Preparation and characterization of PVA/PVP conductive hydrogels formed by freeze–thaw processes as a promising material for sensor applications

Biocompatible and multifunctional stretchable hydrogels have attracted growing interests for applications including electronic skin and soft robotics. This paper presents a conductive and humidity sensitive hydrogel formed by poly (vinyl alcohol) (PVA) and poly (vinylpyrrolidone) (PVP). Different from previous approaches where microwave-assisted aldol condensation reactions are needed to form the material, in this work, we demonstrate forming the hydrogel through only freeze–thaw process. The resulting hydrogel features a gauge factor (~ 0.8), which is higher than that of the strain sensor fabricated through traditional approach during the strain range up to 40%. Furthermore, the structural, elastic, thermal and electrical properties of the polymer blend are evaluated so the operating environment can be identified. Our experimental results show that elasticity of the blend reduces in air due to drying that cannot be completely restored. Moreover, the conductivity of the hydrogel changes with different ambient temperatures and humidity. Finally, the hydrogel is explored as a humidity sensor.