Regulating the π–π interactions of copolymer gelators: Effective molecular design of highly stretchable and tough ionogels for wearable ionotronics

Abstract

The emergence of stretchable ionic conductors has facilitated the development of wearable devices that can perceive changes in their surrounding environment and interpret external stimuli. An example of this is ionic skin, a form of artificial skin that is worn constantly for the real-time monitoring of temperature, pressure, and tension. However, ionic skins are vulnerable to physical damage and stress, which reduces their functionality, performance, and longevity. To obtain mechanically durable ionic skins, the toughness of their constituent ionogels must be improved by increasing their strength and/or stretchability. However, the molecular design and synthesis of these materials remain challenging due to the inherent trade-off between mechanical durability and ionic conductivity. In the present study, we introduced three styrene derivatives containing pendant groups of different sizes to copolymer gelators as ionic liquid (IL)-solvophobic components that form physically crosslinked domains and compared the mechanical and conductivity performance of the resulting ionogels. As the packing density of the styrene decreased, the IL-solvophobic domains became softer and more deformable due to the weaker physical crosslinking via π–π interactions. The optimal ionogel exhibited high stretchability (∼1200 %), excellent toughness (∼3.4 MJ·m−3), and high transparency (∼98 %). The successful use of the optimal ionogel in ionic skin sensors and deformable alternating-current electroluminescent displays demonstrated its broad range of practical applications.