High stretchable, pH-sensitive and self-adhesive rGO/CMCNa/PAA composite conductive hydrogel with good strain-sensing performance

Graphene and its derivatives are considered as one of the most promising functional materials due to their excellent mechanical and electrical properties. Here, we successfully prepared uniform and long-term stable reduced graphene oxide (rGO) dispersion using sodium carboxymethylcellulose (CMCNa) as a stabilizer creatively, and fabricated rGO/CMCNa/polyacrylic acid (PAA) conductive composite hydrogel. The optimal elongation at break of the cylindrical composite hydrogel (1 cm in diameter and 4 cm in length) could reach 1200% at a tensile rate of 50 mm/min. The swelling rate of the composite hydrogel in alkaline environment was much higher than that in acidic environment, indicating excellent pH sensitivity. More importantly, the conductivity of the composite hydrogel could be increased by about 2500% and reached 0.56 S/m due to the construction of the rGO conductive network. The strain sensor based on the rGO/CMCNa/PAA hydrogel showed a wide region of linear response to deformation, up to a strain of 300%. It also exhibited good performance in other aspects, including low hysteresis, a GF value of 1.0, a short response time of 187 ms, and satisfactory stability and repeatability of 2000 cycles at 50% strain. In particularly, the strain sensor could be well adhered to skin without any other adhesives as soft human-motion sensor for real-time and accurate detection of both large-scale and subtle human activities, indicating a great application potential in electronic skin and human health detection.