Elastocaloric Response of Isotropic Liquid Crystalline Elastomers.

Abstract

Liquid crystalline elastomers (LCEs) are soft materials that associate order and deformation. Upon deformation, mechanically induced changes order affect entropy and can produce a caloric output (elastocaloric). Elastocaloric effects in materials continue to be considered for functional use as solid state refrigerants. Prior elastocaloric investigations of LCEs and related materials have measured ≈2°C temperature changes upon deformation (100% strain). Here, the elastocaloric response of LCEs is explored that are prepared with a subambient nematic to isotropic transition temperature. These materials are referred as "isotropic" liquid crystalline elastomers. The LCEs are prepared by a two-step thiol-Michael/thiol-ene reaction. This polymer network chemistry enhances elastic recovery and reduces hysteresis compared to acrylate-based chemistries. The LCEs exhibit appreciable elastocaloric temperature changes upon deformation and recovery (>±3°C, total ΔT of 6°C) to deformation driven by minimal force (<<1MPa). Notably, the strong association of deformation and order and the resulting temperature change attained at low force achieves a responsivity of 14°C MPa-1 which is seven times greater than natural rubber.