Three-Dimensional Printable, Highly Conductive Ionic Elastomers for High-Sensitivity Iontronics

Abstract

The development of hydrogels and ionic gels for applications in fields such as soft electronics and wearable sensors is limited by liquid evaporation or leakage. Ionic conductors without volatile liquids are better choices for flexible and transparent devices. Here, a liquid polymer electrolyte (LPE) is prepared from a mixture of lithium bis­(trifluoromethane)­sulfonimide and polyethylene glycol (PEG) above the melting point of PEG. A three-dimensional (3D) printable solvent-free ionic elastomer (IE) is introduced by photopolymerization of ethyl acrylate and hydroxyethyl acrylate in the prepared LPE. The conductivity is significantly improved by the presence of a high content of the lithium salt. Dynamic cross-linking networks improve the stretchability and resilience of the elastomer. The pattern design capability of the IE is provided by light-curing 3D printing. These features demonstrate that the IE has broad application prospects in flexible sensors, ion skins, and soft robots.

Technology Roadmap for Flexible Sensors

“…Biological sensors work by the transport of ions, instead of electrons. Inspired in this direction, a strong impetus to develop ionotronics utilizing ionically conductive and highly deformable materials such as hydrogels, ionogels, , and ionic elastomers , has emerged . Without the requirement of incorporating electronic conduction, materials design is much simpler.…”

Recent Progresses in Liquid‐Free Soft Ionic Conductive Elastomers†

“…Copyright 2022, American Chemical Society. Panels l—p are adapted with permission from Ref [177]. Copyright 2022, American Chemical Society.…”

Tough, Self-Healing, and Conductive Elastomer ─Ionic PEGgel

“…To overcome these problems, solvent-free systems were developed by mixing electrolyte salts with monomers and further polymerizing to obtain flexible polymer networks. 20,25 In such systems, ions are directly bound to the polymer network through electrostatic interactions or metal−ligand coordination rather than solely serving as mobile charge carriers. 18,20,21 However, the choice of polymer networks for solvent-free ICEs is limited by the low solubility of electrolytes in potential monomers or polymers.…”

“…However, on the other hand, too many solvated ionic electrolytes fail to be effectively bonded with polymer networks and thus give rise to instability or poor performance, for example, electrolyte leakage. To overcome these problems, solvent-free systems were developed by mixing electrolyte salts with monomers and further polymerizing to obtain flexible polymer networks. , In such systems, ions are directly bound to the polymer network through electrostatic interactions or metal–ligand coordination rather than solely serving as mobile charge carriers. ,, However, the choice of polymer networks for solvent-free ICEs is limited by the low solubility of electrolytes in potential monomers or polymers. Also, without solvents, the ionic conductivity of most solvent-free ICEs is lower than 0.02 S m –1 .…”