Static Permittivity and Electro-Optical Properties of Bi-Component Orthoconic Antiferroelectric Liquid Crystalline Mixtures Targeted for Polymer Stabilized Sensing Systems.

Shantiram Nepal,Malay Kumar Das,Madhumita Das Sarkar,Magdalena Urbańska,Michał Czerwiński,Banani Das

doi:10.3390/polym14050956

Abstract

The behavior of two newly formulated bi-component orthoconic antiferroelectric liquid crystalline (OAFLC) systems, i.e., the Compound A + Compound B mixture system and Compound C + Compound B mixture system has been discussed in light of temperature and concentration dependencies of helical pitch length, spontaneous polarization, relaxation time, bulk viscosity, and the anchoring energy strength coefficient, together with static dielectric permittivity (ε) and dielectric anisotropy. Compound A + Compound B mixtures possess spontaneous polarization between 190–340 nC.cm−2 and fast relaxation times between 190–320 µs in the smectic antiferroelectric SmCA* phase at room temperature. Compound C + Compound B mixtures also have a spontaneous polarization in the range of 190–280 nC.cm−2 and relaxation times in the range of 190–230 µs at room temperature. Most of the mixtures have a helical pitch below one micrometer in the SmCA* phase. These advanced mixtures show a broad temperature range of the antiferroelectric SmCA* phase, fast switching of molecules under an applied electric field, negative dielectric anisotropy and a short helical pitch, confirming the advantage of designing new polymer-stabilized OAFLC that is targeted for novel application in sensing devices, utilizing the fast responsive electro-optical modulation elements.

Highlights

The liquid crystalline (LC) state is an intermediate state of matter between the solid and isotropic liquid, which was discovered by an Austrian chemist, Friedrich Reinitzer, in 1888 [1]
Phase transition temperatures and sequence of mesophases for the mixtures were obtained by carefully observing the characteristic textures and their changes in polarizing optical microscope (POM); this was cross-verified by the optical transmission method
The results show that for the appropriate mixture compositions, both at low and high temperatures, AFLC material with a very long helical pitch can be obtained

Summary

Introduction

The liquid crystalline (LC) state is an intermediate state of matter between the solid and isotropic liquid, which was discovered by an Austrian chemist, Friedrich Reinitzer, in 1888 [1]. Meyer et al [3] discovered micro-second switching behavior in the ferroelectric SmC* phase of liquid crystal, i.e., the synclinic state, which was experimentally demonstrated by Clark and Lagerwall [4]. Ferroelectric liquid crystalline materials suffer from reduced brightness due to DC compensation with only one bright state. Chandani et al [5,6] reported the existence of the antiferroelectric (AF) phase, i.e., the anticlinic state of liquid crystal, formed by chiral rod-like molecules. The chiral ferroelectric (FLC) and antiferroelectric (AFLC) materials reveal definite and very attractive properties: the electro-clinic effect is observed in the orthogonal paraelectric SmA* phase [7–10], thickness independent memory effect is observed in de Vries’ electro-clinic liquid crystals [11–13]. The polymer stabilized blue-phase LCD technology [26] with sub-millisecond switching has generated huge interest, and there are ongoing activities and development, both in the ferroelectric and antiferroelectric LC areas [27]

Objectives

Results

Conclusion