Antifreezing and Thermal Hardening of a Gelatin–Smectite\nNanocomposite Hydrogel

A gelatin–smectite\nnanocomposite hydrogel was prepared by\nmixing the components in water and subsequently soaking the resulting\ngel in an aqueous solution of sodium citrate. The nanocomposite hydrogel\nexhibited notable antifreezing capabilities, maintaining flexibility\nat temperatures as low as −10 °C, which was much lower\nthan that for the gelatin hydrogel (−5 °C). Upon heating,\nthe nanocomposite hydrogel underwent phase separation, leading to\nstiffening and a 14.5-fold increase in the modulus compared with that\nat the initial state at room temperature. In addition, the phase-separated\ngel was rehydrated to regenerate its original state. The critical\nroles of smectite and sodium citrate in modulating the mechanical\nproperties of the hydrogel under the conditions (−10 and 45\n°C) were proposed as a result of the regulation of the state\nof water in the hydrogel.