Strategies in the preparation of conductive polyvinyl alcohol hydrogels for applications in flexible strain sensors, flexible supercapacitors, and triboelectric nanogenerator sensors: an overview

Elastic conductors play a crucial role in the fabrication of wearable electronic devices and human–computer interaction devices. Among the various candidates for elastic conductors, hydrogels, featuring 3-D swollen macromolecular networks, exhibit exceptional stretchability and biocompatibility. Notably, physical hydrogels based on poly (vinyl alcohol) (PVA), which contains a substantial number of reactive groups (-OH groups), stand out due to their remarkable biocompatibility, superior mechanical properties, and chemical stability. This review focuses on recent advancements in the composite strategy, preparation, and current applications of PVA-based conductive composite hydrogels. Firstly, PVA-based conductive hydrogels are classified based on various conductive treatments: (i) introduction of conductive fillers to the PVA with a single network structure; (ii) introduction of conductive fillers to the PVA with double/multiple network structures (e.g., PVA/carboxymethylcellulose, PVA/poly(acrylamide)); (iii) creation of double-network PVA hydrogel combined with conductive polymers including poly(3,4-ethylene-dioxythiophene)/poly(styrenesulfonate), poly(aniline), poly(pyrrole); (iv) addition of ions to a pure PVA network; (v) addition of ions to the PVA with double network structures (e.g., PVA/sodium alginate, PVA/hydroxyethylcellulose). This review includes a comparative analysis of different conductive hydrogel systems. Secondly, PVA-based conductive hydrogels with diverse functions, such as strain sensing, shape memory, antifreeze properties, transparency, and pH response, are thoroughly reviewed. Thirdly, the latest advancements in the applications of PVA-based conductive hydrogels are demonstrated, including flexible super-capacitors, human–computer interaction devices, and triboelectric nanogenerator sensors. Finally, a summary of the current state of development and critical issues with PVA conductive hydrogels is provided, along with an outlook on how to address each. Graphical Abstract: Systematic review on PVA conductive hydrogels: outlines preparation strategies and applications in flexible electronic devices. [Figure not available: see fulltext.]