Fabrication of self-healing ion gels and their application in strain sensors

초록

Research is being actively conducted to develop wearable devices with high conductivity, deformability, durability, and room temperature stability. Wearable devices are generally under repetitive mechanical deformation, ultimately leading to mechanical and functional failure. Therefore, there have been recent efforts to impart a self-healing capability to wearable devices. Ion gels are polymer electrolyte composites comprising network-forming polymers and ion-conducting ionic liquids. While the thermal and electrochemical stability of ion gels originates from the intrinsic property of ionic liquids, the electronic and physical properties of ion gels may be tuned or modulated depending on the types of ionic liquids, polymer architecture, and crosslinking mechanisms. This tunability has allowed the implementation of ion gels for various wearable applications, including transistors, actuators, and sensors. The work described herein aims to provide a description of self-healing ion gels based on side-chain architecture and their application in strain sensors. Ion gels were prepared by synthesizing copolymers having various molar ratios of docosyl acrylates and mixing the copolymers with ionic liquids. The evolution of the thermal stability, crystalline structure, ionic liquid content, and mechanical property of the ion gels was monitored while the copolymer composition was systematically varied. The ion gel specimens were cut in half with a blade, and the specimens were brought into contact at room temperature. The recovery of mechanical propertied was studied as a function of healing time. The self-healing efficiency was estimated by comparing the mechanical toughness after and prior to self-healing. Gradual disappearance of a mechanical scratch on the surface of specimens was monitored over time. Ion gel films were attached to body parts (e.g., wrist and finger), and the strain variation due to the body movement was investigated by monitoring the electrical propert