Large Range Thermochromism in Liquid Crystalline Elastomers Prepared with Intra-Mesogenic Supramolecular Bonds

Abstract

Liquid crystalline elastomers (LCEs) that retain the cholesteric phase (CLCEs) are soft, polymeric materials that retain periodic structure and exhibit a selective reflection. While prior studies have examined thermochromism in CLCEs, the association of temperature change and reflection wavelength shift has been limited to 1.4 nm °C−1. Here, CLCEs with intra-mesogenic supramolecular bonds are prepared to enhance tunability as well triple the rate (e.g., 4.8 nm °C−1). Specifically, these materials incorporate liquid crystalline monomers based on dimerized oxy-benzoic acid (OBA) derivatives. Increasing the concentration of the OBA comonomers increases the magnitude of red-shifting thermochromism of the selective reflection. At and above a threshold concentration, the selective reflection in the CLCEs can disappear upon heating, analogous to on-off “switching.” Further, the introduction of the supramolecular bonds within the CLCE enable mechanical programming and enhanced one-time tunable thermochromism via a one-way shape memory process. Accordingly, this research could enable functional use in low temperature sensitive optical elements, fail-safe thermal indicators for food packaging, and smart window coatings.