Electrical and optical alignment processes in some novel liquid-crystalline side-chain polymers as studied by dielectric relaxation spectroscopy

Dielectric relaxation spectroscopy has been used in the present work to study the extent of the macroscopic alignment that is induced in some novel liquid-crystalline (LC) side-chain polymers containing either photoactive cyanoazobenzene groups or cyanoazobenzene groups interdispersed along the chain by nonactive cyanobiphenyl groups. The effects of an applied ac electric field on the cyanoazobenzene mesogenic side groups in a LC homopolymer (LC1) and a LC copolymer (LC2) have been studied. Also, the actions of polarized laser radiation (514 nm mode-lock pulse) on the copolymer via an isomerization mechanism of the cyanoazobenzene moieties have been examined. The changes with temperature through the liquid-crystalline phase to the clearing temperature in the loss part of the complex permittivity of the samples measured in the frequency plane give a good qualitative indication of the changes of alignment that are being induced by light or an electric field since the δ-relaxation process and other component processes may be used as indicators of macroscopic alignment.