Robust and sensitive pressure/strain sensors from solution processable composite hydrogels enhanced by hollow-structured conducting polymers

Flexible sensors based on conductive hydrogels have found potential applications in many emerging electronic devices, but they often suffer from poor mechanical properties, single response mode and low sensitivity. Herein, robust and sensitive pressure/strain sensors are designed and fabricated utilizing novel composite hydrogels composed of hollow polyaniline spheres (HPS), poly(vinyl alcohol) (PVA) and phytic acid (PA). By taking advantages of structure-derived elasticity of hollow spheres, conductivity of doped conducting polymers, flexibility of polymer matrix and physically cross-linked structure, the composite hydrogels exhibit outstanding mechanical properties, strain sensitivity, piezoresistivity and solution processability. The optimized composite hydrogel possesses high tensile strength (9.3 MPa), stretchability (>493%) and toughness (2.6 MJ/m3). Resistive-type strain sensors assembled from the composite hydrogel can achieve a gauge factor (GF) of 2.9 in the strain range of 0%~300%, a GF of 7.4 in the strain range of 300%–450%, a response time of 0.22 s and high reliability (1000 cycles). Capacitive-type pressure sensor with ultrahigh sensitivity of GF = 3.6 kPa−1 is fabricated by sandwiching a dielectric layer between two composite hydrogel films. Interestingly, piezoresistivity of such composite hydrogels makes them promising materials for piezoresistive-type pressure sensors and visualization of pressure. On the basis of their high performances, flexible sensors of the composite hydrogels are applied in monitoring various human motions, physiological activities and bending/vibration deformations in daily life.