Wearable Optical Sensing of Strain and Humidity: A Patterned Dual-Responsive Semi-Interpenetrating Network of a Cholesteric Main-Chain Polymer and a Poly(ampholyte)

Main-chain cholesteric liquid crystal polymers are a promising candidate for the development of responsive photonic devices due to the combination of selective reflection and soft, elastic properties, but it is difficult to enhance these materials with new kinds of responsiveness due to the inherent lack of mesogenic side groups. Here, a new strategy is showed to obtain a dual-responsive elastic cholesteric polymer material by preparing a semi-interpenetrating network consisting of a cholesteric main-chain polymer and a hygroscopic poly(ampholyte). The material is shown to undergo a redshift of the reflected color upon swelling with water, while the color blueshifts when a strain is applied. Color patterns can be prepared by localized photopolymerization at different temperatures, leading to brightly colored responsive images with high contrast. Due to the elastic nature of the material, it can easily be made into a wearable device, and its application as a multifunctional smart sensor for sweat detection and movement detection is demonstrated. The results show that new responsiveness can be added to main-chain cholesteric polymers by preparation of interpenetrating networks, which can be further extended to develop various kinds of multi-responsive smart materials.