Highly linear wearable ionic gel based on self-assembled discoid liquid crystal towards human motion monitoring

Abstract

The development of ionic gel with high flexibility, wide operating temperature range, and excellent physicochemical stability is crucial for the next generation of wearable flexible strain sensors. In this study, a late-model ionic gel named MBTA–TBC was synthesized by click reaction using tri(2-mercapto ethyl)-1,3,5-benzenetricarbonamide (MBTA) as the cross-linking point, tri(2-methacryloyloxyethyl) borate (TBC) as the flexible chain, and bis(trifluoromethane) sulfonimide lithium salt (LiTFSI) as the ionic salt. During the polymerization process, MBTA liquid crystal small molecules will self-assemble to form cross-linking points of approximately 22 nm and anchor TBC flexible chains. Due to the mismatch in modulus between MBTA and TBC, distinctive fishnet-like microstructures with ion channels were formed spontaneously. The formation of ion channels promotes the transport of ions in the gel, and the fishnet microstructure is conducive to energy dissipation, thus enhancing the mechanical stability of the gel. The prepared ionic gel showed unique rheological properties, a high ionic conductivity of 4.1 × 10⁻⁴ mS cm⁻¹, a wide operating temperature range, and adhesive properties. As a flexible strain sensor, it exhibits high sensitivity (GF = 1.29), good linearity (R² = 0.9995), and excellent cyclic stability, and can respond to human joint bending and throat swallowing. The ionic gel shows potential application value in human health monitoring, artificial skin, and soft robots.