(357d) Liquid Crystal Elastomers with Reversible Crosslinking and Low Tg

Liquid crystal elastomers (LCEs) can exhibit large and fully reversible shape-changes, up to 400 % strains in some cases.  LCEs are typically made by attaching liquid crystal molecules (mesogens) to a polysiloxane network. However, preparing monodomain LCEs in which the liquid crystal orientation is aligned uniformly thorugh the sample is challenging since the network must be aligned and crosslinked simultaneously.  Here, we report on the development of epoxy-based main-chain LCEs with reversible network crosslinking.  These materials are made by reacting di-epoxy liquid crystal mesogens with flexible di-acid linking groups. Above a temperature of 160 °C, network bonds re-organize through trans-esterification reactions, enabling the alignment of the liquid crystal orientation after network formation. The glass-transition and smectic-to-isotropic transition temperatures are tuned by varying the length and composition of the linking group, and the use of siloxane-based linkers produces LCEs with a glass-transition temperature below room temperature. We characterize the materials systematically through 2-D X-ray diffraction measurements, dynamic mechanical analysis, and differential scanning calorimetry and demonstrate the use of these materials as active substrates for cell culture.