High-performance PVA-based hydrogels for ultra-sensitive and durable flexible sensors

Constructing highly stretchable and sensitive flexible strain sensors is significant for applications in human–computer interaction, wearable devices, and electronic skins. However, integrating high stretchability and sensitivity into a single system is challenging. In this study, sodium carboxymethyl cellulose (CMC) was interpenetrated into an acrylamide (AM), acrylic acid (AAc), and polyvinyl alcohol (PVA) gel matrix to form a three-dimensional structure. Through simple coordination with polyaniline (PANI) and zinc chloride (ZnCl₂), a high-performance hydrogel, PANI/PVA/CMC-Poly(acrylamide-co-acrylic acid) (P(AM-co-AA))-Zn²⁺ hydrogel, was prepared as the base material. The tensile strength, elongation at break, and elastic modulus of the base hydrogel were 421 kPa, 246%, and 80 kPa, respectively, when the amount of AAc was introduced at 6 mL. To further improve its antifreeze and moisture-preserving properties, the base hydrogel was immersed in a mixed solvent of ethylene glycol (EG) and water, resulting in the optimized PANI/PVA/CMC-P(AM-co-AA)-Zn²⁺/EG hydrogel. The optimized hydrogel exhibited significantly enhanced mechanical properties, including a fracture tensile strength of 838 kPa, a strain of 330%, and an elastic modulus of 302 kPa, when the volume ratio of EG to water reached 1:3. The formation of numerous hydrogen bonds between EG and water molecules prevented ice crystal formation and hindered water evaporation. As a result, the hydrogel exhibited excellent freezing tolerance (-41.6 ℃) and long-lasting moisture (83.7% weight retention after 7 days), maintaining stable mechanical flexibility over a wide temperature range. Due to the presence of conductive polymers and ions, the optimized hydrogel demonstrated high sensitivity (GF = 2.94 for a tensile strain range of 0%-200%) and was able to monitor body movements such as elbow, finger, wrist, and leg bending. These features, combined with its responsiveness to changes in temperature, sweat, and pH, make the optimized hydrogel a promising material for multifunctional sensor applications.