Theory of microphase separation on Side-Chain Liquid-Crystalline Polymers with flexible spacers

TL;DR

This paper develops a microscopic theoretical model to analyze microphase separation in side-chain liquid crystalline polymers, predicting various phase instabilities and microphase formations due to block incompatibility and connectivity constraints.

Contribution

It introduces a free energy functional approach for side-chain liquid crystalline polymers considering both excluded volume and Maier-Saupe interactions, revealing new microphase behaviors.

Findings

Prediction of nematic and smectic instabilities.

Identification of microphases with modulated wave vectors.

Influence of polymerization degree on phase behavior.

Abstract

We model a melt of monodisperse side-chain liquid crystalline polymers as a melt of comb copolymers in which the side groups are rod-coil diblock copolymers. We consider both excluded volume and Maier-Saupe interactions. The first acts among any pair of segments while the latter acts only between rods. Using a free energy functional calculated from this microscopic model, we study the spinodal stability of the isotropic phase against density and orientational fluctuations. The phase diagram obtained in this way predicts nematic and smectic instabilities as well as the existence of microphases or phases with modulated wave vector but without nematic ordering. Such microphases are the result of the competition between the incompatibility among the blocks and the connectivity constrains imposed by the spacer and the backbone. Also the effects of the polymerization degree and structural conformation of the monomeric units on the phase behavior of the side-chain liquid crystalline polymers are studied.