquid Crystal Emulsions

    OpenAIRE

    Mushenheim, Peter C.; Abbott, Nicholas L.

    2014-01-01

    We report the formation and characterization of hierarchical ordering in systems comprised of micrometer-sized droplets of thermotropic nematic liquid crystals (LCs) dispersed in continuous nematic phases of a lyotropic chromonic LC (disodium cromoglycate (DSCG)). Significantly, we find the orientations of the two LC phases to be coupled, with nematic droplets of 4′-pentyl-4-cyanobiphenyl (5CB) exhibiting a bipolar configuration with an axis of symmetry aligned orthogonal to the far-field dir...

  11. Effect of gold nano-particles on switch-on voltage and relaxation frequency of nematic liquid crystal cell

    OpenAIRE

    M. Inam; Singh, G; Biradar, A. M.; Mehta, D. S.

    2011-01-01

    We report the observation of large changes in the electro-optical properties of nematic liquid crystal (NLC) due to inclusion of small concentration of 10 nm diameter gold nanoparticles (GNPs). It is observed that GNPs lower switch-on voltage and also lower the relaxation frequency with applied voltage (AC field) to NLC cell. These studies of GNP doped NLC cell have been done using optical interferometry and capacity measurement by impedance analyzer. The change in threshold voltage and relax...

  12. Increase in interparticle distance of colloidal dipolar chain in nematic liquid crystal by trapping it on splay-bend wall

    OpenAIRE

    K. Tagashira; Asakura, K.; G. Nakazawa; Yoshida, H.; Ozaki, M.

    2012-01-01

    We demonstrate an increase in the interparticle distance of a colloidal dipolar chain in a nematic liquid crystal (NLC). Applying an in-plane electric field perpendicular to the rubbing direction induces a splay-bend wall defect in the middle of the electrode gap, which traps a dipolar chain. Above the Freedericksz threshold electric field, the interparticle distance increases with increasing applied electric field, owing to the reorientation of the NLC molecules. The maximum increase is 32% ...

  13. The Effect of Dissolved Side-Group Polymers on Pattern Dynamics in Nematic Liquid Crystals in a Rotating Magnetic Field

    OpenAIRE

    Pashkovsky, E.; Stille, W; Strobl, G.; Talebi, D.

    1997-01-01

    Patterns formed by inversion walls in nematic layers exposed to a rotating magnetic field were studied. Dilute solutions of a mesogenic side group polymethacrylate in a low molecular weight liquid crystal (5CB) were used in comparison with the pure solvent. As found in a previous work, in this system the intensity of backflow (fluid flow induced by director rotation) can be controlled by the polymer concentration due to a specific increase of shear viscosity coefficients. In the synchronous r...

  14. Preparation and thermo-optical characteristics of a smart polymer-stabilized liquid crystal thin film based on smectic A–chiral nematic phase transition

    International Nuclear Information System (INIS)

    A smart polymer stabilized liquid crystal (PSLC) thin film with temperature-controllable light transmittance was prepared based on a smectic-A (SmA)–chiral nematic (N*) phase transition, and then the effect of the composition and the preparation condition of the PSLC film on its thermo-optical (T-O) characteristics has been investigated in detail. Within the temperature range of the SmA phase, the PSLC shows a strong opaque state due to the focal conic alignment of liquid crystal (LC) molecules, while the film exhibits a transparent state result from the parallel alignment of N* phase LC molecules at a higher temperature. Importantly, the PSLC films with different temperature of phase transition and contrast ratio can be prepared by changing the composition of photo-polymerizable monomer/LC/chiral dopant. According to the competition between the polymerization of the curable monomers and the diffusion of LC molecules, the ultraviolet (UV) curing surrounding temperature and the intensity of UV irradiation play a critical role in tuning the size of the polymer network meshes, which in turn influence the contrast ratio and the switching speed of the film. Our observations are expected to pave the way for preparing smart PSLC thin films for applications in areas of smart windows, thermo-detectors and other information recording devices. (paper)

  15. Homogeneous liquid crystal alignment characteristics on solution-derived HfYGaO films treated with IB irradiation.

    Science.gov (United States)

    Lee, Yun-Gun; Park, Hong-Gyu; Jeong, Hae-Chang; Lee, Ju Hwan; Heo, Gi-Seok; Seo, Dae-Shik

    2015-06-29

    Solution-derived HfYGaO films have been treated by ion beam (IB) irradiation and used as liquid crystal (LC) alignment layers. Solution processing was adopted due to its simplicity, high throughput, and facile composition modification. Homogeneous and uniform LC alignment was achieved on the IB-irradiated HfYGaO films, and when these films were adopted in twisted nematic (TN) cells, electro-optical performance comparable to that of TN cells with conventional polyimide layers was achieved, with almost no capacitance-voltage hysteresis. Moreover, LC cells based on IB-irradiated HfYGaO films had a high thermal budget. The proposed IB-irradiated solution-derived HfYGaO films have considerable potential for use in advanced LC applications. PMID:26191738

  16. Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal.

    Science.gov (United States)

    Vita, Francesco; Hegde, Maruti; Portale, Giuseppe; Bras, Wim; Ferrero, Claudio; Samulski, Edward T; Francescangeli, Oriano; Dingemans, Theo

    2016-02-28

    We report the structural characterization of the nematic phase of 2,6-biphenyl naphthalene (PPNPP). This lath-like all-aromatic mesogen provides a valuable benchmark for classical theories of nematic order. PPNPP exhibits a very high temperature nematic phase (417-489 °C) above an enantiotropic smectic A phase. X-ray diffraction reveals a surprisingly strong tendency towards molecular layering in the nematic phase, indicative of "normal cybotaxis" (i.e. SmA-like stratification within clusters of mesogens). Although stronger at low temperatures, the layering is evident well above the smectic A-nematic transition. The nematic order parameter is evaluated as a function of temperature from the broadening of the wide-angle diffuse diffraction feature. Measured values of the orientational order parameter are slightly larger than those predicted by the Maier-Saupe theory over the entire nematic range except for a narrow region just below the clearing point where they significantly drop below the theoretical prediction. PMID:26781457

  17. The radial-hedgehog solution in Landau–de Gennes' theory for nematic liquid crystals

    KAUST Repository

    MAJUMDAR, APALA

    2011-09-06

    We study the radial-hedgehog solution in a three-dimensional spherical droplet, with homeotropic boundary conditions, within the Landau-de Gennes theory for nematic liquid crystals. The radial-hedgehog solution is a candidate for a global Landau-de Gennes minimiser in this model framework and is also a prototype configuration for studying isolated point defects in condensed matter physics. The static properties of the radial-hedgehog solution are governed by a non-linear singular ordinary differential equation. We study the analogies between Ginzburg-Landau vortices and the radial-hedgehog solution and demonstrate a Ginzburg-Landau limit for the Landau-de Gennes theory. We prove that the radial-hedgehog solution is not the global Landau-de Gennes minimiser for droplets of finite radius and sufficiently low temperatures and prove the stability of the radial-hedgehog solution in other parameter regimes. These results contain quantitative information about the effect of geometry and temperature on the properties of the radial-hedgehog solution and the associated biaxial instabilities. © Copyright Cambridge University Press 2011.

  18. Mueller matrix-based optimization of reflective type twisted nematic liquid crystal SLM at oblique incidences

    Science.gov (United States)

    Verma, R. S.; Swami, M. K.; Manhas, S. S.; Gupta, P. K.

    2010-06-01

    Mueller matrix measurements were used to characterize the polarization properties of liquid crystal-based reflective type twisted nematic (TN) special light modulator (SLM) at oblique incidence of the laser beam. The experimentally obtained Mueller matrices were used to obtain the combination of polarization optics required to optimize it for phase only modulation. The results indicate that minimum intensity modulation is obtained with the use of a polarizer followed by a quarter wave plate (QWP) in polarization state generator (PSG) arm and a QWP followed by an analyzer in polarization state analyzer arm (PSA). Polarization parameters such as retardance, rotation and depolarization were calculated from the experimentally obtained Mueller matrices using polar decomposition method at different angle of incidences of the laser beam and the results has been discussed. The similarity between retardance and depolarization curve as a function of address voltage of TNSLM indicated that depolarization is mainly associated with errors in retardance values. Further, spectral Mueller matrix measurements were used to obtain intensity modulation response in the range of wavelengths 450-700 nm for broadband applications.

  19. Fast optical switching using cyanine dye-doped nematic liquid crystal

    International Nuclear Information System (INIS)

    A cyanine dye, 1,1',3,3,3',3'-hexamethyl-4,4',5,5'-dibenzo-2,2'-indotricarbocyanine perchlorate (NK-2014) was doped in 4-cyano-4'-n-pentylbiphenyl (5CB), and the mixture was sandwiched between two pieces of rubbed glass plates. The third-order nonlinear optical responses of oriented NK-2014-doped 5CB were measured by the resonant femtosecond degenerate four-wave mixing (DFWM) technique at 820 nm. The time resolution of the system was ca. 0.3 ps (FWHM). The electronic component of third-order nonlinear optical susceptibility of one of the present samples was 1.3x10-8 esu (NK-2014 concentration: 1.0 wt%). The slow DFWM response of NK-2014-doped 5CB was accelerated with increasing laser power due to amplified spontaneous emission (ASE). On the other hand, we did not observe a similar phenomenon for NK-2014-doped polyethylene glycol (PEG-400). Oriented NK-2014 molecules in nematic liquid crystal must have very high ASE efficiency. Hence the population grating disappears in ca. 3 ps. NK-2014-doped 5CB can be used as a material for very fast all-optical switching

  20. Effect of Disclination Lines on Free Energy of Nematic Liquid Crystals

    Institute of Scientific and Technical Information of China (English)

    YANG Guo-Hong; ZHANG Hui; TIAN Li-Jun; WANG Yu-Sheng; DUAN Yi-Shi

    2005-01-01

    In the light of φ-mapping method and topological current theory, the effect of disclination lines on the free energy density of nematic liquid crystals is studied. It is pointed out that the total Frank free energy density can be divided into two parts. One is the distorted energy density of director field around the disclination lines. The other is the saddle-splay energy density, which is shown to be centralized at the disclination lines and to be topologically quantized in the unit of kπ /2 when the Jacobian determinant of the director field does not vanish at the singularities of the director field. The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director field at the disclination lines, i.e., the disclination strengthes. When the Jacobian determinant vanishes, the generation, annihilation, intersection, splitting and merging processes of the saddle-splay energy density are detailed in the neighborhoods of the limit points and bifurcation points, respectively. It is shown that the disclination line with high topological quantum number is unstable and will evolve to the low topological quantum number states through the splitting process.

  1. Order Reconstruction in a Nanoconfined Nematic Liquid Crystal between Two Coaxial Cylinders

    Directory of Open Access Journals (Sweden)

    Xuan Zhou

    2015-11-01

    Full Text Available The dynamics of a disclination loop (s = ±1/2 in nematic liquid crystals constrained between two coaxial cylinders were investigated based on two-dimensional Landau–de Gennes tensorial formalism by using a finite-difference iterative method. The effect of thickness (d = R2 − R1, where R1 and R2 represent the internal and external radii of the cylindrical cavity, respectively on the director distribution of the defect was simulated using different R1 values. The results show that the order reconstruction occurs at a critical value of dc, which decreases with increasing inner ratio R1. The loop also shrinks, and the defect center deviates from the middle of the system, which is a non-planar structure. The deviation decreases with decreasing d or increasing R1, implying that the system tends to be a planar cell. Two models were then established to analyze the combined effect of non-planar geometry and electric field. The common action of these parameters facilitates order reconstruction, whereas their opposite action complicates the process.

  2. A molecular nematic liquid crystalline material for high-performance organic photovoltaics

    Science.gov (United States)

    Sun, Kuan; Xiao, Zeyun; Lu, Shirong; Zajaczkowski, Wojciech; Pisula, Wojciech; Hanssen, Eric; White, Jonathan M.; Williamson, Rachel M.; Subbiah, Jegadesan; Ouyang, Jianyong; Holmes, Andrew B.; Wong, Wallace W. H.; Jones, David J.

    2015-01-01

    Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behaviour and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs.

  3. Synthesis and mesomorphic behaviour of achiral four-ring unsymmetrical bent-core liquid crystals: Nematic phases

    Science.gov (United States)

    Paul, Manoj Kumar; Kalita, Gayatri; Laskar, Atiqur Rahman; Debnath, Somen; Gude, Venkatesh; Sarkar, Dipika Debnath; Mohiuddin, Golam; Varshney, Sanjay Kumar; Nandiraju Rao, V. S.

    2013-10-01

    Achiral four ring unsymmetrical bent-core liquid crystals derived from 3-amino-2-methylbenzoic acid have been designed and synthesized with an imine, ester and photochromic azo linking moieties. These hockey-stick shape resembling bent molecules possess an alkoxy chain at one end of the molecule and methyl or methoxy group at the other end. The synthesis, phase transition temperatures and characterization of phase behaviour are discussed. The molecular structure characterization is consistent with data from elemental and spectroscopic analysis. The materials thermal behaviour and phase characterization have been investigated by differential scanning calorimetry and polarizing optical microscopy. All these compounds exhibit enantiotropic nematic phase over wide temperature range. Stable supercooling of nematic phase has been observed in methoxy homologues. The density functional theory (DFT) calculations were performed to obtain the stable molecular conformation, polarizability, dipole moment, Highest occupied molecular orbital (HOMO), Lowest unoccupied molecular orbital (LUMO) energies and bending angle of the compound.

  4. Temperature effects on capillary instabilities in a thin nematic liquid crystalline fiber embedded in a viscous matrix

    Science.gov (United States)

    Cheong, A.-G.; Rey, A. D.

    2002-10-01

    Linear stability analysis of capillary instabilities in a thin nematic liquid crystalline cylindrical fiber embedded in an immiscible viscous matrix is performed by formulating and solving the governing nemato-capillary equations, that include the effect of temperature on the nematic ordering as well as the effect of the nematic orientation. A representative axial nematic orientation texture with the planar easy axis at the fiber surface is studied. The surface disturbance is expressed in normal modes, which include the azimuthal wave number m to take into account non-axisymmetric modes. Capillary instabilities in nematic fibers reflect the anisotropic nature of liquid crystals, such as the ordering and orientation contributions to the surface elasticity and surface normal and bending stresses. Surface gradients of normal and bending stresses provide additional anisotropic contributions to the capillary pressure that may renormalize the classical displacement and curvature forces that exist in any fluid fiber. The exact nature (stabilizing and destabilizing) and magnitude of the renormalization of the displacement and curvature forces depend on the nematic ordering and orientation, i.e. the anisotropic contribution to the surface energy, and accordingly capillary instabilities may be axisymmetric or non-axisymmetric. In addition, when the interface curvature effects are accounted for as contributions of the work of interfacial bending and torsion to the total energy of the system, the higher-order bending moment contribution to the surface stress tensor is critical in stabilizing the fiber instabilities. For the planar easy axis, the nematic ordering contribution to the surface energy, which renormalizes the effect of the fiber shape, plays a crucial role to determine the instability mechanisms. Moreover, the unstable modes, which are most likely observed, can be driven by the dependence of surface energy on the surface area. Low-ordering fibers display the

  5. Tunable microwave bandpass filter integrated power divider based on the high anisotropy electro-optic nematic liquid crystal

    Science.gov (United States)

    Liu, Yupeng; Liu, Yang; Li, Haiyan; Jiang, Di; Cao, Weiping; Chen, Hui; Xia, Lei; Xu, Ruimin

    2016-07-01

    A novel, compact microwave tunable bandpass filter integrated power divider, based on the high anisotropy electro-optic nematic liquid crystal, is proposed in this letter. Liquid crystal, as the electro-optic material, is placed between top inverted microstrip line and the metal plate. The proposed structure can realize continuous tunable bandpass response and miniaturization. The proposed design concept is validated by the good performance of simulation results and experimental results. The electro-optic material has shown great potential for microwave application.

  6. Global Existence and Large Time Behavior of Strong Solutions to the 2-D Compressible Nematic Liquid Crystal Flows with Vacuum

    Science.gov (United States)

    Wang, Teng

    2016-02-01

    This paper is concerned with the strong solutions to the Cauchy problem of a simplified Ericksen-Leslie system of compressible nematic liquid crystals in two or three dimensions with vacuum as far field density. For strong solutions, some a priori decay rate (in large time) for the pressure, the spatial gradient of velocity field and the second spatial gradient of liquid crystal director field are obtained provided that the initial total energy is suitably small. Furthermore, with the help of the key decay rates, we establish the global existence and uniqueness of strong solutions (which may be of possibly large oscillations) in two spatial dimensions.

  7. Interactions of carbon nanotubes in a nematic liquid crystal. II. Experiment

    Science.gov (United States)

    Agha, Hakam; Galerne, Yves

    2016-04-01

    Multiwall carbon nanotube (CNT) colloids with different anchoring conditions are dispersed in pentyl-cyanobiphenyl (5CB), a thermotropic liquid crystal (LC) that exhibits a room-temperature nematic phase. The experiments make use of CNTs treated for strong planar, homeotropic, or Janus anchorings. Observations with a polarizing microscope show that the CNTs placed in a uniform nematic field stabilize parallel or perpendicular to n depending on their anchoring conditions. In the presence of a splay-bend disclination line, they are first attracted toward it and ultimately, they get trapped on it. Their orientation relative to the line is then found to be parallel or perpendicular to it, again depending on the anchoring conditions. When a sufficient number of particles are deposited on a disclination line, they form a micro- or nanonecklace in the shape of a thin thread or of a bottle brush, with the CNTs being oriented parallel or perpendicular to the disclination line according to the anchoring treatment. The system exhibits a rich versatility, even if until now the weak anchorings appear to be difficult to control. In a next step, the necklaces may be glued by means of pyrrole electropolymerization. In this manner, we realize a true materialization of the disclination lines, and we obtain nanowires capable of conducting the electricity in the place of the initial disclinations that just worked as templates. The advantage of the method is that it finally provides nanowires that are automatically connected to predesignated three-dimensional (3D) electrodes. Such a 3D nanowiring could have important applications, as it could allow one to develop electronic circuits in the third dimension. They could thus help with increasing the transistor density per surface unit, although downsizing of integrated circuits will soon be limited to atomic sizes or so. In other words, the predicted limitation to Moore's law could be avoided. For the moment, the nanowires that we obtain

  8. Three-dimensional control of the helical axis of a chiral nematic liquid crystal by light

    Science.gov (United States)

    Zheng, Zhi-Gang; Li, Yannian; Bisoyi, Hari Krishna; Wang, Ling; Bunning, Timothy J.; Li, Quan

    2016-03-01

    Chiral nematic liquid crystals—otherwise referred to as cholesteric liquid crystals (CLCs)—are self-organized helical superstructures that find practical application in, for example, thermography, reflective displays, tuneable colour filters and mirrorless lasing. Dynamic, remote and three-dimensional control over the helical axis of CLCs is desirable, but challenging. For example, the orientation of the helical axis relative to the substrate can be changed from perpendicular to parallel by applying an alternating-current electric field, by changing the anchoring conditions of the substrate, or by altering the topography of the substrate’s surface; separately, in-plane rotation of the helical axis parallel to the substrate can be driven by a direct-current field. Here we report three-dimensional manipulation of the helical axis of a CLC, together with inversion of its handedness, achieved solely with a light stimulus. We use this technique to carry out light-activated, wide-area, reversible two-dimensional beam steering—previously accomplished using complex integrated systems and optical phased arrays. During the three-dimensional manipulation by light, the helical axis undergoes, in sequence, a reversible transition from perpendicular to parallel, followed by in-plane rotation on the substrate surface. Such reversible manipulation depends on experimental parameters such as cell thickness, surface anchoring condition, and pitch length. Because there is no thermal relaxation, the system can be driven either forwards or backwards from any light-activated intermediate state. We also describe reversible photocontrol between a two-dimensional diffraction state, a one-dimensional diffraction state and a diffraction ‘off’ state in a bilayer cell.

  9. Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers.

    Science.gov (United States)

    Pardaev, Shokir A; Shamid, S M; Tamba, M G; Welch, C; Mehl, G H; Gleeson, J T; Allender, D W; Selinger, J V; Ellman, B; Jakli, A; Sprunt, S

    2016-05-11

    The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase - the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like "pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two. PMID:27089236

  10. Effect of Molecular Flexibility on the Nematic-to-Isotropic Phase Transition for Highly Biaxial Molecular Non-Symmetric Liquid Crystal Dimers

    Directory of Open Access Journals (Sweden)

    María Blanca Ros

    2011-09-01

    Full Text Available In this work, a study of the nematic (N–isotropic (I phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the α-(4-cyanobiphenyl-4’-yloxy-ω-(1-pyrenimine-benzylidene-4’-oxy alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the elusive biaxial nematic (NB phase, as they exhibit both molecular biaxiality and flexibility. According to the theory, the uniaxial nematic (NU–isotropic (I phase transition is first-order in nature, whereas the NB–I phase transition is second-order. Thus, a fine analysis of the critical behavior of the N–I phase transition would allow us to determine the presence or not of the biaxial nematic phase and understand how the molecular biaxiality and flexibility of these compounds influences the critical behavior of the N–I phase transition.

  11. Alignment of liquid crystals : on geometrically and chemically modified surfaces

    NARCIS (Netherlands)

    Zhang, Jing

    2013-01-01

    This thesis consists of two main parts. The first part describes a new model to explain the complex role of surface materials and surface geometry in the liquid crystal (LC) alignment, which has been a subject of intensive debate over the last 40 years. The second part presents a potentially cost ef

  12. Photoalignment - an alternative aligning technique for Liquid Crystal Displays

    Directory of Open Access Journals (Sweden)

    M.M. Chrzanowski

    2011-09-01

    Full Text Available Purpose: The main aim of this work is to present our investigation in the field of photoalignment. In this work we introduce useful photoalignment techniques and discuss in detail the results of photocrosslinking and photodegradation in photosensitive polymer materials.Design/methodology/approach: We describe the new procedure investigated in our laboratory for the following materials: HD-4100, HD-4110 and HD-8820 (DuPont Microsystems as well as the characteristics obtained for the thin polyimide layers: optical homogeneity, thickness, surface tension.Findings: Polyimide layers obtained on the glass/ITO substrates which were irradiated using linearly polarised ultraviolet light show the aligning properties for liquid crystal layers. The proposed new technology is fairly fine to obtain 2-3 cm2 layers.Research limitations/implications: The liquid crystal material alignment quality is not perfect, but the works are still in progress. In the next step we will try to use silan-derivative adhesion promoters to lower the aligning layers thickness. This solution will probably also have a big influence on the aligning layers homogeneity.Practical implications: We discuss an alternative technique of the rubbing method for composition of liquid crystal displays. Liquid crystal displays are widely used for many industrial and commercial applications. Multimedia and graphics and medical-imaging systems require top quality images. Such an image can be obtained under the condition of good liquid crystal alignment. Rubbing is a method conventionally used for these purposes. Unfortunately this technique has some disadvantages that are particularly visible in new generation displays. The usage of photodephiniable materials opens the route to obtain an appropriate molecular tilt and controlled anchoring energy as well as preparing layers that are suitable to providing diversified optical axes in one liquid crystal cell.Originality/value: Agents investigated in the

  13. Study of molecular dynamics in nematic and isotropic phases of liquid crystals

    International Nuclear Information System (INIS)

    The hydrodynamic theory of nematic liquid crystals is revised and applied to the study of the nuclear magnetic relaxation in these materials. The expression found for the proton spin-lattice relaxation rate differs somewhat from those published earlier. The mathematical form of the term 1/T1, introduced by Lubensky is now derived and the functions K(T) and γ∼(T) appearing in the Pincus-Lubensky expression for 1/T1 accurately computed. An expression for the viscosity γ∼1(T) is proposed and experimentally verified. These results are then used to give a coherent quantitative interpretation of all known experimental data on p-azoxyanisole (PAA) and its methyl-deuterated derivative PAA-CD3. The frequency dependence of 1/T1 is determined by the long-wavelength thermal fluctuations in the orientational order. The temperature dependence of 1/T1 is dominated by short-range molecular motions. It is shown how to separate the contributions to 1/T1 coming from different groups of protons within a given molecule, and how to distinguish the effects of long-wavelength fluctuations from those produced by short-range molecular reorientations and diffusion. A well-defined link is established between the activation energy characterising the short-range molecular reorientations, and the hydrodynamic viscosity γ∼1. The NMR spectrum of PAA-CD3 is re-examined and it is proved that the structure shown by each component of the fundamental doublet is essentially due to the interaction between protons of different benzene rings within a molecule, and not to the interaction between meta protons of a given ring, as it was generally admitted. In the isotropic phase, molecular self-diffusion seems to give the dominant contribution to the proton spin-lattice relaxation rate. An anomalous decrease of D as the transition point is approached from above is predicted and experimentally observed. (author)

  14. A coupled map lattice model for rheological chaos in sheared nematic liquid crystals.

    Science.gov (United States)

    Kamil, S M; Menon, Gautam I; Sinha, Sudeshna

    2010-12-01

    A variety of complex fluids under shear exhibit complex spatiotemporal behavior, including what is now termed rheological chaos, at moderate values of the shear rate. Such chaos associated with rheological response occurs in regimes where the Reynolds number is very small. It must thus arise as a consequence of the coupling of the flow to internal structural variables describing the local state of the fluid. We propose a coupled map lattice model for such complex spatiotemporal behavior in a passively sheared nematic liquid crystal using local maps constructed so as to accurately describe the spatially homogeneous case. Such local maps are coupled diffusively to nearest and next-nearest neighbors to mimic the effects of spatial gradients in the underlying equations of motion. We investigate the dynamical steady states obtained as parameters in the map and the strength of the spatial coupling are varied, studying local temporal properties at a single site as well as spatiotemporal features of the extended system. Our methods reproduce the full range of spatiotemporal behavior seen in earlier one-dimensional studies based on partial differential equations. We report results for both the one- and two-dimensional cases, showing that spatial coupling favors uniform or periodically time-varying states, as intuitively expected. We demonstrate and characterize regimes of spatiotemporal intermittency out of which chaos develops. Our work indicates that similar simplified lattice models of the dynamics of complex fluids under shear should provide useful ways to access and quantify spatiotemporal complexity in such problems, in addition to representing a fast and numerically tractable alternative to continuum representations. PMID:21198093

  15. Improvement in device performance from a mixture of a liquid crystal and photosensitive acrylic prepolymer with the photoinduced vertical alignment method

    Directory of Open Access Journals (Sweden)

    Czung-Yu Ho, Fa-Hsin Lin, Yu-Tai Tao and Jiunn-Yih Lee

    2011-01-01

    Full Text Available In a multicomponent nematic liquid crystal (NLC mixture of a liquid crystal (negative-type NLC and a photosensitive acrylic prepolymer, photopolymerization upon UV irradiation induces the separation of the LC and photosensitive acrylic prepolymer layers, thereby leading to a vertical arrangement of LC molecules. In this study, we propose a simple vertical alignment method for LC molecules, by adding a chiral smectic A (SmA* liquid crystal having homeotropic texture characteristics to an NLC mixture solution. Measurements of electro-optical properties revealed that the addition of the SmA* LC not only strengthened the anchoring force of the copolymer alignment film surface, but also significantly enhanced the contrast ratio (~73%, response time and grayscale switching performance of the device.

  16. Magnetic Alignment Study of Rare-Earth-Containing Liquid Crystals

    OpenAIRE

    Galyametdinov, Yury; Haase, Wolfgang; Goderis, Bart; Moors, Dries; Driesen, Kris; Van Deun, Rik; Binnemans, Koen

    2007-01-01

    The liquid-crystalline rare-earth complexes of the type [Ln(LH)3(DOS)3]-where Ln is Tb, Dy, Ho, Er, Tm, or Yb; LH is the Schiff base N-octadecyl-4-tetradecyloxysalicylaldimine; and DOS is dodecylsulfate-exhibit a smectic A phase. Because of the presence of rare-earth ions with a large magnetic anisotropy, the smectic A phase of these liquid crystals can be easier aligned in an external magnetic field than smectic A phases of conventional liquid crystals. The magnetic anisotropy of the [Ln(LH)...

  17. Acoustical and optical investigations of the size effect in nematic-isotropic phase transition in liquid crystal microemulsions

    Science.gov (United States)

    Maksimochkin, G. I.; Pasechnik, S. V.; Lukin, A. V.

    2015-07-01

    The absorption of ultrasound (at a frequency of 2.7 MHz) and the depolarized light transmission and scattering (at a wavelength of 630 nm) in liquid crystal (LC) emulsions have been studied during the nematic-isotropic (N-I) phase transition in LC droplets with radii ranging from 150 to 2300 nm. The obtained acoustical and optical data are used to determine the influence of the droplet size on characteristics of the N-I phase transition. It is shown that the acoustical and optical characteristics of LC emulsions have good prospects to be used for the investigation of phase transitions in submicron samples.

  18. Effect of gold nano-particles on switch-on voltage and relaxation frequency of nematic liquid crystal cell

    Directory of Open Access Journals (Sweden)

    M. Inam

    2011-12-01

    Full Text Available We report the observation of large changes in the electro-optical properties of nematic liquid crystal (NLC due to inclusion of small concentration of 10 nm diameter gold nanoparticles (GNPs. It is observed that GNPs lower switch-on voltage and also lower the relaxation frequency with applied voltage (AC field to NLC cell. These studies of GNP doped NLC cell have been done using optical interferometry and capacity measurement by impedance analyzer. The change in threshold voltage and relaxation frequency by doping GNPs in NLC is explained theoretically.

  19. Thermo-switchable multi-wavelength laser emission from a dye-doped nematic liquid-crystal device

    International Nuclear Information System (INIS)

    A sandwich-type laser device with a surface-relief grating inside was infiltrated with dye-doped nematic liquid-crystals which functioned as gain media. The surface-relief grating was fabricated by soft lithographic technique on a sol–gel derived zirconium-doped hybrid film using a polydimethyl–siloxane replica. The optical properties of the distributed feedback (DFB) resonator were modified by introducing a high refractive index layer consisting of niobium pentoxide subsequently. Thermal induced shift of amplified spontaneous emission spectrum, switching of multi-wavelength DFB laser emission and occurrence of random lasing were demonstrated.

  20. Thin aligned organic polymer films for liquid crystal devices

    International Nuclear Information System (INIS)

    This project was designed to investigate the possibility of producing alignment layers for liquid crystal devices by cross-linking thin films containing anisotropic polymer bound chromophores via irradiation with polarised ultraviolet light. Photocross-linkable polymers find use in microelectronics, liquid crystal displays, printing and UV curable lacquers and inks; so there is an increasing incentive for the development of new varieties of photopolymers in general. The synthesis and characterisation of two new photopolymers that are suitable as potential alignment layers for liquid crystal devices are reported in this thesis. The first polymer contains the anthracene chromophore attached via a spacer unit to a methacrylate backbone and the second used a similarly attached aryl azide group. Copolymers of the new monomers with methyl methacrylate were investigated to establish reactivity ratios in order to understand composition drift during polymerisation. (author)

  1. Thin aligned organic polymer films for liquid crystal devices

    CERN Document Server

    Foster, K E

    1997-01-01

    This project was designed to investigate the possibility of producing alignment layers for liquid crystal devices by cross-linking thin films containing anisotropic polymer bound chromophores via irradiation with polarised ultraviolet light. Photocross-linkable polymers find use in microelectronics, liquid crystal displays, printing and UV curable lacquers and inks; so there is an increasing incentive for the development of new varieties of photopolymers in general. The synthesis and characterisation of two new photopolymers that are suitable as potential alignment layers for liquid crystal devices are reported in this thesis. The first polymer contains the anthracene chromophore attached via a spacer unit to a methacrylate backbone and the second used a similarly attached aryl azide group. Copolymers of the new monomers with methyl methacrylate were investigated to establish reactivity ratios in order to understand composition drift during polymerisation.

  2. Transient molecular orientation and rheology in flow aligning thermotropic liquid crystalline polymers

    International Nuclear Information System (INIS)

    Quantitative measurements of molecular orientation and rheology are reported for various transient shear flows of a nematic semiflexible copolyether. Unlike the case of lyotropic liquid crystalline polymers (LCPs), whose structure and rheology in shear are dominated by director tumbling, this material exhibits flow aligning behavior. The observed behavior is quite similar to that seen in a copolyester that we have recently studied [Ugaz and Burghardt (1998)], suggesting that flow aligning dynamics may predominate in main-chain thermotropes that incorporate significant chain flexibility. Since the flow aligning regime has received little attention in previous attempts to model the rheology of textured, polydomain LCPs, we attempt to determine whether available models are capable of predicting the orientation and stress response of this class of LCP. We first examine the predictions of the polydomain Ericksen model, an adaptation of Ericksen's transversely isotropic fluid model which accounts for the polydomain distribution of director orientation while neglecting distortional elasticity. This simple model captures a number of qualitative and quantitative features associated with the evolution of orientation and stress during shear flow inception, but cannot cope with reversing flows. To consider the possible role of distortional elasticity in the re-orientation dynamics upon reversal, we evaluate the mesoscopically averaged domain theory of Larson and Doi [Larson and Doi (1991)], which incorporates a phenomenological description of distortional elastic effects. To date, their approach to account for polydomain structure has only been applied to describe tumbling LCPs. We find that it captures the qualitative transient orientation response to flow reversals, but is less successful in describing the evolution of stresses. This is linked to the decoupling approximation adopted during the model's development. Finally, a modified polydomain Ericksen model is introduced

  3. Laser light scattering technique for non-invasive in situ simultaneous measurements on elastic constants and viscosity coefficients of nematic liquid crystals

    Institute of Scientific and Technical Information of China (English)

    TU; Mei; HUANG; Yaoxiong

    2004-01-01

    The laser light scattering technique for non-invasive in situ simultaneous measurements on elastic constants and viscosity coefficients of nematic liquid crystals is introduced. By measuring the autocorrelation function of the scattered light from nematic liquid crystals at different scattering angles, the splay and twist elastic constants K11 and K22 are obtained from the amplitudes of the autocorrelation function, and the viscosity coefficients of (Splay and (Twist are determined using the viscoelastic ratios K11/( Splay and K22/(Twist from the relaxation parameters of the two modes.

  4. Ordering in nematic liquid crystals from NMR cross-polarization studies

    Indian Academy of Sciences (India)

    K V Ramanathan; Neeraj Sinha

    2003-08-01

    The measurement of dipolar couplings between nuclei is a convenient way of obtatining directly liquid crystalline ordering through NMR since the coupling is dependent on the average orientation of the dipolar vector in the magnetic field which also aligns the liquid crystal. However, measurement of the dipolar coupling between a pair of selected nuclei is beset with problems that require special solutions. In this article the use of cross polarization for measuring dipolar couplings in liquid crystals is illustrated. Transient oscillations observed during cross polarization provide the dipolar couplings between essentially isolated nearest neighbour spins which can be extracted for several sites simultaneously by employing two-dimensional NMR techniques. The use of the method for obtaining heteronuclear dipolar couplings and hence the order parameters of liquid crystals is presented. Several modifications to the basic experiment are considered and their utility illustrated. A method for obtaining proton–proton dipolar couplings, by utilizing cross polarization from the dipolar reservoir, is also presented.

  5. Control of photoluminescence of CdSe/ZnS quantum dots in a nematic liquid crystal by an electric field

    Science.gov (United States)

    Kurochkina, M. A.; Shcherbinin, D. P.; Konshina, E. A.

    2015-11-01

    Photoluminescence (PL) spectra of a nematic liquid crystal suspension doped with 10 wt % CdSe/ZnS semiconductor quantum dots (QDs) with a core size of 3.5 nm in a 20-µm thick plane-parallel cell have been investigated. The spectrum of a homogeneously oriented suspension layer exhibits a significant shift of the PL peak by ~83 nm to a wavelength of 676 nm as compared with the QD spectrum in toluene. The application of a dc electric field with a strength of 0.25 V/µm to the cell leads to a slight hypsochromic shift of this peak, the position of which does not change with a further increase in the field strength up to 2 V/µm. The PL intensity changes exponentially and decreases by a factor of two at the field strength of 1 V/µm. The mechanism of PL quenching of QDs in a homogeneously oriented layer of nematic liquid crystal is discussed.

  6. Influence of virtual surfaces on Frank elastic constants in a polymer-stabilized bent-core nematic liquid crystal

    Science.gov (United States)

    Madhuri, P. Lakshmi; Hiremath, Uma S.; Yelamaggad, C. V.; Madhuri, K. Priya; Prasad, S. Krishna

    2016-04-01

    Effect of a polymer network on the threshold voltage of the Fréedericksz transition, Frank elastic constants, switching speed, and the rotational viscosity are investigated in a polymer-stabilized bent-core nematic liquid crystal with different polymer concentrations. These polymer networks form virtual surfaces with a finite anchoring energy. The studies bring out several differences in comparison to similar studies with a calamitic liquid crystal as the nematic host. For example, on varying the polymer content the threshold voltage decreases initially, but exhibits a drastic increase above a critical concentration. A similar feature—reaching a minimum before rising—is seen for the bend elastic constant, which gets enhanced by an order of magnitude for a polymer content of 2.5 wt %. In contrast, the splay elastic constant has a monotonic variation although the overall enhancement is comparable to that of the bend elastic constant. The behavior changing at a critical concentration is also seen for the switching time and the associated rotational viscosity. The presence of the polymer also induces a shape change in the thermal dependence of the bend elastic constant. We explain the features observed here on the basis of images obtained from the optical and atomic force microscopy.

  7. Acousto-optic effect in a nematic liquid-crystal layer under the binary effect of sound and viscous waves

    International Nuclear Information System (INIS)

    The optical effect in a liquid crystal cell containing a homeotropic layer of nematic liquid crystal (NLC) is analyzed. An NLC layer, located between crossed polaroids and opaque in the absence of external effect, is cleared after irradiation by an ultrasonic beam with a sharp spatial boundary. This enlightenment is suggested to be caused by the reorientation of crystal molecules in the acoustic flows that arise under the binary effect of the layer compression in the irradiated region and the viscous waves propagating from the layer boundaries. The flows were calculated taking into account the stress caused by the velocity convection and crystal structure relaxation. An expression is derived for the cell transparency, and the relative role of the convection and relaxation processes in the effect is determined.

  8. Acousto-optic effect in a nematic liquid-crystal layer under the binary effect of sound and viscous waves

    Energy Technology Data Exchange (ETDEWEB)

    Kozhevnikov, E. N., E-mail: kozhev@ssu.samara.ru [Samara State University (Russian Federation)

    2010-03-15

    The optical effect in a liquid crystal cell containing a homeotropic layer of nematic liquid crystal (NLC) is analyzed. An NLC layer, located between crossed polaroids and opaque in the absence of external effect, is cleared after irradiation by an ultrasonic beam with a sharp spatial boundary. This enlightenment is suggested to be caused by the reorientation of crystal molecules in the acoustic flows that arise under the binary effect of the layer compression in the irradiated region and the viscous waves propagating from the layer boundaries. The flows were calculated taking into account the stress caused by the velocity convection and crystal structure relaxation. An expression is derived for the cell transparency, and the relative role of the convection and relaxation processes in the effect is determined.

  9. Novel polymer as liquid crystal alignment material for plastic substrates

    Energy Technology Data Exchange (ETDEWEB)

    Mahilny, U V; Stankevich, A I; Muravsky, A A [Physical Department of Belarusian State University, Nezavisimosti Ave. 4, 220030 Minsk (Belarus); Murauski, A A, E-mail: mogilny@bsu.b [Center for Display Research, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

    2009-04-07

    Implementation of the roll-to-roll (R2R) process and printable organic electronics realizes the cost reduction potential of liquid crystal displays (LCDs) on plastic substrates. These innovative technologies put a strong limitation on the chemistry and temperature treatment of the LC alignment material applied at the solid-liquid interface inside the LCD. Alignment material is the last uniform layer deposited on each of the substrates before assembling and sealing of the whole display sandwich. Deposition from an aggressive solvent, vacuum deposition or a high baking temperature can not only destroy the complex composite structure of the electronics but can also affect the material properties of the substrate. We developed a new type of polymer alignment material, B-15, which can be deposited from a non-aggressive solvent (ethyl/butyl acetate) on top of the wide range of organic layers (including UV-curable materials and TAC films of plastic polarizer) without barrier layers for chemical protection. B-15 is suitable for the R2R process for only short-time treatment operations: 5 min baking at 90 {sup 0}C is sufficient to remove the residual solvent and hard baking is not required. First, the rubbing process produces an alignment direction on the surface with the azimuthal anchoring energy over 10{sup -4} J m{sup -2}. Next, non-polarized light exposure with a 254 nm Hg line induces photopolymerization, which also shifts the absorption peak far below the 300 nm wavelength. Thus B-15 is a highly photostable alignment material possessing null absorption in both the UV-A and the VIS ranges.

  10. Light scattering study of the "pseudo-layer" compression elastic constant in a twist-bend nematic liquid crystal

    CERN Document Server

    Parsouzi, Z; Welch, C; Ahmed, Z; Mehl, G H; Baldwin, A R; Gleeson, J T; Lavrentovich, O D; Allender, D W; Selinger, J V; Jakli, A; Sprunt, S

    2016-01-01

    The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or "pseudo-layers", each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining "layer" compression and bending ought to be characterized by an effective layer compression elastic constant $B_{eff}$ and average director splay constant $K_1^{eff}$. The magnitude of $K_1^{eff}$ is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, $B_{eff}$ could differ substantially from the typical value of $\\sim 10^6$ Pa in a conventional smectic-A. Here we report the results of a dynamic l...

  11. Singular values, nematic disclinations, and emergent biaxiality

    OpenAIRE

    Dennis, Mark R.; Žumer, Slobodan; Kamien, Randall D.; Čopar, Simon

    2015-01-01

    Both uniaxial and biaxial nematic liquid crystals are defined by orientational ordering of their building blocks. While uniaxial nematics only orient the long molecular axis, biaxial order implies local order along three axes. As the natural degree of biaxiality and the associated frame that can be extracted from the tensorial description of the nematic order vanishes in the uniaxial phase, we extend the nematic director to a full biaxial frame by making use of a singular value decomposition ...

  12. Active Cellular Nematics

    Science.gov (United States)

    Duclos, Guillaume; Erlenkaemper, Christoph; Garcia, Simon; Yevick, Hannah; Joanny, Jean-François; Silberzan, Pascal; Biology inspired physics at mesoscales Team; Physical approach of biological problems Team

    We study the emergence of a nematic order in a two-dimensional tissue of apolar elongated fibroblast cells. Initially, these cells are very motile and the monolayer is characterized by giant density fluctuations, a signature of far-from-equilibrium systems. As the cell density increases because of proliferation, the cells align with each other forming large perfectly oriented domains while the cellular movements slow down and eventually freeze. Therefore topological defects characteristic of nematic phases remain trapped at long times, preventing the development of infinite domains. By analogy with classical non-active nematics, we have investigated the role of boundaries and we have shown that cells confined in stripes of width smaller than typically 500 µm are perfectly aligned in the stripe direction. Experiments performed in cross-shaped patterns show that both the number of cells and the degree of alignment impact the final orientation. Reference: Duclos G., Garcia S., Yevick H.G. and Silberzan P., ''Perfect nematic order in confined monolayers of spindle-shaped cells'', Soft Matter, 10, 14, 2014

  13. Feedback control of flow alignment in sheared liquid crystals

    OpenAIRE

    Strehober, David A.; Schöll, Eckehard; Klapp, Sabine H. L.

    2013-01-01

    Based on a continuum theory, we investigate the manipulation of the non-equilibrium behavior of a sheared liquid crystal via closed-loop feedback control. Our goal is to stabilize a specific dynamical state, that is, the stationary "flow-alignment", under conditions where the uncontrolled system displays oscillatory director dynamics with in-plane symmetry. To this end we employ time-delayed feedback control (TDFC), where the equation of motion for the ith component, q_i(t), of the order para...

  14. Applying a Self-Made Automobile Heterodyne Interferometer to Measure the Parameters of Twisted Nematic Liquid Crystal

    Directory of Open Access Journals (Sweden)

    Shinn-Fwu Wang

    2012-01-01

    Full Text Available A self-made automobile heterodyne interferometer with a closed control loop is presented. In addition, we will apply the self-made automobile heterodyne interferometer to measure the parameters of optically compensated twisted nematic liquid crystal (TN LC. It is worthy to be mentioned that the self-made automobile heterodyne interferometer has a compact size because all the optical components are installed in the mechanism of the system. Besides, the self-made automobile heterodyne interferometer has some much more merits, for example, automobile control, a simple setup, in real-time test, reliability, and so forth. Besides, it is very stable because of its common optical path insensitive to environmental disturbances. And its feasibility is demonstrated.

  15. Reduction of the Residual DC in the Photoaligned Twisted Nematic Liquid Crystal Display Using Polymerized Reactive Mesogen

    Science.gov (United States)

    Lim, Young Jin; Jeong, Il Hwa; Kang, Heon-Seok; Kundu, Sudarshan; Lee, Myong-Hoon; Lee, Seung Hee

    2012-08-01

    A residual direct current (DC) voltage property in the twisted nematic liquid crystal display (TN-LCD) using photoaligned polyimide is studied by the capacitance-voltage hysteresis method. A residual DC is greatly reduced in the photoaligned cell with an additional polymerized layer on a photoaligned layer with the help of a UV-curable reactive mesogen. The surface of the photoaligned layer becomes much more polar than that of the rubbed layer, possibly leading to a larger trapping of ions on the photoaligned layer than on the rubbed polyimide layer. The polar surface can be modified with an additional proposed polymer layer and, thus, the low residual DC voltage can be achieved.

  16. Viewing angle switching of patterned vertical alignment liquid crystal display

    International Nuclear Information System (INIS)

    Viewing angle control of a patterned vertical alignment (PVA) liquid crystal display using only one panel is investigated. In conventional PVA modes, a vertically aligned liquid crystal (LC) director tilts down in four directions making 45 deg. with respect to crossed polarizers to exhibit a wide viewing angle. In the viewing angle control device, one pixel was divided into two sub-pixels such that the LC director in the main pixel is controlled to be tilted down in multiple directions making an angle with the polarizer, playing the role of main display with the wide viewing angle, while the LC director in the sub-pixel is controlled to be tilted down to the polarizer axis, playing the role of sub-pixel to the viewing angle control for the narrow viewing angle. Using sub-pixel control, light leakage or any type of information such as characters and image can be generated in oblique viewing directions without distorting the image quality in the normal direction, which will prevent others from peeping at the displayed image by overlapping the displayed image with the made image

  17. Polyimide liquid crystal alignment layers prepared by soft-Lithography

    Institute of Scientific and Technical Information of China (English)

    HE Yaning; LIU Bin; REN Hongfeng; WANG Xiaogong

    2007-01-01

    Elastomeric replicas of surface relief structures were prepared by molding poly(dimethylsiloxane) (PDMS)precursors against photo-inscribed surface-relief-gratings on azo polymer films.The PI solutions were micro-contact printed with the elastomeric PDMS replica on quartz slides.Good surface-relief-grating structures were formed on the quartz slides.The quartz slides covered with surface-reliefgrating polymide (PI) films were then assembled into liquid crystal (LC) cells.The transmittance passing through the cell between crossed polarizers changed periodically with a regular 90°separation of the rotational angle.The pretilt angle of the cell was found to be 2.8°.Results showed that the PI films with surface-relief-grating structures by this micro-contact printing process have good liquid crystal alignment ability.This preparation method of alignment layers can be considered a potentially useful technique in the LC display (LCD)industry in the future.

  18. Effect of the annealing temperature and ion-beam bombardment on the properties of solution-derived HfYGaO films as liquid crystal alignment layers

    Energy Technology Data Exchange (ETDEWEB)

    Park, Hong-Gyu; Lee, Yun-Gun; Jang, Sang Bok; Lee, Ju Hwan; Jeong, Hae-Chang; Seo, Dae-Shik, E-mail: dsseo@yonsei.ac.kr [Information Display Device Laboratory, Department of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749 (Korea, Republic of); Oh, Byeong-Yun [ZeSHTech Co., Ltd., Business Incubator, Gwangju Institute of Science and Technology, 123, Cheomdangwagi-ro, Buk-gu, Gwangju 500-712 (Korea, Republic of)

    2015-11-15

    Hafnium yttrium gallium oxide (HfYGaO) films were applied to liquid crystal displays (LCDs) as liquid crystal (LC) alignment layers, replacing conventional polyimide (PI) layers. The HfYGaO alignment layers were prepared by fabricating solution-processed HfYGaO films, annealing them, and treating them with ion-beam (IB) irradiation. The authors studied the effects of annealing temperature and IB irradiation of the solution-derived HfYGaO films on the orientation of LC molecules. The LC molecules on the solution-derived HfYGaO films were homogeneously and uniformly aligned by IB irradiation, irrespective of the annealing temperature. Atomic force microscopy analyses revealed that the surface reformation of the HfYGaO films induced by IB irradiation strengthened the van der Waals force between the LC molecules and the HfYGaO films, leading to uniform LC alignment. Enhanced electro-optical characteristics were observed in the twisted-nematic (TN) LCDs based on IB-irradiated HfYGaO films compared with those of TN-LCDs based on PI layers, demonstrating the high application potential of the proposed solution-derived HfYGaO films as LC alignment layers.

  19. The helical phase of chiral nematic liquid crystals as the Bianchi VII(0) group manifold

    CERN Document Server

    Gibbons, G W

    2011-01-01

    We show that the optical structure of the helical phase of a chiral nematic is naturally associated with the Bianchi VII(0) group manifold. The Joets-Ribotta metric governing propagation of the extraordinary rays is invariant under the simply transitive action of the universal cover of the three dimensional Euclidean group of two dimensions. Thus extraordinary light rays are geodesics of a left-invariant metric on this Bianchi type VII(0) group. We are able to solve by separation of variables both the wave equation and the Hamilton-Jacobi equation for this metric. The former reduces to Mathieu's equation and the later to the quadrantal pendulum equation. We further discuss Maxwell's equations for uniaxial optical materials where the configuration is invariant under a group action. The material is not assumed to be impedance matched, thus going beyond the usual scope of transformation optics. We show that for a chiral nematic in its helical phase Maxwell's equations reduce to a generalised Mathieu equation. Ou...

  20. Configurational temperature and local properties of the anisotropic Gay-Berne liquid crystal model: Applications to the isotropic liquid/vapor interface and isotropic/nematic transition

    Science.gov (United States)

    Ghoufi, Aziz; Morineau, Denis; Lefort, Ronan; Malfreyt, Patrice

    2011-01-01

    Molecular simulations in the isothermal statistical ensembles require that the macroscopic thermal and mechanical equilibriums are respected and that the local values of these properties are constant at every point in the system. The thermal equilibrium in Monte Carlo simulations can be checked through the calculation of the configurational temperature, {k_BT_{conf}={}/{}}, where nabla _r is the nabla operator of position vector r. As far as we know, T_{conf} was never calculated with the anisotropic Gay-Berne potential, whereas the calculation of T_{conf} is much more widespread with more common potentials (Lennard Jones, electrostatic, …). We establish here an operational expression of the macroscopic and local configurational temperatures, and we investigate locally the isotropic liquid phase, the liquid / vapor interface, and the isotropic-nematic transition by Monte Carlo simulations.

  1. Orientation of liquid crystalline materials by using carbon nanotubes

    Directory of Open Access Journals (Sweden)

    Kamanina N.V.

    2011-01-01

    Full Text Available The solution of some problems, where the initial black field is necessary for the regime of light transmission through the electrooptical organic nematic liquid crystal structures has been considered via a homeotropic alignment of liquid crystal molecules on the substrate covered by carbon nanotubes. The results of this investigation can be used to develop optical elements for displays with vertical orientations of nematic liquid crystal molecules (for example, for MVA-display technology.

  2. Oscillatory Shear Alignment and Rheology of a Main-chain Thermotropic Liquid Crystalline Polymer.

    Science.gov (United States)

    Kornfield, Julia A.; Zhou, Weijun; Ugaz, Victor M.; Vaish, Nitin; Burghardt, Wesley R.

    2000-03-01

    Orientational flipping is well known in lamellar block copolymers under oscillatory shear. For thermotropic LCPs, two different orientation states have also been reported under steady shear -- oriented either along the flow direction (``parallel'') or along the vorticity direction (``perpendicular''). Here we examine the oscillatory shear behavior of a model thermotropic LCP (DHMS-7,9, T_m=90^circC, T_xn=120^circC, T_ni=192^circC, where T_xn is the transition temperature between an unidentified mesophase ``Phase X'' to nematic phase), which exhibits this type of orientational flipping. Systematic studies have been carried out on DHMS-7,9 as a function of temperature, frequency, and strain amplitude. In the nematic phase, oscillatory shear induces parallel alignment. However, in Phase X, qualitatively different alignment behavior was observed: low frequency and large strain amplitude promote perpendicular alignment, while high frequency and small strain amplitude induce parallel orientation. A possible explanation of this anomalous shear alignment behavior will be provided.

  3. Self-assembled structures of Gaussian nematic particles

    Energy Technology Data Exchange (ETDEWEB)

    Nikoubashman, Arash; Likos, Christos N [Institute of Theoretical Physics, Heinrich Heine University of Duesseldorf, Universitaetsstrasse 1, D-40225 Duesseldorf (Germany)

    2010-03-17

    We investigate the stable crystalline configurations of a nematic liquid crystal made of soft parallel ellipsoidal particles interacting via a repulsive, anisotropic Gaussian potential. For this purpose, we use genetic algorithms (GA) in order to predict all relevant and possible solid phase candidates into which this fluid can freeze. Subsequently we present and discuss the emerging novel structures and the resulting zero-temperature phase diagram of this system. The latter features a variety of crystalline arrangements, in which the elongated Gaussian particles in general do not align with any one of the high-symmetry crystallographic directions, a compromise arising from the interplay and competition between anisotropic repulsions and crystal ordering. Only at very strong degrees of elongation does a tendency of the Gaussian nematics to align with the longest axis of the elementary unit cell emerge.

  4. The Phase Transition of Nematic Liquid Crystal Cells Bounded by Surfactant-Laden Interfaces

    International Nuclear Information System (INIS)

    Taking into account the surface-coupling strength effect, we discuss the phase transitions of a finite thickness cell bounded by surfactant-laden interfaces in a magnetic field perpendicular to the substrate and it is compared with that of a semi-infinite system. It is found that the larger the thickness, the closer the three-dimensional phase transition surface of the finite system to that of the semi-infinite one. The simulation also shows that when a magnetic field is applied to a nematic semi-infinite sample, an orientational phase transition first takes place close to the interface and then extends to the inner space as the temperature increases. (condensed matter: structure, mechanical and thermal properties)

  5. Dielectric relaxation studies in 5CB nematic liquid crystal at 9 GHz under the influence of external magnetic field using microwave cavity spectrometer

    Indian Academy of Sciences (India)

    Manoj Johri; Abhay Saxena; S Johri; S Saxena; D P Singh

    2011-04-01

    Resonance width, shift in resonance frequency, relaxation time and activation energy of 5CB nematic liquid crystal are measured using microwave cavity technique under the influence of an external magnetic field at 9 GHz and at different temperatures. The dielectric response in liquid crystal at different temperatures and the effects of applied magnetic field on transition temperatures are studied in the present work. The technique needs a small quantity (< 0.001 cm3) of the sample and provides fruitful information about the macroscopic structure of the liquid crystal.

  6. A nematic-polar columnar phase sequence in new bent-shaped liquid crystals based on a 7-hydroxynaphthalene-2-carboxylic acid core

    Czech Academy of Sciences Publication Activity Database

    Kohout, M.; Svoboda, J.; Novotná, Vladimíra; Pociecha, D.; Glogarová, Milada; Gorecka, E.

    2009-01-01

    Roč. 19, - (2009), s. 3153-3160. ISSN 0959-9428 R&D Projects: GA AV ČR(CZ) GA202/09/0047; GA AV ČR IAA100100710 Institutional research plan: CEZ:AV0Z10100520 Keywords : liquid crystals * bent-shaped mesogen * columnar phase * nematic phase Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.795, year: 2009

  7. Retrieving the saddle-splay elastic constant K24 of nematic liquid crystals from an algebraic approach.

    Science.gov (United States)

    Fumeron, Sébastien; Moraes, Fernando; Pereira, Erms

    2016-09-01

    The physics of light interference experiments is well established for nematic liquid crystals. Using well-known techniques, it is possible to obtain important quantities, such as the differential scattering cross section and the saddl-splay elastic constant K24. However, the usual methods to retrieve the latter involve adjusting of computational parameters through visual comparisons between the experimental light interference pattern or a (2) H-NMR spectral pattern produced by an escaped-radial disclination, and their computational simulation counterparts. To avoid such comparisons, we develop an algebraic method for obtaining of saddle-splay elastic constant K24. Considering an escaped-radial disclination inside a capillary tube with radius R0 of tens of micrometers, we use a metric approach to study the propagation of the light (in the scalar wave approximation), near the surface of the tube and to determine the light interference pattern due to the defect. The latter is responsible for the existence of a well-defined interference peak associated to a unique angle [Formula: see text] . Since this angle depends on factors such as refractive indexes, curvature elastic constants, anchoring regime, surface anchoring strength and radius R0, the measurement of [Formula: see text] from the interference experiments involving two different radii allows us to algebraically retrieve K24. Our method allowed us to give the first reported estimation of K24 for the lyotropic chromonic liquid crystal Sunset Yellow FCF: K 24 = 2.1 pN. PMID:27589980

  8. Controlling the alignment of liquid crystals by nanoparticle-doped and UV-treated polyimide alignment films

    Science.gov (United States)

    Jeng, Shie-Chang; Hwang, Su-June; Chen, Tai-An; Liu, Han-Shiang; Chen, Mu-Zhe

    2012-03-01

    We have developed two approaches for controlling the pretilt angles of liquid crystal molecules by using conventional polyimide (PI) alignment materials either doping homogeneous PIs with Polyhedral Oligomeric Silsequioxanes (POSS) nanoparticles or treating homeotropic PIs with ultraviolet light. These techniques are very simple and are compatible with current methods familiar in the LCD industry. The characteristics of modified PI alignment films and their applications for photonic devices are demonstrated in this paper.

  9. Elliptical Tracers in Two-dimensional, Homogeneous, Isotropic Fluid Turbulence: the Statistics of Alignment, Rotation, and Nematic Order

    CERN Document Server

    Gupta, Anupam; Pandit, Rahul

    2013-01-01

    We study the statistical properties of orientation and rotation dynamics of elliptical tracer particles in two-dimensional, homogeneous and isotropic turbulence by direct numerical simulations. We consider both the cases in which the turbulent flow is generated by forcing at large and intermediate length scales. We show that the two cases are qualitatively different. For large-scale forcing, the spatial distribution of particle orientations forms large-scale structures, which are absent for intermediate-scale forcing. The alignment with the local directions of the flow is much weaker in the latter case than in the former. For intermediate-scale forcing, the statistics of rotation rates depends weakly on the Reynolds number and on the aspect ratio of particles. In contrast with what is observed in three-dimensional turbulence, in two dimensions the mean-square rotation rate decreases as the aspect ratio increases.

  10. Nematic Liquid Crystals: From Maier-Saupe to a Continuum Theory

    KAUST Repository

    Ball, John M.

    2010-07-20

    We define a continuum energy functional that effectively interpolates between the mean-field Maier-Saupe energy and the continuum Landau-de Gennes energy functional and can describe both spatially homogeneous and inhomogeneous systems. In the mean-field approach the main macroscopic variable, the Q-tensor order parameter, is defined in terms of the second moment of a probability distribution function. This definition imposes certain constraints on the eigenvalues of the Q-tensor order parameter, which may be interpreted as physical constraints. We define a thermotropic bulk potential which blows up whenever the eigenvalues of the Q-tensor order parameter approach physically unrealistic values. As a consequence, the minimizers of this continuum energy functional have physically realistic order parameters in all temperature regimes. We study the asymptotics of this bulk potential and show that this model also predicts a first-order nematic-isotropic phase transition, whilst respecting the physical constraints. In contrast, in the Landau-de Gennes framework the Q-tensor order parameter is often defined independently of the probability distribution function, and the theory makes physically unrealistic predictions about the equilibrium order parameters in the low-temperature regime. Copyright © Taylor & Francis Group, LLC.

  11. treatment of polyimide by an atmospheric pressure plasma of capacitive rf discharge for liquid crystal alignment

    International Nuclear Information System (INIS)

    Uniform planar alignment of liquid crystals is obtained by polyimide films obliquely treated by a stream of argon plasma from capacitive RF discharge at atmospheric pressure. Two liquid crystal alignment modes are discovered differing by their longitudinal or transverse orientation with respect to treatment direction. Optimum parameters of the treatment for obtaining these orientation modes are determined.

  12. Steady-state and time-resolved spectroscopic investigations on intramolecular electron transfer processes within a synthesized methoxynaphthalene dyad by using a nematic liquid crystal medium

    International Nuclear Information System (INIS)

    UV-vis, steady state and time-resolved spectroscopic investigations were made on photoinduced charge separation and thermal charge recombination processes involved within a novel synthesized dyad, 1-(4-chloro-phenyl)-3-(4-methoxy-naphthalen-1-yl)-propenone (MNCA) where the donor 1-methoxynaphthalene (MNT) and the acceptor p-choloroacetophenone (PCA) moieties are connected by a short unsaturated olefinic bond. The measurements were made within the pseudo-ordered domain (just above nematic-isotropic (N-I) phase transition temperature, >308 K) of a nematic liquid crystal, 4-(n-pentyl)-4'-cyanobiphenyl (5CB). Results observed are compared with those obtained from the similar measurements in isotropic media. The charge separation and recombination rates remain more-or-less unchanged within the experimental error irrespective of the polarity of the environment, whether in pseudo-ordered domain (εS∼10.5) of a nematic liquid crystal 5CB or in highly polar isotropic medium ACN (εS∼37.5). The structural rigidity of the dyad MNCA having stable elongated form both in the ground as well as in the photoexcited states seems to be the reason for this unique behavior of solvent insensitivity. The theoretical predictions done by ab initio method density functional theory (DFT) with B3LYP/6-311 G (d, p) basis function correlate well with experimental observations of formations of only one stable elongated (E-type) conformer both in the ground and electronic excited state.

  13. Directed self-assembly of colloidal particles onto the chemically anchoring patterned surface in a nematic liquid crystal

    Science.gov (United States)

    Li, Xiao; Armas-Pérez, Julio; Hernandez-Ortiz, Juan; de Pablo, Juan; Nealey, Paul

    The defects assisted assembly of colloidal particles works are more focused on the defects created in the bulk or the interface of nematic liquid crystal, which usually observe a group of particles spontaneously forming a chain or aggregating over the defects. The confining surface with specific 3D sculptured structures, such as pyramid or zig-zag grooves, offers the opportunity to isolate the trapped particles into certain position. Here, we explore a new method to direct self-assemble the colloidal particles through manipulating defects on the 2D geometry confined anchoring surface. Since the director of the preferred planar orientation of LCs could be manipulated by the pattern geometry and dimension, the topological defects could be engineered based on multi-stable orientation by designed 2D geometry pattern of different controllable direction at sub-micrometer dimension. We demonstrate that the designed one single middle straight stripe with disjoint two groups of straight stripe array on both side of the middle stripe as 45 angle of different orientation director could control the distortion of the disjoint gap space thus acting as defects template to trap the colloidal particles directed self-assembly at the designed positions. Through anchoring distribution on the pattern areas, geometry design of pattern, and also the external electric field applied on the system, those defects areas could be generate, erase, resume or even correct.

  14. A model-free temperature-dependent conformational study of n-pentane in nematic liquid crystals

    Science.gov (United States)

    Burnell, E. Elliott; Weber, Adrian C. J.; Dong, Ronald Y.; Meerts, W. Leo; de Lange, Cornelis A.

    2015-01-01

    The proton NMR spectra of n-pentane orientationally ordered in two nematic liquid-crystal solvents are studied over a wide temperature range and analysed using covariance matrix adaptation evolutionary strategy. Since alkanes possess small electrostatic moments, their anisotropic intermolecular interactions are dominated by short-range size-and-shape effects. As we assumed for n-butane, the anisotropic energy parameters of each n-pentane conformer are taken to be proportional to those of ethane and propane, independent of temperature. The observed temperature dependence of the n-pentane dipolar couplings allows a model-free separation between conformer degrees of order and conformer probabilities, which cannot be achieved at a single temperature. In this way for n-pentane 13 anisotropic energy parameters (two for trans trans, tt, five for trans gauche, tg, and three for each of gauche+ gauche+, pp, and gauche+ gauche-, pm), the isotropic trans-gauche energy difference Etg and its temperature coefficient Etg ' are obtained. The value obtained for the extra energy associated with the proximity of the two methyl groups in the gauche+ gauche- conformers (the pentane effect) is sensitive to minute details of other assumptions and is thus fixed in the calculations. Conformer populations are affected by the environment. In particular, anisotropic interactions increase the trans probability in the ordered phase.

  15. Assessment of incident intensity on laser speckle contrast imaging using a nematic liquid crystal spatial light modulator (Conference Presentation)

    Science.gov (United States)

    Kirby, Mitchell A.; Khaksari, Kosar; Kirkpatrick, Sean J.

    2016-03-01

    In this work the effects of incident intensity and effective camera dynamic range on image acquisition of both frozen and time-averaged dynamic speckle patterns, and their effects on laser speckle contrast imaging are addressed. A nematic liquid crystal, phase-only, spatial light modulator (SLM) was employed to generate laser speckle in a controlled and repeatable fashion. By addressing the calculated spatial contrast of frozen and time-averaged dynamic speckle patterns imaged across a wide range of intensities, we present a description of optimum intensity characteristics that should be observed when using LSCI. The results indicate the importance of assessing the intensity of the signal quantized by the camera in LSCI. By analyzing intensity PDF's during image acquisition of speckle patterns used in LSCI, an optimum incident intensity can be detected when a single, polarized speckle frame displays the first order statistics characteristic of fully developed speckle. Our results indicate that there is a range of laser power densities where the ensuing imaged speckle exhibit optimum sensitivity to flow as well as relatively constant calculated contrast values. It is clear that at high intensities, high frequency information is lost due to camera saturation, resulting in a decrease in contrast. When imaging speckle at low intensity, there is a risk for loss of data during the digital quantization process. The results are presented in a generalized fashion, so they should be applicable to any LSCI system, regardless of incident laser power or camera depth.

  16. Long-time behavior for a nematic liquid crystal model with asymptotic stabilizing boundary condition and external force

    CERN Document Server

    Grasselli, Maurizio

    2011-01-01

    We consider an approximation of the well-known Ericksen-Leslie model for the nematic liquid crystal flow proposed by F.-H. Lin et al. The evolution system consists of the Navier-Stokes equations coupled with a convective Ginzburg-Landau type equation for the (vector-valued) averaged molecular orientations. Here we suppose that the latter is subject to a time-dependent Dirichlet boundary condition h(t), while the Navier--Stokes equations are characterized by a no-slip boundary condition and by a time-dependent external force g(t). We show that, in 2D, each global weak solution converges to a single stationary state when h(t) and g(t) suitably converge to a time-independent boundary datum h_\\infty and 0, respectively. We also provide some estimates of the convergence rate. In the 3D case, we prove a similar long-time behavior for global strong solutions, provided that either the viscosity is large enough or the initial datum is close to a given equilibrium.

  17. Quaternions and hybrid nematic disclinations

    OpenAIRE

    Čopar, Simon; Žumer, Slobodan

    2012-01-01

    Disclination lines in nematic liquid crystals can exist in different geometric conformations, characterized by their director profile. In certain confined colloidal suspensions and even more prominently in chiral nematics, the director profile may vary along the disclination line. We construct a robust geometric decomposition of director profile in closed disclination loops and use it to apply topological classification to linked loops with arbitrary variation of the profile, generalizing the...

  18. Nonlinear optical studies of liquid crystal alignment on a rubbed polyvinyl alcohol surface

    Science.gov (United States)

    Wei, Xing; Hong, Seok-Cheol; Zhuang, Xiaowei; Goto, Tomohisa; Shen, Y. R.

    2000-10-01

    Sum-frequency vibrational spectroscopy and second-harmonic generation have been used to measure the orientational distributions of the polymer chains and adsorbed 8CB liquid crystal molecules on a rubbed polyvinyl alcohol surface. Results show that the polymer chains at the surface appear to be well aligned by rubbing, and the adsorbed liquid crystal molecules are aligned, in turn, by the surface polymer chains. Strong correlation exists between the orientational distributions of the polymer chains and the liquid crystal molecules, indicating that the surface-induced bulk alignment of a liquid crystal film by rubbed polymer surfaces is via an orientational epitaxylike mechanism.

  19. Two-Dimensional Skyrmion Lattice Formation in a Nematic Liquid Crystal Consisting of Highly Bent Banana Molecules.

    Science.gov (United States)

    Kang, Sungmin; Lee, Eun-Woo; Li, Tianqi; Liang, Xiaobin; Tokita, Masatoshi; Nakajima, Ken; Watanabe, Junji

    2016-09-12

    We synthesized a novel banana-shaped molecule based on a 1,7-naphthalene central core that exhibits a distinct mesomorphism of the nematic-to-nematic phase transition. Both the X-ray profile and direct imaging of atomic force microscopy (AFM) investigations clearly indicates the formation of an anomalous nematic phase possessing a two-dimensional (2D) tetragonal lattice with a large edge (ca. 59 Å) directed perpendicular to the director in the low-temperature nematic phase. One plausible model is proposed by an analogy of skyrmion lattice in which two types of cylinders formed from left- and right-handed twist-bend helices stack into a 2D tetragonal lattice, diminishing the inversion domain wall. PMID:27511324

  20. Nematic Fermi Fluids in Condensed Matter Physics

    OpenAIRE

    Fradkin, Eduardo; Kivelson, Steven A.; Lawler, Michael J; Eisenstein, James P.; Mackenzie, Andrew P.

    2010-01-01

    Correlated electron fluids can exhibit a startling array of complex phases, among which one of the more surprising is the electron nematic, a translationally invariant metallic phase with a spontaneously generated spatial anisotropy. Classical nematics generally occur in liquids of rod-like molecules; given that electrons are point like, the initial theoretical motivation for contemplating electron nematics came from thinking of the electron fluid as a quantum melted electron crystal, rather ...

  1. An integrated nematic liquid crystal in-fiber modulator derivates from capillary optical fiber

    Science.gov (United States)

    Guo, Xiaohui; Yang, Xinghua; Li, Song; Liu, Zhihai; Hu, Minggang; Qu, Bin; Yuan, Libo

    2016-05-01

    A novel liquid crystal integrated modulation-depth-adjustable in-fiber modulator is proposed. The liquid crystal is encapsulated in a specially designed capillary optical fiber with tubular structure. The experimental results show that the liquid crystal under the electric field can influence the light intensity in the tubular core of the fiber. The light at 632.8 nm in the circular waveguide can be modulated by only 2.71×10-2 nL of the liquid crystals under electric field. The wide range of modulation-depth from 23% to 50% can be obtained by adjusting the strength of the external electric field. In addition, the modulator shows good stability and repeatability. This work has great potentials in integrated in-fiber optical devices such as tunable modulators, optical switches and electric field sensors.

  2. Versatile alignment layer method for new types of liquid crystal photonic devices

    International Nuclear Information System (INIS)

    Liquid crystal photonic devices are becoming increasingly popular. These devices often present a challenge when it comes to creating a robust alignment layer in pre-assembled cells. In this paper, we describe a method of infusing a dye into a microcavity to produce an effective photo-definable alignment layer. However, previous research on such alignment layers has shown that they have limited stability, particularly against subsequent light exposure. As such, we further describe a method of utilizing a pre-polymer, infused into the microcavity along with the liquid crystal, to provide photostability. We demonstrate that the polymer layer, formed under ultraviolet irradiation of liquid crystal cells, has been effectively localized to a thin region near the substrate surface and provides a significant improvement in the photostability of the liquid crystal alignment. This versatile alignment layer method, capable of being utilized in devices from the described microcavities to displays, offers significant promise for new photonics applications

  3. Versatile alignment layer method for new types of liquid crystal photonic devices

    Energy Technology Data Exchange (ETDEWEB)

    Finnemeyer, V.; Bryant, D.; Lu, L.; Bos, P. [Liquid Crystal Institute, Kent State University, Kent, Ohio 44242 (United States); Reich, R.; Clark, H.; Berry, S.; Bozler, C. [MIT Lincoln Laboratory, 244 Wood St., Lexington, Massachusetts 02420 (United States); Yaroshchuk, O. [Institute of Physics, NAS of Ukraine, 44 Prospect Nauky, Kyiv 03680 (Ukraine)

    2015-07-21

    Liquid crystal photonic devices are becoming increasingly popular. These devices often present a challenge when it comes to creating a robust alignment layer in pre-assembled cells. In this paper, we describe a method of infusing a dye into a microcavity to produce an effective photo-definable alignment layer. However, previous research on such alignment layers has shown that they have limited stability, particularly against subsequent light exposure. As such, we further describe a method of utilizing a pre-polymer, infused into the microcavity along with the liquid crystal, to provide photostability. We demonstrate that the polymer layer, formed under ultraviolet irradiation of liquid crystal cells, has been effectively localized to a thin region near the substrate surface and provides a significant improvement in the photostability of the liquid crystal alignment. This versatile alignment layer method, capable of being utilized in devices from the described microcavities to displays, offers significant promise for new photonics applications.

  4. Optical trapping induced by reorientational nonlocal effects in nematic liquid crystals

    Science.gov (United States)

    Lucchetti, L.; Criante, L.; Bracalente, F.; Aieta, F.; Simoni, F.

    2011-08-01

    We report a detailed analysis of optical trapping of low index particles in liquid crystals under experimental conditions that prevent the effect of conventional trapping originated by optical gradient forces. The observation of stable, long-range trapping shows that this phenomenon in liquid crystals is regulated by a completely different mechanism than in isotropic media. In particular, the role of the nonlocality of optical reorientation is highlighted by showing the dependence of the trapping force on the size of the reoriented area. A model based on the actual form of the Gaussian focused beam impinging on the liquid-crystalline medium in the trapping experiment is also reported, with good agreement with experimental data.

  5. Effects of added silica nanoparticles on the nematic liquid crystal phase formation in beidellite suspensions

    NARCIS (Netherlands)

    Landman, Jasper; Paineau, Erwan; Davidson, Patrick; Bihannic, Isabelle; Michot, Laurent J.; Philippe, Adrian Marie; Petukhov, Andrei V.; Lekkerkerker, Henk N W

    2014-01-01

    In this article, we present a study of the liquid crystal phase behavior of mixed suspensions of the natural smectite clay mineral beidellite and nonadsorbing colloidal silica particles. While virtually all smectite clays dispersed in water form gels at very low concentrations, beidellite displays a

  6. Trade-offs to obtain phase-only modulation with a twisted nematic liquid crystal display

    OpenAIRE

    Márquez Ruiz, Andrés; Gallego Rico, Sergi; Méndez Alcaraz, David Israel; Álvarez López, Mariela Lázara; Fernández Varó, Elena; Ortuño Sánchez, Manuel; Neipp López, Cristian; Beléndez Vázquez, Augusto; Pascual Villalobos, Inmaculada

    2007-01-01

    Phase-only modulation using liquid crystal displays (LCDs) is very interesting for many applications (optical signal processing, holographic data storage, ...), however, in general they offer a limited phase modulation depth. In this paper we show various alternatives in order to enhance the phase modulation depth.

  7. Electrolyte effects on the chiral induction and on its temperature dependence in a chiral nematic lyotropic liquid crystal.

    Science.gov (United States)

    Dawin, Ute C; Osipov, Mikhail A; Giesselmann, Frank

    2010-08-19

    We present a study on the effect of added CsCl and of temperature variation on the chiral induction in a chiral nematic lyotropic liquid crystal (LC) composed of the surfactant cesium perfluorooctanoate (CsPFO), water, and the chiral dopant d-Leucine (d-Leu). The chiral induction was measured as the helical pitch P. The role of the additives CsCl and d-Leu on the phase behavior is investigated and discussed. The thermal stabilization effect of CsCl is shown to lead to an apparent salt effect on the pitch when the pitch is compared at a constant temperature. This apparent effect is removed by comparing the pitch measured for different salt concentrations at a temperature relative to the phase-transition temperatures; thus, the real salt effect on the pitch is described. High salt concentrations are shown to increase the pitch, that is, hinder the chiral induction. The effect is discussed in terms of a decreased solubilization of the amphiphilic chiral solute d-Leu in the micelles due to the salt-induced screening of the surfactant head groups and the consequential denser packing of the surfactants. The temperature variation of the pitch is investigated for all CsCl concentrations and is found to be essentially independent of the salt concentration. The temperature variation is analyzed and discussed in the context of a theoretical model taking into account specific properties of lyotropic liquid crystals. A hyperbolic decrease of the pitch is found with increasing temperature, which is known, from thermotropic liquid crystals, to stem from pretransitional critical fluctuations close to the lamellar phase. However, the experimental data confirmed the theoretical prediction that, at high temperature, that is, far away from the transition into the lamellar phase, the pitch is characterized by a linear temperature dependence which is determined by a combination of steric and dispersion chiral interactions. The parameters of the theoretical expression for the pitch have

  8. Reexamination of the mean-field phase diagram of biaxial nematic liquid crystals: Insights from Monte Carlo studies

    Science.gov (United States)

    Kamala Latha, B.; Jose, Regina; Murthy, K. P. N.; Sastry, V. S. S.

    2015-07-01

    Investigations of the phase diagram of biaxial liquid-crystal systems through analyses of general Hamiltonian models within the simplifications of mean-field theory (MFT), as well as by computer simulations based on microscopic models, are directed toward an appreciation of the role of the underlying molecular-level interactions to facilitate its spontaneous condensation into a nematic phase with biaxial symmetry. Continuing experimental challenges in realizing such a system unambiguously, despite encouraging predictions from MFT, for example, are requiring more versatile simulational methodologies capable of providing insights into possible hindering barriers within the system, typically gleaned through its free-energy dependences on relevant observables as the system is driven through the transitions. The recent paper from this group [Kamala Latha et al., Phys. Rev. E 89, 050501(R) (2014), 10.1103/PhysRevE.89.050501], summarizing the outcome of detailed Monte Carlo simulations carried out employing an entropic sampling technique, suggested a qualitative modification of the MFT phase diagram as the Hamiltonian is asymptotically driven toward the so-called partly repulsive regions. It was argued that the degree of (cross) coupling between the uniaxial and biaxial tensor components of neighboring molecules plays a crucial role in facilitating a ready condensation of the biaxial phase, suggesting that this could be a plausible factor in explaining the experimental difficulties. In this paper, we elaborate this point further, providing additional evidence from curious variations of free-energy profiles with respect to the relevant orientational order parameters, at different temperatures bracketing the phase transitions.

  9. Nonlinear experimental dye-doped nematic liquid crystal optical transmission spectra estimated by neural network empirical physical formulas

    Science.gov (United States)

    Yildiz, Nihat; San, Sait Eren; Köysal, Oğuz

    2010-09-01

    In this paper, two complementary objectives related to optical transmission spectra of nematic liquid crystals (NLCs) were achieved. First, at room temperature, for both pure and dye (DR9) doped E7 NLCs, the 10-250 W halogen lamp transmission spectra (wavelength 400-1200 nm) were measured at various bias voltages. Second, because the measured spectra were inherently highly nonlinear, it was difficult to construct explicit empirical physical formulas (EPFs) to employ as transmittance functions. To avoid this difficulty, layered feedforward neural networks (LFNNs) were used to construct explicit EPFs for these theoretically unknown nonlinear NLC transmittance functions. As we theoretically showed in a previous work, a LFNN, as an excellent nonlinear function approximator, is highly relevant to EPF construction. The LFNN-EPFs efficiently and consistently estimated both the measured and yet-to-be-measured nonlinear transmittance response values. The experimentally obtained doping ratio dependencies and applied bias voltage responses of transmittance were also confirmed by LFFN-EPFs. This clearly indicates that physical laws embedded in the physical data can be faithfully extracted by the suitable LFNNs. The extraordinary success achieved with LFNN here suggests two potential applications. First, although not attempted here, these LFNN-EPFs, by such mathematical operations as derivation, integration, minimization etc., can be used to obtain further transmittance related functions of NLCs. Second, for a given NLC response function, whose theoretical nonlinear functional form is yet unknown, a suitable experimental data based LFNN-EPF can be constructed to predict the yet-to-be-measured values.

  10. Evolution of non-isothermal Landau-De Gennes nematic liquid crystals flows with singular potential

    Czech Academy of Sciences Publication Activity Database

    Feireisl, Eduard; Rocca, E.; Schimperna, G.; Zarnescu, A.

    2014-01-01

    Roč. 12, č. 2 (2014), s. 317-343. ISSN 1539-6746 R&D Projects: GA ČR GA201/09/0917 Institutional support: RVO:67985840 Keywords : liquid crystals * global existence of weak solutions * Navier-Stokes equations Subject RIV: BA - General Mathematics Impact factor: 1.120, year: 2014 http://intlpress.com/site/pub/pages/journals/items/cms/content/vols/0012/0002/a006/index.html

  11. 100 GHz electrically tunable planar Bragg grating via nematic liquid crystal overlay towards reconfigurable WDM networks

    OpenAIRE

    Adikan, Faisal Rafiq Mahamd; Gates, James C.; Major, Huw E.; Gawith, Corin B.E.; Smith, Peter G. R.; Dyadyusha, Andriy; Kaczmarek, Malgosia; Sparrow, Ian J.G.

    2007-01-01

    Novel liquid crystal-based integrated optical devices with >140GHz electrical tuning are presented for application towards reconfigurable wavelength division multiplexing (WDM) networks. Initial results with Bragg wavelength tuning covering five 25GHz WDM channel spacing have been achieved with 170V (peak-to-peak) sinusoidal voltages applied across electro-patterned ITO-covered glass electrodes placed 60?m apart. These prototype devices were fabricated using direct UV grating writing, with an...

  12. Global Well-Posedness with Large Oscillations and Vacuum to the Three-Dimensional Equations of Compressible Nematic Liquid Crystal Flows

    CERN Document Server

    Li, Jing; Zhang, Jianwen

    2012-01-01

    This paper is concerned with the three-dimensional equations of a simplified hydrodynamic flow modeling the motion of compressible, nematic liquid crystal materials. The authors establish the global existence of classical solution to the Cauchy problem with smooth initial data which are of small energy but possibly large oscillations with constant state as far-field condition which could be either vacuum or non-vacuum. The initial density is allowed to vanish and the spatial measure of the set of vacuum can be arbitrarily large, in particular, the initial density can even have compact support. As a byproduct, the large-time behavior of the solution is also studied.

  13. Doped ionic liquid crystals as effective weakly alignment media for polar solutes

    Science.gov (United States)

    Di Pietro, Maria Enrica; Celebre, Giorgio; De Luca, Giuseppina

    2016-06-01

    The ionic liquid crystal 1-dodecyl-3-methylimidazolium tetrafluoroborate slightly doped with water is presented as a promising NMR alignment medium for the measurement of residual dipolar couplings for polar molecules dissolved therein.

  14. Linear-dichroic infrared spectroscopy—Validation and experimental design of the new orientation technique of solid samples as suspension in nematic liquid crystal

    Science.gov (United States)

    Ivanova, B. B.; Simeonov, V. D.; Arnaudov, M. G.; Tsalev, D. L.

    2007-05-01

    A validation of the developed new orientation method of solid samples as suspension in nematic liquid crystal (NLC), applied in linear-dichroic infrared (IR-LD) spectroscopy has been carried out using a model system DL-isoleucine ( DL-isoleu). Accuracy, precision and the influence of the liquid crystal medium on peak positions and integral absorbances of guest molecules have been presented. Optimization of experimental conditions has been performed as well. An experimental design for quantitative evaluation of the impact of four input factors: the number of scans, the rubbing-out of KBr-pellets, the amount of studied compounds included in the liquid crystal medium and the ratios of Lorentzian to Gaussian peak functions in the curve fitting procedure on the spectroscopic signal at five different frequencies, indicating important specifities of the system has been studied.

  15. Phase separation of monomer in liquid crystal mixtures and surface morphology in polymer-stabilized vertical alignment liquid crystal displays

    Energy Technology Data Exchange (ETDEWEB)

    Lyu, Jae Jin; Lee, Jun Hyup; Kim, Kyeong Hyeon [Development Center, LCD Business, SAMSUNG Electronics Co. LTD., Tangjeong-Myeon, Asan, Chungnam 336-741 (Korea, Republic of); Kikuchi, Hirotsuku; Higuchi, Hiroki [Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga-Koen, Kasuga 816-8580 (Japan); Kim, Dae Hyun; Lee, Seung Hee, E-mail: jsquare.lyu@samsung.com, E-mail: lsh1@chonbuk.ac.kr [Department of BIN Fusion Technology and Department of Polymer-Nano Science and Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of)

    2011-08-17

    The polymer-stabilized vertically aligned (PS-VA) liquid crystal display (LCD) driving mode has high potential for manufacturing low power consuming displays due to the higher transmittance and fast response as compared with the existing patterned vertically aligned and multi-domain vertically aligned modes. In this paper we have investigated the reaction mechanisms of monomer-liquid crystal blends to form a surface pre-tilt angle of liquid crystal in vertical alignment LCD associated with a fishbone electrode structure. The observed sizes of polymer bumps formed on the substrates were found to be dependent on the exposed UV wavelength and were almost equal in both top and bottom substrates. When a large UV wavelength was used, the phase separation mechanism of monomer in PS-VA mode was found nearly isotropic rather than anisotropic in contrast to the previous studies.

  16. Field-induced periodic distortions in a nematic liquid crystal: deuterium NMR study and theoretical analysis.

    Science.gov (United States)

    Sugimura, A; Zakharov, A V

    2011-08-01

    The peculiarities in the dynamic of the director reorientation in a liquid crystal (LC) film under the influence of the electric E field directed at an angle α to the magnetic B field have been investigated both experimentally and theoretically. Time-resolved deuterium NMR spectroscopy is employed to investigate the field-induced director dynamics. Analysis of the experimental results, based on the predictions of hydrodynamic theory including both the director motion and fluid flow, provides an evidence for the appearance of the spatially periodic patterns in 4-n-pentyl-4'-cyanobiphenyl LC film, at the angles α>60∘, in response to the suddenly applied E. These periodic distortions produce a lower effective rotational viscosity. This gives a faster response of the director rotation than for a uniform mode, as observed in our NMR experiment. PMID:21929001

  17. The corkscrew instability of a Freedericksz domain wall in a nematic liquid crystal

    CERN Document Server

    Munoz, A D L; Müller, M; Schoepf, W; Rehberg, I

    2003-01-01

    A liquid crystal with slightly positive dielectric anisotropy is investigated in the planar configuration. This system allows for competition between electroconvection and the homogeneous Freedericksz transition, leading to a rather complicated bifurcation scenario. We report measurements of a novel instability leading to the 'corkscrew' pattern. This state is closely connected to the Freedericksz state as it manifests itself as a regular modulation along a Freedericksz domain wall, although its frequency dependence indicates that electroconvection must play a crucial role. It can be understood in terms of a pitchfork bifurcation from a straight domain wall. Quantitative characterization is performed in terms of amplitude, wavelength and relaxation time. Its wavelength is of the order of the probe thickness, while its ondulation amplitude is an order of magnitude smaller. The relaxation time is comparable to the one obtained for electroconvection.

  18. The corkscrew instability of a Freedericksz domain wall in a nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Munoz, Alberto de Lozar; Bock, Thomas; Mueller, Matthias; Schoepf, Wolfgang; Rehberg, Ingo [Experimentalphysik V, Universitaet Bayreuth, D-95440 Bayreuth (Germany)

    2003-06-01

    A liquid crystal with slightly positive dielectric anisotropy is investigated in the planar configuration. This system allows for competition between electroconvection and the homogeneous Freedericksz transition, leading to a rather complicated bifurcation scenario. We report measurements of a novel instability leading to the 'corkscrew' pattern. This state is closely connected to the Freedericksz state as it manifests itself as a regular modulation along a Freedericksz domain wall, although its frequency dependence indicates that electroconvection must play a crucial role. It can be understood in terms of a pitchfork bifurcation from a straight domain wall. Quantitative characterization is performed in terms of amplitude, wavelength and relaxation time. Its wavelength is of the order of the probe thickness, while its ondulation amplitude is an order of magnitude smaller. The relaxation time is comparable to the one obtained for electroconvection.

  19. Bifurcation properties of nematic liquid crystals exposed to an electric field: Switchability, bistability, and multistability

    KAUST Repository

    Cummings, L. J.

    2013-07-01

    Bistable liquid crystal displays (LCDs) offer the potential for considerable power savings compared with conventional (monostable) LCDs. The existence of two (or more) stable field-free states that are optically distinct means that contrast can be maintained in a display without an externally applied electric field. An applied field is required only to switch the device from one state to the other, as needed. In this paper we examine the basic physical principles involved in generating multiple stable states and the switching between these states. We consider a two-dimensional geometry in which variable surface anchoring conditions are used to control the steady-state solutions and explore how different anchoring conditions can influence the number and type of solutions and whether or not switching is possible between the states. We find a wide range of possible behaviors, including bistability, tristability, and tetrastability, and investigate how the solution landscape changes as the boundary conditions are tuned. © 2013 American Physical Society.

  20. Towards an optimal model for a bistable nematic liquid crystal display device

    KAUST Repository

    Cummings, L. J.

    2013-03-13

    Bistable liquid crystal displays offer the potential for considerable power savings compared with conventional (monostable) LCDs. The existence of two stable field-free states that are optically distinct means that contrast can be maintained in a display without an externally applied electric field. An applied field is required only to switch the device from one state to the other, as needed. In this paper we examine a theoretical model of a possible bistable device, originally proposed by Cummings and Richardson (Euro J Appl Math 17:435-463 2006), and explore means by which it may be optimized, in terms of optical contrast, manufacturing considerations, switching field strength, and switching times. The compromises inherent in these conflicting design criteria are discussed. © 2013 Springer Science+Business Media Dordrecht.

  1. Two-step electrical percolation in nematic liquid crystals filled with multiwalled carbon nanotubes

    Science.gov (United States)

    Tomylko, Serhiy; Yaroshchuk, Oleg; Lebovka, Nikolai

    2015-07-01

    Percolation of carbon nanotubes (CNTs) in liquid crystals (LCs) opens the way for a unique class of anisotropic hybrid materials with a complex dielectric constant widely controlled by CNT concentration. Percolation in such systems is commonly described as a one-step process starting at a very low loading of CNTs. In the present study the two-step percolation was observed in the samples of thickness 250 μ m obtained by pressing the suspension between two substrates. The first threshold concentration, Cnp1˜10-4 wt.%, was sensitive to temperature and phase state of LC, while the second one, Cnp2˜10-1 wt.%, remained practically unchanged in the temperature tests. The two-stage nature of percolation was explained on a base of mean-field theory assuming core-shell structure of CNTs.

  2. Trajectory attractors for the Sun–Liu model for nematic liquid crystals in 3D

    International Nuclear Information System (INIS)

    In this paper we prove the existence of a trajectory attractor (in the sense of Chepyzhov and Vishik) for a nonlinear PDE system obtained from a 3D liquid crystal model accounting for stretching effects. The system couples a nonlinear evolution equation for the director d (introduced in order to describe the preferred orientation of the molecules) with an incompressible Navier–Stokes equation for the evolution of the velocity field u. The technique is based on the introduction of a suitable trajectory space and of a metric accounting for the double-well type nonlinearity contained in the director equation. Finally, a dissipative estimate is obtained by using a proper integrated energy inequality. Both the cases of (homogeneous) Neumann and (non-homogeneous) Dirichlet boundary conditions for d are considered. (paper)

  3. Modeling the Mechanisms of the Photomechanical Response of a Nematic Liquid Crystal Elastomer

    CERN Document Server

    Dawson, Nathan J; Neal, Jeremy; Luchette, Paul; Palffy-Muhoray, Peter

    2011-01-01

    Recent studies of azo-dye doped liquid crystal elastomers show a strong photomechanical response. We report on models that predict experimental results that suggest photothermal heating is the dominant mechanism in a planar constrained geometry. We compare our models with experiments to determine key material parameters, which are used to predict the dynamical response as a function of intensity. We show that a local strain from photothermal heating and a nonlocal strain from thermal diffusion is responsible for the observed length changes over time. This work both elucidates the fundamental mechanisms and provides input for the design of photomechanical optical devices, which have been shown to have the appropriate properties for making smart materials.

  4. Effects of Flexibility on Liquid Crystalline Polymer Behavior: The Nematic Broken Road

    Science.gov (United States)

    Leal, L. Gary; Charuv, Chaubal

    1998-03-01

    A new theory for Liquid Crystalline Polymers is developed and its behavior in simple shear flow is analyzed. The theory accounts for molecular flexibility by employing a microstructure consisting of two rigid rods linked by a joint with a tunable stiffness. The probability distribution function equation for the orientation of the arms of the broken rod is derived. The adaptation of the Smoothed Particle Hydrodynamics (SPH) technique for obtaining numerical solutions to this theory is detailed. The behavior of the theory at equilibrium is derived analytically and compared with numerical results; the SPH technique is then used to obtain results in flow. It is found that in the limit of a nearly stiff joint, the model gives behavior that is very similar to that of rigid rod polymers, the only difference being a lesser tendency to tumble due to greater variation in the order parameter. For nearly free joints, the shear flow induces interesting dynamics for the transition between states with the arms outstretched and those where they are folded up (so-called ''hairpins'' of main-chain LCPs).

  5. Backflow in an Inverse Twisted Nematic Liquid Crystal Cell%反扭曲向列相液晶盒中的引流

    Institute of Scientific and Technical Information of China (English)

    张志东; 姜丽; 魏怀鹏

    2006-01-01

    Based upon Erickson-Leslie hydrodynamic equations, we study an inverse twisted nematic liquid crystal cell, in which the liquid crystal is untwisted in the field-off state and twisted in the field-on state. The time evolution of director configuration and the velocity of flow are obtained. An abnormal director profile caused by the backflow appears after the switch of a holding voltage.%根据Erickson-Leslie流体动力学方程,研究了反扭曲向列相液晶盒.该液晶盒只有在有外场的情况下才会扭曲.通过计算模拟得出指向矢构形和流速与时间的关系.在外加电压情况下,由于存在引流效应导致指向矢分布不正常.

  6. Deuteron and proton NMR study of D2, p-dichlorobenzene and 1,3,5-trichlorobenzene in bimesogenic liquid crystals with two nematic phases

    Science.gov (United States)

    Burnell, E. E.; Ahmed, Z.; Welch, C.; Mehl, G. H.; Dong, R. Y.

    2016-08-01

    The solutes dideuterium, 1,3,5-trichlorobenzene and p-dichlorobenzene (pdcb) are co-dissolved in a 61/39 wt% mixture of CBC9CB/5CB, a bimesogenic liquid crystal with two nematic phases. NMR spectra are collected for each solute. The local electric field gradient (FZZ) is obtained from the dideuterium spectrum. A double Maier-Saupe potential (MSMS) is used to rationalize the order parameters of pdcb. The liquid-crystal fields G1 and G2 are taken to be due to size and shape interactions and interactions between the solute molecular quadrupole and the mean FZZ of the medium. The FZZ 's obtained from D2 and G2 (from pdcb) are compared and discussed.

  7. Substrate-induced bulk alignment of liquid crystals

    DEFF Research Database (Denmark)

    Zhang, Zhengping; Chakrabarti, A.; Mouritsen, Ole G.;

    1996-01-01

    The Gay-Berne model for liquid crystals in the presence of a substrate surface is studied using the hybrid Monte Carlo method. A simple non-mean-field substrate-molecule potential is proposed to describe the effects of rubbed polymer-coated substrates on the liquid crystals. Effects of the...

  8. Photo polymerization-induced vertical phase separation and homeotropic alignment in liquid crystal and polymer mixtures

    International Nuclear Information System (INIS)

    We presented a novel method for the homeotropic alignment of LC by using the irradiation of UV light on the LC/NOA65 mixture cell, in which the photo-initiated-polymerization-induced phase separation lowers the surface energy. When the amount of polymer content is sufficiently small, the gravel and network patterns were formed at the substrates via the vertical phase separation. We found that surface roughness plays an important role in the formation of the homeotropic alignment of LC. We also observed the alignment transition of the cells by varying the mixing ratio of LC/NOA65 or the UV radiation time. Furthermore, the present proposed method has great potential for application in display devices. For decades, studies on the alignment of liquid crystal (LC) molecules have been of significant interest due to their immediate applications for display devices and the intriguing physiochemical properties they exhibit at the surface of mixtures. Usually, homeotropic (or vertical) alignment, in which the long axes of the LC molecules are oriented in a direction perpendicular to the surface, is achieved by using surfactants such as lecithin, silanes or polyimide. Recently homeotropic alignment of liquid crystal molecules was achieved by irradiating photosensitive polymers, by doping nanoparticles into LC, by utilizing nano/micro patterns, or by incorporating self-assembled monolayers (SAMs). However, a clear understanding about the alignment mechanism is still elusive. In this paper, we report a novel method for homeotropic alignment of LC by utilizing the phase separation of LC/polymer mixtures

  9. Regular and Chaotic Flow Behavior and Orientational Dynamics of Tumbling Nematics

    Science.gov (United States)

    Hess, S.; Heidenreich, S.; Ilg, P.; Kröger, M.

    2006-05-01

    We consider liquid crystalline polymers under plane Couette flow and investigate the influence of fluctuating shear rates on the orientational dynamics. With help of phase portraits and time evolution diagrams of the alignment tensor components, we discuss the effect of fluctuations on the flow-aligned, isotropic and periodic solutions. To explore the effect of fluctuations on the chaotic behavior we calculated the greatest Lyapunov exponent for different fluctuation strengths. We found that fluctuations of the shear rate in general have little effect on the dynamics of tumbling nematics. Further we present a new amended potential modeling the isotropic-to-nematic transition. In contrast to the Landau-de Gennes potential our potential has the advantage to restrict the order parameter to physically admissible values. In the end we present some results of the orientational dynamics for a spatially inhomogeneous system.

  10. Molecular orientation behavior of chiral nematic liquid crystals based on the presence of blue phases using polarized microscopic FT-IR spectroscopy

    Science.gov (United States)

    Matsumura, Masanori; Katayama, Norihisa

    2016-07-01

    Study on molecular orientation behavior of highly twisted chiral nematic liquid crystals (N∗LCs) expressing blue phases (BPs) is important for developing new devices. This study examines the change of molecular orientation of N∗LCs due to the presence of BPs. Polarized microscopic FT-IR spectroscopy was used to study the in- and out-of-plane molecular orientations of N∗LCs that undergo a phase transition involving BPs. The band intensity ratio of CN to CH2 stretching modes (CN/CH2) in the IR spectra was used to determine the orientation of N∗LC molecules. The measured spectra indicated that the helical axis of N∗LC molecules was perpendicular to the substrate before heating and inclined on the substrate after cooling the sample which has phase transition from BP I to chiral nematic (N∗). The N∗LC molecule in the cell of rubbed orientation film exhibited the in-plane anisotropy after a heating-cooling ramp only in samples that passed through BP I. These results indicate that the changes of molecular orientation of N∗LC by phase transition are affected by BP I.

  11. Comparison of photoinduced reorientation of ortho-, meta-, and para-methyl red-doped nematic liquid crystals on rubbed polyimide

    Science.gov (United States)

    Statman, David; Statman, Ariel T.; Wozniak, Kaitlin; Brennan, Christopher

    2015-08-01

    We compare the photoinduced reorientation of the easy axis on rubbed polyimide surfaces for the nematic E7 doped with three isomers of methyl red; ortho, meta, and para. Using optical techniques, the angle and the pitch of the director at the polymer surface were measured before, during, and after photoexcitation of the dye. Optical absorbances were also measured before and after photoexcitation. Extrapolation lengths, hence anchoring energies, were determined with the on/off application of a magnetic field for meta- and para-methyl red-doped nematics. Because of an elastic reorientation of the easy axis in the presence of the magnetic field, we could not determine the extrapolation length of the ortho-methyl red-doped nematic. Our results confirm that photoinduced reorientation is facilitated by desorption of all dyes from the polymer surface. While there is little evidence of weak photoinduced adsorption of meta- and para-methyl red to the surface during photoexcitation, there is strong evidence of photoinduced adsorption of ortho-methyl red, which is long lasting.

  12. Ultraviolet-light-treated polyimide alignment layers for polarization-independent liquid crystal Fresnel lenses

    Science.gov (United States)

    Hwang, S.-J.; Chen, T.-A.; Lin, K.-R.; Jeng, S.-C.

    2012-04-01

    The surface energy of a conventional homeotropic polyimide (PI) alignment layer was altered via ultraviolet (UV) light irradiation, and the pretilt angle of the PI was changed along with the surface energy. The surface energy can be controlled by either UV exposure time or irradiation intensity. A switchable liquid crystal Fresnel lens (LCFL) was created by the UV-treated alignment layers to form a Fresnel zone-distribution hybrid alignment, vertically aligned and hybrid aligned LC in the odd and even zones, respectively. The LCFL was made polarization-independent by circular buffing, and it had a diffraction efficiency of ˜22% at a low driving voltage of ˜1.2 V.

  13. Alignment of nanostructure templated from lyotropic liquid crystals in membrane preparation

    International Nuclear Information System (INIS)

    This project is developing a new class of efficient and low-cost porous membrane materials for water treatment and desalination contributing to alleviate water shortage problems in Australia. We have recently synthesized well oriented Lyotropic liquid crystal (LLC) templated membranes with an average diameter of 2mm and enhanced the retention of the original order of nanostructure after photopolymerization. We will further improve the alignment of lyotropic liquid crystal when template is formed. These LLC membranes will have great potential to significantly reduce the energy used in the desalination processes. The alignment of the LLC nanostructure is very significant and challenging. Long-range orientational order of LLC has potential applications, such as tissue engineering, gas separation, water purification, and high-density storage media. However, polydomain structures of LLC samples are randomly distributed and alignment of the lyotropic liquid crystals of the template during the membrane synthesis process will improve the performance. Magnetic field and electric field are employed to align the LLC nanostructure in nanoparticles-doped samples before polymerization. After alignment, it is expected that the nanostructure pores are well oriented in the direction perpendicular to the surface of membrane. Small Angle Scattering of X-ray and Neutron will be performed as the main means to characterize and evaluate the alignment of the LLC nanostructure.

  14. Liquid crystal quenched orientational disorder at an AFM-scribed alignment surface.

    Science.gov (United States)

    Pendery, J S; Atherton, T J; Nobili, M; Petschek, R G; Lacaze, E; Rosenblatt, C

    2015-03-21

    A polyimide substrate was scribed using the stylus of an atomic force microscope, then covered with a nematic liquid crystal. The fiber from a near field scanning optical microscope was immersed into the liquid crystal and rastered approximately 80 nm above the surface, thereby obviating smearing effects that occur in thicker samples. By appropriate averaging of multiple data sets, a histogram of the "frozen-in" director deviation Δφ from the average easy axis was obtained, having a full-width-half-maximum of ∼0.02 rad. Additionally, the spatial autocorrelation function of Δφ was extracted, where the primary correlation length was found to be comparable to, but larger than, the liquid crystal's extrapolation length. A secondary characteristic length scale of a few μm was observed, and is thought to be an artifact due to material ejection during the scribing process. Our results demonstrate the utility of nanoscale imaging of the interface behavior inside the liquid crystal. PMID:25643289

  15. Patterning-induced surface chirality and modulation of director twist in a nematic cell.

    Science.gov (United States)

    Choi, Yoonseuk; Atherton, Timothy; Ferjani, Sameh; Petschek, Rolfe G; Rosenblatt, Charles

    2009-12-01

    A substrate coated with a polyimide alignment layer is scribed bidirectionally with the stylus of an atomic force microscope to create an easy axis for liquid-crystal orientation. The resulting noncentrosymmetric topography breaks two-dimensional inversion symmetry and results in a spatial amplitude modulation of an imposed twisted nematic state. This is observed optically as spatially periodic light and dark stripes. When the alignment layer is scribed unidirectionally the centrosymmetric topography maintains inversion symmetry, and no stripes are observed. The appearance of the twist modulation is consistent with a chiral term in the free energy. PMID:20365110

  16. Optical-to-optical interface device. [consisting of two transparent electrodes on glass substrates that enclose thin film photoconductor and thin layer of nematic liquid crystal

    Science.gov (United States)

    Jacobson, A. D.

    1973-01-01

    Studies were conducted on the performance of a photoactivated dc liquid crystal light valve. The dc light valve is a thin film device that consists of two transparent electrodes, deposited on glass substrates, that enclose a thin film photoconductor (cadmium sulfide) and a thin layer of a nematic liquid crystal that operates in the dynamic scattering mode. The work was directed toward application of the light valve to high resolution non-coherent light to coherent light image conversion. The goal of these studies was to improve the performance and quality of the already existing dc light valve device and to evaluate quantitatively the properties and performance of the device as they relate to the coherent optical data processing application. As a result of these efforts, device sensitivity was improved by a factor of ten, device resolution was improved by a factor of three, device lifetime was improved by two-orders of magnitude, undesirable secondary liquid crystal scattering effects were eliminated, the scattering characteristics of the liquid crystal were thoroughly documented, the cosmetic quality of the devices was dramatically improved, and the performance of the device was fully documented.

  17. Electric field induced biaxiality and the electro-optic effect in a bent-core nematic liquid crystal

    Science.gov (United States)

    Nagaraj, Mamatha; Panarin, Y. P.; Manna, U.; Vij, J. K.; Keith, C.; Tschierske, C.

    2010-01-01

    We report the observation of a biaxial nematic phase in a bent-core molecular system using polarizing microscopy, electro-optics, and dielectric spectroscopy, where we find that the biaxiality exists on a microscopic scale. An application of electric field induces a macroscopic biaxiality and in consequence gives rise to electro-optic switching. This electro-optic effect shows significant potential in applications for displays due to its fast high-contrast response. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field.

  18. A new family of four-ring bent-core nematic liquid crystals with highly polar transverse and end groups

    Directory of Open Access Journals (Sweden)

    Kalpana Upadhyaya

    2013-01-01

    Full Text Available Non-symmetrically substituted four-ring achiral bent-core compounds with polar substituents, i.e.., chloro in the bent or transverse direction in the central core and cyano in the lateral direction at one terminal end of the molecule, are designed and synthesized. These molecules possess an alkoxy chain attached at only one end of the bent-core molecule. The molecular structure characterization is consistent with data from elemental and spectroscopic analysis. The materials thermal behaviour and phase characterization have been investigated by differential scanning calorimetry and polarizing microscopy. All the compounds exhibit a wide-ranging monotropic nematic phase.

  19. Alignment and Graphene-Assisted Decoration of Lyotropic Chromonic Liquid Crystals Containing DNA Origami Nanostructures.

    Science.gov (United States)

    Martens, Kevin; Funck, Timon; Kempter, Susanne; Roller, Eva-Maria; Liedl, Tim; Blaschke, Benno M; Knecht, Peter; Garrido, José Antonio; Zhang, Bingru; Kitzerow, Heinz

    2016-03-01

    Composites of DNA origami nanostructures dispersed in a lyotropic chromonic liquid crystal are studied by polarizing optical microscopy. The homogeneous aqueous dispersions can be uniformly aligned by confinement between two glass substrates, either parallel to the substrates owing to uniaxial rubbing or perpendicular to the substrates using ozonized graphene layers. These opportunities of uniform alignment may pave the way for tailored anisometric plasmonic DNA nanostructures to photonic materials. In addition, a decorated texture with nonuniform orientation is observed on substrates coated with pristine graphene. When the water is allowed to evaporate slowly, microscopic crystal needles appear, which are aligned along the local orientation of the director. This decoration method can be used for studying the local orientational order and the defects in chromonic liquid crystals. PMID:26849188

  20. Computer simulation of confined liquid crystal dynamics

    CERN Document Server

    Webster, R E

    2001-01-01

    are performed of the formation of structures in confined smectic systems where layer tilt is induced by an imposed surface pretilt. Results show that bookshelf, chevron and tilled layer structures are observable in a confined Gay-Berne system. The formation and stability of the chevron structure are shown to be influenced by surface slip. Results are presented from a series of simulations undertaken to determine whether dynamic processes observed in device-scale liquid crystal cells confined between aligning substrates can be simulated in a molecular system using parallel molecular dynamics of the Gay-Berne model. In a nematic cell, on removal of an aligning field, initial near-surface director relaxation can induce flow, termed 'backflow' in the liquid. This, in turn, can cause director rotation, termed 'orientational kickback', in the centre of the cell. Simulations are performed of the relaxation in nematic systems confined between substrates with a common alignment on removal of an aligning field. Results...

  1. Direct visualization and measurement of the extrapolation length on cooling toward the nematic-smectic-A phase transition temperature.

    Science.gov (United States)

    Choi, Yoonseuk; Rosenblatt, Charles

    2010-05-01

    A herringbone "easy axis" pattern is scribed into a polyimide alignment layer for liquid-crystal orientation using the stylus of an atomic force microscope. Owing to the liquid crystal's bend elasticity K33 , the nematic director is unable to follow the sharp turn in the scribed easy axis, but instead relaxes over an extrapolation length L=K33/W2φ, where W2φ is the quadratic azimuthal anchoring strength coefficient. By immersing a tapered optical fiber into the liquid crystal, illuminating the fiber with polarized light, and scanning the fiber close to the substrate, a visualization and direct measurement of L are obtained on approaching the nematic-smectic- A phase transition temperature T NA from above. L is found to exhibit a sharp pretransitional increase near T NA, consistent with a diverging bend elastic constant. PMID:20866248

  2. Vortex and disclination structures in a nematic-superconductor state

    OpenAIRE

    Barci, Daniel G.; Clarim, Rafael V.; Júnior, Nei L. Silva

    2016-01-01

    The nematic-superconductor state, an example of a quantum liquid crystal that breaks gauge as well as rotation invariance, was conjecture to exist in the pseudogap regime of the cuprates high $T_c$ superconductors. We present a detailed study of the structure of topological defects supported by the nematic-superconductor state. By means of a Ginzburg-Landau approach, we study the main relevant imprints on the superconductor order parameter caused by nematicity. Due to a geometrical coupling, ...

  3. Improved liquid crystal pretilt angles by patterned dual alignment coating structures.

    Science.gov (United States)

    Wu, G M; Chien, H W; Chen, C N; Lin, C Y; Huang, J A; Zeng, H L

    2010-07-01

    The pretilt angles for the optically compensated bend (OCB) mode liquid crystals have been improved using novel patterned dual alignment coating structures in this study. The transition from the splay configuration to the bend configuration can thus be effectively reduced. The dual alignment coating structures consisted of a horizontal alignment polyimide (PI) and a patterned vertical alignment liquid crystal polymer (LCP). Three patterning masks were designed for the photolithography process. The pretilt angles were demonstrated to be increased to 34 degrees for the triangle lattice array-patterned cells. It became 31 degrees for the square lattice array-patterned cells, and 24 degrees for the honeycomb lattice array-patterned cells. The improved pretilt angles were illustrated by the force balance model that can be predicted by the LCP area ratio. The effective control over the pretilt angle could improve the response time to 2 ms when the voltage was ramped up to 5.5 V for the OCB mode liquid crystal devices. PMID:21128462

  4. Liquid crystal alignment on inkjet printed and air-buffed polyimide with nano-grove surface

    International Nuclear Information System (INIS)

    We have found that liquid crystal (LC) can be aligned on an inkjet printed and air-buffed polyimide (PI) surface. Surface anisotropy is introduced by inkjet printing and air blowing from a PI ink cartridge and an empty cartridge of an inkjet printer, respectively. LC molecules align on the PI surfaces with the nano-scale grooves, which are validated with atomic force microscope images. The pretilt angles of the LCs could be varied from 0 deg. to 90 deg., by controlling the composition of a mixture of homogeneous and homeotropic PIs.

  5. Interfacial and morphological features of a twist-bend nematic drop.

    Science.gov (United States)

    Krishnamurthy, Kanakapura S; Kumar, Pramoda; Palakurthy, Nani B; Yelamaggad, Channabasaveshwar V; Virga, Epifanio G

    2016-06-14

    In this experimental and theoretical study, we examine the equilibrium shapes of quasi-two-dimensional twist-bend nematic (Ntb) drops formed within a planarly aligned nematic layer of the liquid crystal CB7CB. Initially, at the setting point of the Ntb phase, the drops assume a nonequilibrium cusped elliptical geometry with the major axis orthogonal to the director of the surrounding nematic fluid; this growth is governed principally by anisotropic heat diffusion. The drops attain equilibrium through thermally driven dynamical evolution close to their melting temperature. They are associated with a characteristic twin-striped morphology that transforms into the familiar focal conic texture as the temperature is lowered. At equilibrium, large millimetric drops are tactoidlike, elongated along the director of the surrounding nematic fluid. This geometry is explained using a mathematical model that features two dimensionless parameters, of which one is the structural cone angle of the Ntb phase and the other is the relative strength of mismatch elastic energy at the drop's interface. Both parameters are extracted from the observations by measuring the aspect ratio of the equilibrium shapes and the inner corner angle of the cusps. PMID:27162094

  6. Liquid crystal pretilt angle control using adjustable wetting properties of alignment layers

    International Nuclear Information System (INIS)

    The authors demonstrate the production of amorphous fluorinated carbon (a-C:F) thin film with adjustable wetting properties, inducing variable liquid crystal (LC) pretilt angles. To control the surface wetting properties, they apply a dual radio frequency magnetron system with a controlled power ratio of targets. In this manner we obtain various compositional surfaces with fluorine and carbon components and adjust the surface energy with regard to the various compositions. Whereas the fluorine-rich a-C:F layer shows a preference for homeotropic (vertical) LC alignment, the carbon-rich a-C:F layer shows a planar LC alignment. To achieve uniform LC alignment with a proper pretilt angle, an accelerated Ar+ ion beam irradiates the films after the deposition process. The ion beam selectively destroys the surface bonding of the a-C:F films, yielding an intermediate pretilt angle

  7. Critical Slowing of Density Fluctuations Approaching the Isotropic-Nematic Transition in Liquid Crystals: 2D IR Measurements and Mode Coupling Theory.

    Science.gov (United States)

    Sokolowsky, Kathleen P; Bailey, Heather E; Hoffman, David J; Andersen, Hans C; Fayer, Michael D

    2016-07-21

    Two-dimensional infrared (2D IR) data are presented for a vibrational probe in three nematogens: 4-cyano-4'-pentylbiphenyl, 4-cyano-4'-octylbiphenyl, and 4-(trans-4-amylcyclohexyl)-benzonitrile. The spectral diffusion time constants in all three liquids in the isotropic phase are proportional to [T*/(T - T*)](1/2), where T* is 0.5-1 K below the isotropic-nematic phase transition temperature (TNI). Rescaling to a reduced temperature shows that the decays of the frequency-frequency correlation function (FFCF) for all three nematogens fall on the same curve, suggesting a universal dynamic behavior of nematogens above TNI. Spectral diffusion is complete before significant orientational relaxation in the liquid, as measured by optically heterodyne detected-optical Kerr effect (OHD-OKE) spectroscopy, and before any significant orientational randomization of the probe measured by polarization selective IR pump-probe experiments. To interpret the OHD-OKE and FFCF data, we constructed a mode coupling theory (MCT) schematic model for the relationships among three correlation functions: ϕ1, a correlator for large wave vector density fluctuations; ϕ2, the orientational correlation function whose time derivative is the observable in the OHD-OKE experiment; and ϕ3, the FFCF for the 2D IR experiment. The equations for ϕ1 and ϕ2 match those in the previous MCT schematic model for nematogens, and ϕ3 is coupled to the first two correlators in a straightforward manner. Resulting models fit the data very well. Across liquid crystals, the temperature dependences of the coupling constants show consistent, nonmonotonic behavior. A remarkable change in coupling occurs at ∼5 K above TNI, precisely where the rate of spectral diffusion in 5CB was observed to deviate from that of a similar nonmesogenic liquid. PMID:27363680

  8. Diffusivity Maximum in a Reentrant Nematic Phase

    Directory of Open Access Journals (Sweden)

    Martin Schoen

    2012-06-01

    Full Text Available We report molecular dynamics simulations of confined liquid crystals using the Gay–Berne–Kihara model. Upon isobaric cooling, the standard sequence of isotropic–nematic–smectic A phase transitions is found. Upon further cooling a reentrant nematic phase occurs. We investigate the temperature dependence of the self-diffusion coefficient of the fluid in the nematic, smectic and reentrant nematic phases. We find a maximum in diffusivity upon isobaric cooling. Diffusion increases dramatically in the reentrant phase due to the high orientational molecular order. As the temperature is lowered, the diffusion coefficient follows an Arrhenius behavior. The activation energy of the reentrant phase is found in reasonable agreement with the reported experimental data. We discuss how repulsive interactions may be the underlying mechanism that could explain the occurrence of reentrant nematic behavior for polar and non-polar molecules.

  9. Ion-induced pattern formation on indium tin oxide for alignment of liquid crystals

    International Nuclear Information System (INIS)

    Indium tin oxide (ITO) is broadly used as a transparent conducting material for electrodes in optoelectronic devices. Irradiation of ITO with low energy ions can result in the formation of periodic surface nanopatterns which can serve as an alternative for the polymer alignment layer in liquid crystal devices. We investigated the formation of the ion-induced surface nanopatterns on ITO with focus on the influence of the crystalline structure of the material. We find that the crystallinity plays a crucial role in the pattern formation, with no pattern developing on an amorphous ITO surface. We discuss these findings in the context of the state-of-the-art theory for ion-induced patterning. We show that the ion-induced pattern plays a critical role in the liquid crystal alignment on ITO surfaces

  10. Ion-induced pattern formation on indium tin oxide for alignment of liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Škereň, T., E-mail: tomas.skeren@fjfi.cvut.cz [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven Belgium (Belgium); Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, Břehová 7, 115 19 Prague 1 (Czech Republic); Doornaert, D. [Laboratory for Acoustics and Thermal Physics, Department of Physics and Astronomy, KU Leuven, B-3001 Heverlee (Belgium); Wave Propagation and Signal Processing Research Group, KU Leuven Campus Kortrijk, E. Sabbelaan 53, B-8500 Kortrijk (Belgium); Glorieux, C. [Laboratory for Acoustics and Thermal Physics, Department of Physics and Astronomy, KU Leuven, B-3001 Heverlee (Belgium); Modarresi, H. [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven Belgium (Belgium); Guan, T. [Departement Elektrotechniek ESAT-MICAS, KU Leuven, Kasteelpark Arenberg 10, B-3001 Leuven (Belgium); Temst, K. [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven Belgium (Belgium); Vandervorst, W. [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven Belgium (Belgium); IMEC, Kapeldreef 75, B-3001 Leuven (Belgium); Vantomme, A. [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven Belgium (Belgium)

    2015-08-31

    Indium tin oxide (ITO) is broadly used as a transparent conducting material for electrodes in optoelectronic devices. Irradiation of ITO with low energy ions can result in the formation of periodic surface nanopatterns which can serve as an alternative for the polymer alignment layer in liquid crystal devices. We investigated the formation of the ion-induced surface nanopatterns on ITO with focus on the influence of the crystalline structure of the material. We find that the crystallinity plays a crucial role in the pattern formation, with no pattern developing on an amorphous ITO surface. We discuss these findings in the context of the state-of-the-art theory for ion-induced patterning. We show that the ion-induced pattern plays a critical role in the liquid crystal alignment on ITO surfaces.

  11. Evidence for a jacketed nematic polymer

    OpenAIRE

    Hardouin, F.; Mery, S.; Achard, M.; Noirez, L.; Keller, P.

    1991-01-01

    The evidence for a “jacketed” structure at the scale of the chain dimensions in the nematic phase of a “side-on fixed” liquid crystal polysiloxane is reported by using small angle neutron scattering. We relate this anisotropy of chain conformation to the first measurements of the rotational viscosity coefficient in this new type of liquid crystal side-chain polymer.

  12. Controlling pre-tilt angles of liquid crystal using mixed polyimide alignment layer.

    Science.gov (United States)

    Wu, Wei-Yen; Wang, Chen-Chen; Fuh, Andy Y

    2008-10-13

    Three approaches to controlling liquid crystal (LC) pre-tilt angle in a cell are demonstrated using a polyimide (PI) alignment layer on substrates, in the form of a mixture of horizontal (H) and vertical (V) polyimides. The concentration ratio of H- to V-PI, baking temperature, and rubbing strength influence the pre-tilt angle, and highlight parameters for controlling the pre-tilt angle of an LC cell. Finally, a variable polarization converter is demonstrated using this approach. PMID:18852824

  13. Director tumbling of nematic wormlike micelles under shear: time-resolved rheo-NMR experiments

    International Nuclear Information System (INIS)

    Nematic liquid crystals show a complex flow behavior due to the coupling between orientation and flow. Some materials show a stable director orientation in steady shear flow (flow aligning), while for others no stable director orientation exists (tumbling). Director tumbling gives rise to oscillations of shear and normal stresses in rheological experiments and can be detected by optical methods, for example by microscopy or birefringence measurements. We have used deuterium NMR spectroscopy to observe shear-induced director orientations. In the lyotropic system cetylpyridinium chloride/hexanol/brine, which forms a nematic phase of wormlike micelles, time-resolved observations of the director orientation by means of deuterium NMR spectroscopy of D2O have been possible for the first time. The time-dependence of the director orientations in both shear start-up and flow-reversal experiments will be presented. (orig.)

  14. A polarization-independent liquid crystal phase modulation using polymer-network liquid crystal with orthogonal alignment layers

    Science.gov (United States)

    Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih; Lin, Yi-Hsin

    2012-10-01

    A polarization-independent liquid crystal (LC) phase modulation using polymer-network liquid crystals with orthogonal alignments layers (T-PNLC) is demonstrated. T-PNLC consists of three layers. LC directors in the two layers near glass substrates are orthogonal to each other. In the middle layer, LC directors are perpendicular to the glass substrate. The advantages of such T-PNLC include polarizer-free, larger phase shift (~0.4π rad) than the residual phase type (<0.05π rad), and low operating voltage (< 30Vrms). It does not require bias voltage for avoiding scattering because the refractive index of liquid crystals matches that of polymers. The phase shift of T-PNLC is affected by the cell gap and the curing voltages. The potential applications are laser beam steering, spatial light modulators and electrically tunable micro-lens arrays.

  15. Hierarchical organization in liquid crystal-in-liquid crystal emulsions.

    Science.gov (United States)

    Mushenheim, Peter C; Abbott, Nicholas L

    2014-11-21

    We report the formation and characterization of hierarchical ordering in systems comprised of micrometer-sized droplets of thermotropic nematic liquid crystals (LCs) dispersed in continuous nematic phases of a lyotropic chromonic LC (disodium cromoglycate (DSCG)). Significantly, we find the orientations of the two LC phases to be coupled, with nematic droplets of 4'-pentyl-4-cyanobiphenyl (5CB) exhibiting a bipolar configuration with an axis of symmetry aligned orthogonal to the far-field director of the DSCG phase. We determine that this coupling of orientations does not result from either anisometric LC droplet shape or interfacial ionic phenomena but rather is consistent with the influence of van der Waals interactions that arise from the anisotropic polarizabilities of nematic 5CB (Δn = +0.18) and DSCG (Δn = -0.02) phases. We also find that it is possible to rotate and uniformly align the nematic droplets by using a weak magnetic field (B ∼ 0.3 T). An analysis of the dynamics of relaxation of the orientations of the 5CB droplets following removal of the magnetic field reveals the DSCG and 5CB droplets to be coupled by energies of ∼10(4) kT, consistent with a simple theoretical estimate of the influence of anisotropic van der Waals interactions. We also observed the nematic 5CB droplets to form dimers and larger assemblies mediated by the elasticity of the nematic DSCG. Overall, these results reveal that LC-in-LC emulsions define a new class of hierarchically ordered soft matter in which both thermotropic and lyotropic LCs are coupled in their ordering. PMID:25278032

  16. Multi-Particle Collision Dynamics Algorithm for Nematic Fluids

    OpenAIRE

    Shendruk, Tyler N.; Yeomans, Julia M.

    2015-01-01

    Research on transport, self-assembly and defect dynamics within confined, flowing liquid crystals requires versatile and computationally efficient mesoscopic algorithms to account for fluctuating nematohydrodynamic interactions. We present a multi-particle collision dynamics (MPCD) based algorithm to simulate liquid-crystal hydrodynamic and director fields in two and three dimensions. The nematic-MPCD method is shown to successfully reproduce the features of a nematic liquid crystal, includin...

  17. Correlation between hydrophobic and molecular shape descriptors and retention data of polycyclic aromatic hydrocarbons in reversed-phase chromatography on non-liquid-crystalline, nematic, and smectic stationary phases

    Energy Technology Data Exchange (ETDEWEB)

    Gritti, F. [E.N.S.C.P.B. Universite Bordeaux, Pessac (France); C.R.P.P., CNRS, Universite Bordeaux, Pessac (France); Sourigues, S.; Felix, G. [E.N.S.C.P.B. Universite Bordeaux, Pessac (France); Achard, M.F.; Hardouin, F. [C.R.P.P., CNRS, Universite Bordeaux, Pessac (France)

    2002-07-01

    The local anisotropic ordering of side-chain liquid-crystalline polymer (SCLCP) stationary phases has been revealed statistically. For this purpose the RP HPLC separation of polycyclic aromatic hydrocarbons (PAH) on silica coated with three classes (non-liquid-crystalline, nematic, and smectic) of side-chain polymer (SCP) has been compared. The logarithm of the capacity factor (log k) was correlated with three PAH descriptors - the connectivity index ({chi}) or the hydrophobic fragmental constant (log P), the length-to-breadth ratio (L/B), and a non-planarity term (N{sub p}). Statistical results revealed good correlation between the model and experimental data, enabling the different stationary phases to be compared. Recognition of solute size seems similar for each class of polymer but solute non-planarity recognition grows continuously as ordering of the liquid-crystal polymer increases. Recognition of solute lengthening is non-existent for non-liquid-crystalline polymers and suddenly appears with liquid crystalline polymers. Shape recognition is better for smectic than for nematic SCP. The predictive ability of this model was tested on highly condensed aromatic compounds. The connectivity index {chi} did not seem appropriate for such systems. Its replacement by Rekker's hydrophobic fragmental constant, log P, was necessary for fitting the retention of these solutes on liquid-crystalline stationary phases. (orig.)

  18. A novel method to produce nonlinear empirical physical formulas for experimental nonlinear electro-optical responses of doped nematic liquid crystals: Feedforward neural network approach

    International Nuclear Information System (INIS)

    Among other significant obstacles, inherent nonlinearity in experimental physical response data poses severe difficulty in empirical physical formula (EPF) construction. In this paper, we applied a novel method (namely layered feedforward neural network (LFNN) approach) to produce explicit nonlinear EPFs for experimental nonlinear electro-optical responses of doped nematic liquid crystals (NLCs). Our motivation was that, as we showed in a previous theoretical work, an appropriate LFNN, due to its exceptional nonlinear function approximation capabilities, is highly relevant to EPF construction. Therefore, in this paper, we obtained excellently produced LFNN approximation functions as our desired EPFs for above-mentioned highly nonlinear response data of NLCs. In other words, by using suitable LFNNs, we successfully fitted the experimentally measured response and predicted the new (yet-to-be measured) response data. The experimental data (response versus input) were diffraction and dielectric properties versus bias voltage; and they were all taken from our previous experimental work. We conclude that in general, LFNN can be applied to construct various types of EPFs for the corresponding various nonlinear physical perturbation (thermal, electronic, molecular, electric, optical, etc.) data of doped NLCs.

  19. A novel method to produce nonlinear empirical physical formulas for experimental nonlinear electro-optical responses of doped nematic liquid crystals: Feedforward neural network approach

    Energy Technology Data Exchange (ETDEWEB)

    Yildiz, Nihat, E-mail: nyildiz@cumhuriyet.edu.t [Cumhuriyet University, Faculty of Science and Literature, Department of Physics, 58140 Sivas (Turkey); San, Sait Eren; Okutan, Mustafa [Department of Physics, Gebze Institute of Technology, P.O. Box 141, Gebze 41400, Kocaeli (Turkey); Kaya, Hueseyin [Cumhuriyet University, Faculty of Science and Literature, Department of Physics, 58140 Sivas (Turkey)

    2010-04-15

    Among other significant obstacles, inherent nonlinearity in experimental physical response data poses severe difficulty in empirical physical formula (EPF) construction. In this paper, we applied a novel method (namely layered feedforward neural network (LFNN) approach) to produce explicit nonlinear EPFs for experimental nonlinear electro-optical responses of doped nematic liquid crystals (NLCs). Our motivation was that, as we showed in a previous theoretical work, an appropriate LFNN, due to its exceptional nonlinear function approximation capabilities, is highly relevant to EPF construction. Therefore, in this paper, we obtained excellently produced LFNN approximation functions as our desired EPFs for above-mentioned highly nonlinear response data of NLCs. In other words, by using suitable LFNNs, we successfully fitted the experimentally measured response and predicted the new (yet-to-be measured) response data. The experimental data (response versus input) were diffraction and dielectric properties versus bias voltage; and they were all taken from our previous experimental work. We conclude that in general, LFNN can be applied to construct various types of EPFs for the corresponding various nonlinear physical perturbation (thermal, electronic, molecular, electric, optical, etc.) data of doped NLCs.

  20. A novel method to produce nonlinear empirical physical formulas for experimental nonlinear electro-optical responses of doped nematic liquid crystals: Feedforward neural network approach

    Science.gov (United States)

    Yildiz, Nihat; San, Sait Eren; Okutan, Mustafa; Kaya, Hüseyin

    2010-04-01

    Among other significant obstacles, inherent nonlinearity in experimental physical response data poses severe difficulty in empirical physical formula (EPF) construction. In this paper, we applied a novel method (namely layered feedforward neural network (LFNN) approach) to produce explicit nonlinear EPFs for experimental nonlinear electro-optical responses of doped nematic liquid crystals (NLCs). Our motivation was that, as we showed in a previous theoretical work, an appropriate LFNN, due to its exceptional nonlinear function approximation capabilities, is highly relevant to EPF construction. Therefore, in this paper, we obtained excellently produced LFNN approximation functions as our desired EPFs for above-mentioned highly nonlinear response data of NLCs. In other words, by using suitable LFNNs, we successfully fitted the experimentally measured response and predicted the new (yet-to-be measured) response data. The experimental data (response versus input) were diffraction and dielectric properties versus bias voltage; and they were all taken from our previous experimental work. We conclude that in general, LFNN can be applied to construct various types of EPFs for the corresponding various nonlinear physical perturbation (thermal, electronic, molecular, electric, optical, etc.) data of doped NLCs.

  1. Sorption and selective chromatographic properties of isomer-selective composite sorbent based on a eutectic mixture of nematic liquid crystals and perbenzoylated β-cyclodextrin

    Science.gov (United States)

    Onuchak, L. A.; Kapralova, T. S.; Kuraeva, Yu. G.; Belousova, Z. P.; Stepanova, R. F.

    2015-12-01

    Mesomorphic, sorption, and selective properties of a three-component sorbent based on a mixture of nematic ( N) liquid crystals of 4-methoxy-4'-ethoxyazoxybenzene (MEAB) and 4,4'-diethoxyazoxybenzene (azoxyphenetol, AOP) of an eutectic composition and heptakis-(2,3,6-tri- O-benzoyl)-β-cyclodextrin (Bz-β-CD) are studied. For 30 organic compounds of different classes with linear and cyclic molecular structures, including optical isomers of limonene, pinene, camphene, and butanediol-2,3, thermodynamic functions are determined for their gas-phase sorption using a three-component MEAB-AOP-Bz-β- CD sorbent (62: 28: 10 wt %). It is found that the investigated sorbent possesses high structural selectivity (αp/m = 1.128-1.059, 100-130°C, N) and moderate enantioselectivity (1.07-1.02) within a broad temperature range (95-170°C) including both mesomorphic and isotropic phases of the sorbent. It is shown that the enantioselectivity of the sorbent is apparent under conditions of both increasing retention when a chiral Bz-β-CD additive is introduced into the MEAB-AOP system (limonenes, pinenes, camphenes) and decreasing retention (butanediols-2,3).

  2. Viral nematics in confined geometries.

    Science.gov (United States)

    Manyuhina, O V; Lawlor, K B; Marchetti, M C; Bowick, M J

    2015-08-14

    Motivated by recent experiments on the rod-like virus bacteriophage fd, confined to circular and annular domains, we present a theoretical study of structural transitions in these geometries. Using the continuum theory of nematic liquid crystals, we examine the competition between bulk elasticity and surface anchoring, mediated by the formation of topological defects. We show analytically that bulk defects are unstable with respect to defects sitting at the boundary. In the case of an annulus, whose topology does not require the presence of topological defects, we find that nematic textures with boundary defects are stable compared to defect-free configurations when the anchoring is weak. Our simple approach, with no fitting parameters, suggests a possible symmetry breaking mechanism responsible for the formation of one-, two- and three-fold textures under annular confinement. PMID:26135676

  3. Liquid crystal alignment by polyhedral oligomeric silsesquioxane (POSS)-polyimide nanocomposites

    Science.gov (United States)

    Liu, Han-Shiang; Jeng, Shie-Chang

    2013-05-01

    Polyimide (PI) films are widely used in the liquid crystal display (LCD) industry to align liquid crystal (LC) molecules in a specific orientation with a pretilt angle θp on the PI alignment films. It was observed that physical dispersion of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in commercial homogenous PIs decreases the surface energy of the PI alignment films and generates a controllable θp in the range 0° < θp < 90°, which is not easily achieved by complicate PI synthesis. Characteristics of POSS-PI nanocomposites were studied to investigate the influence of POSS nanoparticles on PIs. Increased absorption in the infrared spectra and decreased decomposition temperature and glass transition temperature with POSS doped concentration in PI were observed due to the increase in free volume of POSS-PI nanocomposites. Such nanoscale hybridization suggests a novel approach to tune the properties of PIs through modification of molecular interaction. A fast response no-bias optically-compensated bend (OCB) LCD with a pretilt angle of 68° was also demonstrated in this work.

  4. Long-range nematic order and anomalous fluctuations in suspensions of swimming filamentous bacteria

    CERN Document Server

    Nishiguchi, Daiki; Chaté, Hugues; Sano, Masaki

    2016-01-01

    We study the collective dynamics of long, filamentous, non-tumbling bacteria swimming in a very thin fluid layer. The strong confinement induces nematic alignment upon collision, which, for large enough density of cells, gives rise to global nematic order. We show that this homogeneous but fluctuating phase, observed on the largest experimentally-accessible scale of millimeters, exhibits the same properties as the Vicsek-style model of polar particles with nematic alignment: true long-range nematic order and non-trivial giant number fluctuations

  5. Three-dimensional molecular dynamics simulations of reorientation process and backflow generation in nematic liquid crystals under application of electric fields

    Science.gov (United States)

    Sunarso, Alfeus; Tsuji, Tomohiro; Chono, Shigeomi

    2011-08-01

    The dynamic responses of nematic liquid crystals in a parallel-plate cell under the application of electric fields were investigated using three-dimensional molecular dynamics simulations, which should provide more precise dynamics as compared to those in two-dimensional molecular dynamics simulations as in our previous work [Sunarso et al., Appl. Phys. Lett. 93, 244106 (2008)]. The study is focused on the reorientation process and the generation of backflow, which should be important in the development of liquid crystalline actuators. It is shown that bulk reorientation is coupled with the generation of backflow owing to the conversion of electric-field-induced molecular rotation into bulk translational motion. The increase in electric torque due to the increase in electric field strength results in a faster change in the bulk orientation, thus accelerating the development of the flow field and increasing the magnitude of the generated velocity field. Different initial orientation angles result in similar dynamics, although the magnitude of the generated velocity decreases with increasing initial orientation angle. The development of velocity profiles confirms the results of the experiment and the simulation using a macroscopic continuum approach. Simulations under various molecular aspect ratios show that with an increase in the aspect ratio, the reorientation process becomes slower due to the increase in moment of inertia and elastic torque, whereas the magnitudes of the velocity show the trade-off between the speed of the orientation change and the effectiveness of the molecular motion conversion. Furthermore, the simulation results show the spatial variation in the reorientation process as the result of interplay between electric torque, elastic torque, and backflow.

  6. Hydrogen bonding intermolecular effect on electro-optical response of doped 6PCH nematic liquid crystal with some azo dyes

    Science.gov (United States)

    Kiani, S.; Zakerhamidi, M. S.; Tajalli, H.

    2016-05-01

    Previous studies on the electro-optical responses of dye-doped liquid crystal have shown that dopant material have a considerable effect on their electro-optical responses. Despite the studies carried out on electro-optical properties of dye-doped liquid crystal, no attention has been paid to study of the interaction and structural effects in this procedure. In this paper, linear dyes and with similar structure were selected as dopants. The only difference in used dyes is the functional groups in their tails. So, doping of these dyes into liquid crystals determines the influence of interaction type on electro-optical behaviours of the doped systems. Therefore, in this work, two aminoazobenzene ("A-dye": hydrogen bond donor) and dimethyl-aminoazobenzene ("B-dye") dyes with different compositional percentages in liquid crystal host were used. Electro-optical Kerr behaviour, the pre-transition temperature and third order nonlinear susceptibility were investigated. The obtained results effectively revealed that type of interactions between the dye and liquid crystal is determinative of behavioral difference of doped system, compared to pure liquid crystal. Also, pre-transitional behaviour and thereupon Kerr electro-optical responses were affected by formed interactions into doped systems. In other words, it will be shown that addition of any dopants in liquid crystal, regardless of the nature of interactions, cannot cause appropriate electro-optical responses. In fact, type of dye, nature of interactions between dopant and liquid crystalline host as well as concentration of dye are the key factors in selecting the appropriate liquid crystal and dopant dye.

  7. Manipulation of modified clay particles in a nematic solvent by a magnetic field

    International Nuclear Information System (INIS)

    The magnetic alignment of organically modified montmorillonite platelets in magnetic fields is studied using small-angle x-ray scattering. When suspended in non-mesogenic solvents such as dodecanol the platelets are found to align parallel to the magnetic field due to the negative anisotropy of the magnetic susceptibility of the montmorillonite. Alignment of the clay in the nematic phase of 5CB was possible for sufficiently dilute samples and at sufficiently high field strengths. However, in this case the platelets aligned with their normals parallel to the field. It is argued that this is due to homeotropic anchoring of the liquid crystal at the clay particle surfaces leading to the particle orientation being slaved to the director alignment. Alignment of the 5CB director parallel to the field was only apparent at high fields and low particle concentrations, where the magnetic coherence length of the liquid crystal would be smaller than the typical size of a domain between stacks of clay platelets. A simple theoretical model is presented to aid the interpretation of the observations. The observed degree of particle alignment is often less than predicted, probably as the result of interactions between stacks of particles opposing reorientation

  8. Theoretical analysis of the influence of flexoelectric effect on the defect site in nematic inversion walls

    Science.gov (United States)

    Gui-Li, Zheng; Hui, Zhang; Wen-Jiang, Ye; Zhi-Dong, Zhang; Hong-Wei, Song; Li, Xuan

    2016-03-01

    Based on the experimental phenomena of flexoelectric response at defect sites in nematic inversion walls conducted by Kumar et al., we gave the theoretical analysis using the Frank elastic theory. When a direct-current electric field normal to the plane of the substrate is applied to the parallel aligned nematic liquid crystal cell with weak anchoring, the rotation of ±1 defects in the narrow inversion walls can be exhibited. The free energy of liquid crystal molecules around the +1 and -1 defect sites in the nematic inversion walls under the electric field was formulated and the electric-field-driven structural changes at the defect site characterized by polar and azimuthal angles of the local director were simulated. The results reveal that the deviation of azimuthal angle induced by flexoelectric effect are consistent with the switching of extinction brushes at the +1 and -1 defects obtained in the experiment conducted by Kumar et al. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374087, 11274088, and 11304074), the Natural Science Foundation of Hebei Province, China (Grant Nos. A2014202123 and A2016202282), the Research Project of Hebei Education Department, China (Grant Nos. QN2014130 and QN2015260), and the Key Subject Construction Project of Hebei Province University, China.

  9. New Photocrosslinking Polymeric Materials for Liquid Crystal Photoalignment

    OpenAIRE

    Mahilny, Uladzimir; Trofimova, Alexandra; Stankevich, Alexander; Tolstik, Alexei; Murauski, Anatoli; Muravsky, Alexander

    2013-01-01

    The photoinduced alignment (photoalignment) of nematic liquid crystals (LC) is of great interest as a contactless technique to create patterned LC aligning layers which have good prospect as basic elements of nonlinear optical devices like controllable waveguide structures with discrete diffraction, statical and dynamical photonic media etc. LC photoalignment on the surface of benzaldehyde polymeric layer caused by photochemical reaction of benzaldehyde side groups is investigated exper...

  10. Liquid Crystals: Alignment and Graphene-Assisted Decoration of Lyotropic Chromonic Liquid Crystals Containing DNA Origami Nanostructures (Small 12/2016).

    Science.gov (United States)

    Martens, Kevin; Funck, Timon; Kempter, Susanne; Roller, Eva-Maria; Liedl, Tim; Blaschke, Benno M; Knecht, Peter; Garrido, José Antonio; Zhang, Bingru; Kitzerow, Heinz

    2016-03-01

    On page 1658, H. Kitzerow and co-workers show that stable dispersion of the nanostructures in a liquid crystal and uniform alignment of the resulting composite are possible. DNA origami nanostructures decorated with gold nanoparticles (inset: TEM image) are dispersed in a uniformly aligned liquid crystal (background: image observed by polarizing microscopy). The unusual optical properties of such plasmonic nanostructures - for example a large circular dichroism in the case of the nanohelix - are expected to be enhanced if the nanostructures are uniformly aligned. PMID:27000497

  11. Homogeneous alignment of liquid crystalline dendrimers confined in a slit-pore. A simulation study

    International Nuclear Information System (INIS)

    In this work we present results from isobaric-isothermal (NPT) Monte Carlo simulation studies of model liquid crystalline dendrimer (LCDr) systems confined in a slit-pore made of two parallel flat walls. The dendrimers are modelled as a collection of spherical and ellipsoidal particles corresponding to the junction points of the dendritic core and to the mesogenic units respectively. Assuming planar uniform (unidirectional) soft anchoring of the mesogenic units on the substrates we investigate the conformational and alignment properties of the LCDr system at different thermodynamic state points. Tractable coarse grained force fields have been used from our previous work. At low pressures the interior of the pore is almost empty, since almost all LCDrs are anchored to the substrates forming two-dimensional smectic-like structures with the mesogens aligned along the aligning direction of the substrates. As the pressure grows the LCDrs occupy the whole pore. However, even at low temperatures, the smectic organization does not transmit in the interior of the pore and is preserved for distances of 2–3 mesogenic diameters from the walls. For this reason, the global orientational order decreases with increasing pressure (density). In the vicinity (2–3 mesogenic diameters) of the pore walls, mesogenic units preserve the smectic structure whose layers are separated by layers of spherical beads. In this region individual LCDrs possess a rod like shape. (paper)

  12. Homogeneous alignment of liquid crystalline dendrimers confined in a slit-pore. A simulation study

    Science.gov (United States)

    Workineh, Zerihun G.; Vanakaras, Alexandros G.

    2016-03-01

    In this work we present results from isobaric-isothermal (NPT) Monte Carlo simulation studies of model liquid crystalline dendrimer (LCDr) systems confined in a slit-pore made of two parallel flat walls. The dendrimers are modelled as a collection of spherical and ellipsoidal particles corresponding to the junction points of the dendritic core and to the mesogenic units respectively. Assuming planar uniform (unidirectional) soft anchoring of the mesogenic units on the substrates we investigate the conformational and alignment properties of the LCDr system at different thermodynamic state points. Tractable coarse grained force fields have been used from our previous work. At low pressures the interior of the pore is almost empty, since almost all LCDrs are anchored to the substrates forming two-dimensional smectic-like structures with the mesogens aligned along the aligning direction of the substrates. As the pressure grows the LCDrs occupy the whole pore. However, even at low temperatures, the smectic organization does not transmit in the interior of the pore and is preserved for distances of 2-3 mesogenic diameters from the walls. For this reason, the global orientational order decreases with increasing pressure (density). In the vicinity (2-3 mesogenic diameters) of the pore walls, mesogenic units preserve the smectic structure whose layers are separated by layers of spherical beads. In this region individual LCDrs possess a rod like shape.

  13. Atomistic cluster alignment method for local order mining in liquids and glasses

    International Nuclear Information System (INIS)

    An atomistic cluster alignment method is developed to identify and characterize the local atomic structural order in liquids and glasses. With the 'order mining' idea for structurally disordered systems, the method can detect the presence of any type of local order in the system and can quantify the structural similarity between a given set of templates and the aligned clusters in a systematic and unbiased manner. Moreover, population analysis can also be carried out for various types of clusters in the system. The advantages of the method in comparison with other previously developed analysis methods are illustrated by performing the structural analysis for four prototype systems (i.e., pure Al, pure Zr, Zr35Cu65, and Zr36Ni64). The results show that the cluster alignment method can identify various types of short-range orders (SROs) in these systems correctly while some of these SROs are difficult to capture by most of the currently available analysis methods (e.g., Voronoi tessellation method). Such a full three-dimensional atomistic analysis method is generic and can be applied to describe the magnitude and nature of noncrystalline ordering in many disordered systems.

  14. From rods to helices: evidence of a screw-like nematic phase

    OpenAIRE

    Kolli, Hima Bindu; Frezza, Elisa; Cinacchi, Giorgio; Ferrarini, Alberta; Giacometti, Achille; Hudson, Toby S.

    2014-01-01

    Evidence of a special chiral nematic phase is provided using numerical simulation and Onsager theory for systems of hard helical particles. This phase appears at the high density end of the nematic phase, when helices are well aligned, and is characterized by the C$_2$ symmetry axes of the helices spiraling around the nematic director with periodicity equal to the particle pitch. This coupling between translational and rotational degrees of freedom allows a more efficient packing and hence an...

  15. Effective angular and wavelength modeling of parallel aligned liquid crystal devices

    Science.gov (United States)

    Martínez, Francisco J.; Márquez, Andrés; Gallego, Sergi; Francés, Jorge; Pascual, Inmaculada; Beléndez, Augusto

    2015-11-01

    Parallel aligned liquid crystal (PA-LC) devices are widely used in many optics and photonics applications to control the amplitude, phase and/or state of polarization (SOP) of light beams. Simplified models yet with a good predictive capability are extremely useful in the optimal application of these devices. In this paper we propose and demonstrate the validity of a novel model enabling to calculate the voltage dependent retardance provided by parallel-aligned liquid crystal (PA-LC) devices for a very wide range of incidence angles and any wavelength in the visible. We derive the theoretical expressions, and both experimental and theoretical retardance results are obtained showing a very good agreement. The proposed model is robust and well adapted to a reverse-engineering approach for the calibration of its parameters, whose values are obtained without ambiguities. The model is based on only three physically related magnitudes: two off-state parameters per wavelength and one global voltage dependent parameter, the tilt angle of the LC molecules. To our knowledge it represents the most simplified model available for PA-LC devices yet showing predictive capability. Not only eases the design of experiments dealing with unconventional polarization states or complex amplitude modulation, but it also serves to analyze the physics and dynamics of PA-LC cells since we have estimation for their voltage dependent tilt angle within the device.

  16. Characterizations of gas purge valves for liquid alignment and gas removal in a microfluidic chip

    International Nuclear Information System (INIS)

    Two polydimethylsiloxane (PDMS) gas purge valves for excessive gas removal in general lab-on-a-chip applications are presented in this paper. Both valves are devised based on a three-layer configuration comprising a top layer for liquid channels, a membrane and a bottom layer for gas channels. The pneumatic valves work as a normal gateway for fluids when the membrane is bulged down (open state) by vacuum or pushed up (closed state) by pressure. In the closed state, the air in front of a liquid can be removed through a small notch or a permeable PDMS membrane by compressing the liquid. The purge valve with a small notch across its valve seat, termed surface-tension (ST) valve, can be operated with pressure under 11.5 kPa. The liquid is mainly retained by the surface tension resulting from the hydrophobic channel walls. In contrast, the purge valve with vacuum-filled grooves adjacent to a liquid channel, termed gas-permeation (GP) valve, can be operated at pressure above 5.5 kPa. Based on the principle of gas permeation, the excessive air can be slowly removed through the vent grooves. Detailed evaluations of both valves in a pneumatically driven microfluidic chip were conducted. Specifically, the purge valves enable users to remove gas and passively align liquids at desired locations without using sensing devices or feedback circuits. Finally, a rapid mixing reaction was successfully performed with the GP valves, showing their practicability as incorporated in a microfluidic chip. (paper)

  17. Liquid crystal alignment in electro-responsive nanostructured thermosetting materials based on block copolymer dispersed liquid crystal

    International Nuclear Information System (INIS)

    Novel well-defined nanostructured thermosetting systems were prepared by modification of a diglicydylether of bisphenol-A epoxy resin (DGEBA) with 10 or 15 wt% amphiphilic poly(styrene-b-ethylene oxide) block copolymer (PSEO) and 30 or 40 wt% low molecular weight liquid crystal 4'-(hexyl)-4-biphenyl-carbonitrile (HBC) using m-xylylenediamine (MXDA) as a curing agent. The competition between well-defined nanostructured materials and the ability for alignment of the liquid crystal phase in the materials obtained has been studied by atomic and electrostatic force microscopy, AFM and EFM, respectively. Based on our knowledge, this is the first time that addition of an adequate amount (10 wt%) of a block copolymer to 40 wt% HBC-(DGEBA/MXDA) leads to a well-organized nanostructured thermosetting system (between a hexagonal and worm-like ordered structure), which is also electro-responsive with high rate contrast. This behavior was confirmed using electrostatic force microscopy (EFM), by means of the response of the HBC liquid crystal phase to the voltage applied to the EFM tip. In contrast, though materials containing 15 wt% PSEO and 30 wt% HBC also form a well-defined nanostructured thermosetting system, they do not show such a high contrast between the uncharged and charged surface

  18. Reduced operating voltage and grey-to-grey response time in a vertically aligned liquid crystal display using a mixture of two polyimide alignment materials

    Science.gov (United States)

    Lee, Ji-Hoon; Choi, Young Eun; Lee, Jun Hee; Lee, Byeong Hoon; Song, Won Il; Jeong, Kwang-Un; Lee, Gi-Dong; Lee, Seung Hee

    2013-12-01

    We proposed a method to reduce the operating voltage and the grey-to-grey switching time of a vertically aligned liquid crystal display using a mixture of planar and vertical polyimide alignment materials. The surface anchoring energy of the two-polyimide mixture was smaller than that of the pure vertical polyimide and consequently, liquid crystal molecules were easily switched to a planar state with an electric field, resulting in a greater maximum retardation than that of the pure polyimide at the same applied voltage. Rising time was also significantly reduced due to the suppressed optical bouncing effect in the mixed planar polyimide, and the decaying time showed negligible change. With the proposed approach, we can reduce the cell gap to obtain half-wave retardation allowing for faster response time while keeping a low operating voltage.

  19. Reduced operating voltage and grey-to-grey response time in a vertically aligned liquid crystal display using a mixture of two polyimide alignment materials

    International Nuclear Information System (INIS)

    We proposed a method to reduce the operating voltage and the grey-to-grey switching time of a vertically aligned liquid crystal display using a mixture of planar and vertical polyimide alignment materials. The surface anchoring energy of the two-polyimide mixture was smaller than that of the pure vertical polyimide and consequently, liquid crystal molecules were easily switched to a planar state with an electric field, resulting in a greater maximum retardation than that of the pure polyimide at the same applied voltage. Rising time was also significantly reduced due to the suppressed optical bouncing effect in the mixed planar polyimide, and the decaying time showed negligible change. With the proposed approach, we can reduce the cell gap to obtain half-wave retardation allowing for faster response time while keeping a low operating voltage. (paper)

  20. Role of space charges on light-induced effects in nematic liquid crystals doped by methyl red

    Science.gov (United States)

    Lucchetti, L.; Simoni, F.

    2014-03-01

    We show that both the extraordinarily large nonlinear response and the light-induced permanent reorientation in liquid crystals doped by the azo dye methyl red originates from the same phenomenon of modification of the charge density on the irradiated surface. The demonstration is done by applying ac voltage to the samples, showing that in this case no permanent anchoring is possible. The measurements confirm the role of photoisomerization that gives a transient contribution to the actual reorientation process only in the high dose regime. This result allows us to draw a picture for light-induced effects that might be applied to a large class of compounds.

  1. Geodesic defect anchoring on nematic shells.

    Science.gov (United States)

    Mirantsev, Leonid V; Sonnet, André M; Virga, Epifanio G

    2012-08-01

    Nematic shells are colloidal particles coated with nematic liquid crystal molecules, which may freely glide and rotate on the colloid's surface while keeping their long axis on the local tangent plane. Molecular dynamics simulations on a nanoscopic spherical shell indicate that under appropriate adhesion conditions for the molecules on the equator, the equilibrium nematic texture exhibits at each pole a pair of +1/2 defects so close to one another to be treated as one +1 defect. Spirals connect the polar defects, though the continuum limit of the interaction potential would not feature any elastic anisotropy. A molecular averaging justifies an anchoring defect energy that feels the geodesics emanating from the defect. All our observations are explained by such a geodesic anchoring, which vanishes on flat manifolds. PMID:23005713

  2. Anisotropy and Raman absorption of the polyimide surface irradiated by the ion beam for liquid crystal alignment

    International Nuclear Information System (INIS)

    In this paper, polyimide surfaces irradiated by an ion-beam for liquid crystal alignment are investigated by using atomic force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. A liquid crystal cell aligned homogeneously through the ion-beam exposure exhibits electro-optic switching behavior similar to that of a rubbing-aligned liquid crystal cell. However, we found that the surface morphology and bonding molecules of ion-beam-treated polyimide surfaces show properties very different from mechanically-rubbed ones. Experimental results show that optical anisotropy of ion-beam-treated polyimide surfaces results in the formation of hydrogenated amorphous carbon-like structure with a short main-chain, while mechanical rubbing has little effect on structural and compositional variations of polyimide layers

  3. Experimental Determination of the Mechanisms of Photomechanical Effects in a Nematic Liquid Crystal Elastomer in a Photomechanical Optical Device Geometry

    CERN Document Server

    Dawson, Nathan J; Neal, Jeremy; Luchette, Paul; Palffy-Muhoray, Peter

    2011-01-01

    Azo-dye doped liquid crystal elastomers (LCE) are known to show a strong photomechanical response. We report on experiments that suggest that photothermal heating is the underlying mechanism for the photomechanical optical device geometry. In particular, we use optical interferometry to probe the length change of the material and direct temperature measurements to determine heating. LCEs with various dopants and optical density were used to study the individual mechanisms. In the high dye-doped limit, most of the light is absorbed near the entry surface, which causes a local strain from photothermal heating and a nonlocal strain from thermal diffusion. This work is the first step in the design of independent parallel-beam photomechanical actuating/sensing devices, which could be cascaded together to make smart structures.

  4. Thermodynamic and mesoscopic modeling of tumbling nematics, of shear-thickening fluids and of stick-slip-like flow behavior

    Directory of Open Access Journals (Sweden)

    Heidenreich, Sebastian

    2008-02-01

    Full Text Available Shear thickening, i.e. the increase of the viscosity with increasing shear rate as it occurs in dense colloidal dispersions and polymeric fluids is an intriguing phenomenon with a considerable potential for technical applications. The theoretical description of this phenomenon is patterned after the thermodynamic and mesoscopic modeling of the orientational dynamics and the flow behavior of liquid crystals in the isotropic and nematic phases, where the theoretical basis is well-established. Even there the solutions of the relevant equations recently yielded surprises: not only stable flow alignment and a periodic behavior (tumbling are found as response to an imposed stationary shear flow but also irregular and chaotic dynamics occurs for certain parameter ranges. To treat shear-thickening fluids, a non-linear Maxwell model equation for the symmetric traceless part of the stress tensor has been proposed in analogy to the equations obeyed by the alignment tensor of nematics. The fluid-solid transition is formally analogous to the isotropic-nematic transition. In addition to shear-thickening and shear-thinning fluids, substances with yield stress can be modeled. Furthermore, periodic stick-slip-like motions and also chaotic behavior are found. In the latter cases, the instantaneous entropy production is not always positive. Yet it is comforting that its long-time average is in accord with the second law.

  5. Liquid crystal wavefront corrector with modal response based on spreading of the electric field in a dielectric material

    NARCIS (Netherlands)

    Loktev, M.; Vdovine, G.V.; Klimov, N.; Kotova, S.

    2007-01-01

    A novel liquid crystal (LC) wavefront corrector with smooth modal influence functions is proposed and realized. The device consists of a thin layer of planar aligned nematic LC sandwiched between a glass plate with a conductive electrode and a plate made of ceramic material with a very high dielectr

  6. Enhanced photoinduced nematic reorientation in mixture with azo-dye-substituted polymer

    CERN Document Server

    Parfenov, A

    2000-01-01

    The optically induced reorientation of nematic liquid crystal doped withazo-dye substituted polymer is investigated measuring photoinducedbirefringence. These measurement reveal the value (Dn~0.1) of inducedbirefringence of liquid crystal with dye polymer which significantly exceedsthe value of birefringence previously obtained in nematic mixture with the lowmolecular weight dye. More than one order of enhancement is connected withlower diffusivity of polymer.

  7. Towards the biaxial nematic phase via specific intermolecular interactions

    CERN Document Server

    Omnes, L

    2001-01-01

    The work described in this thesis has been focussed on the search of an elusive liquid crystal phase, known as the biaxial nematic phase. Indeed, despite nearly thirty years of intense research, no-one has been able to characterise unambiguously a biaxial nematic phase in a low-molar-mass thermotropic system. Our research is based on the concept of molecular biaxiality as distinct from shape biaxiality. Thus, we are seeking to design palladium complexes where specific intermolecular interactions could exist. Therefore, a few original synthetic strategies were developed to tackle the challenge of discovering the biaxial nematic phase

  8. Photo-aligned blend films of azobenzene-containing polyimides with and without side-chains for inducing inclined alignment of liquid crystal molecules

    Science.gov (United States)

    Usami, Kiyoaki; Sakamoto, Kenji

    2011-08-01

    We have succeeded in controlling the pretilt angle of liquid crystal (LC) molecules over the whole range of 0 to 90° by using photo-aligned blend films of two azobenzene-containing polyimides (Azo-PIs) with and without side-chains. The Azo-PIs were synthesized from pyromellitic dianhydride and a mixture of 4,4'-diaminoazobenzene and 4-(4'-propylbi(cyclohexan)-4-yl)phenyl 3,5-diaminobenzoate (PBCP-DABA). PBCP-DABA is a diamine to introduce a side-chain structure into the polyimide. Defect-free uniform LC alignment was obtained in the pretilt angle (θp) ranges of θp ≤ 11° and θp ≥ 78°. Previously, we reported that the pretilt angle can be controlled using pure photo-aligned films of Azo-PIs with different molar fractions of PBCP-DABA. For the pure photo-aligned films, the defect-free pretilt angle ranges were θp < 5° and θp ≥ 85°. These results suggest that the azimuthal anchoring strength of the blend Azo-PI film is stronger than that of the pure films of Azo-PIs with side-chains, at least for the pretilt angle range from 5 to 11°. We found that the defect-free pretilt angle range can be extended by using the blend Azo-PI films instead of the pure Azo-PI films.

  9. Polarized luminescence from aligned samples of nematogenic lanthanide complexes

    OpenAIRE

    Galyametdinov, Yury G.; Knyazev, Andrey A.; Dzhabarov, Vagif I.; Cardinaels, Thomas; Driesen, Kris; Görller-Walrand, Christiane; Binnemans, Koen

    2008-01-01

    The first examples of lanthanidomesogens that exhibit a low viscous nematic phase are presented. The compounds are one of the rare examples of liquid-crystalline lanthanide complexes that show polymorphism in the mesophase region (smectic A and nematic phases). The temperatures at which the nematic phase occurs are low and the nematic temperature range is broad, which makes these materials interesting for further physical studies. Moreover, the compounds are thermally stable. It is illustrate...

  10. Fabrication of a Mono-Domain Alignment Ferroelectric Liquid Crystal Device Using a Polar Self-Assembled Monolayer

    Institute of Scientific and Technical Information of China (English)

    ZOU Zhong-Fei; YAO Li-Shuang; TANG Xian-Zhu; JI Xin-Jian; XUAN Li

    2008-01-01

    A mono-domain ferroelectric liquid crystal device (FLCD) is fabricated using a novel method. The cell used in this method is an asymmetric cell, typically the combination of a polar self-assembled monolayer (SAM) for one substrate and a rubbed polyimide for the other substrate. A defect-free alignment of ferroelectric liquid crystal is fabricated without applying a dc voltage to remove degeneracy in the layer structure. The contact angles of self-assembled monolayer and PI-2942 are measured and the polarity of SAM is higher than the PI alignment. It is found that the polarity of self-assembled monolayer is a key factor in the formation of mono-domain alignment of FLC.

  11. Surface Modification of Plate-Like Nanoparticles and Their Assembly into Nematic Organogels

    Science.gov (United States)

    Cipriano, Bani; Raghavan, Srinivasa

    2006-03-01

    Plate-like clay nanoparticles (e.g., laponite) form gels in water at sufficiently high concentration. A remarkable feature of these gels is the appearance of birefringent textures characteristic of nematic liquid crystals. Here we report the counterpart of this phenomenon in organic solvents, i.e., the formation of nematic textures by adding organically modified clay nanoparticles into non-polar liquids such as toluene and chloroform. We present the phase diagram (isotropic/nematic phases) for these gels. The viscoleastic properties of the resulting gels are characterized by use of rheological methods. The quality of the dispersions and the birefringent textures are evaluated using optical microscopy and x-ray scattering techniques. The finding that organoclays self assemble into a nematic phase in non-polar mediums may well provide a route for in-situ formation of nematic polymer nanocomposites. We also describe preliminary efforts towards achieving nematic ordering of particles in polymers.

  12. Comparison of Friction Characteristics on TN and VA Mode Alignment Films with Friction Force Microscopy

    Science.gov (United States)

    Kwak, Musun; Chung, Hanrok; Kwon, Hyukmin; Kim, Jehyun; Han, Daekyung; Yi, Yoonseon; Lee, Sangmun; Lee, Chulgu; Cha, Sooyoul

    Using frictional force microscopy (FFM), the friction surface characteristics were compared between twisted nematic (TN) mode and vertical alignment (VA) mode alignment films (AFs). The friction asymmetry was detected depending on temperature conditions on TN mode AF, but not on VA mode AF. The difference between two modes was explained by leaning intermolecular repulsion caused by the pre-tilt angle uniformity and the density of side chain. No level difference according to temperature conditions appeared when the pre-tilt angle were measured after liquid crystal (LC) injection.

  13. Nematic droplets on fibers.

    Science.gov (United States)

    Batista, V M O; Silvestre, N M; Telo da Gama, M M

    2015-12-01

    The emergence of new techniques for the fabrication of nematic droplets with nontrivial topology provides new routes for the assembly of responsive devices. Here we explore some of the properties of nematic droplets on fibers, which constitute the basic units of a type of device that is able to respond to external stimuli, including the detection of gases. We perform a numerical study of spherical nematic droplets on fibers. We analyze the equilibrium textures for homogeneous and hybrid boundary conditions and find that in some cases the nematic avoids the nucleation of topological defects, which would provide a different optical response. We consider in detail a homeotropic nematic droplet wrapped around a fiber with planar anchoring. We investigate the effect of an electric field on the texture of this droplet. In the presence of a dc field, the system undergoes an orientational transition above a given threshold E(c), for which a ring defect is transformed into a figure-eight defect. We also consider ac fields, at high and low frequencies, and find that the textures are similar to those observed for static fields, in contrast with recently reported experiments. PMID:26764711

  14. Magnetic Field Alignment of PS-P4VP: a Non-Liquid Crystalline Coil-Coil Block Copolymer

    Science.gov (United States)

    Rokhlenko, Yekaterina; Zhang, Kai; Larson, Steven; Gopalan, Padma; O'Hern, Corey; Osuji, Chinedum

    2015-03-01

    Magnetic fields provide the ability to control alignment of self-assembled soft materials such as block copolymers. Most prior work in this area has relied on the presence of ordered assemblies of anisotropic liquid crystalline species to ensure sufficient magnetic anisotropy to drive alignment. Recent experiments with poly(styrene-b-4-vinylpyridine), a non-liquid crystalline BCP, however, show field-induced alignment of a lamellar microstructure during cooling across the order-disorder transition. Using in situ x-ray scattering, we examine the roles of field strength and cooling rate on the alignment response of this low MW coil-coil BCP. Alignment is first observed at field strengths as low as 1 Tesla and improves markedly with both increasing field strength and slower cooling. We present a geometric argument to illustrate the origin of a finite, non-trivial magnetic susceptibility anisotropy for highly stretched surface-tethered polymer chains and corroborate this using coarse-grained molecular dynamics simulations. We rationalize the magnetic field response of the system in terms of the mobility afforded by the absence of entanglements, the intrinsic anisotropy resulting from the stretched polymer chains and sterically constrained conjugated rings, and the large grain size in these low molecular weight materials.

  15. Intermediate pre-tilt angle control by a composite alignment thin film structure for liquid crystal displays.

    Science.gov (United States)

    Wu, G M; Chien, H W; Huang, J W; Zeng, H L

    2010-04-01

    We designed a patterned composite alignment thin film structure using a horizontal alignment polyimide (PI) layer and vertical alignment liquid crystal polymer (LCP) pillars. The LCP polymer precursor concentration was varied at 0-10% and the pillars were introduced by a photolithography process. Both single-sided and double-sided liquid crystal display cells were assembled for a series of electro-optical characterization techniques. The horizontal PI alignment layer alone had a designated control of the pre-tilt angle of 7 degrees after the prescribed mechanical rubbing process. The pre-tilt angle was improved to 24 degrees when the LCP precursor concentration was 5%. It was further increased to 61 degrees at the concentration of 10%. In addition, the study on the electrical response time and gray level variation demonstrated promising results for potential applications. The field-on response time was only 2.79 ms and the field-off response time was 0.35 ms for the double-sided liquid crystal display cells using a ramping voltage of 5.5 V. The effective control of the cell pre-tilt angle suggested that the display power consumption and response time would be greatly improved. PMID:20208122

  16. Biased liquid crystal infiltrated photonic bandgap fiber

    DEFF Research Database (Denmark)

    Weirich, Johannes; Lægsgaard, Jesper; Scolari, Lara;

    2009-01-01

    A simulation scheme for the transmission spectrum of a photonic crystal fiber infiltrated with a nematic liquid crystal and subject to an external bias is presented. The alignment of the biased liquid crystal is simulated using the finite element method to solve the relevant system of coupled...... partial differential equations. From the liquid crystal alignment the full tensorial dielectric permittivity in the capillaries is derived. The transmission spectrum for the photonic crystal fiber is obtained by solving the generalized eigenvalue problem deriving from Maxwell’s equations using a vector...... element based finite element method. We demonstrate results for a splay aligned liquid crystal infiltrated into the capillaries of a four-ring photonic crystal fiber and compare them to corresponding experiments....

  17. STATISTICAL MODELS FOR SEMI-RIGID NEMATIC POLYMERS

    Institute of Scientific and Technical Information of China (English)

    WANG Xinjiu

    1995-01-01

    Semi-rigid liquid crystal polymer is a class of liquid crystal polymers different from long rigid rod liquid crystal polymer to which the well-known Onsager and Flory theories are applied. In this paper, three statistical models for the semi-rigid nematic polymer were addressed. They are the elastically jointed rod model, worm-like chain model, and non-homogeneous chain model.The nematic-isotropic transition temperature was examined. The pseudo-second transition temperature is expressed analytically. Comparisons with the experiments were made and the agreements were found.

  18. Topology and geometry of nematic braids

    Energy Technology Data Exchange (ETDEWEB)

    Čopar, Simon, E-mail: simon.copar@fmf.uni-lj.si

    2014-05-01

    Topological analysis of disclinations in nematic liquid crystals is an interesting and diverse topic that goes from strict mathematical theorems to applications in elaborate systems found in experiments and numerical simulations. The theory of nematic disclinations is shown from both the geometric and topological perspectives. Entangled disclination line networks are analyzed based on their shape and the behavior of their cross section. Methods of differential geometry are applied to derive topological results from reduced geometric information. For nematic braids, systems of −1/2 disclination loops, created by inclusion of homeotropic colloidal particles, a formalism of rewiring is constructed, allowing comparison and construction of an entire set of different conformations. The disclination lines are described as ribbons and a new topological invariant, the self-linking number, is introduced. The analysis is generalized from a constant −1/2 profile to general profile variations, while retaining the geometric treatment. The workings of presented topological statements are demonstrated on simple models of entangled nematic colloids, estimating the margins of theoretical assumptions made in the formal derivations, and reviewing the behavior of the disclinations not only under topological, but also under free-energy driven constraints.

  19. Integral equation theory for nematic fluids

    Directory of Open Access Journals (Sweden)

    M.F. Holovko

    2010-01-01

    Full Text Available The traditional formalism in liquid state theory based on the calculation of the pair distribution function is generalized and reviewed for nematic fluids. The considered approach is based on the solution of orientationally inhomogeneous Ornstein-Zernike equation in combination with the Triezenberg-Zwanzig-Lovett-Mou-Buff-Wertheim equation. It is shown that such an approach correctly describes the behavior of correlation functions of anisotropic fluids connected with the presence of Goldstone modes in the ordered phase in the zero-field limit. We focus on the discussions of analytical results obtained in collaboration with T.G. Sokolovska in the framework of the mean spherical approximation for Maier-Saupe nematogenic model. The phase behavior of this model is presented. It is found that in the nematic state the harmonics of the pair distribution function connected with the correlations of the director transverse fluctuations become long-range in the zero-field limit. It is shown that such a behavior of distribution function of nematic fluid leads to dipole-like and quadrupole-like long-range asymptotes for effective interaction between colloids solved in nematic fluids, predicted before by phenomenological theories.

  20. Multifunctional polymer nanocomposites with uniaxially aligned liquid crystal polymer fibrils and graphene nanoplatelets

    Science.gov (United States)

    Leung, S. N.; Khan, M. O.; Naguib, H.; Dawson, F.

    2014-02-01

    Polymer nanocomposites have actively been studied to replace metals in different emerging applications because of their light weight, superior manufacturability, and low processing cost. For example, extensive research efforts have been made to develop advanced thermally conductive polymer nanocomposites, with good processability, for heat management applications. In this study, liquid crystal polymer (LCP)-based nanocomposites have shown to possess much higher effective thermal conductivity (keff) (i.e., as high as 2.58 W/m K) than neat polymers (i.e., ˜0.2-0.4 W/m K). The fibrillation of LCP in LCP-graphene nanoplatelet (GNP) nanocomposites also demonstrated more pronounced increase in keff than that of polyphenylene sulfide (PPS)-GNP nanocomposites. Furthermore, ultra-drawing of LCP-GNP nanocomposite led to additional increase in the nanocomposite's keff because of the alignments of LCP fibrils and the embedded GNP. Experimental results also revealed that, unlike keff, the electrical conductivity (σ) of nanocomposites was unaffected by the types of polymer matrix. This exhibited that the keff and σ were promoted by different mechanisms, suggesting a potential route to tailor polymer nanocomposite's keff and σ independently.

  1. Self-assembled ordered structures in thin films of HAT5 discotic liquid crystal

    OpenAIRE

    Piero Morales; Jan Lagerwall; Paolo Vacca; Sabine Laschat; Giusy Scalia

    2010-01-01

    Thin films of the discotic liquid crystal hexapentyloxytriphenylene (HAT5), prepared from solution via casting or spin-coating, were investigated by atomic force microscopy and polarizing optical microscopy, revealing large-scale ordered structures substantially different from those typically observed in standard samples of the same material. Thin and very long fibrils of planar-aligned liquid crystal were found, possibly formed as a result of an intermediate lyotropic nematic state arising d...

  2. Isotropic-nematic transition and dynamics of rigid charged molecules

    Science.gov (United States)

    Karatrantos, Argyrios

    2016-03-01

    Using molecular dynamics, an isotropic-nematic transition was found in bulk salt-free solutions of charged rods with their counterions in the semidilute regime. This phase transition is driven primarily by electrostatics, rather than by excluded volume. The counterion condensation effect, which is controlled by the Manning parameter, leads to liquid crystalline phases of rods. For elevated values of the Manning parameter, an attraction is obtained between the rods, and the nematic phase appears. For small values of the Manning parameter the counterions de-condense, and the nematic phase disappears. Instead, in a neutral system of rods and spheres there is no appearance of nematic phase. The diffusivity of both rods and counterions is reduced with the Manning parameter.

  3. Helical polyacetylene synthesized with a chiral nematic reaction field

    Science.gov (United States)

    Akagi; Piao; Kaneko; Sakamaki; Shirakawa; Kyotani

    1998-11-27

    Helical polyacetylene was synthesized under an asymmetric reaction field consisting of chiral nematic (N*) liquid crystals (LCs). The chiral nematic LC was prepared by adding a chiroptical binaphthol derivative as a chiral dopant to a mixture of two nematic LCs. Acetylene polymerizations were carried out using the catalyst titanium tetra-n-butoxide-triethylaluminum dissolved in the chiral nematic LC solvent. The polyacetylene film was shown by scanning electron microscopy to consist of clockwise or counterclockwise helical structure of fibrils. A Cotton effect was observed in the region of the pi --> pi* transition of the polyacetylene chain in circular dichroism spectra. The high electrical conductivities of approximately 1500 to 1800 siemens per centimeter after iodine doping and the chiral helicity of these films may be exploited in electromagnetic and optical applications. PMID:9831554

  4. Computer simulation of liquid crystals

    International Nuclear Information System (INIS)

    In this thesis computer simulations of liquid crystal systems were performed focusing on the isotropic-nematic interface and on the effects of confinement. A range of idealised and atomistic models were employed using both Monte-Carlo and Molecular Dynamics techniques. The structure of the planar isotropic - nematic (I-N) interface was investigated using constant volume Monte-Carlo simulation of systems of hard-ellipsoids confined between parallel hard walls. The nematic phase is observed to wet the hard walls, establishing two planar I-N interfaces per simulation box. The microscopic pressure tensor in the vicinity of the interface was calculated for both planar and normal alignment of the nematic. The surface tension, calculated directly from the pressure tensor, is lowest in the case of planar alignment indicating that this is the preferred alignment at the interface. The form of the transverse pressure across the interface is dramatically different for the two orientations. For the case of planar alignment we observe a large tension (low transverse pressure) on the nematic side and a small compressive region (high transverse pressure) on the isotropic side. For the case of normal alignment we see a large compression on the nematic side followed by tension on the isotropic side. Comparisons are made with the results of Onsager theory, showing excellent agreement. Gay-Berne particles confined to very thin films are investigated using constant pressure Monte-Carlo simulation. Orientational wetting is again observed at the liquid-wall interface. For homeotropic alignment at the wall we observe strong layering of particles into planes parallel to the walls and long-range orientational order which persists well beyond the range of the fluid-wall interaction. The average system order parameter is strongly dependent on the film thickness, the order being highest when the film thickness is commensurate with the formation of an integral number of molecular layers. An

  5. Post-Tanner spreading of nematic droplets

    International Nuclear Information System (INIS)

    The quasistationary spreading of a circular liquid drop on a solid substrate typically obeys the so-called Tanner law, with the instantaneous base radius R(t) growing with time as R∼t1/10-an effect of the dominant role of capillary forces for a small-sized droplet. However, for droplets of nematic liquid crystals, a faster spreading law sets in at long times, so that R∼tα with α significantly larger than the Tanner exponent 1/10. In the framework of the thin film model (or lubrication approximation), we describe this 'acceleration' as a transition to a qualitatively different spreading regime driven by a strong substrate-liquid interaction specific to nematics (antagonistic anchoring at the interfaces). The numerical solution of the thin film equation agrees well with the available experimental data for nematics, even though the non-Newtonian rheology has yet to be taken into account. Thus we complement the theory of spreading with a post-Tanner stage, noting that the spreading process can be expected to cross over from the usual capillarity-dominated stage to a regime where the whole reservoir becomes a diffusive film in the sense of Derjaguin.

  6. Biaxial order and a rotation of the minor director in the nematic phase of an organo-siloxane tetrapode by the electric field

    Science.gov (United States)

    Merkel, K.; Nagaraj, M.; Kocot, A.; Kohlmeier, A.; Mehl, G. H.; Vij, J. K.

    2012-03-01

    Biaxiality in the nematic phase for a liquid crystalline tetrapode made up of organo-siloxanes mesogens is investigated using polarized infrared spectroscopy. An ordering of the minor director for the homeotropically aligned sample is found to depend on the amplitude of the in-plane electric field. On increasing the in-plane electric field, the minor director, lying initially along the rubbing direction, rotates to the direction of the applied field. The scalar order parameters of the second rank tensor are found to depend significantly on the strength of the electric field. A most significant increase is found in the nematic order parameter and in the parameter that characterizes the phase biaxiality.

  7. Superior optical properties of homogeneous liquid crystal alignment on a tin (IV) oxide surface sequentially modulated via ion beam irradiation.

    Science.gov (United States)

    Kang, Young-Gu; Park, Hong-Gyu; Kim, Hyung-Jun; Kim, Young-Hwan; Oh, Byeong-Yun; Kim, Byoung-Yong; Kim, Dai-Hyun; Seo, Dae-Shik

    2010-10-11

    We first investigated the alignment characteristics of tin (IV) oxide (SnO(2)) thin films deposited by radio-frequency (RF) magnetron sputtering. This study demonstrates that liquid crystal (LC) molecules could be aligned homogeneously by controlling the Ion Beam (IB) irradiation energy densities. We also show that the pretilt angle of the LC molecules has a close relation with the surface energy. X-ray photoelectron spectroscopy (XPS) indicates that a non-stoichiometric SnO(2-x) surface converted by ion beam irradiation can horizontally align the LC molecules. The measured electro-optical (EO) characteristics showed high performance, comparable with those of rubbed and ion-beam irradiated polyimide (PI) layers. PMID:20941057

  8. Search for Technihadrons in Dielectron channel and alignments of the ATLAS liquid Argon Electromagnetic calorimeters

    International Nuclear Information System (INIS)

    The LHC campaign in the first years of data taking was successful. The 2011 run has allowed to record more than 5 fb-1 of data at √(s) = 7 TeV with the ATLAS experiment. In the work presented in this this thesis the whole 2011 data set is used to performed different studies. This thesis is organized in five chapters. In the first chapter is presented a theoretical introduction to the Standard Model (SM) and to one of its possible extension the TechniColor model (TC). The second chapter gives an overview of the LHC complex and of the ATLAS detector components. In the third chapter the timing analysis on all the readout channels of the Liquid Argon Calorimeter is reported. A precise timing alignment over the whole calorimeter is used to synchronize the detector readout system with the LHC bunch crossing and has also application in some physics analysis such as those looking for long lived particles. In the searches for new phenomena an excellent electron identification capability, with high efficiency and high jet rejection rate, is required over a broad energy range. The fourth chapter of this thesis presents the measurements of the trigger and the identification electron efficiency using Z → ee events. Finally the last chapter describes a search for resonant deviations from the Standard Model in the high masses of the dielectron spectrum within two different Technicolor scenarios the Low-scale Technicolor and the Minimal Walking Technicolor. The significance of potential excess of the TC candidate events over the SM background expectation is evaluated in the dilepton invariant mass distribution. In the absence of any significant signal 95% confidence level limits are set on the cross section and on the resonance mass. (author)

  9. Computer simulation of confined liquid crystal dynamics

    International Nuclear Information System (INIS)

    Results are presented from a series of simulations undertaken to determine whether dynamic processes observed in device-scale liquid crystal cells confined between aligning substrates can be simulated in a molecular system using parallel molecular dynamics of the Gay-Berne model. In a nematic cell, on removal of an aligning field, initial near-surface director relaxation can induce flow, termed 'backflow' in the liquid. This, in turn, can cause director rotation, termed 'orientational kickback', in the centre of the cell. Simulations are performed of the relaxation in nematic systems confined between substrates with a common alignment on removal of an aligning field. Results show /that relaxation timescales of medium sized systems are accessible. Following this, simulations are performed of relaxation in hybrid aligned nematic systems, where each surface induces a different alignment. Flow patterns associated with director reorientation are observed. The damped oscillatory nature of the relaxation process suggests that the behaviour of these systems is dominated by orientational elastic forces and that the observed director motion and flow do not correspond to the macroscopic processes of backflow and kickback. Chevron structures can occur in confined smectic cells which develop two domains of equal and opposite layer tilt on cooling. Layer lilting is thought to be caused by a need to reconcile a mismatch between bulk and surface smectic layer spacing. Here, simulations are performed of the formation of structures in confined smectic systems where layer tilt is induced by an imposed surface pretilt. Results show that bookshelf, chevron and tilled layer structures are observable in a confined Gay-Berne system. The formation and stability of the chevron structure are shown to be influenced by surface slip. (author)

  10. Two Glass Transitions Associated to Different Dynamic Disorders in the Nematic Glassy State of a Non-Symmetric Liquid Crystal Dimer Dopped with g-Alumina Nanoparticles

    Directory of Open Access Journals (Sweden)

    Sergio Diez-Berart

    2015-06-01

    Full Text Available In the present work, the nematic glassy state of the non-symmetric LC dimer α-(4-cyanobiphenyl-4′-yloxy-ω-(1-pyrenimine-benzylidene-4′-oxy undecane is studied by means of calorimetric and dielectric measurements. The most striking result of the work is the presence of two different glass transition temperatures: one due to the freezing of the flip-flop motions of the bulkier unit of the dimer and the other, at a lower temperature, related to the freezing of the flip-flop and precessional motions of the cyanobiphenyl unit. This result shows the fact that glass transition is the consequence of the freezing of one or more coupled dynamic disorders and not of the disordered phase itself. In order to avoid crystallization when the bulk sample is cooled down, the LC dimer has been confined via the dispersion of γ-alumina nanoparticles, in several concentrations.

  11. Faster in-plane switching and reduced rotational viscosity characteristics in a graphene-nematic suspension

    Science.gov (United States)

    Basu, Rajratan; Kinnamon, Daniel; Skaggs, Nicole; Womack, James

    2016-05-01

    The in-plane switching (IPS) for a nematic liquid crystal (LC) was found to be considerably faster when the LC was doped with dilute concentrations of monolayer graphene flakes. Additional studies revealed that the presence of graphene reduced the rotational viscosity of the LC, permitting the nematic director to respond quicker in IPS mode on turning the electric field on. The studies were carried out with several graphene concentrations in the LC, and the experimental results coherently suggest that there exists an optimal concentration of graphene, allowing a reduction in the IPS response time and rotational viscosity in the LC. Above this optimal graphene concentration, the rotational viscosity was found to increase, and consequently, the LC no longer switched faster in IPS mode. The presence of graphene suspension was also found to decrease the LC's pretilt angle significantly due to the π-π electron stacking between the LC molecules and graphene flakes. To understand the π-π stacking interaction, the anchoring mechanism of the LC on a CVD grown monolayer graphene film on copper substrate was studied by reflected crossed polarized microscopy. Optical microphotographs revealed that the LC alignment direction depended on monolayer graphene's hexagonal crystal structure and its orientation.

  12. Photoinduced modification of poly[methyl(phenyl)silanediyl] films for liquid crystal alignment and polarized light-emitted diodes

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav; Stumpe, J.; Sapich, B.; Kaminorz, Y.; Kadashchuk, A.

    Potsdam: University of Potsdam, Institute of Physics, 2001 - (Wong, J.; Albrecht, F.; Oda, M.; Neher, D.; Schrader, S.), s. 113-116 [European Conference on Organic Electronics and Related Phenomena 2001. Potsdam (DE), 18.11.2001-21.11.2001] R&D Projects: GA AV ČR IAA1050901; GA ČR GA202/01/0518; GA MŠk ME 440 Institutional research plan: CEZ:AV0Z4050913 Keywords : poly[methyl(phenyl)silanediyl] * liquid crystal alignment * bond scission Subject RIV: CD - Macromolecular Chemistry

  13. Homeotropic Alignment of a Discotic Liquid Crystal Induced by a Sacrificial Layer

    DEFF Research Database (Denmark)

    Pouzet, Eric; De Cupere, Vinciane; Heintz, Christophe;

    2009-01-01

    A convenient method to induce face-on orientation of an alkoxy phtalocyanine discotic mesogen is described. The alignment is imposed by the confinement of the discotic thin films with a top sacrificial polymer layer that is easily removed by washing with a selective solvent, after thermal annealing....... Thin films have been characterized by optical and atomic force microscopy, UV-Vis absorption spectroscopy, and grazing incidence wide angle X-ray scattering. The data converge in showing the central role of the sacrificial layer in promoting alignment with the planar molecules orienting parallel to the...

  14. Distortional Lifshitz Vectors and Helicity in Nematic Free Energy Density

    OpenAIRE

    Sparavigna, Amelia Carolina

    2013-01-01

    Here we discuss the free energy of nematic liquid crystals using two vectors and the helicity, with the aim of having a compact form of its density. The two vectors are due to the splay and bend distortions of the director field. They have a polar nature, whereas the helicity is a pseudoscalar.

  15. Growth mechanism of vertically aligned fullerene micro tubes prepared by the liquid-liquid interfacial precipitation method

    Science.gov (United States)

    Toita, S.; Miyazawa, K.; Hotta, K.; Tachibana, M.

    2009-04-01

    C60-based materials such as FNWs and FNTs are new candidates for organic electronics and solar cells. Recently, a method to produce vertically-aligned fullerene microtube crystals (VFMTs) has been established. The VFMTs are exepected to be used as field emission devices, solar cells, fuel cells, and so forth. To realize such attractive applications, structures and arrangements of VFMTs should be controlled. In oder to know the growth mechanism of VFMTs, Scanning electron microscopy (SEM) observations were performed for several injection periods of VFMTs. In the initial stage of synthesis (IPA injection time of 60 min), vertically aligned thin non-tubular fullerene microwhiskers (VFMWs) formed on AAO substrates. The outer and inner diameter of VFMWs became increased with increasing the injected amount of IPA. And also the size of tube holes became larger. The tubular structures appeared at an injection time of around 90 min. At an injection time of 120 min, vertically aligned FMTs with hexagonal cross sections and holes were obtained and their diameter and structure did not change up to the final stage of injection time of 3 00 min.

  16. Poly(esterimide) bearing azobenzene units as photoaligning layer for liquid crystals

    Science.gov (United States)

    Węgłowski, Rafał; Piecek, Wiktor; Kozanecka-Szmigiel, Anna; Konieczkowska, Jolanta; Schab-Balcerzak, Ewa

    2015-11-01

    The custom synthesized azobenzene side-chain poly(esterimide) was used as an aligning material for nematic liquid crystal molecules. The anisotropy of the poly(esterimide) layer was generated by a linearly polarized UV light, as a consequence of multiple trans-cis-trans isomerization cycles. The photoalignment effect was studied by assembling a twisted nematic cell with a proper liquid crystal mixture and geometry to fulfill Mauguin's limit. The polarizing microscope pictures of the fabricated cells confirmed the twisted arrangement of liquid crystal molecules. The results of electro-optic measurements indicated a stronger anchoring of the liquid crystal molecules by photoaligned poly(esterimide) than that obtained in the case of a rubbed polyimide.

  17. Dielectric and magnetic anisotropy of a nematic ytterbium complex

    International Nuclear Information System (INIS)

    The sign and the magnitude of the dielectric anisotropy of an ytterbium-based paramagnetic nematic liquid crystal complex, namely, tris[1-(4-(4-propylcyclohexyl)phenyl)octane-1,3-dione]-[5,5'-di (heptadecile)-2,2'-bipyridine]ytterbium, are determined. The temperature dependence of the permittivity components of the complex is obtained in the temperature range of a nematic phase. The sign of the anisotropy of the magnetic susceptibility of this compound is experimentally determined

  18. Dielectric and magnetic anisotropy of a nematic ytterbium complex

    Energy Technology Data Exchange (ETDEWEB)

    Dobrun, L. A., E-mail: l.dobrun@spbu.ru; Sakhatskii, A. S.; Kovshik, A. P.; Ryumtsev, E. I.; Kolomiets, I. P. [St. Petersburg State University (Russian Federation); Knyazev, A. A.; Galyametdinov, Yu. G. [Kazan National Research Technological University (Russian Federation)

    2015-05-15

    The sign and the magnitude of the dielectric anisotropy of an ytterbium-based paramagnetic nematic liquid crystal complex, namely, tris[1-(4-(4-propylcyclohexyl)phenyl)octane-1,3-dione]-[5,5'-di (heptadecile)-2,2'-bipyridine]ytterbium, are determined. The temperature dependence of the permittivity components of the complex is obtained in the temperature range of a nematic phase. The sign of the anisotropy of the magnetic susceptibility of this compound is experimentally determined.

  19. Modeling Liquid-Crystal Devices with the Three-Dimensional Full-Vector Beam Propagation Method

    OpenAIRE

    Wang, Qian; Farrell, Gerald; Semenova, Yuliya

    2006-01-01

    Simulation of light propagation within nematic liquid-crystal (LC) devices is considered, of which the director is aligned normal to the z axis. A three-dimensional full-vector finite-difference beam propagation method for an anisotropic medium is presented and an alternating direction implicit scheme is adopted. Simulations of light propagation in a bulk polarization converter, a waveguide with a LC covering layer, and an integrated polarization splitter and optical switch are presented. Com...

  20. Light propagation mechanism switching in a liquid crystal infiltrated microstructured polymer optical fibre

    Science.gov (United States)

    Rutkowska, K. A.; Milenko, K.; Chojnowska, O.; Dąbrowski, R.; Woliński, T. R.

    2015-12-01

    In this work studies on propagation properties of a microstructured polymer optical fibre infiltrated with a nematic liquid crystal are presented. Specifically, the influence of an infiltration method on the LC molecular alignment inside fibre air-channels and, thus, on light guidance is discussed. Switching between propagation mechanisms, namely the transition from modified total internal reflection (mTIR) to the photonic bandgap effect obtained by varying external temperature is also demonstrated.

  1. Electroosmotically enabled Electrorheological Effects in a Planar Nematic Crystal Flow

    CERN Document Server

    Dhar, Jayabrata; Chakraborty, Suman

    2016-01-01

    Study of electrokinetics of nematic liquid crystals (LCs) with dissolved impurities hold utmost importance in understanding director distribution characteristics and modified flow rheology. However, no concrete theory for the non-uniform potential and ionic species distribution, due to an induced electrical double layer (EDL) at the LC-substrate interface, derived from fundamental principles have been put forward in this regard. In this work, we have developed coupled governing equations from fundamental free energy considerations for the potential distribution and the director configuration of the nematic LC within the induced electrical double layer which is generated due to certain physico-chemical interactions at the LC-substrate interface. With these considerations, an electroosmotically-enabled nematodynamics for a particular LC, namely, MBBA, with strong planar anchoring at the boundaries is studied. We obtained multiple solution for director configuration, which is an integral characteristics of nemat...

  2. Instabilities, defects, and defect ordering in an overdamped active nematic.

    Science.gov (United States)

    Putzig, Elias; Redner, Gabriel S; Baskaran, Arvind; Baskaran, Aparna

    2016-05-01

    We consider a phenomenological continuum theory for an extensile, overdamped active nematic liquid crystal, applicable in the dense regime. Constructed from general principles, the theory is universal, with parameters independent of any particular microscopic realization. We show that it exhibits two distinct instabilities, one of which arises due to shear forces, and the other due to active torques. Both lead to the proliferation of defects. We focus on the active torque bend instability and find three distinct nonequilibrium steady states including a defect-ordered nematic in which +½ disclinations develop polar ordering. We characterize the phenomenology of these phases and identify the relationship of this theoretical description to experimental realizations and other theoretical models of active nematics. PMID:26983376

  3. Flow of a viscous nematic fluid around a sphere

    CERN Document Server

    Gómez-González, Manuel

    2013-01-01

    We analyze the creeping flow generated by a spherical particle moving through a viscous fluid with nematic directional order, in which momentum diffusivity is anisotropic and which opposes resistance to bending. Specifically, we provide closed-form analytical expressions for the response function, i.e. the equivalent to Stokes's drag formula for nematic fluids. Particular attention is given to the rotationally pseudo-isotropic condition defined by zero resistance to bending, and to the strain pseudo-isotropic condition defined by isotropic momentum diffusivity. We find the former to be consistent with the rheology of biopolymer networks and the latter to be closer to the rheology of nematic liquid crystals. These "pure" anisotropic conditions are used to benchmark existing particle tracking microrheology methods that provide effective directional viscosities by applying Stokes's drag law separately in different directions. We find that the effective viscosity approach is phenomenologically justified in rotati...

  4. Modulated nematic structures induced by chirality and steric polarization

    Science.gov (United States)

    Longa, Lech; PajÄ k, Grzegorz

    2016-04-01

    What kind of one-dimensional modulated nematic structures (ODMNS) can form nonchiral and chiral bent-core and dimeric materials? Here, using the Landau-de Gennes theory of nematics, extended to account for molecular steric polarization, we study a possibility of formation of ODMNS, both in nonchiral and intrinsically chiral liquid crystalline materials. Besides nematic and cholesteric phases, we find four bulk ODMNS for nonchiral materials, two of which, to the best of our knowledge, have not been reported so far. These two structures are longitudinal (NLP) and transverse (NTP) periodic waves where the polarization field being periodic in one dimension stays parallel and perpendicular, respectively, to the wave vector. The other two phases are the twist-bend nematic phase (NTB) and the splay-bend nematic phase (NSB), but their fine structure appears more complex than that considered so far. The presence of molecular chirality converts nonchiral NTP and NSB into new NTB phases. Surprisingly, the nonchiral NLP phase can stay stable even in the presence of intrinsic chirality.

  5. Control of active liquid crystals with a magnetic field.

    Science.gov (United States)

    Guillamat, Pau; Ignés-Mullol, Jordi; Sagués, Francesc

    2016-05-17

    Living cells sense the mechanical features of their environment and adapt to it by actively remodeling their peripheral network of filamentary proteins, known as cortical cytoskeleton. By mimicking this principle, we demonstrate an effective control strategy for a microtubule-based active nematic in contact with a hydrophobic thermotropic liquid crystal. By using well-established protocols for the orientation of liquid crystals with a uniform magnetic field, and through the mediation of anisotropic shear stresses, the active nematic reversibly self-assembles with aligned flows and textures that feature orientational order at the millimeter scale. The turbulent flow, characteristic of active nematics, is in this way regularized into a laminar flow with periodic velocity oscillations. Once patterned, the microtubule assembly reveals its intrinsic length and time scales, which we correlate with the activity of motor proteins, as predicted by existing theories of active nematics. The demonstrated commanding strategy should be compatible with other viable active biomaterials at interfaces, and we envision its use to probe the mechanics of the intracellular matrix. PMID:27140604

  6. Modulating alignment of membrane proteins in liquid-crystalline and oriented gel media by changing the size and charge of phospholipid bicelles

    International Nuclear Information System (INIS)

    We demonstrate that alignment of a structured peptide or small protein solubilized in mixed phospholipid:detergent micelles or bicelles, when embedded in a compressed gel or liquid crystalline medium, can be altered by either changing the phospholipid aggregate shape, charge, or both together. For the hemagglutinin fusion peptide solubilized in bicelles, we show that bicelle shape and charge do not change its helical hairpin structure but impact its alignment relative to the alignment medium, both in charged compressed acrylamide gel and in liquid crystalline d(GpG). The method can be used to generate sets of residual dipolar couplings that correspond to orthogonal alignment tensors, and holds promise for high-resolution structural refinement and dynamic mapping of membrane proteins.

  7. Modulating alignment of membrane proteins in liquid-crystalline and oriented gel media by changing the size and charge of phospholipid bicelles

    Energy Technology Data Exchange (ETDEWEB)

    Lorieau, Justin L.; Maltsev, Alexander S.; Louis, John M.; Bax, Ad, E-mail: bax@nih.gov [National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health, Laboratory of Chemical Physics (United States)

    2013-04-15

    We demonstrate that alignment of a structured peptide or small protein solubilized in mixed phospholipid:detergent micelles or bicelles, when embedded in a compressed gel or liquid crystalline medium, can be altered by either changing the phospholipid aggregate shape, charge, or both together. For the hemagglutinin fusion peptide solubilized in bicelles, we show that bicelle shape and charge do not change its helical hairpin structure but impact its alignment relative to the alignment medium, both in charged compressed acrylamide gel and in liquid crystalline d(GpG). The method can be used to generate sets of residual dipolar couplings that correspond to orthogonal alignment tensors, and holds promise for high-resolution structural refinement and dynamic mapping of membrane proteins.

  8. Thermodynamic and transport anomalies near isotropic-nematic phase transition

    OpenAIRE

    Jose, Prasanth P.; Bagchi, Biman

    2008-01-01

    A theoretical study of the variation of thermodynamic and transport properties of calamitic liquid crystals across the isotropic-nematic phase transition is carried out by calculating the {\\it wavenumber (k) and time (t)} dependent intermediate scattering function of the liquid, via computer simulations of model nematogens. The objective is to understand the experimentally observed anomalies and sharp variation in many thermodynamic and transport properties, namely specific heat $C$, sound at...

  9. Vertical alignment of liquid crystal through ion beam exposure on oxygen-doped SiC films deposited at room temperature

    International Nuclear Information System (INIS)

    The authors report the vertical alignment of liquid crystal (LC) through the ion beam exposure on amorphous oxygen-doped SiC (SiOC) film surfaces deposited at room temperature. The optical transmittance of these films was similar to that of polyimide layers, but much higher than that of SiOx films. The light leakage of a LC cell aligned vertically on SiOC films was much lower than those of a LC cell aligned on polyimide layers or other inorganic films. They found that LC molecules align vertically on ion beam treated SiOC film when the roughness of the electrostatic force microscopy (EFM) data is high on the SiOC film surface, while they align homogeneously when the roughness of the EFM data is low

  10. Oxide mediated liquid-solid growth of high aspect ratio aligned gold silicide nanowires on Si(110) substrates

    International Nuclear Information System (INIS)

    Silicon nanowires grown using the vapor-liquid-solid method are promising candidates for nanoelectronics applications. The nanowires grow from an Au-Si catalyst during silicon chemical vapor deposition. In this paper, the effect of temperature, oxide at the interface and substrate orientation on the nucleation and growth kinetics during formation of nanogold silicide structures is explained using an oxide mediated liquid-solid growth mechanism. Using real time in situ high temperature transmission electron microscopy (with 40 ms time resolution), we show the formation of high aspect ratio (∼15.0) aligned gold silicide nanorods in the presence of native oxide at the interface during in situ annealing of gold thin films on Si(110) substrates. Steps observed in the growth rate and real time electron diffraction show the existence of liquid Au-Si nano-alloy structures on the surface besides the un-reacted gold nanostructures. These results might enable us to engineer the growth of nanowires and similar structures with an Au-Si alloy as a catalyst.

  11. Viewing angle compensation of various LCD modes by using a liquid crystalline polymer film

    Science.gov (United States)

    Matsumoto, Takuya; Nishimura, Suzushi

    2013-09-01

    The authors have developed liquid crystalline retardation films to improve certain aspects of LCD image quality such as viewing angle performance and coloration. We have successfully created several types of optical retardation films using a rod-like liquid crystalline polymer. The resulting liquid crystalline polymer films have several advantages over conventional uni- or biaxially stretched retardation films. Precisely controlled structures such as twisted nematic, homogeneous nematic, hybrid nematic and homeotropic structures can provide ideal compensation of various LCD types, such as STN, TN, ECB, VA and IPS-LCDs. Twisted nematic film effectively prevents coloration of STN-LCDs, which is a critical flaw affecting color representation. Short pitch cholesteric film, which utilizes said rod-like liquid crystalline polymer and is the optical equivalent of a negative C-plate, can expand the viewing angle of VA-LCDs. Hybrid nematic film is quite unique in that the film functions not only as a wave plate but also as a viewing angle compensator for TN and ECB-LCDs. Homeotropic film, which acts as a positive-C plate, greatly improves the viewing angle performance of IPS and CPVA-LCDs. Our homeotropically aligned liquid crystalline film, called "NV film", is the world's thinnest retardation film. The thickness of the liquid crystalline layer is a mere 1 micrometer. Homeotropic film can be used to expand the viewing angle not only of LCDs but also OLED displays. And NV film, when used in in combination with a quarter wavelength plate, can expand the viewing angles of the circular polarizers used to prevent reflection in OLED displays.

  12. Nematic order by elastic interactions and rigidity sensing of living cells

    CERN Document Server

    Friedrich, Benjamin M

    2010-01-01

    We predict spontaneous nematic order in an ensemble of active force generators with elastic interactions as a minimal model for early cytoskeletal self-polarization. Mean-field theory is formally equivalent to Maier-Saupe theory for a nematic liquid. However, the elastic interactions are long-ranged (and thus depend on cell shape and matrix elasticity) and originate in cell activity. Depending on the density of force generators, we find two regimes of cellular rigidity sensing for which nematic order depends on matrix rigidity either in a step-like manner or with a maximum at an optimal rigidity.

  13. Alignment of liquid crystal on poly[methyl(phenyl)silylene] films treated with polarized UV light

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav; Zakrevskyy, Y.; Stumpe, J.; Sapich, B.; Kadashchuk, A.

    2006-01-01

    Roč. 39, č. 2 (2006), s. 690-696. ISSN 0024-9297 R&D Projects: GA MŠk 1P04OCD14.30 Grant ostatní: NATO(XE) PST .CLG 978952 Keywords : liquid crystal Subject RIV: CH - Nuclear ; Quantum Chemistry Impact factor: 4.277, year: 2006

  14. The development of self-assembled liquid crystal display alignment layers

    NARCIS (Netherlands)

    Hoogboom, J.; Elemans, J.A.A.W.; Rowan, A.E.; Rasing, T.H.M.; Nolte, R.J.M.

    2007-01-01

    From simple pocket calculators to mobile telephones and liquid crystal display (LCD)-TV, over the past few decades, devices based on LCD technology have proliferated and can now be found in all conceivable aspects of everyday life. Although used in cutting-edge technology, it is surprising that a vi

  15. Field-driven dynamics of nematic microcapillaries.

    Science.gov (United States)

    Khayyatzadeh, Pouya; Fu, Fred; Abukhdeir, Nasser Mohieddin

    2015-12-01

    Polymer-dispersed liquid-crystal (PDLC) composites long have been a focus of study for their unique electro-optical properties which have resulted in various applications such as switchable (transparent or translucent) windows. These composites are manufactured using desirable "bottom-up" techniques, such as phase separation of a liquid-crystal-polymer mixture, which enable production of PDLC films at very large scales. LC domains within PDLCs are typically spheroidal, as opposed to rectangular for an LCD panel, and thus exhibit substantially different behavior in the presence of an external field. The fundamental difference between spheroidal and rectangular nematic domains is that the former results in the presence of nanoscale orientational defects in LC order while the latter does not. Progress in the development and optimization of PDLC electro-optical properties has progressed at a relatively slow pace due to this increased complexity. In this work, continuum simulations are performed in order to capture the complex formation and electric field-driven switching dynamics of approximations of PDLC domains. Using a simplified elliptic cylinder (microcapillary) geometry as an approximation of spheroidal PDLC domains, the effects of geometry (aspect ratio), surface anchoring, and external field strength are studied through the use of the Landau-de Gennes model of the nematic LC phase. PMID:26764713

  16. Fabrication and characterization of Mach–Zehnder interferometer based on a hollow optical fiber filled with radial-aligned liquid crystal

    Science.gov (United States)

    Ho, Bo-Yan; Peng, Fenglin; Wu, Shin-Tson; Hwang, Shug-June

    2016-07-01

    We demonstrate a high sensitivity all-fiber Mach–Zehnder interferometer (MZI) based on radial-aligned liquid crystal (LC) in a hollow optical fiber (HOF). The transmission spectrum of the liquid crystal-filled fiber MZI (LCF-MZI) was measured at different temperatures, and the thermal-induced wavelength shift of the interference spectrum probed. The experimental results indicate that the LC alignment and refractive indices inside the hollow capillary are significantly influenced by the temperature, which in turn changes the optical properties of LCF-MZI. Our experimental data on notch wavelength shift agree well with the measured refractive index temperature gradient.

  17. Vertically Aligned Ge Nanowires on Flexible Plastic Films Synthesized by (111)-Oriented Ge Seeded Vapor-Liquid-Solid Growth.

    Science.gov (United States)

    Toko, Kaoru; Nakata, Mitsuki; Jevasuwan, Wipakorn; Fukata, Naoki; Suemasu, Takashi

    2015-08-19

    Transfer-free fabrication of vertical Ge nanowires (NWs) on a plastic substrate is demonstrated using a vapor-liquid-solid (VLS) method. The crystal quality of Ge seed layers (50 nm thickness) prepared on plastic substrates strongly influenced the VLS growth morphology, i.e., the density, uniformity, and crystal quality of Ge NWs. The metal-induced layer exchange yielded a (111)-oriented Ge seed layer at 325 °C, which allowed for the VLS growth of vertically aligned Ge NWs. The Ge NW array had almost the same quality as that formed on a bulk Ge(111) substrate. Transmission electron microscopy demonstrated that the Ge NWs were defect-free single crystals. The present investigation paves the way for advanced electronic optical devices integrated on a low-cost flexible substrate. PMID:26230716

  18. Effect of two-dimensional confinement on switching of vertically aligned liquid crystals by an in-plane electric field.

    Science.gov (United States)

    Choi, Tae-Hoon; Woo, Jae-Hyeon; Choi, Yeongyu; Yoon, Tae-Hoon

    2016-09-01

    We investigated the two-dimensional (2-D) confinement effect of liquid crystals (LCs) on the switching of vertically aligned LCs by an in-plane electric field. When an in-plane field is applied to a vertical alignment (VA) cell, virtual walls are built at the center of the interdigitated electrodes and at the middle of the gaps between them. The LC molecules are confined not only by the two substrates but also by the virtual walls so that the turn-off time of a VA cell driven by an in-plane field is dependent on the pitch of the interdigitated electrodes as well as the cell gap. Therefore, the turn-off time of a VA cell driven by an in-plane field can be reduced simply by decreasing the pitch of the interdigitated electrodes as a result of the enhanced anchoring provided by the virtual walls. The experimental results showed good agreement with a simple model based on the 2-D confinement effect of LCs. PMID:27607702

  19. Phase behaviour of liquid-crystal monolayers of rod-like and plate-like particles.

    Science.gov (United States)

    Martínez-Ratón, Yuri; Varga, Szabolcs; Velasco, Enrique

    2014-05-28

    Orientational and positional ordering properties of liquid crystal monolayers are examined by means of Fundamental-Measure Density Functional Theory. Particles forming the monolayer are modeled as hard parallelepipeds of square section of size σ and length L. Their shapes are controlled by the aspect ratio κ = L/σ (>1 for prolate and order to achieve the lowest possible occupied area per particle. This phase is a uniaxial nematic even at very low densities. In contrast, for plate-like particles, the lowest occupied area can be achieved by random in-plane ordering in the monolayer, i.e., planar nematic ordering takes place even at vanishing densities. It is found that the random in-plane ordering is not favorable at higher densities and the system undergoes an in-plane ordering transition forming a biaxial nematic phase or crystallizes. For certain values of the aspect ratio, the uniaxial-biaxial nematic phase transition is observed for both rod-like and plate-like shapes. The stability region of the biaxial nematic phase enhances with decreasing aspect ratios for plate-like particles, while the rod-like particles exhibit a reentrant phenomenon, i.e., a sequence of uniaxial-biaxial-uniaxial nematic ordering with increasing density if the aspect ratio is larger than 21.34. In addition to this, packing fraction inversion is observed with increasing surface pressure due to the alignment along the layers normal. At very high densities the nematic phase destabilizes to a nonuniform phases (columnar, smectic, or crystalline phases) for both shapes. PMID:24880324

  20. Polysilane template layers for liquid crystal alignment and preparation of polarized light-emitting diodes

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav; Rais, David; Stumpe, J.; Zakrevskyy, Y.

    Rudolstadt : TITK Institute, Technical University Ilmenau, 2006, s. 129-133. [International Symposium on Technologies for Polymer Electronics TPE 06. Rudolstadt (DE), 16.05.2006-18.05.2006] R&D Projects: GA AV ČR IAA100100622; GA MŠk OC 138 Institutional research plan: CEZ:AV0Z40500505 Keywords : polysilane * liquid crystal * light emitting diodes( LED ) Subject RIV: CD - Macromolecular Chemistry

  1. Solubilization of functionalized (5, 5) single-walled carbon nanotubes in 5CB nematic liquid crystals: simulation using Flory–Huggins theory

    International Nuclear Information System (INIS)

    This work analyzes the solubility behavior between a 4'-n-pentyl-4-cyano-biphenyl (5CB) liquid crystal and a maleic anhydride (MA)-grafted surface-modified (5, 5) single-walled carbon nanotube (SWCNT-MA) using the Flory–Huggins model. The statistical thermodynamics of the Flory–Huggins mean-field theory, and its extension to modeling of macromolecular or polymer solutions, is adopted for the first time to investigate solubility as it is related to blending of liquid crystals with carbon nanotubes. This theory incorporated with Monte Carlo calculation reveals that, at room temperature, this functionalized carbon nanotube with all regular commonly seen CNT lengths can spontaneously and fully dissolve in 5CB nematogen when the grafting ratio of the MA functional group reaches 30 at. wt%. We believe that this mesoscale simulation offers a reliable and useful analytical method for 'liquid crystal soluble' carbon nanotubes, since this novel composite material can form a homogeneous nanosolution, and realize its potential in the future

  2. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    Science.gov (United States)

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

    2016-01-01

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field. PMID:26817823

  3. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    Science.gov (United States)

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

    2016-01-01

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field.

  4. Role of Molecular Structure on X-ray Diffraction in Uniaxial and Biaxial Phases of Thermotropic Liquid Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra; (Kent); (CLCR); (Platypus)

    2009-04-29

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  5. Equilibrium and shear-induced conformations of a side-chain liquid crystal polymer

    Science.gov (United States)

    Castelletto, V.; Noirez, L.; Vigoureux, P.

    2000-11-01

    These studies delineate the conformations adopted by a side-chain liquid-crystalline polymer subjected to a steady-state shear flow as well as the corresponding me so pha se director orientations. Two distinct director orientations are identified in the nematic phase, giving evidence of a shear-induced transition from a flow-aligning to a non flow-aligning behavior. This transition coincides, at rest, with a subtle change from prolate to oblate polymer main-chain conformation. In the smectic phase, the layers form multilayer cylinders oriented along the velocity axis.

  6. Liquid crystal orientation on solution processed zinc oxide inorganic films according to molecular concentration

    Science.gov (United States)

    Lee, Jong-Jin; Han, Jae-Jun; Park, Hong-Gyu; Kim, Dai-Hyun; Byun, Sang-Un; Seo, Dae-Shik

    2013-10-01

    In this paper we present the characteristics of molar concentration-dependent zinc oxide (ZnO) inorganic films deposited by the solution process for application in liquid crystal displays. ZnO surfaces supported homogeneously aligned liquid crystal (LC) molecules based on an ion-beam (IB) irradiation system. Uniform LC alignment was obtained at ZnO molar concentrations greater than 0.25 mol l-1. X-ray photoelectron spectroscopic (XPS) analysis revealed that changes in the orientation of LC molecules occurred on the ZnO layer. The electro-optic characteristics of the aligned homogenous LCs and twisted nematic (TN) mode based on the ZnO layer were comparable to those based on polyimide, which showed good potential as ZnO surfaces as an alignment layer.

  7. Effect of Electric Field Alignment on Morphology and Ionic Conductivity of Polymerized Ionic Liquid Block Copolymers

    Science.gov (United States)

    Sharick, Sharon; Nykaza, Jacob; Elabd, Yossef A.; Winey, Karen I.

    2014-03-01

    Polymerized ionic liquid (PIL) block copolymers are appealing for numerous electrochemical applications, including solid polymer electrolyte membranes for batteries and anion exchange membranes for fuel cells. The extent to which the reduced segmental motion caused by the non-conducting polymer segments and grain boundaries between block copolymer microdomains are detrimental to ionic conductivity is unknown. Increased long-range morphological order and connectivity of PIL microdomains are key to understanding the ion transport mechanism and may improve the ionic conductivity of PIL block copolymers. The effect of electric field on the morphology and ionic conductivity of poly(styrene- b-1-[2-(methacryloyloxy)ethyl]-3-butylimidazolium-bis(trifluoromethanesulfonyl)imide)) (PS- b-PMEBIm-TFSI) will be discussed as a function of microdomain orientation. Electric field is used to increase the perpendicular orientation of ion-conducting pathways with respect to the electrodes. The morphology and ionic conductivity were characterized by small-angle X-ray scattering and electrochemical impedance spectroscopy, respectively. The ionic conductivity of unoriented and oriented block copolymers will be compared to the PIL homopolymer, PMEBIm-TFSI, using the Sax and Ottino model.

  8. Reconfigurable knots and links in chiral nematic colloids

    OpenAIRE

    Tkalec, Uroš; Ravnik, Miha; Čopar, Simon; Žumer, Slobodan; Muševič, Igor

    2011-01-01

    Tying knots and linking microscopic loops of polymers, macromolecules, or defect lines in complex materials is a challenging task for material scientists. We demonstrate the knotting of microscopic topological defect lines in chiral nematic liquid crystal colloids into knots and links of arbitrary complexity by using laser tweezers as a micromanipulation tool. All knots and links with up to six crossings, including the Hopf link, the Star of David and the Borromean rings are demonstrated, sta...

  9. Switchable liquid-crystal phase-shift mask for super-resolution photolithography based on Pancharatnam-Berry phase

    Science.gov (United States)

    Glazar, Nikolaus; Culbreath, Christopher; Li, Yannian; Yokoyama, Hiroshi

    2015-11-01

    We present a novel liquid-crystal-based phase-shift mask that utilizes the Pancharatnam-Berry phase for super-resolution photolithography. Using an automated maskless photoalignment technique, we pattern an azobenzene alignment layer in a nematic liquid-crystal cell to fabricate the mask. Since the image is formed by phase cancellation, the minimum feature size is not restricted by the diffraction limit; here, we obtain submicron features. The liquid-crystal properties of the cell allow the mask to be switched on and off by applying a voltage. The cost effectiveness and flexibility of this technique make it a promising new technology for photolithography.

  10. Energy exchange between electromagnetic waves on the director diffraction grating in planar waveguide with nematic layer

    International Nuclear Information System (INIS)

    The energy exchange between two coupled TE modes on the diffraction grating of the director in a planar waveguide containing a nematic liquid crystal layer is calculated. The diffraction grating is induced by an external electric field in the nematic layer with periodic anchoring energy at the waveguide surface. The intensity of the signal mode at the output of the nematic layer is calculated as a function of the amplitude and period of the anchoring-energy modulation, the nematic layer sizes, and the electric-field strength. The cases of modes with the same and opposite directions are considered. Analytical expressions for the maximum intensities of the signal mode are derived. In both cases the maximum intensity of the signal mode increases with an increase in the electric-field strength

  11. Pulsed zero field NMR of solids and liquid crystals

    International Nuclear Information System (INIS)

    This work describes the development and applications to solids and liquid crystals of zero field nuclear magnetic resonance (NMR) experiments with pulsed dc magnetic fields. Zero field NMR experiments are one approach for obtaining high resolution spectra of amorphous and polycrystalline materials which normally (in high field) display broad featureless spectra. The behavior of the spin system can be coherently manipulated and probed in zero field with dc magnetic field pulses which are employed in a similar manner to radiofrequency pulses in high field NMR experiments. Nematic phases of liquid crystalline systems are studied in order to observe the effects of the removal of an applied magnetic field on sample alignment and molecular order parameters. In nematic phases with positive and negative magnetic susceptibility anisotropies, a comparison between the forms of the spin interactions in high and low fields is made. High resolution zero field NMR spectra of unaligned smectic samples are also obtained and reflect the symmetry of the liquid crystalline environment. These experiments are a sensitive measure of the motionally induced asymmetry in biaxial phases. Homonuclear and heteronuclear solute spin systems are compared in the nematic and smectic phases. Nonaxially symmetric dipolar couplings are reported for several systems. The effects of residual fields in the presence of a non-zero asymmetry parameter are discussed theoretically and presented experimentally. Computer programs for simulations of these and other experimental results are also reported. 179 refs., 75 figs

  12. Photoalignment control: self-focusing effect in hybrid- and homeotropic-aligned dye-doped polymer-stabilized liquid crystals

    Science.gov (United States)

    Wang, J.; Shishido, A.

    2015-09-01

    Nonlinear optics has drawn much attention for its great potential in applications, such as frequency conversion, multiple-photon absorption, self-focusing, and so on. However, such optical nonlinearities are generally observed at very high light intensities. In this study, we designed hybrid-aligned dye-doped polymer-stabilized liquid crystals (PSLC), in which the molecular director orientation gradually changes from homeotropic at one surface to homogeneous at the other. In such film, the threshold intensity required to form self-focusing effect was markedly reduced by a factor of 8.5 compared to that in a conventional homeotropic cell, which enabled the generation of the self-focusing effect using a handheld 1-mW laser pointer. In addition, we investigated the structural effect of dye molecules: azo-dye methyl red (MR, photoisomerizable)-doped PSLC was prepared and its NLO response was evaluated. It turned out that such MR-based LC system was not effective for self-focusing effect compared to oligothiophene-doped systems.

  13. Laser-pointer-induced self-focusing effect in hybrid-aligned dye-doped liquid crystals

    Science.gov (United States)

    Wang, Jing; Aihara, Yosuke; Kinoshita, Motoi; Mamiya, Jun-Ichi; Priimagi, Arri; Shishido, Atsushi

    2015-05-01

    Nonlinear optics deals with phenomena where “light controls light” e.g., there is mediation by an intensity-dependent medium through which light propagates. This field has attracted much attention for its immense potential in applications dependent on nonlinear processes, such as frequency conversion, multiple-photon absorption, self-phase modulation, and so on. However, such nonlinearities are typically only observed at very high light intensities and thus they require costly lasers. Here, we report on a self-focusing effect induced with a 1 mW handheld laser pointer. We prepared polymer-stabilized dye-doped liquid crystals, in which the molecular director orientation gradually changes from homeotropic at one surface to homogeneous at the other. This is referred to as hybrid alignment. In such films, the threshold intensity needed to form diffraction rings was reduced by a factor of 8.5 compared to that in conventional homeotropic cells, which enabled the induction of the self-focusing effect with a laser pointer.

  14. Statistical Physics of Isotropic-Genesis Nematic Elastomers: I. Structure and Correlations at High Temperatures

    Science.gov (United States)

    Lu, Bing-Sui; Ye, Fangfu; Xing, Xiangjun; Goldbart, Paul M.

    2013-07-01

    Isotropic-genesis nematic elastomers (IGNEs) are liquid crystalline polymers (LCPs) that have been randomly, permanently cross-linked in the high-temperature state so as to form an equilibrium random solid. Thus, instead of being free to diffuse throughout the entire volume, as they would be in the liquid state, the constituent LCPs in an IGNE are mobile only over a finite, segment specific, length-scale controlled by the density of cross-links. We address the effects that such network-induced localization have on the liquid-crystalline characteristics of an IGNE, as probed via measurements made at high temperatures. In contrast with the case of uncross-linked LCPs, for IGNEs these characteristics are determined not only by thermal fluctuations but also by the quenched disorder associated with the cross-link constraints. To study IGNEs, we consider a microscopic model of dimer nematogens in which the dimers interact via orientation-dependent excluded volume forces. The dimers are, furthermore, randomly, permanently cross-linked via short Hookean springs, the statistics of which we model by means of a Deam-Edwards type of distribution. We show that at length-scales larger than the size of the nematogens this approach leads to a recently proposed, phenomenological Landau theory of IGNEs [Lu et al., Phys. Rev. Lett.108, 257803 (2012)], and hence predicts a regime of short-ranged oscillatory spatial correlations in the nematic alignment, of both thermal and glassy types. In addition, we consider two alternative microscopic models of IGNEs: (i) a wormlike chain model of IGNEs that are formed via the cross-linking of side-chain LCPs; and (ii) a jointed chain model of IGNEs that are formed via the cross-linking of main-chain LCPs. At large length-scales, both of these models give rise to liquid-crystalline characteristics that are qualitatively in line with those predicted on the basis of the dimer-and-springs model, reflecting the fact that the three models inhabit a

  15. DNA hosted and aligned in aqueous interstitia of a lamellar liquid crystal – a membrane–biomacromolecule interaction model system

    KAUST Repository

    Carlsson, Nils

    2013-01-01

    We report that DNA molecules can be intercalated and macroscopically oriented in the aqueous interstitia of a lyotropic lamellar liquid crystal. Using UV-vis linear dichroism and fluorescence spectroscopy we show that double-stranded oligonucleotides (25 base pairs) in the water-octanoate-decanol system remain base-paired in the B conformation and are confined in two dimensions, with the helix axis preferentially parallel to the lipid bilayer surfaces but free to rotate within this plane. The degree of helix confinement and the corresponding 2-D orientation can be improved by decreasing the thickness of the water interstitia via the fraction of water in the ternary mixture. Not surprisingly, the corresponding single-stranded oligonucleotides are not aligned, with their persistence length being short in comparison to the lamellar interstitium thickness. We propose this as a model system for studying interactions of DNA-ligand complexes near a lipid bilayer membrane which we demonstrate by using dye probes that are either covalently attached to one end of the oligonucleotide or reversibly bound by intercalation between the base pairs. Three cationic dyes, all strongly bound by intercalation to DNA when free in solution, are found to not bind to DNA but to prefer the membrane surface. The covalently attached Cy5 also binds to the bilayer while Cy3 tends to end-stack to the oligonucleotide duplex. The orientation of Cy5 parallel to the membrane indicates that electrostatic surface binding predominates over insertion into the hydrophobic interior of the membrane. Anionic and zwitterionic dyes (FAM and ROX) are found to remain randomly oriented in the water between the lipid bilayer surfaces. © The Royal Society of Chemistry.

  16. Steady-state hydrodynamic instabilities of active liquid crystals: Hybrid lattice Boltzmann simulations

    Science.gov (United States)

    Marenduzzo, D.; Orlandini, E.; Cates, M. E.; Yeomans, J. M.

    2007-09-01

    We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of an active nematic liquid crystal sandwiched between confining walls with various anchoring conditions. We confirm the existence of a transition between a passive phase and an active phase, in which there is spontaneous flow in the steady state. This transition is attained for sufficiently “extensile” rods, in the case of flow-aligning liquid crystals, and for sufficiently “contractile” ones for flow-tumbling materials. In a quasi-one-dimensional geometry, deep in the active phase of flow-aligning materials, our simulations give evidence of hysteresis and history-dependent steady states, as well as of spontaneous banded flow. Flow-tumbling materials, in contrast, rearrange themselves so that only the two boundary layers flow in steady state. Two-dimensional simulations, with periodic boundary conditions, show additional instabilities, with the spontaneous flow appearing as patterns made up of “convection rolls.” These results demonstrate a remarkable richness (including dependence on anchoring conditions) in the steady-state phase behavior of active materials, even in the absence of external forcing; they have no counterpart for passive nematics. Our HLB methodology, which combines lattice Boltzmann for momentum transport with a finite difference scheme for the order parameter dynamics, offers a robust and efficient method for probing the complex hydrodynamic behavior of active nematics.

  17. Steady-state hydrodynamic instabilities of active liquid crystals: hybrid lattice Boltzmann simulations.

    Science.gov (United States)

    Marenduzzo, D; Orlandini, E; Cates, M E; Yeomans, J M

    2007-09-01

    We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of an active nematic liquid crystal sandwiched between confining walls with various anchoring conditions. We confirm the existence of a transition between a passive phase and an active phase, in which there is spontaneous flow in the steady state. This transition is attained for sufficiently "extensile" rods, in the case of flow-aligning liquid crystals, and for sufficiently "contractile" ones for flow-tumbling materials. In a quasi-one-dimensional geometry, deep in the active phase of flow-aligning materials, our simulations give evidence of hysteresis and history-dependent steady states, as well as of spontaneous banded flow. Flow-tumbling materials, in contrast, rearrange themselves so that only the two boundary layers flow in steady state. Two-dimensional simulations, with periodic boundary conditions, show additional instabilities, with the spontaneous flow appearing as patterns made up of "convection rolls." These results demonstrate a remarkable richness (including dependence on anchoring conditions) in the steady-state phase behavior of active materials, even in the absence of external forcing; they have no counterpart for passive nematics. Our HLB methodology, which combines lattice Boltzmann for momentum transport with a finite difference scheme for the order parameter dynamics, offers a robust and efficient method for probing the complex hydrodynamic behavior of active nematics. PMID:17930285

  18. Interfacial motion in flexo- and order-electric switching between nematic filled states

    International Nuclear Information System (INIS)

    We consider a nematic liquid crystal, in coexistence with its isotropic phase, in contact with a substrate patterned with rectangular grooves. In such a system the nematic phase may fill the grooves without the occurrence of complete wetting. There may exist multiple (meta)stable filled states, each characterized by the type of distortion (bend or splay) in each corner of the groove and by the shape of the nematic–isotropic interface, and additionally the plateaux that separate the grooves may be either dry or wet with a thin layer of nematic. Using numerical simulations, we analyse the dynamical response of the system to an externally-applied electric field, with the aim of identifying switching transitions between these filled states. We find that order-electric coupling between the fluid and the field provides a means of switching between states where the plateaux between grooves are dry and states where they are wetted by a nematic layer, without affecting the configuration of the nematic within the groove. We find that flexoelectric coupling may change the nematic texture in the groove, provided that the flexoelectric coupling differentiates between the types of distortion at the corners of the substrate. We identify intermediate stages of the transitions, and the role played by the motion of the nematic–isotropic interface. We determine quantitatively the field magnitudes and orientations required to effect each type of transition. (paper)

  19. Anomalous Brownian motion of colloidal particle in a nematic environment: effect of the director fluctuations

    Directory of Open Access Journals (Sweden)

    T. Turiv

    2015-06-01

    Full Text Available As recently reported [Turiv T. et al., Science, 2013, Vol. 342, 1351], fluctuations in the orientation of the liquid crystal (LC director can transfer momentum from the LC to a colloid, such that the diffusion of the colloid becomes anomalous on a short time scale. Using video microscopy and single particle tracking, we investigate random thermal motion of colloidal particles in a nematic liquid crystal for the time scales shorter than the expected time of director fluctuations. At long times, compared to the characteristic time of the nematic director relaxation we observe typical anisotropic Brownian motion with the mean square displacement (MSD linear in time τ and inversly proportional to the effective viscosity of the nematic medium. At shorter times, however, the dynamics is markedly nonlinear with MSD growing more slowly (subdiffusion or faster (superdiffusion than τ. These results are discussed in the context of coupling of colloidal particle's dynamics to the director fluctuation dynamics.

  20. Silicon oxide deposition for enhanced optical switching in polydimethylsiloxane-liquid crystal hybrids.

    Science.gov (United States)

    De Sio, Luciano; Vasdekis, Andreas E; Cuennet, Julien G; De Luca, Antonio; Pane, Alfredo; Psaltis, Demetri

    2011-11-01

    We report an optical switch based on a diffraction grating by combining PDMS microstructures with a photo-responsive Nematic Liquid Crystal (NLC). The grating was realized via replica molding and was subsequently coated with a thin SiO layer. SiO induced a full planar alignment of the liquid crystal. The induced parallel alignment of the LC reduces the response time of the structure by approximately an order of magnitude compared to the same structures without SiO. We explored the effect of the pump intensity on the transmission properties and time response of the switch and identified a strong dependence on the probe polarization, due to the full planar alignment in this structure. The aforementioned inclusion of the SiO layer enables enhanced performance of optical devices based on the fusion of nematogens with soft and flexible substrates. PMID:22109231

  1. Modulational instability of nematic phase

    Indian Academy of Sciences (India)

    T Mithun; K Porsezian

    2014-02-01

    We numerically observe the effect of homogeneous magnetic field on the modulationally stable case of polar phase in = 2 spinor Bose–Einstein condensates (BECs). Also we investigate the modulational instability of uniaxial and biaxial (BN) states of polar phase. Our observations show that the magnetic field triggers the modulational instability and demonstrate that irrespective of the magnetic field effect the uniaxial and biaxial nematic phases show modulational instability.

  2. 用液晶与聚合物混合材料的各向异性相分离制备快速响应液晶盒%Fast Switching Nematic Liquid Crystal Cell Fabricated by Anisotropic Phase-separation From a Liquid Crystal and Polymer Composite Material

    Institute of Scientific and Technical Information of China (English)

    王庆兵

    2004-01-01

    展示一种新型含有超薄液晶层( 小于1 μm) 的快速响应液晶盒, 总的响应时间( τon+τoff) 可以达到1.3 ms.这种液晶器件可以通过对一种液晶和聚合物混合材料的各向异性相分离制备获得. 偏光显微镜和扫描电子显微镜的观测结果确认了一种液晶/聚合物的双层膜机构的形成. 实验结果表明液晶层的厚度可以简单地通过改变液晶在混合材料中的含量来精确调节.这种制备方法可以用来制作含有超薄液晶层的快速显示液晶器件用于视频显示方面的应用.%It is demonstrated that a nematic liquid crystal (LC) cell containing a very thin (《1 μm) LC film can perform very fast switching, with a total response time as fast as 1.3 ms. Such type of LC devices can be prepared by a photo-induced anisotropic phase-separation from a nematic LC and polymer composite material. The formation of the LC/polymer bi-layer structure in the cell after the anisotropic phase-separation was confirmed by employing polarized light microscope and scanning electron microscope. It is also found that LC layer thickness can be fine tuned by adjusting the LC concentration in the composite mixture. Such a technique can be used to fabricate LC devices containing very thin LC film and performing fast switching for TV and Video applications where fast response time is required.

  3. The use of mould-templated surface structures for high-quality uniform-lying-helix liquid-crystal alignment

    Science.gov (United States)

    Outram, B. I.; Elston, S. J.; Tuffin, R.; Siemianowski, S.; Snow, B.

    2013-06-01

    The chiral-flexoelectrooptic effect in a Uniform Lying Helix (ULH) configuration provides a sub-millisecond in-plane rotation of the optic axis with the application of a transverse field. This enables displays with a wide viewing angle without costly in-plane-type electrodes. The salient challenge is one of alignment of the ULH, which is not topologically compatible with uniform alignment surface treatments. Here, we create a micro-grooved surface structure with features on the micron scale by using a replica-moulding technique. When the cell is assembled, the micro-grooves create channels, and using surface-energy considerations, we explain how and show experimentally that the channels align a cholesteric material in the ULH geometry with the helicoidal axis oriented parallel to the channels. The resultant alignment provides a high level of contrast between crossed polarizers and exhibits an electrooptic response with a switching time of the order of tens of microseconds.

  4. Twist transition of nematic hyperbolic hedgehogs

    Science.gov (United States)

    James, Richard; Fukuda, Jun-ichi

    2014-04-01

    Stability of an idealized hyperbolic hedgehog in a nematic liquid crystal against a twist transition is investigated by extending the methodology of Rüdinger and Stark [Liq. Cryst. 26, 753 (1999), 10.1080/026782999204840], where the hedgehog is confined between two concentric spheres. In the ideal hyperbolic-hedgehog the molecular orientation is assumed to rotate proportionally with respect to the inclination angle, θ (and in the opposite sense). However, when splay, k11, and bend, k33, moduli differ this proportionality is lost and the liquid crystal deforms relative to the ideal with bend and splay. Although slight, these deformations are shown to significantly shift the transition if k11/k33 is small. By increasing the degree of confinement the twist transition can be inhibited, a characteristic both hyperbolic and radial hedgehogs have in common. The twist transition of a hyperbolic defect that accompanies a particle is found to be well predicted by the earlier stability analysis of a thick shell.

  5. Influence of magnetic field on the director profile in nematic layer with curved surface

    Czech Academy of Sciences Publication Activity Database

    Vasil'ev, A.N.; Podoliak, Natalia

    2010-01-01

    Roč. 55, č. 2 (2010), s. 300-304. ISSN 1063-7745 Institutional research plan: CEZ:AV0Z10100520 Keywords : nematic liquid crystal layer * magnetic field Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.644, year: 2010

  6. Correlation and disorder-enhanced nematic spin response in superconductors with weakly broken rotational symmetry

    DEFF Research Database (Denmark)

    Andersen, Brian Møller; Graser, S.; Hirschfeld, P. J.

    2012-01-01

    Recent experimental and theoretical studies have highlighted the possible role of an electronic nematic liquid in underdoped cuprate superconductors. We calculate, within a model of d-wave superconductor with Hubbard correlations, the spin susceptibility in the case of a small explicitly broken...

  7. Magnetic alignment and patterning of cellulose fibers

    International Nuclear Information System (INIS)

    The alignment and patterning of cellulose fibers under magnetic fields are reported. Static and rotating magnetic fields were used to align cellulose fibers with sizes ranging from millimeter to nanometer sizes. Cellulose fibers of the millimeter order, which were prepared for papermaking, and much smaller fibers with micrometer to nanometer sizes prepared by the acid hydrolysis of larger ones underwent magnetic alignment. Under a rotating field, a uniaxial alignment of fibers was achieved. The alignment was successfully fixed by the photopolymerization of a UV-curable resin precursor used as matrix. A monodomain chiral nematic film was prepared from an aqueous suspension of nanofibers. Using a field modulator inserted in a homogeneous magnetic field, simultaneous alignment and patterning were achieved

  8. Magnetic alignment and patterning of cellulose fibers

    Directory of Open Access Journals (Sweden)

    Fumiko Kimura and Tsunehisa Kimura

    2008-01-01

    Full Text Available The alignment and patterning of cellulose fibers under magnetic fields are reported. Static and rotating magnetic fields were used to align cellulose fibers with sizes ranging from millimeter to nanometer sizes. Cellulose fibers of the millimeter order, which were prepared for papermaking, and much smaller fibers with micrometer to nanometer sizes prepared by the acid hydrolysis of larger ones underwent magnetic alignment. Under a rotating field, a uniaxial alignment of fibers was achieved. The alignment was successfully fixed by the photopolymerization of a UV-curable resin precursor used as matrix. A monodomain chiral nematic film was prepared from an aqueous suspension of nanofibers. Using a field modulator inserted in a homogeneous magnetic field, simultaneous alignment and patterning were achieved

  9. Magnetic alignment and patterning of cellulose fibers

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, Fumiko; Kimura, Tsunehisa [Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan)], E-mail: tkimura@kais.kyoto-u.ac.jp

    2008-04-01

    The alignment and patterning of cellulose fibers under magnetic fields are reported. Static and rotating magnetic fields were used to align cellulose fibers with sizes ranging from millimeter to nanometer sizes. Cellulose fibers of the millimeter order, which were prepared for papermaking, and much smaller fibers with micrometer to nanometer sizes prepared by the acid hydrolysis of larger ones underwent magnetic alignment. Under a rotating field, a uniaxial alignment of fibers was achieved. The alignment was successfully fixed by the photopolymerization of a UV-curable resin precursor used as matrix. A monodomain chiral nematic film was prepared from an aqueous suspension of nanofibers. Using a field modulator inserted in a homogeneous magnetic field, simultaneous alignment and patterning were achieved.

  10. Liquid crystal applications and uses, v.3

    CERN Document Server

    Bahadur, Birenda

    1992-01-01

    This book reviews comprehensively the technological, scientific, artistic and medical applications of liquid crystals. It starts with the basics of liquid crystals and covers electro-optical, thermo-optical, colour, polymeric, lyotropic, and scientific applications of liquid crystalline materials. It discusses the fabrication and operational principles of a full range of liquid crystal displays including dynamic scattering, twisted nematic, supertwisted nematic, dichroic, smectic A, ferroelectric, polymer dispersed, light valve, active matrix, etc., in detail. It also covers the emerging appli

  11. Liquid crystal applications and uses, v.2

    CERN Document Server

    Bahadur, Birenda

    1991-01-01

    This book reviews comprehensively the technological, scientific, artistic and medical applications of liquid crystals. It starts with the basics of liquid crystals and covers electro-optical, thermo-optical, colour, polymeric, lyotropic, and scientific applications of liquid crystalline materials. It discusses the fabrication and operational principles of a full range of liquid crystal displays including dynamic scattering, twisted nematic, supertwisted nematic, dichroic, smectic A, ferroelectric, polymer dispersed, light valve, active matrix, etc., in detail. It also covers the emerging appli

  12. Liquid crystal applications and uses, v.1

    CERN Document Server

    Bahadur, Birenda

    1990-01-01

    This book reviews comprehensively the technological, scientific, artistic and medical applications of liquid crystals. It starts with the basics of liquid crystals and covers electro-optical, thermo-optical, colour, polymeric, lyotropic, and scientific applications of liquid crystalline materials. It discusses the fabrication and operational principles of a full range of liquid crystal displays including dynamic scattering, twisted nematic, supertwisted nematic, dichroic, smectic A, ferroelectric, polymer dispersed, light valve, active matrix, , in detail. It also covers the emerging applicati

  13. Orientations of Chromonic Liquid Crystals by Imprinted or Rubbed Polymer Films

    Science.gov (United States)

    Yi, Youngwoo; McGuire, Aya; Clark, Noel

    2014-03-01

    A variety of novel alignment effects of chromonic liquid crystal phases of sunset yellow (SSY)/water, disodium cromoglycate (DSCG)/water, and their mixtures by thiol-ene polymer films topographically imprinted with linear channels are observed using polarizing optical microscopy. Nematic DSCG and SSY at low concentration and their nematic mixtures orient with the long axes of stacked chromonic aggregates on average parallel to the channels, that is, with the molecular planes normal to the channel axis. On the contrary, nematic SSY in contact with the rubbed polyimide films orients with the long axes on average in-plane perpendicular to the rubbing direction, arguably, due to a tongue-groove interaction between SSY and the stretched PI chains. Furthermore, multi-stable alignments are observed in SSY solutions of sufficiently high concentration, including preferential in-plane orientation of the long axes of the aggregates parallel to, perpendicular to, and 45° rotated from the channels. This work was supported by NSF grant DMR 1207606, NSF MRSEC grant DMR 0820579, and NSF Research Experience for Undergraduate programs.

  14. Report on twisted nematic and supertwisted nematic device characterization program

    Science.gov (United States)

    1995-01-01

    In this study we measured the optical characteristics of normally white twisted nematic (NWTN) and super twisted nematic (STN ) cells. Though no dynamic computer model was available, the static observations were compared with computer simulated behavior. The measurements were taken as a function of both viewing angle and applied voltage and included in the static case not only luminance but also contrast ratio and chromaticity . We employed the computer model Twist Cell Optics, developed at Kent State in conjunction with this study, and whose optical modeling foundation, Iike the ViDEOS program, is the 4 x 4 matrix method of Berreman. In order to resolve discrepancies between the experimental and modeled data the optical parameters of the individual cell components, where not known, were determined using refractometry, profilometry, and various forms of ellipsometry. The resulting agreement between experiment and model is quite good due primarily to a better understanding of the structure and optics of dichroic sheet polarizers. A description of the model and test cells employed are given in section 2. Section 3 contains the experimental data gathered and section 4 gives examples of the fit between model and experiment. Also included with this report are a pair of papers which resulted from the research and which detail the polarizer properties and some of the cell characterization methods.

  15. Localization of Waves without Bistability Worms in Nematic Electroconvection

    CERN Document Server

    Riecke, H; Riecke, Hermann; Granzow, Glen D.

    1998-01-01

    A general localization mechanism for waves in dissipative systems is identified that does not require the bistability of the basic state and the nonlinear plane-wave state. The mechanism explains the two-dimensional localized wave structures (`worms') that recently have been observed in experiments on electroconvection in nematic liquid crystals where the transition to extended waves is supercritical. The mechanism accounts for the propagation direction of the worms and certain aspects of their interaction. The dynamics of the localized waves can be steady or irregular.

  16. Dynamics of phase ordering of nematics in a pore

    International Nuclear Information System (INIS)

    We study the kinetics of phase ordering of a nematic liquid crystal, modeled by a spin-rotor Hamiltonian, confined within a parallel piped pore. The dynamics of the rotor obeys the time-dependent Ginzburg-Landau equation. We study the generation and evolution of a variety of defect structures, and the growth of domains, with different anchoring conditions at the pore surface. Unlike in binary fluids, mere confinement with no anchoring field, does not result in slow dynamics. Homeotropic anchoring, however, leads to slow logarithmic growth. Interestingly, homogeneous anchoring dynamically generates wall defects, resulting in an Ising like structure factor at late times. (author). 27 refs, 4 figs

  17. In situ deuteron NMR investigations of sheared liquid crystalline polymers.

    Science.gov (United States)

    Siebert, Hartmut; Becker, Patrick; Quijada-Garrido, Isabel; Grabowski, David A; Schmidt, Claudia

    2002-01-01

    The flow behavior of nematic liquid crystalline polysiloxanes of the side-chain type is studied by in situ 2H NMR spectroscopy on samples under shear in a cone-and-plate cell. The director orientation as a function of applied shear rate is determined from the quadrupole splitting of the spectra. The data analysis yields the two Leslie viscosity coefficients alpha2 and alpha3 and the flow-alignment parameter lambda = -(alpha3 + alpha2)/(alpha3 - alpha2). The values of lambda were determined for several homopolymers with only one type of side chain and random copolymers containing two different side chains. The results show that the flow behavior is related to the phase structure of the polymers, which varies with their composition. Only polymers with large amounts of smectic clusters in the nematic state show the tumbling instability (absolute value(lambda) polymers are flow aligning (absolute value(lambda) > or = 1). For some polymers, a transition from tumbling at low temperature to flow aligning at high temperatures was observed. PMID:12469817

  18. The elusive thermotropic biaxial nematic phase in rigid bent-core molecules

    Indian Academy of Sciences (India)

    Bharat R Acharya; Andrew Primak; Theo J Dingemans; Edward T Samulski; Satyendra Kumar

    2003-08-01

    The biaxial nematic liquid crystalline phase was predicted several decades ago. Several vigorous attempts to find it in various systems resulted in mis-identifications. The results of X-ray diffraction and optical texture studies of the phases exhibited by rigid bent-core molecules derived from 2,5-bis-(-hydroxyphenyl)-1,3,4-oxadiazole reveal that the biaxial nematic phase is formed by three compounds of this type. X-ray diffraction studies reveal that the nematic phase of these compounds has the achiral symmetry D2h, in which the overall long axes of the molecules are oriented parallel to each other to define the major axis of the biaxial phase. The apex of the bent-cores defines the minor axis of this phase along which the planes containing the bent-cores of neighboring molecules are oriented parallel to each other.

  19. Surface Alignment Analysis of Polyimide Liquid Crystal Vertical Alignment Films%聚酰亚胺液晶垂直取向膜的表面取向分析

    Institute of Scientific and Technical Information of China (English)

    姜莹; 孙振; 房玉庆; 汪映寒

    2011-01-01

    采用均苯四甲酸二酐(PMDA)、4,4'-二胺基二苯甲烷(MDA)以及侧基含联苯和己基的二胺(TBCA)三元共聚制备了聚酰亚胺垂直取向剂,摩擦前后得到相同的垂直取向效果,探讨了侧链二胺TBCA的含量对聚酰亚胺取向膜垂直取向性能的影响,采用衰减全反射红外光谱(ATR-FTIR)对摩擦前后聚酰亚胺膜表面侧链的相对含量进行了对比,并运用原子力显微镜(AFM)考察了表面细微沟纹对液晶分子取向的影响.结果表明,在取向膜未经摩擦没有产生表面沟纹的情况下液晶分子也能取向,并且这类取向膜表面侧链的含量与摩擦后的含量相当.%Polyimide (PI) was synthesized by copolymerization of PMDA, MDA and TBCA in this paper.The films prepared by PI can induce the same vertical alignment before and after rubbing.The effect of content of TBCA on the alignment property was discussed, the relative content of surface side chains was observed by the ATR-FTIR spectra of the PI films' surface, and the effect of the microgrooves on the liquid crystal was investigated by atomic force microscope (AFM).The PI films without microgrooves before rubbing can align liquid crystal molecules.Moreover, the content of surface side chains of this PI films before rubbing is the same as that after rubbing.

  20. Stability of liquid crystalline bridges

    Science.gov (United States)

    Mahajan, Milind P.; Tsige, Mesfin; Taylor, P. L.; Rosenblatt, Charles

    1999-02-01

    The stability of cylindrical bridges of the liquid crystal octylcyanobiphenyl in an immiscible liquid bath was investigated in the nematic and smectic A phases. In the nematic phase the bridge was found to destabilize at a length-to-diameter (slenderness) ratio R similar to that of ordinary Newtonian fluids. On the other hand, the Bingham behavior of the smectic A phase, i.e., an apparent yield stress, enabled the formation of stable columns with R well in excess of π.