Multifunctional PVA/gelatin DN hydrogels with strong mechanical properties enhanced by Hofmeister effect

Due to the low mechanical strength, poor tensile property, and inability to work under extreme conditions, hydrogels encounter obstacles in their practical applications. It was found that the Hofmeister effect could strengthen and toughen the single hydrogel networks. Herein, poly (vinyl alcohol) (PVA)/gelatin dual-network (DN) hydrogels with strong mechanical properties were prepared and improved by Hofmeister effect using Na2SO4 as the salting-out solution. The hydrophilic anion SO42- induced a salting-out effect, which made the interplay in PVA and gelatin stronger, and the network structure more compact and stable. Moreover, the dual-assisted effect of freeze-thaw and freezing salting-out further enhanced the mechanical properties. The as-obtained DN hydrogel had excellent overall mechanical properties with a fracture tensile strain, a tensile strength and a toughness of 1281%, 1.12 MPa and 7.19 MJ/m3, respectively. In addition, it had the ability to withstand weights more than 5000 times its own mass. The hysteresis energy, Young's modulus, and toughness recovery of the hydrogel reached 91.21%, 97.36%, and 97.47% of the original values when the interval time was 180 min. Furthermore, after treatment with ethylene glycol /H2O solution, the hydrogel was given high temperature resistance, anti-freezing and moisturizing properties, while maintaining its good mechanical properties in a wide temperature range. The weight remained at 84.7% and 71.45% of the original weight after one week at 25 °C and 12 h at 60 °C, respectively. This kind of multifunctional DN hydrogel with high mechanical properties will find wider application in the field of flexible electronic devices.