Developing a carbon composite hydrogel with a highly conductive network to improve strain sensing performance

Both carbon aerogels and conductive hydrogels have provoked immense research interest as flexible sensing materials. However, conventional carbon aerogels show limited stretchability, while conductive hydrogels generally show limited conductivity. Herein, we develop a carbon composite hydrogel with a highly conductive network by encapsulating a cellulose fiber-derived carbon aerogel with a liquid metal-based conductive hydrogel formed by the in situ free radical polymerization of acrylic acid. The as-prepared carbon composite hydrogel inherits its high conductivity from the cellulose fiber-derived carbon aerogel and its good stretchability, adhesion and self-healing properties from the liquid metal-based hydrogel. Moreover, the carbon composite hydrogel possesses a high tensile strength and toughness due to the rigid network of the carbon aerogel. When serving as the tensile strain sensing material, the carbon composite hydrogel shows a very high sensitivity (gauge factor = 13.1 in the strain range of 400–500%), ultralow detection limit (0.1%), quick response and recovery time (166 ms at the strain of 1%) and excellent durability (1000 cycles under at 10% and 100% strains). In addition, the carbon composite hydrogel can obtain good temperature tolerance, adapt to high humidity and sustain its good sensing performance at low and high temperatures simply by coating a layer of glycerin on its surface. This work broadens the prospects for the design and preparation of conductive hydrogel-based strain sensors, and it facilitates their application in monitoring the biomedical signals of humans.