Interfacial Click Chemistry Enabled Strong Adhesion toward Ultra-Durable Crack-Based Flexible Strain Sensors

Flexible strain sensors, particularly crack-based ones, have evoked great interests in recent years because of their excellent sensitivity and promising applications in health monitoring and human-machine interactions. However, the poor durability originated from the weak interfacial bonding between fragile conductive layer and stretchable elastic substrate makes it difficult to meet the needs of practical use. Herein, a strategy enabled by interfacial click chemistry is proposed for effectively enhancing the adhesion strength (τ), thereby improving the durability of the flexible strain sensors. It is found that the strong interfacial adhesion can bear larger cyclic shear force, effectively suppress the crack propagation of the conductive layer, and prevent the conductive layer from peeling off, thus stabilize the conductive path under specific strain during cyclic test, resulting in excellent durability. Moreover, the device durability (number of stable cycles, i.e., C_n) is found to linearly depend on τ, based on which “durability-adhesion coefficient (C_DA)” is defined. So far it is known, this is the first report to quantitatively establish the relationship between interfacial adhesion strength and cycling durability of crack-based strain sensors, providing a new viewpoint for future design of flexible devices with high reliability.