Temperature-Modulated Photomechanical Actuation of Photoactive Liquid Crystal Elastomers

TL;DR

This paper develops a theoretical model to understand how temperature influences the photomechanical behavior of liquid crystal elastomers, considering molecular to mesoscale processes, and explores various control scenarios including snap-through instability.

Contribution

It introduces a continuum framework incorporating temperature-dependent processes to analyze temperature-modulated photomechanical actuation in liquid crystal elastomers.

Findings

Temperature affects the backward isomerization of chromophores.

Coupling of temperature and light controls enables new actuation behaviors.

Model predicts stress-stretch responses under different thermal conditions.

Abstract

Photoactive liquid crystal elastomers are polymer networks of liquid crystal mesogens embedded with chromophores like azobenzene. They undergo large deformation when illuminated by light of a certain wavelength through photochemical reaction, inspiring exciting new applications. However, despite the recent progresses in both the experiment and theory of these materials, the fundamental understanding of the temperature effect on their photomechanical actuation through various molecular-to-mesoscale processes have remained largely unexplored. This paper constructs a theoretical model to investigate this temperature-modulated photomechanical actuation, by integrating different temperature-dependent processes into a continuum framework. The model studies a special working condition where the material is subjected to a uniaxial tensile load, a prescribed temperature, and a polarized light illumination. We explore the free energy landscape of the system and the uniaxial stress-stretch responses under various conditions. We exploit the coupling between individual controls of temperature and light in a single photomechanical actuation for several working scenarios, including the temperature-modulated photomechanical snap-through instability, specific work, and blocking stress. We study the effect of the temperature-dependent backward isomerization of chromophores on the photomechanical actuation. These results are hoped to motivate future fundamental studies and new applications of various photomechanical material systems.