Pre-transition electrooptic properties of solutions of liquid-crystal polysiloxanes in the phase-separation region

This paper discusses the electrooptic Ken: effect in dilute solutions close to their stratification temperature and in melts in the neighborhood of the temperature of the isotropic-liquid-nematic-phase transition of two comb-shaped liquid-crystal polysiloxanes with different chemical structures of the mesogenic side groups. It is shown that pretransition effects associated with self-organization processes of the molecules of the polymers in the critical temperature region are observed both in solutions and in melts of the polymers. The largest variations were observed close to the stratification temperature of polysiloxane solutions, where not only did the absolute magnitude of the Ken constant increase (by a factor of about 10(3)), but the sign of the effect also changed. The electrooptic properties studied here in polysiloxanes are compared with the features of the chemical structure of the polymers and low-molecular-weight analogs of their mesogenic groups. (C) 1998 The Optical Society of America.