Photopyroelectric Calorimetry for the Thermal and Optical Evaluations over Phase Transitions in Liquid Crystals

We report on calorimetric and optical evaluations performed by Photopyroelectric calorimetry on two phenomena involving changes in average molecular alignment. We first study the possibility to obtain permanent homeotropic single domain alignment in the smecticA phase by applying a "vertical" strain field in the volume of samples of 4-decyl-4′-cyanobiphenyl and of 4-octyl-4′- cyanobiphenyl, liquid crystals. We then report on the effects produced by the illumination by UV light on 4-octyl-4′- cyanobiphenyl samples hosting photochromic molecules in terms of the change induced to the phase transitions characteristics and the average molecular alignment.