Impact of molecular architectures on mesogen reorientation relaxation and post-relaxation stress of liquid crystal elastomers under electric fields

Abstract

Applying electric fields to liquid crystal elastomers (LCEs) has attracted attention as a fast and energy-efficient actuation method for soft robotics. It is helpful to predict the minimum electric field strength that can drive the mesogen reorientation and the time required for the reorientation of LCEs with specific molecular architecture to optimize LCE electrical actuation. In this study, molecular dynamics (MD) simulations of main- and side-chain LCE systems under an applied electric field were performed, and the relaxations of stress and orientational order were observed. The minimum electric field strength that can drive the reorientation for each LCE molecular system was estimated. The time required for reorientation follows a power law of the electric field strength, and the reorientation time for side-chain LCEs is much shorter than that for main-chain LCEs. The behavior of the relaxation value of stress with respect to the electric field strength differed markedly between the main- and side-chain LCEs. These results suggest that designing LCEs at the molecular architecture level and using different LCE molecules in different actuation sites are essential to more precise soft robotics.