Ionically Conductive and Self-Healing Polyampholyte Hydrogels for Wearable Resistive Strain Sensors and Capacitive Pressure Sensors

Abstract

Hydrogels are promising materials for flexible wearable sensors, but they often suffer from unpredictable mechanical damage. In this work, self-healing polyampholyte hydrogels are developed and explored in constructing wearable mechanosensors including resistive strain sensors and capacitive pressure sensors. In order to prepare the polyampholyte hydrogels, sodium p-styrenesulfonate (NaSS) and (methacryloxyethyl)trimethylammonium chloride (DMC) are used as the anionic and cationic monomers, respectively, and N,N′-methylenebis(acrylamide) (MBAA) is used as the chemical cross-linking agent. The resulting hydrogels, denoted as NaSS/DMC polyampholyte hydrogels, exhibit outstanding self-healing ability, transparency, ionic conductivity, and stretchability. Resistive strain sensors assembled from such polyampholyte hydrogels exhibit a gauge factor (GF) of 2.9 over a strain range of 0–350%, a low response time of 250 ms, and excellent cycling stability. Moreover, sandwich-structured capacitive pressure sensors are assembled utilizing polyampholyte hydrogels containing reliefs as the electrodes. The pressure sensors achieve a GF of 2.17 kPa–1, a sensing range of 0–7.35 kPa, and high cycling stability. The applications of such wearable mechanosensors in monitoring various strains and pressures in daily life are demonstrated. Overall, this work not only develops a smart hydrogel with outstanding self-healing ability but also provides a clue to construct soft electronics for wearable devices.