Fast preparation of adhesive, anti-freezing hydrogels with strain- and magnetic-responsive conductivities†

Abstract

Incorporation of magnetic components enables flexible conductive hydrogels to exhibit strain-response properties in the presence of a magnetic field. However, the utilization of flexible conductive hydrogels is constrained under low-temperature conditions, and the mechanical properties of most magnetic hydrogels are poor. In this work, a conductive sensor was developed through Ca²⁺-initiated radical polymerization, utilizing the synergistic effects of sodium lignosulfonate (SL), calcium chloride (CaCl₂), and Fe₃O₄@laponites (XLG). Fe₃O₄@XLG not only served as a physical crosslinking agent but also functioned as a magnetic component. Due to the presence of both physical and chemical crosslinking, the Ca²⁺-Fe₃O₄@XLG/SL/polyacrylamide (PAM) hydrogel had good mechanical properties. After being placed at −20 °C for 24 h, the Ca²⁺-Fe₃O₄@XLG/SL/PAM hydrogel remained intact, soft, and tough, and it still exhibited good stretchability (1029%) and strength (69.7 kPa). In addition, the hydrogel also exhibited good adhesion with various substrates. Strain sensors assembled from the nanocomposite hydrogels achieved a gauge factor of 5.14, a response time of 166 ms, and good stability. The Ca²⁺-Fe₃O₄@XLG/SL/PAM hydrogels had magnetic response properties, and they could respond quickly to magnetic field changes in the form of resistance changes. Thus, they have potential applications in magnetic field signal monitoring and soft actuators.