Modeling the Mechanisms of the Photomechanical Response of a Nematic Liquid Crystal Elastomer

TL;DR

This paper develops models to understand the photomechanical response of azo-dye doped liquid crystal elastomers, identifying photothermal heating as the key mechanism and aiding the design of smart optical materials.

Contribution

It introduces predictive models validated against experiments, clarifying the dominant photothermal mechanism and providing parameters for designing photomechanical devices.

Findings

Photothermal heating is the primary mechanism behind the response.

Models accurately predict experimental length changes.

Thermal diffusion contributes to nonlocal strain effects.

Abstract

Recent studies of azo-dye doped liquid crystal elastomers show a strong photomechanical response. We report on models that predict experimental results that suggest photothermal heating is the dominant mechanism in a planar constrained geometry. We compare our models with experiments to determine key material parameters, which are used to predict the dynamical response as a function of intensity. We show that a local strain from photothermal heating and a nonlocal strain from thermal diffusion is responsible for the observed length changes over time. This work both elucidates the fundamental mechanisms and provides input for the design of photomechanical optical devices, which have been shown to have the appropriate properties for making smart materials.