Ultra-strength and anti-freezing zwitterionic hydrogels with high ion conductivity: Effect of the hydrophobic monomer in hydrogels mechanical properties

Abstract

Zwitterionic hydrogels have emerged as a promising option due to their remarkable ionic conductivity. However, these hydrogels often suffer from poor mechanical properties due to their super hydrophilicity. Herein, we propose the use of a rigid aryl imidazolium monomer (AIm) for crosslinking with poly(vinyl alcohol) (PVA) to create a unique zwitterion hydrogel. Chlorosulfonic acid acts as an agent to introduce anionic groups, facilitating the transfer of Zn²⁺ ions in zwitterionic hydrogel. We achieve extraordinary mechanical properties by incorporating an optimal amount of AIm into the PZW2 hydrogel (tensile stress 0.9 MPa and stretch 1400 %). Above all, the PZW2 hydrogel exhibits remarkable resistance to freezing, remaining unfrozen even at up to −80 °C. This anti-freezing property is attributed to the cation-dipole interactions and the presence of ZnCl₂, effectively preventing water from freezing within the hydrogel structure. Furthermore, the PZW2 hydrogel demonstrates a high ionic conductivity of 4.34 S m⁻¹ at room temperature. This can be attributed to the presence of anionic and cationic charges within the PZW2 hydrogel, which facilitates the transfer of ions through a hopping mechanism. The PZW2 hydrogel demonstrates better performance compared to most antifreeze conductive hydrogels. At −20 °C, it achieves an impressive ionic conductivity of 2.73 S m⁻¹ and retains outstanding mechanical characteristics with a stretchability of 1000 %. Ultimately, the PZW2 hydrogel demonstrates a sensitive response performance with a gauge factor of 1.59, making it highly suitable for potential sensor applications.