MXene-enhanced deep eutectic solvent-based flexible strain sensor with high conductivity and anti-freezing using electrohydrodynamic direct-writing method

Abstract

Hydrogel devices suffer from dehydration and low-temperature freezing issues, which can be overcome using a deep eutectic solvent (DES) instead of water. However, the poor mechanical properties of DES gels limit their application in flexible sensing. In this study, a gel precursor solution composed of acrylic acid, hydroxyethyl cellulose (HEC), and a DES was printed in polydimethylsiloxane molds using the electrohydrodynamic printing method and subsequently cured under UV light to form DES gel films with improved electrical conductivity. Further, the mechanical and electrical properties of flexible strain sensors developed using DES gel films were improved by introducing multi-layer accordion-like MXene nanosheets into the interpenetrating network formed by HEC and polyacrylic acid (PAA). Specifically, the newly formed MXene-PAA-HEC eutectogel exhibited a tensile strength of 0.26 MPa at 422 % strain, an electrical conductivity of 0.235 S/m, fast response (123 ms) and recovery (103 ms) capabilities, and good fatigue resistance (stability over 1000 tensile–release cycles). In addition, the DES gel inherited the freeze-resistance property of the DES with low-temperature stability, extending the application range of flexible sensors. Owing to their excellent electromechanical properties, wide operating range, and eco-friendliness, the MXene-PAA-HEC DES gels can be used to monitor human motion, creating new possibilities for developing green, flexible, and high-performing electronic devices with biocompatibility and multifunctional characteristics.