Dynamic Soft Elasticity in Monodomain Nematic Elastomers

TL;DR

This study investigates the dynamic mechanical response of monodomain nematic liquid crystalline elastomers, revealing a power-law behavior in their soft-elasticity regime and analyzing the limits of time-temperature superposition across phase transitions.

Contribution

It provides new insights into the frequency-dependent behavior of nematic elastomers and the limitations of time-temperature superposition near the nematic-isotropic transition.

Findings

Power-law dependence of G' on frequency in the soft-elastic regime

Master Curves obtained between glassy and nematic transition temperatures

Breakdown of time-temperature superposition at the clearing point Tni

Abstract

We study the linear dynamic mechanical response of monodomain nematic liquid crystalline elastomers under shear in the geometry that allows the director rotation. The aspects of time-temperature superposition are discussed at some length and Master Curves are obtained between the glassy state and the nematic transition temperature Tni. However, the time-temperature superposition did not work through the clearing point Tni, due to change from the ``soft-elasticity'' nematic regime to the ordinary isotropic rubber response. We focus on the low-frequency region of the Master Curves and establish the power-law dependence of the modulus G' ~ omega^a. This law agrees very well with the results of static stress relaxation, where each relaxation curve obeys the analogous power law G' ~ t^{-a} in the corresponding region of long times and temperatures.