Flexible Sensing Materials with Polyrotaxane-Enabled Interfacial Modulation for Controlling Crack Evolution

Abstract To solve the inherent trade-off between sensitivity and detection range of flexible strain sensors, this study adopted an interfacial engineering strategy based on the dynamic sliding effect of polyrotaxane (PR). PR contains cyclodextrin rings that slide along the polymer backbone and move freely under external stress. This unique sliding structure effectively dissipates mechanical energy and relieves stress concentration during stretching, precisely regulating the initiation and propagation of microcracks in the conductive layer, restraining catastrophic crack expansion, and facilitating the formation of uniformly distributed mesh-like microcracks. Compared with PR-free PC and CC control systems, the PR-regulated PCC sample exhibits distinctly smaller crack spacing of 755 μm and conductive-island area of 33,024 μm2 at 50% tensile strain. Benefiting from such optimized microcrack architecture, the PCC sensor achieves a high gauge factor (GF) of 348.59 and a broad effective working strain range up to 287.68%. Meanwhile, N,N′-carbonyldiimidazole (CDI) serves as a coupling agent to construct a covalent-hydrogen-bond synergistic network among the conductive layer, PR and SEBS substrate, which further strengthens interfacial adhesion and improves overall structural stability in cooperation with the PR sliding effect. Owing to the dynamic sliding behavior of PR, the sensor delivers efficient energy dissipation, low hysteresis, and reliable electrical responses over 600 stretching cycles under diverse stretching rates from 10 to 100 mm/min. This study develops a universal design strategy for high-performance microcrack-type strain sensors based on PR dynamic regulation. The prepared sensor exhibits great application potential in biomedical monitoring, soft robotics, and human–machine interface fields.