Premium
17.1: Invited Paper : Novel Uses of Organosiloxane Liquid Crystals
Author(s) -
Coles Harry J.
Publication year - 2000
Publication title -
sid symposium digest of technical papers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.351
H-Index - 44
eISSN - 2168-0159
pISSN - 0097-966X
DOI - 10.1889/1.1832924
Subject(s) - mesogen , liquid crystal , birefringence , materials science , moiety , dichroic glass , ferroelectricity , antiferroelectricity , tilt (camera) , phase (matter) , mesophase , crystallography , optoelectronics , optics , organic chemistry , chemistry , liquid crystalline , dielectric , mechanical engineering , physics , engineering
In this paper, we will show how, using organosiloxane liquid crystals with the same chiral mesogen, we can generate (through a template effect) ferroelectric or antiferroelectric phases simply by controlling the length of the siloxy group. By partially fluorinating the aromatic rings or perfluorinating the terminal chains we generate extremely high spontaneous polarisation materials with very broad temperature ranges. By controlling the cross‐section of the mesogen in relation to that of the organosiloxane moiety we can select the tilt angle at will. Materials have been synthesised and studied that exhibit tilt angles of 45° in the antiferroelectric phase over 60°C wide temperature ranges and this makes them ideal for many AF device applications. Response times of 10 to 100μs were recorded in moderate fields (≤ 10V/μm) and for P s ∼ 10–100 nC/cm 2 and the materials gave excellent bi‐ or tri‐stability. This molecular control of the bulk electro‐optic properties leads to a new range of materials suitable for both birefringence and dye guest host devices. We have applied these principles to a number of asymmetric organosiloxane liquid crystals in which the dichroic and fluorescent dye moieties form part of the mesogen and give extremely high solubility. By using these materials we have been able to generate both bistable digital and analogue devices with switching properties independent of temperature over a wide temperature range.