Highly Stretchable and Compressible Cellulose Ionic\nHydrogels for Flexible Strain Sensors

Abstract

Stretchable and compressible\nhydrogels based on natural polymers\nhave received immense considerations for electronics. The feasibility\nof using pure natural polymer-based hydrogels could be improved if\ntheir mechanical behaviors satisfy the requirements of practical applications.\nHerein, we report highly stretchable (tensile strain ∼126%)\nand compressible (compression strain ∼80%) cellulose ionic\nhydrogels (CIHs) among pure natural polymer-based hydrogels including\ncellulose, chitin, and chitosan via chemical cross-linking based on\nfree radical polymerization of allyl cellulose in NaOH/urea aqueous\nsolution. In addition, the hydrogels have good transparency (transmittance\nof ∼89% at 550 nm) and ionic conductivity (∼0.16 mS\ncm^–1) and can be worked at −20 °C without\nfreezing and visual loss of transparency. Moreover, the CIHs can serve\nas reliable and stable strain sensors and have been successfully used\nto monitor human activities. Significantly, the various properties\nof hydrogel can be controlled through rationally adjusting the chemically\ncross-linked density. Our methodology will prove useful in developing\nthe satisfied mechanical and transparent CIHs for a myriad of applications\nin flexible electronics.