A semi-interpenetrating network ionic hydrogel for strain sensing with high sensitivity, large strain range, and stable cycle performance

Transparent conductive hydrogels with intrinsic flexibility, high sensitivity and outstanding repeatability and nearly real-time response are highly demanded for wearable devices/sensors. Here we report a novel ionic conductor hydrogel consisting of interpenetrating sodium carboxymethylcellulose (CMC) microsheets and polyacrylamide (PAAm) network. Intrinsic interactions between the CMC and PAAm endow the hydrogel with outstanding physical, mechanical robustness. The ionic hydrogel shows a very high transparency (98.2%), high adhesion efficiency (64% in strength), outstanding repeatability (500 cycles at the strain of 300%), sensitivity (Gauge factor = 3.15), and nearly real-time response (360 ms) to a small amount of stress. Additionally, two pieces of the semi-interpenetrating hydrogel can be bonded together with CMC membrane instantly without any external stimulation. Strain sensor based on the semi-interpenetrating network hydrogel has been demonstrated reliable in detecting a small strain caused by a subtle vibration up to a very large deformation by stretching. The hydrogel-based strain sensor may be applied in human motion detection, smart cushion and soft robotics.