Low-Temperature Ionic Conductivity Enhanced by Disrupted Ice Formation in Polyampholyte Hydrogels

The phase behavior of water in hydrogels has a broad impact on many health and energy applications. Our previous study showed that polyampholyte hydrogel has the potential to be used as an aqueous gel electrolyte in electrochemical storage devices at −30 °C due to enhanced low-temperature conductivity. In this study, we detail the impact polymer structure has on this enhanced conductivity, explaining this finding with a model charge-balanced polyampholyte, poly(4-vinylbenzenesulfonate-co-[3-(methacryloylamino)propyl]trimethylammonium chloride), a hydrogel whose polymer and water structures are probed by variable-temperature SAXS, WAXS, and solid-state NMR spectroscopy. SAXS results at room temperature indicate a networked globule structure in the charge-balanced polyampholyte hydrogels. The globular radius of gyration is ∼2.5 nm, whereas the globular size and its clustering structure are dependent on synthesis parameters. Variable-temperature SAXS data reveal a temperature-dependent structure evolution of...