Dry Ionic Soft Materials from Zwitterionic Polymerizable Eutectic Solvents

Dry ionic soft materials derived from polymerizable eutectic solvents (PES) have rapidly emerged as a versatile platform for flexible electronic devices, owing to their solvent-free nature, mechanical compliance, and ionic functionality. To date, most PES-based dry systems rely on quaternary ammonium halide salts, where mobile halide anions play a central role in ionic transport while also raising biocompatibility concerns in biointegrated applications. Herein, we expand the library of ionic dry polymerized eutectic soft materials (polyES) by introducing betaine (Bet), a biocompatible zwitterionic hydrogen-bond acceptor, into PES systems based on acrylic acid (Bet/AA) as the hard component and itaconic acid (Bet/IA) as the soft component. The Bet/AA and Bet/IA PES were mixed and then combined with PEGDA as the cross-linker and camphorquinone as the photoinitiator. By systematically varying the Bet/IA content, the influence of PES composition on the polymeric network structure and functional properties was evaluated. The resulting polyES display ionic conductivities on the order of 10 –5 S·cm –1 at room temperature despite the absence of free counterions. Mechanical testing reveals a broad tunability, with tensile strengths decreasing from 0.45 to 0.11 MPa, while elongation at break increases from ∼490% to over 1000% as Bet/IA content rises. The materials further exhibit cyclic adhesion to diverse substrates and self-healing efficiencies up to ∼65% after 24 h at room temperature. This work broadens the compositional and conceptual landscape of PES-derived dry polyES and highlights Bet as an underexplored building block for the design of multifunctional soft materials for potential wearable electronic applications.