Epitropic Liquid-Crystal Hexadecane Layer in the Rheological Model of a Heterophase Interlayer

The hydrodynamic model of a heterophase interlayer of a liquid, which includes an epitropic liquid-crystal (ELC) layer, is supplemented with its structural-rheological model. The application of these models and the technique developed for processing the results of viscosity measurements for n-hexadecane interlayers in the tribotriads has made it possible to conduct a detailed determination of the properties of its ELC layer and the overlapped layer, such as the equilibrium thickness and viscosity, their temperature variation, and the activations energy of the viscous flow.     

相场晶体法模拟过冷熔体中的晶体生长

利用相场晶体(phase-field crystal)模型,采用有限差分法,模拟了过冷熔体中晶体生长过程,研究了不同相区、不同过冷度对晶体生长过程的影响.结果表明,在共存区中,随着演化的进行,晶体生长被抑制,液-晶边界层逐渐变厚;在单相区中,随着过冷度的增大,晶态区面积显著增加,液-晶边界层逐渐变薄.晶体生长速度和过冷度成近似线性的关系. 关键词： 相场晶体 自由能函数 过冷熔体 晶体生长     

Slow tumbling of paramagnetic probes in the solid phase of the liquid-crystal p (p methoxybenzlidene) amino benzonitrile

A marked broadening of the extrema resonances of the electron paramagnetic resonance spectra of vanadyl acetylacetonate and copper benzoyl acetonate doped into the solid phase of the nematic liquid-crystal p (p methoxybenzlidene) amino benzonitrile is observed as the temperature is increased to the solid to liquid-crystal transition at 106°C. The effects are a result of slow tumbling of the paramagnetic probes which is shown to follow a thermally activated Arrhenius behavior. The motion is consistent with previous Raman and neutron scattering studies in the solid phase which suggest the possibility of large amplitude fluctuations and a soft disordered regime in the solid near the transition to the liquid-crystal phase.     

Rotational reorientation of the director in twisted nematic liquid-crystal cells

The orientational relaxation of the director to its equilibrium orientation under electric, elastic, and viscous torques arising in twisted nematic liquid-crystal cells is investigated. It is shown that the relaxation time of the director depends strongly on the external electric field strength and weakly on the energy of anchoring of liquid-crystal molecules to the surfaces of the cell. The relaxation time of the director anomalously increases in electric fields close to the Fréedericksz threshold. It is established that, at specific strengths of the external electric field, the relaxation can occur in the form of traveling waves propagating from one edge to the other edge of the twisted nematic liquid-crystal cell. The calculations of the relaxation processes in the vicinity of the nematic-smectic A phase transition temperature demonstrate that the distortion of the director field is uniform over the entire cross section of the liquid-crystal cell and does not depend on the strength of anchoring of the liquid-crystal molecules to the surfaces of the cell.     

基于亚波长光栅结构的硅基液晶器件模型研究

金(Au)亚波长光栅被溅射到经典硅基液晶(LCoS)的ITO电极上,它与薄液晶盒和底层铝电极组成复合共振波导结构,简称GLCoS。与基于液晶传播效应的LCoS截然不同,在GLCoS中,上电极的表面等离激元与光栅槽中的TM-FP (TM-Fabry Pérot)共振耦合,诱导一个0阶反射的相位调制;铝(Al)电极既是反射背板又与Au光栅、薄液晶盒组成波导,使共振耦合得到增强。在操控光波阵面的同时,GLCoS也作为电控器件,施加电压改变液晶的折射率,进而控制开腔FP的边缘介质条件,达到有源0~2π相位调制。实验结果表明,本文结构可用于1μm量级像素的相位空间光调制器,在高空间带宽积的全息视频显示中具有广阔的应用前景。     

Topologically patterning of polyvinyl alcohol microstructures for vertical-/hybrid-aligned nematic liquid-crystal gratings doped with polyhedral oligomeric silsesquioxane nanoparticles

We demonstrate a soft lithography approach for fabrication of a topographically patterned polyvinyl alcohol(PVA) liquid-crystal(LC) alignment layer. This specific approach employs modified micromolding in capillaries for negative replication of the PVA microstructures on indium tin oxide(ITO) substrates from patterned poly(dimethylsiloxane) molds in a single step, leading to planar alignment on the desired regions. By doping with polyhedral oligomeric silsesquioxane nanoparticles, which can induce vertical alignment on bare ITO surfaces,periodic LC phase gratings based on an alternating vertical-aligned/hybrid-aligned nematic geometry are presented as an application, and a theoretical model was used to simulate and examine the experimental results.     

Recording of thin phase holograms in polymer-dispersed liquid-crystal composites based on fullerene-containing π-conjugated organic systems

The recording of thin phase holograms in promising fullerene-containing, polymer-dispersed liquid-crystal composites based on 2-cyclooctylamino-5-nitropyridine and N-(4-nitrophenyl)-(L)-prolinol using picosecond laser pulses is studied for the first time. The anisotropy of the refractive index substantially increases after laser irradiation and exceeds by a factor of five this anisotropy for liquid-crystal cells containing dyes. The results of our studies suggest that the fullerene-containing, polymer-dispersed liquid-crystal systems can be used as passive media for reversible data recording.     

Evidence for triclinic symmetry in smectic liquid crystals of bent-shape molecules.

The first experimental evidence for triclinic symmetry of bulk smectic liquid-crystal samples of achiral banana-shaped molecules is presented. This phase corresponds to the so-called Sm-CG phase consisting of biaxial molecules and characterized by two tilt directions with respect to the layer normal: tilt of the molecular plane (clinic) and tilt of the molecular kink direction (leaning). Each smectic layer has a polarization component normal to the smectic layers (C1 symmetry). The observations suggest that the phase tentatively labeled as B7 is identical with the Sm-CG phase.     

Dynamics of 8CB confined into porous silicon probed by incoherent neutron backscattering experiments

Confinement in the nanochannels of porous silicon strongly affects the phase behavior of the archetype liquid-crystal 4-n-octyl-4-cyanobiphenyl (8CB). A very striking phenomenon is the development of a short-range smectic order, which occurs on a very broad temperature range. It suggests in this case that quenched disorder effects add to usual finite size and surface interaction effects. We have monitored the temperature variation of the molecular dynamics of the confined fluid by incoherent quasielastic neutron scattering. A strongly reduced mobility is observed at the highest temperatures in the liquid phase, which suggests that the interfacial molecular dynamics is strongly hindered. A continuously increasing slowdown appears on cooling together with a progressive growth of the static correlation length.     

Orientational Order in Liquid Crystal Complexes Based on Lanthanides

In this study, we have for the first time determined the degree of an orientational order S for a series of liquid-crystal complexes based on lanthanides (Eu⁺³, Gd⁺³, Tb⁺³, Dy⁺³) with the same ligand composition in the temperature range of existence of the nematic phase by using experimental refractometry results. We have also found an even-odd alternative S as number of protons in the ions complexing agent has consecutively increased. The obtained values of S have been compared with the corresponding degrees of order of the calamite organic liquid crystals.

     

Optical and dielectric properties of the mesogen 4-cyano-4′-n–octyl biphenyl as a function of temperature

The effect of temperature on certain optical and dielectric properties of one member, namely 4-cyano-4′-n–octyl biphenyl (8CB) of the mesogenic series 4-cyano-4′-n–alkyl biphenyl (nCB), is reported. The dependence of the ordinary and extraordinary components of polarisability, α_o and α_e, on temperature is studied using a He–Ne laser beam, and the variation of orientational order parameter with temperature in the entire mesogenic phase determined from the optical studies. The dependence of the effective molecular dipole moment, μ_eff, in the liquid-crystal phase, and the angle of inclination, β, of the dipole moment with the preferred direction have been investigated. An experimental estimate of the correlation factor ‘g’, which is indicative of the nature of the molecular association in the mesophase, has been obtained.     

Ringed spherulitic and undulated textures in the nematic phase of a mixture of trans-4-hexylcyclohexanecarboxilic and benzoic acids

We present a polarizing optical microscopy study of a liquid-crystal mixture of trans-4-hexylcyclohexanecarboxilic (C6) and benzoic acids. Both materials have carboxylic groups that can form dimers through hydrogen bonding. The mixture is nematic at room temperature and has the clearing point at 88°C. The nematic phase shows ringed spherulites, sometimes looking like spiral structures, and undulated textures, which remain visible when heating the sample till 71°C. This is the temperature of a texture transition inside the nematic phase.     

Discontinuity of the Magnetization in Diluted O(n)-Models

We study the annealed site-diluted versions of the classical O(n) Heisenberg ferromagnets. It is shown that if the temperature is low enough, then at some value of the chemical potential there is phase coexistence between a magnetized, high-density state (liquid-crystal state) and a low-density state (gaseous state) with no magnetic order.     

用小角X射线散射法研究CH2Cl2,CHCl3和CCl4对磷脂酰胆碱液晶态结构的影响机理

本文采用小角X射线散射法分别研究CH₂Cl₂,CHCl₃和CCl₄对磷脂酰胆碱液晶态结构的影响机理,通过比较得知,CH₂Cl₂,CHCl₃和CCl₄对磷脂酰胆碱液晶态结构影响的不同之处,主要是它们空间旋转电子云密度分布不同所致,空间旋转电子云密度分布呈球状或椭球状的物质都有使磷脂酰胆碱液晶形成片层六角形的机理,呈圆锥状的物质有诱发磷 关键词：     

MEASUREMENTS OF LOCAL HEAT TRANSFER COEFFICIENTS FROM A FLAT PLATE TO A PAIR OF CIRCULAR AIR IMPINGING JETS

Local heat transfer coefficients from a flat plate to a pair of circular air impinging jets are investigated experimentally, A pair of well-controlled, fully developed circular air impinging jets at room temperature are used in the experiments. The experimental method in this investigation is the transient liquid-crystal technique. During the experiments, the surface liquid-crystal color distribution of the test plate is recorded using a video imaging acquisition system, and the color information is translated into a surface temperature distribution through a digital color image processing unit. Local heat transfer coefficients art obtained using a surface transient heat conduction analysis. The flow Reynolds number of the jet is kept at 23,000. The jet-to-plate distance and the jet-to-jet spacing are varied in the experiment. Detailed radial heat transfer distributions at different radial directions are obtained and analyzed for L/D = 2, 4, 6, 8, and 10. The effect of jet spacing distance (S/D =1.75, 3.5,5.25, 7.0) is analyzed by comparing to data obtained from a single jet with similar flow configurations.     

Digital phase-shifting interferometer with an electrically addressed liquid-crystal spatial light modulator

A digital phase-shifting interferometer with a liquid-crystal-display coupled, parallel aligned, nematic liquid-crystal spatial light modulator is developed. The optical phase shift in the Michelson-type polarization interferometer is achieved by a digital phase shift of a grating displayed on the spatial light modulator. Accurate experimental results of using the heterodyne system for pi/2 phase steps were demonstrated. A phase-shifting interferometer with no moving parts and no requirement for calibration of the value of the phase shift was achieved.     

Phase-only optical encryption

We have implemented a phase-only optical encryption and decryption system with a readout based on the generalized phase-contrast method. The experimental system has been implemented with liquid-crystal spatial light modulators to generate binary phase-encrypted masks and a decrypting key. A phase-contrast filter is used to display the phase information.     

Dipole moments and the mechanism of molecular motion in a cyanobiphenyl-containing liquid-crystal monomer in a solution and in the bulk of the material in the absence of external orienting fields

The dipole moments and dielectric polarization relaxation of a low-molecular liquid-crystal monomer, namely, 4-[ω-(2-propenoyloxy)pentyloxy]-4′-cyanobiphenyl (CBO-5A), are investigated in a mesomorphic phase, an isotropic melt, and a chloroform solution in the absence of external orienting fields. Analysis of the dipole polarization of the CBO-5A monomer in the chloroform solution (x ₂ ～ 0.0566 mol/mol) demonstrates that the temperature dependences of the permittivity and the dipole moment measured with decreasing temperature are characteristic of molecular association with the Kirkwood factor g = 0.77. It is found that the Kirkwood factor g for the isotropic melt is 0.55. The values of g < 1 indicate the presence of associates with a tendency toward antiparallel orientation of the CBO-5A molecules in both the solution and the melt. Dielectric absorption of relaxation nature is observed in the chloroform solution at temperatures in the range from ?50 to ?20°C. Two relaxation processes of dipole polarization are observed in the isotropic and liquid-crystal phases of the CBO-5A monomer in the bulk of the material. Examination of the temperature dependences of the dielectric relaxation time revealed that molecules of the CBO-5A liquid-crystal monomer in the bulk can be involved in several types of motion occurring through either the local mechanism or the cooperative mechanism.     

Effect of ordering on spinodal decomposition of liquid-crystal/polymer mixtures

Partially phase-separated liquid-crystal/polymer dispersions display highly fibrillar domain morphologies that are dramatically different from the typical structures found in isotropic mixtures. To explain this, we numerically explore the coupling between phase ordering and phase-separation kinetics in model two-dimensional fluid mixtures phase separating into a nematic phase, rich in liquid crystal, coexisting with an isotropic phase, rich in polymer. We find that phase ordering can lead to fibrillar networks of the minority polymer-rich phase.     

Polarization of light by a polymer film containing elongated drops of liquid crystal with inhomogeneous interfacial anchoring

An optico-mechanical model describing the coherent (directed) transmittance and the degree of polarization of forward-transmitted light by a polymer film with elongated liquid-crystal (LC) drops has been developed. This model, based on the Foldy–Twersky and anomalous-diffraction approximations, makes it possible to analyze the optical response of a film under extension as a function of the film thickness, refractive index of the polymer, the sizes and anisometry parameters of liquid-crystal drops, their concentration, internal structure, polydispersity, and orientation of optical axes. The model is verified based on the comparison of numerical and experimental data for the inverse modification of interfacial anchoring by an ion-forming surfactant. The internal drop structure is determined by solving the problem of minimizing the volume free energy density. A comparative analysis of the calculated transmittance and degree of polarization for films with uniform homeotropic and modified inhomogeneous interfacial anchoring is performed. The spectral polarization characteristics of a film with elongated LC drops and single-domain internal structure, formed under mechanical extension with the aid of surfactants, are investigated.