Highly sensitive strain sensors with wide operation range from strong MXene-composited polyvinyl alcohol/sodium carboxymethylcellulose double network hydrogel

Double network (DN) conductive hydrogels have become a hotspot for wearable sensors. However, building DN hydrogel-based strain sensors with excellent mechanical strength, high sensitivity, and wide operation window still remains a challenge. This paper fabricates a high-performance strain sensor from MXene-composited polyvinyl alcohol/sodium carboxymethyl-cellulose (PVA/CMC) DN hydrogel which is further reinforced by tannic acid (TA). In this PCTM (short for PVA/CMC/TA/MXene hydrogel), PVA serves as the flexible backbone, CMC mainly functions as the rigid subnetwork skeleton in the hydrogel, and naturally occurring TA further enhances the mechanical properties of the hydrogel via tight hydrogen bonds between TA and the polymer chains of PVA and CMC. MXene is utilized to build the conductive path, and its abundant hydrophilic functional groups help to achieve a uniform distribution in the hydrogel, which is beneficial for achieving high sensitivity and wide operation window. The unique multiple synergetic networks of PCTM impart promising mechanical strength (a fracture tensile strength of 1.8 MPa at a fracture strain of 740%) and high sensitivity with a wide detection window (a gauge factor of 2.9 at a strain range of 0-700%) as well as long-term durability over 3000 continuous cycles. Moreover, the sensor also exhibits accurate response to different types of human motions. As a proof of concept, a PCTM sensor is fabricated for visual detection of the pressure, suggesting its promising potentials for stretchable electronic sensors.