Surface Modification of Super Arborized Silica for Flexible and Wearable Ultrafast-Response Strain Sensors with Low Hysteresis.

Conductive hydrogels exhibit high potential in the fields of wearable sensors, healthcare monitoring, and e-skins. However, it remains a huge challenge to integrate high elasticity, low hysteresis, and excellent stretch-ability in physical crosslinking hydrogels. This study reports the synthesis of polyacrylamide (PAM)-3-(trimethoxysilyl) propyl methacrylate-grafted super arborized silica nanoparticle (TSASN)-lithium chloride (LiCl) hydrogel sensors with high elasticity, low hysteresis, and excellent electrical conductivity. The introduction of TSASN enhances the mechanical strength and reversible resilience of the PAM-TSASN-LiCl hydrogels by chain entanglement and interfacial chemical bonding, and provides stress-transfer centers for external-force diffusion. These hydrogels show outstanding mechanical strength (a tensile stress of 80-120 kPa, elongation at break of 900-1400%, and dissipated energy of 0.8-9.6 kJ m -3 ), and can withstand multiple mechanical cycles. LiCl addition enables the PAM-TSASN-LiCl hydrogels to exhibit excellent electrical properties with an outstanding sensing performance (gauge factor = 4.5), with rapid response (210 ms) within a wide strain-sensing range (1-800%). These PAM-TSASN-LiCl hydrogel sensors can detect various human-body movements for prolonged durations of time, and generate stable and reliable output signals. The hydrogels fabricated with high stretch-ability, low hysteresis, and reversible resilience, can be used as flexible wearable sensors.