Hydrophobic deep eutectic solvent-based ionic conductive gels with highly stretchable, fatigue-resistant and adhesive performances for reliable flexible strain sensors

Owing to the advantages of temperature resistance, low cost, and biocompatibility, deep eutectic solvent (DES)-based ionic conductive gels have attracted increasing research interest for flexible devices in recent years. However, current DES gels are all based on hydrophilic DES, which tend to absorb a large amount of environmental moisture, resulting in gel softening and adversely affecting the durability of the device. In this work, we highlight for the first time that N , N -dimethylacrylamide monomer, and the obtained polymer can form hydrogen-bonding networks with hydrophobic DES, methyl trioctyl ammonium chloride/ethyl 4-hydroxybenzoate (1:2), thereby obtaining a hydrophobic DES-based gel through photo-polymerization. The resultant DES gel displays high stretchability (~900%), toughness (341.14 kJ m −3 ), anti-fatigue property (recovery after 500 compression cycles), desirable conductivity (0.12 mS cm −1 ), adhesiveness and high transparency (>90% visible light transmittance). Notably, the hydrophobic DES-based gel absorbs only 2 wt% water but exhibits significant water-induced stiffening after exposing in ambient air for 1 week. These properties lead to the successful realization of the DES gels as wearable sensors to precisely monitor human motion. This work may open new avenues for the development of hydrophobic DES-based gel ionotronics with functional performance.