Anomalous thermally expanded polymer networks for flexible perceptual devices

Summary Thermo-responsive polymeric metamaterials have become indispensable because of their wide applications to human-machine interaction, soft robots, wearable devices, augmented/virtual reality, etc. Polymer network-regulated sensing materials could present higher flexibility and adaptability compared to those with rigid structures or silicon-based materials, and their responses to thermal stimulation are more easily triggered and implemented compared to other stimuli, such as light, electricity, etc. Progress relies on the development of programmable materials with tunable thermal expansion on the micro-/macroscale, sheds light on this direction, and facilitates devices that exhibit unprecedented adaptation, sensitivity, and agility. and facilitates devices that exhibit unprecedented adaptation, sensitivity, and agility. This review refines the perceptual elements of positive, negative, anisotropic, tunable, and zero thermal expansion behaviors of polymers and further summarizes corresponding mechanisms, materials design, tuning methods, and related applications to flexible perceptual devices, including 2D response as sensor, 2D/3D/4D response as actuator, and insensitive response as stabilizator. The framework of research progress is presented from a single perceptual element to an integrated perceptual system, from microscopic regulation to macroscopic response. We present an overview of the current research status, which will be an important guide for future development in this field, and simultaneously provide a reference for the broader scientific community.