Strain induced homeotropic alignment in the smecticA phase of liquid crystals

Abstract

We present a method to align liquid crystal (LC) samples in their SmecticA phase, useful to obtain permanent\ud homeotropic single domains even in compounds where the nematic phase is absent. It is based on the application\ud of a strain field, within the sample volume, which tends to align the molecules all towards a common direction.\ud The study was carried out in samples of 4-decyl-4-cyanobiphenyl (10CB), 4-octyl-4-cyanobiphenyl (8CB)\ud and n-hexyl-4-n-pentyloxy biphenyl-4-carboxylate (65OBC) LCs, and the alignment efficiency was monitored by\ud polarisation microscopy observations and by thermal diffusivity measurements

Photopyroelectric Calorimetry Study of the Smectic A-Hexatic B Transition in Single Homeotropic Domain 65OBC Liquid Crystal Samples

“…The power density and the temperature rate change were decreased as much as possible to minimize the influence of thermal gradients which induce smearing of the Vs temperature profiles of the observed quantities. Following the successful single domain alignment of LC samples in the nematic phase induced by the strain fields resulting from the flow of the sample with respect of the cell walls [15], we have succeeded in obtaining single domain homeotropically aligned samples of LC in their smectic A phase, by inducing strain fields in the sample volume produced by displacement of LC sample cell cover, in our case the pyroelectric transducer, as reported in details elsewhere [16]. The achievement of the homeotropic alignment was verified both by the polarization microscopy imaging, performed at the same time as the calorimetric evaluations, and by monitoring the changes in the thermal diffusivity and conductivity which show larger values for homeotropic samples than for non aligned focal conics ones.…”