Ionically conductive hydrogels with high mechanical strength for wearable sensors.

Abstract

Conductive hydrogels have great potential as sensing materials for wearable flexible electronics; however, their practical applications are often limited by low mechanical strength, poor adhesion, and low self-healing efficiency. To meet the requirements of flexible wearable sensors, in this study we introduced zinc trifluoromethanesulfonate (Zn(CF₃SO₃)₂) into the network structure of polyacrylic acid (PAA) and prepared a polyacrylic acid/zinc trifluoromethanesulfonate (PAA/Zn(CF₃SO₃)₂) conductive hydrogel <i>via</i> free radical polymerization. The addition of Zn(CF₃SO₃)₂ not only improves the ionic conductivity but also enhances the crosslinking density through metal coordination. The PAA/Zn(CF₃SO₃)₂(6 wt%) conductive hydrogel exhibits excellent mechanical properties, with a tensile strength of 1.628 MPa, an elongation at break of 670%, and a high electrical conductivity of 1.212 S m^-1. Furthermore, this hydrogel exhibits good moisture retention, anti-swelling, self-healing, and adhesive properties. Importantly, the wearable sensor based on the PAA/Zn(CF₃SO₃)₂(6 wt%) hydrogel exhibits a wide detection range, fast response time, negligible hysteresis, and high sensitivity (GF = 4.56 at 400-600% strain), enabling accurate capture of large-scale human motions as well as movements such as mouth opening and swallowing. This study demonstrates a multifunctional, high-performance conductive hydrogel, showing promise for applications in wearable health monitoring.