Viscosity Of Liquid Crystals Research Articles

Molecules structure and viscosity relationship of nematic liquid crystal and BPNN-QSAR model

Nematic liquid crystal materials designed for optics, microwave communication tuning, etc. need high response speed, which is related to the rotational viscosity and the birefringent index of the liquid crystal. In order to achieve a wide tuning range of phase modulation, the nematic liquid crystals often employ large π-electron conjugated systems and large polar groups to enhance the birefringence and dielectric anisotropy of the liquid crystal molecule, which, however, increases the viscosity of the liquid crystal material, deteriorating the response speed of the microwave device. Herein, we explore the viscosity of the nematic liquid crystal from the perspective of liquid crystal compound structure by testing the viscosity of our designed and synthesized forty-two different nematic liquid crystals by using a rotating rheometer at 25 ℃. To the best of our knowledge, the BPNN-QSAR quantitative structure-activity model between nematic liquid crystal molecular structure and viscosity is established for the first time. The correlation coefficient between the predicted value and the experimental value is <i>q</i><sup>2</sup> = 0.607 > 0.5, indicating that the model can be used to predict the viscosity performances of liquid crystal compounds. Besides, the molecular structure descriptors affecting the viscosity properties are explored. Based on the practical application and this model, seven liquid crystal molecules of two series with large birefringent index are designed and tested. The viscosity predicted by the BPNN model is smaller than that of the molecules of the same type and matches with the measured viscosity.

A bistable ion-doped cholesteric liquid crystal smart window with a small amount of polymer

Bistable liquid crystal devices, which require electricity only at the switching processes of the two states, have advantages in energy saving and safety compared with monostable liquid crystal devices. Due to electrohydrodynamic and dielectric effects, the ion-doped cholesteric liquid crystal can switch between a focal conic state and a planar state with different frequencies of the driving voltage. However, the cholesteric liquid crystal that self-assembles from the dynamic scattering state always has a poor focal conic state, resulting in a low contrast ratio. This paper presents a bistable polymer-stabilized ion-doped cholesteric liquid crystal device. The introduction of a small amount of polymer network can greatly enhance the light scattering capabilities of the focal conic state, endowing the device with excellent electro-optic performance. The electro-optical properties of the device are investigated with the various content of monomer and chiral dopant, and rotational viscosity of liquid crystal. Liquid crystal with a low rotational viscosity coefficient is beneficial to the formation of a good polymer network. The pitch induced by chiral dopant impacts the formation process of the polymer network, which subsequently affects the electro-optical properties. The bistable device has a low driving voltage and a high contrast ratio, making it ideal for use in smart windows.

New Diluter Solubilized in Liquid Crystal Compounds for High Stability and Fast Response Speed Liquid Crystal Displays

Diluters play a crucial role for reducing the rotational viscosity of liquid crystal (LC) materials for improving the response property of LC displays (LCDs). However, conventional diluters tend to deteriorate relatively easily under ultraviolet (UV) exposure, due to existence of vinyl groups. Hence, it was difficult to prepare polymer layers in the LC cells by exposing UV for polymerization regarding polymer-sustained vertically-aligned (PS-VA) and polyimide-free (PI-free) technologies. In this study, however, we succeeded to develop a high stable diluter, which shows a symmetrical structure and carries fluorinated groups for stable nematic phase and high affinity with other fluorinated LC compounds. With the use of the symmetrical-structured diluter, we developed the PS-VA and the PI-free in-plane switching cells with a fast response rate and high voltage holding ratio, by combining a reactive monomer including an azobenzene moiety.

Liquid-Crystal Metasurfaces Self-Assembled on Focused Ion Beam Patterned Polymer Layers: Electro-Optical Control of Light Diffraction and Transmission.

Self-assembling of liquid-crystal metasurfaces on polymer layers patterned by a focused ion beam manifests itself in distinctly colored optical transmission, as light from certain spectral bands is efficiently diffracted by the periodic liquid crystal modulations. We explore the metasurface electro-optics by applying voltage across the liquid crystal to straighten its director distribution and reroute the diffracted light into the direct transmission. We show that the characteristic times of switching from the diffracting to the transmitting state can be decreased down to a millisecond by increasing the driving voltage up to 6-8 V, while the main part of the relaxation back into the periodically deformed diffracting state occurs within about a few milliseconds, i.e., by an order of magnitude faster than the relaxation of the analogous homogeneous electro-optical liquid crystal cell. We explain the profound dynamics in terms of superimposed exponential modes governed by an interplay of the metasurface geometric parameters, the liquid crystal viscosity, and elasticity.

Negative viscosity of liquid crystals in the presence of turbulence: Conductivity dependence, phase diagram, and self-oscillation.

Recently, we reported the discovery of enormous negative viscosity of a nematic liquid crystal in the presence of turbulence induced by ac electric fields, which enabled us to observe unique phenomena related to the negative viscosity, such as spontaneous shear flow, hysteresis in flow curves, and self-oscillation [Orihara etal., Phys. Rev. E 99, 012701 (2019)10.1103/PhysRevE.99.012701]. In the present paper, we report the rheological properties of another nematic liquid crystal, which is a homologue of the previous one. The properties of the present liquid crystal are strongly dependent on electrical conductivity. Three samples with different conductivities were prepared by changing the amount of an ionic dopant. It was found that the lowest-conductivity sample without dopant shows no negative viscosity whereas the other ion-doped samples exhibit negative viscosity with strong dependence on the frequency of the ac electric field, consistent with microscopic observations. Phase diagrams of the negative- and positive-viscosity states in the amplitude and frequency plane are constructed to show the conductivity effect. Furthermore, we propose a model to reproduce another type of self-oscillation found in the present study.

Microemulsions and Lyotropic Liquid Crystals of Lecithin as Systems for Transdermal Drug Delivery

Reverse microemulsions in the lecithin–oleic acid–paraffin oil–avocado oil–tea tree essential oil–water system and lamellar liquid crystals in the lecithin–avocado oil–tea tree essential oil–water system were studied as systems for transdermal drug delivery. Oil- and water-soluble substances, as well as substances that are poorly soluble in water and oil in the form of solid-phase particles, can be introduced into liquid crystals in concentrations of a few percent. Oil-soluble substances can be introduced into reverse microemulsions in concentrations of a few percent and water-soluble substances can be introduced in concentrations of tenths of a percent. The dialysis method showed that the rate of release of water-soluble substances from the reverse microemulsion containing 4.8 wt % water is approximately 2.5 times higher than that from the lamellar liquid crystal containing 15 wt % water. This is explained by the fact that the viscosity of liquid crystals is more than 100 times higher than the viscosity of microemulsions.

EFFECT OF NANO- AND MICROPARTICLES OF IRON (III) OXIDE ON VISCOSITY OF LAMELLAR LIQUID CRYSTALS OF LECITHIN

The addition of low concentrations (0.001 – 0.1 wt. %) of iron (III) oxide nanoparticles with diameter of 10-20 nm was shown to result in the increase in a viscosity of lamellar liquid crystals in the systems of lecithin – water and lecithin – dodecane – water by 35-60% and 15-20%, respectively, whereas the addition of 1-5 µm microparticles does not affect the viscosity. An increase in a viscosity of the liquid crystals with the growth of the nanoparticles concentration from 0.001 to 0.1 wt. % is observed. It is assumed that the nanoparticles act as "bridges" between the bilayers of the lamellar liquid crystal.

Rotational viscosity comparison of liquid crystals based on the molecular dynamics of mixtures

It is critical to improve the response speed of a liquid crystal wavefront corrector in order to increase the bandwidth of a liquid crystal adaptive optics system. The design of liquid crystal molecules with small rotational viscosity becomes a basic method of increasing the response speed of a liquid crystal wavefront corrector. Various phases of liquid crystal from molecular dynamics simulation are given in this paper, and the detailed computational methods of order parameter and rotational viscosity are also presented. Rotational viscosities of liquid crystals are compared based on the molecular dynamics of mixtures. The data fluctuation is reduced effectively through several simulations and the multiple analysis of original data. A detailed process of molecular dynamics of mixtures is given in this paper and the result is greatly satisfactory. We believe that one can perform a better molecular design using this process and obtain a better understanding of molecular interactions of LCs.

21am2-F1 剪断配向と光配向が微小隙間に閉じ込められた液晶の粘性に及ぼす影響の解明

21am2-F1 剪断配向と光配向が微小隙間に閉じ込められた液晶の粘性に及ぼす影響の解明

Abnormal switching behavior of nanoparticle composite systems

We have investigated the properties of liquid crystals (LCs) doped with ZnO (8% Cu doped) nanoparticles. The electro-optic properties of LCs have changed with varying concentration of ZnO nanoparticles. The dielectric anisotropy obtained from the values of dielectric permittivity at 5 kHz in the nematic and smectic phases was found to increase with increasing concentration of nanoparticles in LCs. It has been established that the effect of nanoparticles on the dielectric anisotropy depends on the physical properties of LCs; the nanoparticle disturbs the orientation ordering of LC molecules. The nanoparticle also influences the switching behavior, splay elastic constant, rotational viscosity and threshold voltage of pure LCs. A small quantity of nanoparticles causes slight reduction of the splay elastic constant and rotational viscosity of LC cells.

Study the coupling effect of shear and electric field on rheological behaviors of liquid crystals

The rheological behaviors of 5CB liquid crystal under the coupling effect of shear and electric field are investigated by theoretical and experimental study. Establish calculating equation of the system Gibbs free energy by adopting the continuum theory of liquid crystals which contains anchoring energy, elastic free energy, dielectric free energy and flow energy. Then the molecular orientation angle distribution and apparent viscosity of liquid crystal under the coupling effect are obtained by minimizing the Gibbs free energy, revealing the microscopic mechanism of rheological behaviors and influence rules of coupling effect from the molecular model. Meanwhile the calculated results are verified by rheological test. Comparative Analysis of the errors and reasons of theoretical and experimental results, which demonstrates that anchoring effect plays an important role in the molecular orientation and viscosity of liquid crystal. Both the theoretical and experimental results indicate that liquid crystals have electroviscous effect and behavior like non-Newtonian liquids under electric field. The viscosities of liquid crystals are determined by the coupling and competition action of shear and electric field, which can reach 4 times of its original value under electric field. This property of controllable viscosity is important in tribology, which can self-adaptively satisfy the requirement of viscosities for different working conditions as a "smart lubrication" under certain condition.

Photoalignment in Rheology of Liquid Crystals

The application of photoalignment technique for rheological study of liquid crystals is considered. Such technique can be used for the initial preparation and rotation of mono domain samples of liquid crystals. It provides new possibilities in measurements of anisotropic viscosities of liquid crystals. Three shear and the rotational viscosities of nematic liquid crystals can be determined at additional usage of the electric field.

P‐213L: Late‐News Poster: Optimization of High‐Aperture‐Ratio Fringe‐Field‐Switching Pressure‐Resistance Characteristic for Touch‐Screen Display

AbstractCurrently, smart phone and table pc like I phone and I pad with touch pad are main trend in the mobile market. Using touch pad, display image is distorted by external pressure with touch pen and fingers. Because such defects, improvement of pressure resistant characteristic by external pressure (Trace mura) is became more important factor. To solve the problem, we studied pressure resistant characteristic by rubbing uniformity, alignment anchoring force, rotational viscosity of liquid crystal and pixel electrode length of domain structure. Through these experiment results, we have found the design of improving pressure resistant characteristic (Trace mura). Low rotational viscosity of liquid crystal shows stronger pressure resistant characteristic than high rotational viscosity of liquid crystal and as the length of pixel electrode is shorter, pressure resistant characteristic (Trace mura) is good. It is much advantageous for touch pad display field.

Rotational dissipation and the Miesowicz coefficients

In this work, we will study the relative contribution of each of the two dissipative channels of the Eriksen, Leslie, and Parodi (ELP) approach to the observed values of the Miesowicz viscosity coefficients of the nematic liquid crystals. According to the fundamental equation of the liquid crystal's viscosity dissipative process, TS=-integral d3r(sigma)ijA(ij)+hxN , there are two channels by which the nematic viscous dissipation can occur: or it occurs by means of a shear flow configuration, where A(ij) is the characterizing term, or it occurs by means of a rotational configuration, where N is the characterizing term (these parameters will be defined in the paper). It will be also shown that this relative contribution can be measured by a simple relationship connecting the Miesowicz coefficients, which exhibits a quasitemperature independent behavior, suggesting that it is nearly constant through the entire domain of the nematic phase.

Electromigration of microspheres in ferroelectric smectic liquid crystals

When an electric field is applied to microspheres which are dispersed in a ferroelectric smectic liquid crystal, particle translation along the smectic layer plane, i.e., in a direction nearly perpendicular to that of the director, can be observed. Under certain electric field conditions the translation is shown to be linear in time. We have determined the stability regime of linear particle displacement in the parameter space of amplitude and frequency for various applied wave forms. This regime enlarges for increasing electric field amplitude and frequency, with a threshold behavior observed for small parameters. The upper stability boundary is related to the reciprocal ferroelectric switching time. The microspheres translational velocity is independent of the applied electric field amplitude, but increases linearly with applied frequency. The microsphere velocity also increases with increasing temperature, which is indicative of the respective decrease in liquid crystal viscosity. Possible mechanisms of electric-field-induced particle motion are discussed.

2-9 液晶の正確な応答の解析に必要な3つの粘性係数の測定(第2部門 情報ディスプレイ)

2-9 液晶の正確な応答の解析に必要な3つの粘性係数の測定(第2部門 情報ディスプレイ)

Rotational viscosity in liquid crystals: A molecular dynamics study

The molecular dynamics (MD) simulations at various temperatures have been performed for the 4-alkyl-4′-cyanobiphenyls ( nCB) with three alkyl groups, pentyl (5CB), heptyl (7CB), and octyl (8CB), in the nematic and isotropic phases. The rotational diffusion coefficient (RDC) was determined by using simulated second and fourth rank order parameters (OPs) and correlation time. The rotational viscosity coefficient (RVC) was computed by the Nemtsov–Zakharov and Fialkowski methods based on statistical mechanical approaches. Temperature and size dependence of the simulated RDC, RVC and OPs have been discussed. Reasonable aggreement between the simulated and experimental values was found.

液晶のER効果を利用した静圧軸受に関する基礎的研究(S23-4 複雑流体の流れとその応用(4),S23 複雑流体の流れとその応用)

In this research, we utilize the ER effect of liquid crystal to the lift and height control of a flat plate on radial flows as a fundamental test to the application of liquid crystal to hydrostatic bearing. The electric field was applied to the radial flow between the lifted plate and electrodes. Rectangular pulse wave with controlled duty ratio was employed to adjust the apparent viscosity of liquid crystal. We found that our method was useful to the height and parallelism control of the lifted plate and the lift obtained in the experiment was in good agreement with the estimation from ER effect of liquid crystal.

Influence of Liquid-Crystal Directors in an Electric Field on Elastic Wave Propagating in Liquid-Crystal Cell

Propagation characteristics of a shear-horizontal (SH) wave in a trilayer structure composed of a liquid-crystal layer sandwiched between two glass plates are examined by numerical analysis and experimental investigation from the viewpoint of the anisotropy of the viscosity. Electric field dependences of the viscosities of two kinds of nematic liquid crystals with positive and negative dielectric anisotropies are related to the SH wave phase velocity. The orientation of the liquid-crystal director is a key factor for affecting the viscosity change. The present technique is promising for evaluating the anisotropy of the viscosity of liquid crystal.

Nematic liquid crystal viscosity: inadequacies of microscopic theories

Recently Janik et al. reported measurements of the Miesowicz viscosity coefficients of the nematic liquid crystal and confronted them with the results of the available theoretical models. They found that none of them can be successfully applied for the purpose of the Miesowicz-type experiment. In this paper I present an explanation why the microscopic theories seem inadequate. In particular, I analyze the applicability and conclusions of the Osipov-Terentjev model, whose final predictions are highlighted to be the same as those of the Kuzuu-Doi theory. It has been shown that the microscopic theories can perfectly explain the behavior of the Miesowicz coefficients difference eta(3)-eta(2) but are inadequate to study their ratio eta(3)/eta(2), which is contributed by the Leslie coefficient alpha(4). A disagreement between experimental data and the theoretical results for alpha(4) is attributed to the fact that the isotropic contribution to alpha(4) in the nematic phase is beyond the scope of the theories that are based on the anisotropic orientational distributions.