Tough and Stretchable Phenolic‐Reinforced Double Network Deep Eutectic Solvent gels for Multifunctional Sensors with Environmental Adaptability

Abstract Conductive gels are perfect for various sensor applications due to their inherent stretchability, flexibility, and electrical conductivity. However, their poor environmental adaptability and low fracture toughness restrict their potential applications. In this study, resorcinol‐formaldehyde resin (RF) is used for the first time as a rigid network compounded with a flexible polyacrylic acid (PAA) network to successfully prepare a double network (DN) deep eutectic solvent gel (RF/PAA DN gel). The gel has high stress strength (1.04 MPa), compressive strength (10.63 MPa), and toughness (1.07 MJ m −3 ). The addition of RF significantly improves the mechanical properties and gives the RF/PAA DN gel certain photothermal effects, swelling resistance, and flame retardancy, broadening the scope of use and application of the gel. Importantly, as a multifunctional sensor, it can combine deformation sensing, temperature sensing, optical sensing, humidity sensing, and underwater sensing into one, with a wide range of stimuli responses and excellent sensing properties. Excellent environmental suitability also allows its use in a wide range of temperatures (−20−90 °C), humidity (55%−90% RH), underwater, and in fire conditions. The work provides new ideas for choosing rigid networks and a novel strategy for developing multifunctional sensors with excellent performance in complex environments.