Antifreezing and Thermal Hardening of a Gelatin–Smectite Nanocomposite Hydrogel

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