Novel Ferroelectric and Electroclinic Organosiloxane Liquid Crystals

Abstract

A new series of organosiloxane ferroelectric liquid crystalline materials have been synthesized, and their mesomorphic and physical properties have been characterized. The new series contains a siloxy chain attached to the hydrocarbon chain at the nonchiral end of the molecule. All materials show a very low melting point ('5 "C) and exhibit chiral smectic A (SmA) and chiral smectic C (SmC*) mesophases. The changes in the siloxy chain length strongly affect the mesomorphic behavior and electrooptic properties of these materials. Increasing the number of siloxy units in the chain increases the temperature range of the SmA phase, with a concomitment decrease in the SmA-SmC* transition temperature. The electroclinic effect in the smectic A phase is characterized by a large electroclinic coefficient (-4 "V-l pm-l at T-TAc* = 2 "C) and low switching time (<40 ps). One of the materials shows one of the highest value of spontaneous polarization P, ever reported in the SmC* phase for similar siloxane materials with P, = 342 nC cm-2 at 25 "C.

Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

“…Upon further increasing the electric field, the response time decreases. This behavior contrasts with that for a conventional SmA ‫ء‬ phase, where the response time is independent of E in the small approximation and has a small dependence on electric field for larger , 3,19 as observed in KN125. 4,20 For higher temperatures within SmA ‫ء‬ phase in TSiKN65, it was found that the response time increases to a certain value of the electric field, 3,4 but the reasons were not given nor was it highlighted as an anomalous property of the material.…”

“…This behavior contrasts with that for a conventional SmA ‫ء‬ phase, where the response time is independent of E in the small approximation and has a small dependence on electric field for larger , 3,19 as observed in KN125. 4,20 For higher temperatures within SmA ‫ء‬ phase in TSiKN65, it was found that the response time increases to a certain value of the electric field, 3,4 but the reasons were not given nor was it highlighted as an anomalous property of the material. The observed unusual behavior of the field dependent response time can well be explained by the de Vries scenario upon assuming that the reorientation of the molecular dipoles with the electric field is of the Langevin type and by considering an increase in the effective dipole moment ͑ eff ͒ with increasing field as discussed below.…”

“…Electroclinic liquid crystals have a potential for development of projection displays, spatial light modulators, optical correlators, smart pixel image processors, etc., where speed, high contrast, and gray scale are of the utmost importance. [2][3][4] However, application of electric field in the SmA ‫ء‬ phase parallel to the smectic layers induces stripes arising from a reduction in the layer spacing due to the molecular tilting and a consequent smectic layer buckling. 5,6 This has a detrimental effect on the contrast ratio of electrooptic devices.…”

Phase Behavior and Electro-Optical Studies in Mixtures of Chiral and Non-Chiral Tilted Smectic C-Type Liquid Crystals

“…This molecular arrangement confers to the materials some of the robust mechanical properties of polymers but retains the fast electro-optic response of the low molar mass liquid crystal moiety. Due to their potential applications, low molar mass organosiloxane liquid crystals are presently the object of intense investigations [4][5][6][7]. However, it has been shown that binary mixtures of an achiral swallow-tailed compound [8] with antiferro-electric liquid crystal (S)-MHPOBC display V-shaped switching of its electro-optical response in antiferroelectric liquid crystal mixtures.…”

Studies on Room Temperature Ferroelectric Liquid Crystal, 12CN5(R*)

“…This LC was prepared by the esterification of the cinamic acid derivative 1 and phenolic derivative 2 in the presence of 1-(3-(dimethylamino)propyl)-3-ethylcarbidimide methiodine (EDC.CH 3 I) and (dimethylamino)pyridine (DMAP) [6] as shown below:…”