Fully Physically Crosslinked Hydrogel with Ultrastretchability, Transparency, and Freezing-Tolerant Properties for Strain Sensor.

Nowadays, conductive hydrogels show significant prospects as strain sensors due to their good stretchability and signal transduction abilities. However, traditional hydrogels possess poor anti-freezing performance at low temperatures owing to the large number of water molecules, which limits their application scope. To date, constructing a hydrogel-based sensor with balanced stretchability, conductivity, transparency, and anti-freezing properties via simple methods has proven challenging. Here, a fully physically crosslinked poly(hydroxyethyl acrylamide)-glycerol-sodium chloride (PHEAA-Gl-NaCl) hydrogel was obtained by polymerizing hydroxyethyl acrylamide in deionized water and then soaking it in a saturated NaCl solution of glycerol and water. The PHEAA-Gl-NaCl hydrogel had good transparency (93%), stretchability (1300%), and fracture stress (~287 kPa). Owing to the presence of glycerol and sodium chloride, the PHEAA-Gl-NaCl hydrogel had good anti-freezing properties and conductivity. Furthermore, the PHEAA-Gl-NaCl hydrogel-based strain sensor possessed good sensitivity and cyclic stability, enabling the detection of different human motions stably and in a wide temperature range. Based on the above characteristics, the PHEAA-Gl-NaCl hydrogel has broad application prospects in flexible electronic materials.