Effects of network structure on the mechanical and thermal responses of liquid crystal elastomers

Thermoresponsive liquid crystal elastomers (LCEs) have a high potential to be used for actuation applications. There has been a substantial amount of literature on synthesis of different LCE networks and their corresponding performance. However, much of the prior work focuses on the experimental aspect of the effects of mesogenic species, crosslinkers, and spacers on the thermal and mechanical response of LCE. Here we have built on these prior studies, and expanded understanding of LCE work capacity and thermal properties to the molecular and network structures by comparing the experimental results to the theoretically predicted values based on a random walk model derived from classical rubber elasticity. A previously developed two stage thiol-acrylate LCE chemistry was used as the model system. On the basis of increasing the chain entropy, we varied crosslinker concentration, crosslinker functionality, and liquid crystal mesogen length and showed that average molecular weight between crosslinks and molecular weight of the Kuhn segment play important roles in controlling the work capacity. The rubber elastic model predicted network performance agreed reasonably well with the experimental results.