A Highly Sensitive Complex Ion-Conductive Hydrogel for Flexible 3d Tactile Interactive Applications

Abstract

Ion-conductive hydrogels possess great potential in the field of flexible sensing due to their unique mechanical characteristics and internal ionic conduction. However, the drawback lies in their inability to simultaneously achieve excellent mechanical strength and high conductivity, which largely limits their practical applications. Here, we report a PVA/PAANa ion-conductive composite hydrogel with dual improvement in both aspects, which owns the macroscopic honeycomb-like porewall structure and a microscopic triple network (TN). Specifically, the H-bonding-rich networks are firstly formed intrinsically within between the PVA chains and between the PVA and PAANa chains, through thermal polymerization and combined freeze-thawing approach. Next the conductive percolation network is incorporated through the addition of silver nanowires, to further boost the overall conductivity. Then, Na+ ions are introduced through salting-out effect to enhance its electrostatic interactions with COO- groups in the hydrogel, forming an electrostatic network. Hence, based on the salting-out assisted freeze-thaw strategy, the ion-conductive composite hydrogel achieved Young's modulus of 201 kPa, toughness of 0.66 MJ/m3, and a conductivity of 0.646 S/m. When implemented as a pressure-sensitive tactile sensor, the hydrogel exhibited a pressure sensitivity of 0.189 kPa-1 (pressure range: 0.797- 2.171 kPa) with a response time of 143 ms, and an exceptional fatigue resistance with signal stability maintained over 1500 compression cycles. Lastly, a 3x3 tactile sensor array based on P/P/A-NaCl hydrogels was designed for multi-dimensional sensing and pressure distribution mapping. As a flexible tactile sensor, the proposed ion-conductive hydrogel shows promising potential for diverse interactive applications in human health monitoring, sports tracking, and soft robotics.

Keywords: Ion-conductive hydrogels, Triple-Network, Flexible tactile sensor, Array image mapping, Interactive application