Ultra-Sensitive Pressure Sensor Based On Polypyrrole Films With Three-Scale Nested Wrinkling Structures

Pressure sensors have a variety of applications including wearable devices and electronic skins.To satisfy the practical applications,pressure sensors with a high sensitivity,a low detection limit,and a low-cost preparation are extremely needed.Herein,we fabricate highly sensitive pressure sensors based on hierarchically patterned polypyrrole?PPy?films,which are composed of three-scale nested surface wrinkling microstructures through a simple process.Namely,double-scale nested wrinkles are generated via in situ self-wrinkling during oxidative polymerization growth of PPy film on an elastic poly?dimethylsiloxane?substrate in the mixed acidic solution.Subsequent heating/cooling processing induces the third surface wrinkling and thus the controlled formation of three-scale nested wrinkling microstructures.In this paper,we first studied the effects of PDMS substrate thickness and PPy polymerization time on the surface morphology of PPy film with two-scale wrinkle structure and the sensitivity of the corresponding pressure sensor,and we determined the optimal PDMS substrate thickness and PPy polymerization time.Subsequently,we investigated the effect of heat-induced effect on the surface morphology,surface resistivity and sensitivity of the corresponding pressure sensor of PPy film with three-scale nested wrinkle structure.It was found that the surface morphology of PPy film is the main influence on the sensitivity of pressure sensor.The multiscale nested microstructures combined with stimulus-responsive characteristic and self-adaptive ability of wrinkling morphologies in PPy films offer the as-fabricated piezoresistive pressure sensors with a high sensitivity(19.32 kPa^-1),a low detection limit?1 Pa?,an ultrafast response?20 ms and 30 ms?,and excellent durability and stability?more than1000 circles?,these comprehensive sensing properties being higher than the reported results in literature.Moreover,the pressure sensors have been successfully applied in the wearable electronic fields?e.g.,pulse detection and voice recognition?and microcircuit controlling,as demonstrated here.