Polydomain growth at isotropic-nematic transitions in liquid crystalline polymers

TL;DR

This study investigates the dynamics of isotropic-nematic phase transitions in liquid crystalline polymers, revealing a self-similar growth of polydomains with a crossover in growth behavior influenced by rotational diffusion.

Contribution

It introduces a detailed analysis of polydomain growth and defect interactions during phase transitions in liquid crystalline polymers using Ginzburg-Landau modeling.

Findings

Polydomain size grows as l~t^{1/4} in early stages.

A crossover to l~t^{1/2} occurs when rotational diffusion becomes significant.

Disclination pairs either annihilate or stabilize depending on initial separation.

Abstract

We studied the dynamics of isotropic-nematic transitions in liquid crystalline polymers by integrating time-dependent Ginzburg-Landau equations. In a concentrated solution of rodlike polymers, the rotational diffusion constant Dr of the polymer is severely suppressed by the geometrical constraints of the surrounding polymers, so that the rodlike molecules diffuse only along their rod directions. In the early stage of phase transition, the rodlike polymers with nearly parallel orientations assemble to form a nematic polydomain. This polydomain pattern with characteristic length l, grows with self-similarity in three dimensions (3D) over time with a l~1/4 scaling law. In the late stage, the rotational diffusion becomes significant, leading a crossover of the growth exponent from 1/4 to 1/2. This crossover time is estimated to be of the order t~1/Dr. We also examined time evolution of a pair of disclinations placed in a confined system, by solving the same time-dependent Ginzburg-Landau equations in two dimensions (2D). If the initial distance between the disclinations is shorter than some critical length, they approach and annihilate each other; however, at larger initial separations they are stabilized.