Temperature Dependence Of Response Time Research Articles

Induced dielectric relaxation and enhanced electro-optic parameters in Ni nanoparticles – ferroelectric liquid crystal dispersions

We demonstrate here collective and non-collective dielectric relaxation processes of nickel nanoparticles dispersed ferroelectric liquid crystal in a wide frequency range (20Hz–5MHz). A high frequency relaxation mode in conjunction with the collective dielectric mode was induced in ferroelectric liquid crystal-Ni dispersions. This relaxation mode persists even in the Sm A phase of the material. Occurrence of additional relaxation mode has been examined in the light of magnetic dipole and exchange interactions among the dispersed nanoparticles. In lower concentrations of nanoparticles, the effect is believed to originate from magnetic dipole interactions; however, in higher concentrations, exchange interactions dominate over the superparamagnetic relaxation that leads to strong dielectric absorption. Further, temperature and concentration dependence of relaxation frequency and amplitude of induced mode also indicated that the process must be driven by strong interparticle interactions of exchange type. Secondly, coupling of ferromagnetic nanoparticles with ferroelectric liquid crystal (FLC) molecules also serves to influence the LC director orientation and affect the order parameter of FLC-Ni NPs dispersions. In addition to this, temperature dependence of response time in FLC-Ni mixtures showed significant improvement, which has been attributed to a combined effect of decreased rotational viscosity and slightly increased spontaneous polarisation.

Synthesis of Semi-Perflnorinated FLCs and the Effect of Fluorination Extent on Mesomorphic Properties

A series of semi-perfluorinated ferroelectric liquid crystals, 5-(n-perfluoroalkyl)alkyloxy-2-[p-(2-fluorooctyloxy)phenyl]pyrimidines, was synthesized and their mesomorphic properties investigated. Compared with non-fluorinated analogue, chiral smectic C phase is strongly enhanced. All of the compounds showed chiral smectic C phase enantiotropically. As fluorination extent of the achiral tail increased, tilt angle, spontaneous polarization and response time increased. Especially, when the length of the achiral tail is seven and fluorination extent is 60%, chiral smectic C phase is so stable that smectic A phase completely disappeared. What's more, its spontaneous polarization is more than 300nC.cm−2. All the compounds showed little temperature dependence of response time.

Behaviour of Ionic Effects on Response Times of Surface Stabilized Ferroelectric Liquid Crystal Devices

The response time measurements of a new room temperature ferroelectric liquid crystal have been done by using the field reversal method. The response time has been found to be frequency dependent and decreases considerably at frequencies above 10 kHz. The temperature dependence of response time showed the presence of ionic effects as is evident from the appearance of the second peak in the current response to an applied bipolar pulse.