Stabilization of Long-Pitch Supertwisted Nematic Structures

Stabilized reverse twisted nematic liquid crystal devices (RTN-LCDs) were fabricated using formation of a polymer matrix under UV irradiation with an applied voltage (sustain voltage) in the vicinity of the alignment layers. In the absence of an applied voltage, the non-stabilized RTN structure gradually returns to a splay twist structure. The sustain voltage was decreased with an increase in temperature. A stabilized long-pitch supertwisted nematic (LPSTN) structure could also be formed during the RTN structure stabilization process with a much lower sustain voltage at a temperature near the clearing point. The chiral pitch for the LPSTN structure is longer than that for a typical STN structure. LPSTN-LCDs similar to RTN-LCDs show a large reduction in both the threshold and saturation voltage compared with those for TN-LCDs consisted of the same LC materials. Furthermore, a notable feature of LPSTN-LCDs is a change to a TN structure when a high voltage is applied. A black state can be realized due to the change from the LPSTN structure to the RTN structure unlike the typical STN mode under the crossed nicols condition. In contrast STN-LCDs retain their color due to the retardation because the RTN and LPSTN states are considered topologically equivalent.

MESOPHASE AND GLASS FORMATION IN BINARY SYSTEMS CEASIUM AND BARIUM ALKANOATESMESOPHASE AND GLASS FORMATION IN BINARY SYSTEMS CEASIUM AND BARIUM ALKANOATES

Phase equilibria in binary systems of individually non-mesomorphic components: propionates, isobutyrates, butyrates and valerates of cesium and barium at temperatures from 20 to 400 °C have been investigated by the me­thods of differential thermal analysis and polarization polythermal microscopy. In all systems, the formation of intermediate li­quid-crystalline solutions of smectic modification (type A) was established. The tempe­rature-concentration regions of the formation of ionic liquid crystals and glasses are determined. The studies carried out show that in binary systems of cesium and barium alkanoates interme­diate liquid-crystal solutions are generated due to the latent mesomorphism of the correspon­ding cesium alkanoate and due to the eutectic decrease in liquidus temperatures in the binary systems. The thermal stability of the induced mesophase in the case of systems of the consi­dered type is influenced by the following factors: the degree of ordering of the melt, which correlates with the length of the alkyl chain of the alkanoate anion, and a decrease in the temperatures of the liquidus line relative to the latent clearing temperature. The possible influence of compounds melting congruently or incongruently, formed in binary systems, should also be taken into account. Experimental data indicate the largest temperature-concentration range of the mesophase in the butyrate system, where there are the most favorable conditions for the implementation of intermediate li­quid crystal solutions. Such conditions are the lar­gest decrease in liquidus temperatures in a series of systems relative to the latent clearing point, as well as an additional increase in thermal stability due to the formation of a congruently melting compound of anisometric structure. In the case of the valerate system, a certain increase in anisotropy in comparison with the butyrate system is leveled by high liquidus temperatures; here is the narrowest region of existence of the intermediate mesophase due to its thermal destabilization.

Characteristic of Color-Play on Liquid Crystal Sheet Based on Image Analysis

In this research, we compare two samples of Liquid Crystal sheet (LCs), R30C5W and R35C5W to get information about the characteristic of LCs based on the color-play of the LCs surface caused by increasing of temperature. We analize the color-play of the samples quantitatively by image analysis using hue parameter, texture analysis method by choosing entropy and energy parameter, and color-play area measurement. According to the experiment results, both samples show the similar characteristic in color-play behaviour, illustrated by similar curve for each sample, the different only in the starting temperature of the color-play and the clearing point temperature. The samples also show the same behavior in increasing of the color-play area linearly by increasing of temperature. Based on the graph of hue, entropy and energy parameters, it can be measured the clearing-point temperature of samples at 43 °C and 49 °C for LCs R30C5W and LCs R35C5W respectively. Moreover, the changes of color from red to blue cause the irregularity of pattern illustrated by increasing of entropy values and decreasing of energy values. Study the characteristic of LCs in various types is important particularly before it is used for many application purposes, for instance in heat transfer observation.

The Effect of Operating Temperature on the Response Time of Optically Driven Liquid Crystal Displays

Optically driven liquid crystal displays (ODLCDs) realizes their display function by tuning the easy axis of liquid crystal (LC) molecules under polarized blue light, which has been utilized in some optical devices due to its advantages of ultra-low power consumption. However, a big issue arises in response time, i.e., the rewriting time of the ODLCD. The rewriting time of ODLCD samples was studied. Rotational viscosity plays a very important role for decreasing the rewriting time of the ODLCD. The operating temperature was changed from room temperature to nearly clearing point, the rewriting time decreased a lot as the rotational viscosity decreased for the five different kinds of the LCs. The rewriting time can be decreased from 5.2 s to 0.2 s around 25 times for the LC N4.

Syntheses and Characterization of Chiral Branched-Arm Liquid Crystals-Basing on Isosorbide as Chiral Core

A new series of two-arm (MB1, MB2), four-arm (MB3), six-arm (MB4) chiral liquid crystalline compound containing isosorbide as chiral core were first synthesized. Four precursors of branched-arm B1~B4 were obtained at first and then were esterized separately with isosorbide and got four chiral branched-arm liquid crystals (MB1~MB4). The chemical structures and LC properties of the liquid crystalline molecule were measured by spectrum and thermal analysis techniques. XRD curves of MB1~MB4 samples only showed broad peaks at wide-angle, but no sharp peak was seen for all the samples. The results showed that MB1~MB4 appeared cholesteric phase with oily streak texture or lined texture and finger print texture. Isosorbide successfully induced cholesteric phase. The values of melting point and clearing point for MB1~MB4 decreased. The quantity of branched-arm and chiral core had effects on their liquid crystalline properties.