Indirect method for preparing dual crosslinked eutectogels with high strength, stretchability, conductivity and rapid self-recovery capability as flexible and freeze-resistant strain sensors

Abstract

The growing demand for stretchable conductor materials in flexible electronic technologies has led to increased focus on developing conductive gels. However, existing hydrogels have poor temperature resistance, and ionogels may have potential toxicity, limiting their use in bio-related applications. This work focuses on the development of the emerging eutectogels with both mechanical and electrical properties, which have traditionally been challenging to achieve. We present an indirect method to prepare dual crosslinked eutectogels that possess high strength, stretchability, conductivity and rapid self-recovery capability. The approach involves using water molecules as a co-solvent to form a deep eutectic solvent through a three-step process, followed by ionically cross-linking poly(acrylamide-co-acrylic acid) with Fe3+. The resulting eutectogels have a balanced mechanical strength with a tensile strength up to 6.17 MPa, large stretchability up to 1067%, a modulus of 1.25 MPa, and excellent toughness of 20.95 MJ/m3. In addition, the eutectogels exhibit high ionic conductivity of 10.29 mS/cm, rapid self-recovery and low temperature tolerance capability (up to −50 °C). To our knowledge, the eutectogels with balanced tensile strength, toughness, conductivity, and low-temperature tolerance can hardly be achieved. Moreover, the conductive eutectogel also exhibit high sensitivity with a gauge factor of 9.47 at strain of 700% with fast response time, making them promising candidates for soft human-motion sensors that can accurately detect human motions with high sensitivity and good durability over a wide temperature range. The findings provide new insights into developing eutectogels with both mechanical and electrical properties, opening opportunities in flexible electronics, soft robotics, and energy storage devices.