DIELECTRIC-RELAXATION AROUND THE NEMATIC-ISOTROPIC TRANSITION OF LIQUID-CRYSTALLINE POLYMERS

This study is concerned with a series of acrylate based side-chain liq uid crystalline (LC) polymers. Previous studies have shown that these LC polymers have a preference for parallel or perpendicular alignment with respect to the polymer chain which depends on the length of the c oupling chain joining the mesogenic unit to the polymer backbone. On t he other hand, the dielectric relaxation of these side-chain LC polyme rs shows a strong relaxation associated to the mesogenic unit dynamics . For samples with parallel alignment, it was found that the dielectri c relaxation of the nematic is weaker and broader than the relaxation of the isotropic. By contrast, for samples with perpendicular alignmen t, the isotropic to nematic transition reduces the broadening the rela xation and increases the relaxation strength. These two features are m ore evident for samples with short coupling units for which the dielec tric relaxation observed appears to be strongly coupled with the backb one dynamics.