Highly Sensitive and Oxidation Resistance Polyacrylic/Polyacrylamide Hydrogel for Multifunctional Flexible Sensors

Multifunctional flexible sensors have been widely applied in various fields. However, integrating excellent electrical conductivity, mechanical properties, and durability into multifunctional flexible sensors remains a significant challenge. In this study, a PAA/PAM composite hydrogel system containing MXene (Ti3C2Tx) and tannic acid (TA) was introduced to address the above issues. This composite hydrogel aims to solve the long-standing problems of poor stability of conductive networks and limited application scenarios in the field of multifunctional flexible sensors. Through surface engineering of two-dimensional materials and dynamic cross-linking strategies, this composite material achieved performance breakthroughs. Additionally, the material obtained self-healing ability through dynamic hydrogen-bond reorganization. MXene can form a highly conductive network, but its structural degradation due to surface hydroxyl oxidation in an oxidative environment severely limits its practical application. To overcome this limitation, this study innovatively used TA polyphenols to construct an antioxidant layer on the MXene surface. After adding TA, the conductivity of the composite hydrogel decreased by 37.12% within 24 days. Despite this decrease, the multifunctional sensor still maintained high sensitivity for finger movement monitoring, with a current fluctuation of only 0.08%. After adding MXene, the conductivity of the hydrogel increased from 42.9 mS/m to a maximum of 77.5 mS/m. The tensile strain value of the composite hydrogel increased from 0.1 MPa to a maximum of 0.4 MPa. Experimental results show that the strain coefficient (GF) of the optimized composite material at 20% strain is 12.3. Moreover, the tensile strength of the hydrogel is 400% higher than that of the blank control group, highlighting its outstanding performance in numerous wearable applications. In this study, by modifying and protecting the conductive fillers, the sensing and mechanical properties of multifunctional flexible sensors were enhanced, providing a strategy for interface engineering design of two-dimensional materials in multifunctional flexible electronic devices.