Molecular dynamics of a smectic liquid-crystalline side-chain polymer in its unaligned and aligned states as studied by dielectric relaxation spectroscopy

Abstract

Dielectric relaxation data are presented for unaligned, partially aligned and aligned thin films of a smectic liquid-crystalline side-chain polymer in the ranges 12 to 10⁵Hz and 299 to 343 K. The unaligned material exhibits a complicated dielectric absorption which has been resolved into two broad components (δ and α processes). The dielectric absorption changes remarkably on alignment of the material such that the δ process is enhanced by a factor of three and the α process is considerably diminished. A consideration is given of the molecular theory for dielectric relaxation in these materials and the variation in dielectric properties is shown to depend on the dipole components μml∥ and μml_⊢, the order parameter S for the mesogenic head groups and the order parameter S _d for the director alignment.