Electric field induced AC alignment and realignment, a study of a liquid-crystalline copolymer having longitudinally and laterally attached mesogenic groups as side chains monitored through dielectric spectroscopy and optical thermomicroscopy

A study of a liquid crystal side chain copolymer with a siloxane backbone has been carried out using dielectric relaxation spectroscopy and optical microscopy. We have found that this particular copolymer, a mixture of longitudinally and laterally attached mesogens, can be aligned both homeotropically and planarly between two electrodes using a directing AC field of specific frequency by cooling from the melt or more importantly at temperatures below the clearing point (T_c). The switching of the material from homeotropic to planar and the reverse has been studied at temperatures below T_c. It is shown that the kinetics of realignment are strongly dependent on the electrical/thermal history of the sample. The dielectric data allows the state of alignment of the sample to be monitored and the molecular dynamics to be studied. The optical textures of the polymer which were subjected to different AC electric fields have been observed and provide complementary information to the dielectric work on the state of the aligned sample.