Understanding the effect of liquid crystal content on the phase behavior and mechanical properties of liquid crystal elastomers

Abstract

Liquid crystal elastomers are stimuli-responsive, shape-shifting materials. They typically require high temperatures for actuation which prohibits their use in many applications, such as biomedical devices. In this work, we demonstrate a simple and general approach to tune the order-to-disorder transition temperature (T_ODT) or nematic-to-isotropic transition temperature (T_NI) of LCEs through variation of the overall liquid crystal mass content. We demonstrate reduction of the T_NI in nematic LCEs through the incorporation of non-mesogenic linkers or the addition of lithium salts, and show that the T_NI varies linearly with liquid crystal mass content over a broad range, approximately 50 °C. We also analyze data from prior reports that include three different mesogens, different network linking chemistries, and different alignment strategies, and show that the linear trend in T_ODT with liquid crystal mass content also holds for these systems. Finally, we demonstrate a simple approach to quantifying the maximum actuation strain through measurement of the soft elastic plateau and demonstrate applications of nematic LCEs with low T_ODTs, including the first body-responsive LCE that curls around a human finger due to body heat, and a fluidic channel that directionally pumps liquid when heated.