Robust and ultrasensitive hydrogel sensors enhanced by MXene/cellulose nanocrystals

As a new two-dimensional material, MXene has caused extensive research in field of supercapacitor, electromagnetic shielding, strain sensing field due to its excellent mechanical properties and electrical conductivity. MXene with good water dispersibility can be used as an ideal nano-material to enhance the conductivity of hydrogels. However, MXene is easy to accumulate in the hydrogel system, and there are rare articles on MXene hydrogels. In this paper, we combine cellulose nanocrystals (CNCs) and MXene to prepare CNC/MXene nanosheets and take advantage of CNC’s excellent dispersibility in water and the electrostatic repulsion between CNCs to avoid the accumulating of MXene and enhance the mechanical properties of the hydrogel. Based on it, we prepared a physical–chemical double crosslinking and double-network CNC/MXene hydrogel by in situ polymerization and cycle freeze-thaw method. The CNC/MXene hydrogel we prepared exhibited excellent mechanical properties; it could be stretched to 7 times its original length and could reach 1.025 MPa tensile stress. When the compression strain was 80%, the compression stress could reach 1.1 MPa. After unloading the compression pressure, it could rapidly return to its original length within 0.17 s, which would impact greatly on the practical application of CNC/MXene hydrogel. What's more, the conductivity of it was up to 0.4 S/m and the thermal conductivity was 0.38 W/mK. So, the hydrogel prepared by us has a wide range of application prospects in the fields of human motion monitoring, electronic skin, man–machine interface, etc.