Slow stress relaxation in randomly disordered nematic elastomers and gels

TL;DR

This paper investigates the ultra-slow logarithmic stress relaxation in disordered nematic elastomers and gels, revealing universal behavior during the polydomain-monodomain transition and proposing a theoretical model based on cooperative domain reorientation.

Contribution

It introduces a new theoretical model capturing the cooperative re-orientation dynamics responsible for slow stress relaxation in disordered nematic elastomers.

Findings

Universal logarithmic relaxation behavior observed.

Model accurately fits experimental stress relaxation data.

Parameters derived from the model match experimental observations.

Abstract

Randomly disordered (polydomain) liquid crystalline elastomers align under stress. We study the dynamics of stress relaxation before, during and after the Polydomain-Monodomain transition. The results for different materials show the universal ultra-slow logarithmic behaviour, especially pronounced in the region of the transition. The data is approximated very well by an equation Sigma(t) ~ Sigma_{eq} + A/(1+ Alpha Log[t]). We propose a theoretical model based on the concept of cooperative mechanical resistance for the re-orientation of each domain, attempting to follow the soft-deformation pathway. The exact model solution can be approximated by compact analytical expressions valid at short and at long times of relaxation, with two model parameters determined from the data.