Highly stretchable, self-adhesive, ambient-stable, and wide-temperature adaptable hydrophobic ionogels for wearable strain sensors

Abstract

The development of hydrophobic ionogels with high stretchability, good recoverability, and excellent stability in widely varying environments is essential for next-generation wearable sensors. Herein, a highly stretchable hydrophobic ionogel was facilely designed and formed by a one-pot polymerization of diacetone acrylamide (DAAM) in a hydrophobic ionic liquid of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI) with a topological structural macro-crosslinker of an acrylate-terminated hyperbranched polyester. The unique deformable covalent crosslinking networks formed by multifunctional hyperbranched macromolecular and reversible noncovalent bond junctions formed by hydrogen bonding endowed the ionogels with high stretchability (>1000%), good resilience, and excellent durability. These ionogels also showed a special rheological property, good air/underwater self-adhesiveness, excellent optical transparency (90.5%), harsh temperature tolerance (−85 °C to 240 °C), and high ionic conductivity (10⁻³ S cm⁻¹). Importantly, the hydrophobic ionic liquid BMIMTFSI endowed the ionogels with an excellent humidity-resistance ability and suitable underwater stability. In addition, these ionogels could be used to fabricate long-term durable and stable strain sensors, no matter in air with different humidity environments or in aquatic environments, and also showed superior sensing performance, even under both extremely cold (−50 °C) and hot (200 °C) conditions.