A tough and strain-stiffening ionogel enabled by moderate microphase separation for epidermal multi-sensor

Stretchable ionogels demonstrate promising potentials in the next-generation epidermal electronics, due to their high conductivity, non-volatility and thermal stability. Nevertheless, the typical plasticization of ionic liquids (ILs) renders it challenging to achieve high toughness with skin-like strain-stiffening feature. Here we introduce moderate microphase separation structure by randomly polymerizing two types of monomers with different compatibility with ILs to obtain an ionogel with two-phase structure (continuous phase and microphase). The homogenous continuous phase endows the ionogel with high stretchability (over 1000% strain) via the reversible breakage of ion-dipole and dipole-dipole interactions, while the moderate microphase can strengthen the ionogel at large deformation. These two phases cooperate to realize a high toughness (5.26 MJ/m³) with strain-stiffening feature (“S” shaped stress-strain curve). Moreover, this ionogel also shows brilliant ant-swelling capability in multiple solvents, self-healing capability and high sensitivity to strain and temperature, inspiring us to explore the application as epidermal multi-sensor for human motions detection, air velocity recognition and physiological signal monitoring in aquatic environments.