Dielectric relaxation in ‘diluted’ siloxanes with swallow-tailed side groups

Abstract

Polysiloxanes consisting of 36-SiCH₃Z-O- units, where Z is a swallow-tailed liquid crystal moiety S or a CH₃ group, were synthesized. Dielectric constants and relaxation frequencies were measured from 0.1 Hz to 10 MHz for four different molar ratios of CH₃ and S groups and compared with the data for the respective monomeric liquid crystal material. In all cases a δ- and α-relaxation were detected. The relaxation frequencies f _R of the α-process increase with increasing degree of dilution and can be related to the decreasing glass temperature. The δ-process approaches the f _R-values of the monomer by dilution. Both the dielectric increments of the δ-process, as well as the static dielectric constants parallel to the director, prove that the swallow-tailed units are strongly antiparallel oriented. This correlation cannot be destroyed by dilution.