One-step enhancement of anti-freezing and tough poly(vinyl alcohol) hydrogels via the Hofmeister effect

The mechanical properties and anti-freezing performance of hydrogels are typically low, as they tend to have high water contents and their mechanical properties are dominated by the crosslinking polymer networks. Therefore, the mechanical properties and anti-freezing performance of hydrogels can be improved by increasing the crosslinking degree and decreasing the water content. Nevertheless, increasing mechanical strength typically leads to decreasing elongation at break, and decreasing water content may limit the applications of hydrogels in ionic conduction. Owing to the Hofmeister effect, homogeneous hydrophobic entangled crosslinked network and Hydrogen bonding induced crystal crosslinked network can be developed in poly(vinyl alcohol) (PVA) hydrogel via self-assembly of polymer chains. The hydration of the introduced inorganic ions and water molecules equips PVA hydrogel with excellent mechanical flexibility and anti-freezing performance while maintaining a certain water content. In this study, PVA hydrogel with high mechanical properties (tensile strength 25.02 MPa, elongation at break 935%, and toughness 132.93 MJ m
-3
) and anti-freezing performance (freezing point -47.6°C) was obtained via a one-step immersion process enabled by the Hofmeister effect. The effects of salt solutions on the structure and performance for as-prepared PVA hydrogel were explored. The results indicated that as the salt ions enter the hydrogel, the crosslinked network in the hydrogel gradually become dense and uniform. The presence of uniform channels and salt ions is conducive to the improvement of hydrogel ionic conductivity. The as-prepared PVA hydrogel is a promising candidate for flexible ionic conductors with good mechanical properties at a wide range of working temperatures.