Rod to coil transitions in nematic polymers

Abstract

The order parameter and anisotropy (elongation) of the configurations of a nematic polymer in the nematic phase are calculated. At low temperatures exponentially rapid growth of chain dimensions as a function of inverse temperature is found. In the nematic direction the chain eventually adopts a rod-like state. The thermal activation of hairpins (abrupt reversals in chain directions) causes this behaviour. However, at even lower temperatures the deviation from rod-like alignment is governed by gentle meandering away from the mean field direction. A Maier-Saupe mean field theory of the nematic-isotropic transition is constructed calculating for long chains the transition temperature as a function of chain properties and predicting a universal jump in the order parameter at the transition, Delta S_ni=¹/₃.