Tough, Ion-Conductive Poly(vinyl alcohol)/Polyelectrolyte Hydrogels Based on a Double Network for Use as Strain Sensors

With the rapid development of soft electronics in recent years, the demand for hydrogel materials as a conductive material with a high degree of flexibility, widely adjustable mechanical strength, and a wide range of application scenarios has grown rapidly. In recent years, hydrogels have been reported as flexible strain sensors in application scenarios such as wearable devices, healthcare detection, and electronic skins. However, conventional hydrogels are generally not very tough and mechanically strong and do not adapt well to the environment. In this context, we have designed and synthesized an ion-conductive double-network hydrogel (DN-F/T gel) with a strong interaction between poly(vinyl alcohol) (PVA) and phytic acid (PA) as the first heavy network and a second ionic network consisting of the anionic monomer sodium p-styrenesulfonate (NaSS) copolymerized with the cationic monomer [2-(acryloyloxy)ethyl]trimethylammonium chloride solution (DAC). The hydrogel has a tensile strength of 1.52 MPa at 417% and a toughness of 3.30 MJ m–3. While excellent flexibility and toughness are ensured, the dissipation energy of the hydrogel stabilizes after repeated cycling tests. With the addition of the ionic cross-linked network and phytic acid, the conductivity of the dual-network hydrogel is substantially improved, with stable responsiveness under various strain and cycling tests and good performance as a strain sensor and writing recognition material. It has good swelling resistance in water, with a swelling rate of 63% after 15 days of immersion. This enriches the application prospects for its use in complex scenarios, such as those encountered in underwater sports. These properties all contribute to the durability, stability, and suitability of hydrogel strain sensors.