Effects of Blockiness and Polydispersity on the Phase Behaviour of non-Markovian Random Block Copolymers

Abstract

A model of non-Markovian random block copolymers is developed and used to study the effects of blockiness and compositional polydispersity on the phase behaviour of random block copolymers. The model approximates a random copolymer as a series of segments with equal lengths, while each segment is composed of sequences of different monomers drawn randomly from a distribution. The phase behaviour of the model random copolymers is first examined using the random phase approximation (RPA) to study the effects of blockiness and polydispersity on the order-disorder transition. It is observed that the critical point is inversely proportional to the blockiness. Compositional polydispersity is found to facilitate phase separation, and could induce macrophase separation. Next, the model is implemented into self-consistent field theory (SCFT) in order to elucidate the full phase behaviour of symmetric (A/B)-A random copolymers. Finally, the model is applied to the particular case of poly(styrenesulfonate-b-methylbutylene) (PSS-PMB) to study the effects of blockiness on the phase behaviour. In particular, the stability and structure of the `swollen gyroid' morphology predicted by previous Monte Carlo simulations is examined.