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Articles 1 - 7 of 7

Full-Text Articles in Physics

Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik Aug 1994

Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik

Chemical Physics Publications

To verify the status of the divergence K13 term in the elastic theory of liquid crystals we study submicron films placed onto an isotropic fluid substrate in the Langmuir trough (Langmuir liquid crystal, LLC). The upper and lower surfaces favor normal and tangential molecular orientation, respectively. The periodic domain phase is observed in a nematic LLC. The dependence of the periodicity L of the domains vs film thickness h can be explained only if the elastic energy is accompanied by divergence terms with nonzero constants K13 and K24. It is found that for 5CB K13 almost-equal-to -0.2K11.


Effect Of Chiral Dopant On The Performance Of Polymer Dispersed Liquid Crystal Light Valve, Z. J. Lu, Deng-Ke Yang Jul 1994

Effect Of Chiral Dopant On The Performance Of Polymer Dispersed Liquid Crystal Light Valve, Z. J. Lu, Deng-Ke Yang

Chemical Physics Publications

We have experimentally studied the effect of chiraldopant on the electro‐optical performance of a polymer‐dispersed liquid crystal(PDLC) light valve. Adding a small amount of chiraldopant decreases the turn‐OFF time significantly but increases the drive voltage only slightly. A phenomenological theory is presented to explain the experimental results.


Surface Anchoring And Growth-Pattern Of The Field-Driven 1st-Order Transition In A Smectic-A Liquid-Crystal, Zili Li, Oleg Lavrentovich Jul 1994

Surface Anchoring And Growth-Pattern Of The Field-Driven 1st-Order Transition In A Smectic-A Liquid-Crystal, Zili Li, Oleg Lavrentovich

Chemical Physics Publications

It is demonstrated that a surface energy anisotropy (anchoring) defines the growth pattern of the field-induced transition in a smectic-A liquid crystal (Sm-A). The stable domain phase nucleates as rounded domains but expands as stripes. The change in growth pattern is accounted for a large anchoring strength Wa10-2-10-3 J/m2 which is connected with the layer breaking in the vicinity of the cell plates. The temperature dependence of Wa for Sm-A (substance CCN-47) is measured for the first time: Wa(TA-N-T)0.65±0.09.


Cholesteric Reflective Display - Drive Scheme And Contrast, Deng-Ke Yang, J. William Doane, Z. Yaniv, J. Glasser Apr 1994

Cholesteric Reflective Display - Drive Scheme And Contrast, Deng-Ke Yang, J. William Doane, Z. Yaniv, J. Glasser

Chemical Physics Publications

We studied the electro‐optical response of a bistable cholesteric texture (BCT) display to ac voltage pulses. The material can be driven into states where planar and focal conic textures coexist at zero field and gray scale memory is achieved. According to the properties of the BCT display we designed two drive schemes; one for binary operation and the other for gray scale operation. We made a 320×320 pixel reflective display with a resolution of 80 lines/in. on a passive matrix. Measurement in an integration chamber showed that the display has higher contrast and better viewing angle than ...


Control Of Reflectivity And Bistability In Displays Using Cholesteric Liquid-Crystals, Deng-Ke Yang, John L. West, Liang-Chy Chien, J. William Doane Mar 1994

Control Of Reflectivity And Bistability In Displays Using Cholesteric Liquid-Crystals, Deng-Ke Yang, John L. West, Liang-Chy Chien, J. William Doane

Chemical Physics Publications

It is demonstrated that the reflective properties and bistability of cholesteric liquid crystals can be controlled by proper surface treatment and dispersed polymers. Dispersing a polymer in the liquid crystal or using a cell with an inhomogeneous surface anchoring creates permanent defects which result in long-term bistability, high contrast at large viewing angles, and gray scale. The wide-angle, reflective feature makes cholesteric materials suitable for displays without backlights and bistability provides flicker-free operation.


Anchoring Transition In A Nematic Liquid-Crystal Composed Of Centrosymmetric Molecules, V. G. Nazarenko, Oleg Lavrentovich Feb 1994

Anchoring Transition In A Nematic Liquid-Crystal Composed Of Centrosymmetric Molecules, V. G. Nazarenko, Oleg Lavrentovich

Chemical Physics Publications

A temperature-driven anchoring transition strongly influenced by ionic impurities appears in a nematic liquid crystal composed of centrosymmetric molecules. Two anchoring parameters, the tilt angle and the anchoring strength, were measured. The observed phenomena are explained as a result of a balance between the orienting tendencies of electric double layers and direct molecular interactions at the interface.


Periodic Stripe Domains And Hybrid-Alignment Regime In Nematic Liquid-Crystals - Threshold Analysis, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi Feb 1994

Periodic Stripe Domains And Hybrid-Alignment Regime In Nematic Liquid-Crystals - Threshold Analysis, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi

Chemical Physics Publications

Recently we investigated the occurrence of static periodic stripes in a hybrid aligned nematic cell. Assuming that the tilt anchoring was stronger at the planar wall than at the homeotropic wall, we have found the critical thickness of the cell for the transition from planar to periodic alignment as a function of the surface energy in the presence of a magnetic field. Here we study, for the same kind of cell, the critical thickness between the periodic and the aperiodic deformed structure by means of an appropriate numerical technique. As expected, such a threshold was found to be greater than ...