Self-healable functional polymers and polymer-based composites

Polymers and polymer composites with advanced functions have attracted great attention following the development of modern science and technologies. Nevertheless, damages of microstructures and variations of chemical constitutes are inevitably induced during their manufacturing and operation, causing undesired attenuation or even loss of functionalities. To address the problems, self-healable functional polymeric materials, which focus on autonomous restoration of non-structural functionalities for improving the lifespan and durability, have emerged in recent years as a huge surge of interest because of their apparent potential benefits. As dictated by the diverse working principles of the individual functionalities, the technical advance of self-healing functional polymers and composites exhibits distinct characteristics from that of self-healing structural materials specializing in strength recovery. This review summarizes the state-of-the-art achievements in the field, and discusses the common features and issues in most of the reported self-healing functional materials including healable electroconductive, thermally conductive, dielectric, optically transparent, superhydrophobic, superhydrophilic, and power conversion and storage related polymers. The review will subsequently discuss (i) the damage modes relating to different causes, (ii) the mechanisms of self-healing based on chemical and physical methodologies, and (iii) molecular level design schemes and synthesis strategies for self-healing functional polymeric materials. The advantages and inadequacies of representative works are discussed, and the critical challenges and opportunities for future research are highlighted. It is hoped that the present article would inspire more innovative explorations of self-healing functional polymeric materials, as well as promote their practical application.