Dissipative properties and chain evolution of highly strained nanocomposite hydrogel

The dissipative property is crucial to the toughness and recovery of hydrogels. In our investigation, systematic uniaxial tension tests were conducted to evaluate the dissipative properties of poly (N-isopropylacrylamide) nanocomposite hydrogels. Two dissipative mechanisms are presented for both small and large stretches. Before yielding, most dissipation results from the orientation of clay platelets along the tensile direction; after yielding, polymer chains peel off from clay platelets to induce hysteresis. For the first time, a quadratic power law between the hysteresis work and the maximum stretch is obtained. The hysteresis work is irrelevant to the detailed loading history. When the hydrogel is unloaded to a critical displacement, polymer chains can re-adsorb to the surfaces of clay platelets. The quantity of re-ruptured physical bonds is proportional to the product of re-adsorption ratio and that of initially ruptured bonds. These results may be useful for the toughening design of hydrogels.