Highly Sensitive and Stable Encapsulated Ionic Polymer–Metal Composite Sensor Under the Optimal Water Content

Sensitivity and stability are crucial for sensors in practical applications. For ionic polymer–metal composite (IPMC) sensors, these properties are closely related to inner water molecules, due to the unique composite structure. In this article, a technique for encapsulating IPMC sensors under the optimal water content is proposed for the first time. First, by means of gravimetric analysis, the amount of water removed from the saturated IPMC sensor by evaporation was measured to acquire the optimal water content. Second, IPMC sensors were encapsulated by polyolefin (POF) shrink film under the optimal water content (denoted as IPMC-OE). The results manifest that the sensing property obviously increased after quantitative removal of water molecules (i.e., the ratios of water lost range from 1.8 to 3.6). The sensitivity of IPMC-OE is 4–6 times higher than that of the naked IPMC sensor not encapsulated by a polymer film (denoted as IPMC-N). Besides, the stability of IPMC-OE has also been evidently enhanced. The proposed method is a simple, low-cost, and facile strategy. The IPMC-OE sensors maintain high signal strength and stable output signal after up to 19000 deformation cycles. Moreover, apart from underwater detection of biomimetic robotic fish and UUV, the monitoring of wrist pulse, breathing, and finger bending has also been accomplished in the air by IPMC-OE sensors. It is also proved that sensing in media ranging from water to air and a physical quantity ranging from displacement to water flow velocity can be realized. The article guides the performance optimization and practical application of IPMC sensors.