High-entropy thermal-stiffening hydrogels with fast switching dynamics.

Thermal-stiffening hydrogels exhibit a dramatic soft-to-stiff transition upon heating, making them ideal candidates for temperature-triggered self-protection and shape memory applications. However, their practical use is still hampered by a slow recovery process (generally >30 min) during cooling, attributed to sluggish mass diffusion and delayed phase dissolution. Herein, we present a high-entropy phase separation design to significantly accelerate the recovery dynamics of these materials. We demonstrate this concept using a thermal-stiffening poly(calcium acrylate)-based copolymer hydrogel by incorporating hydrophilic units. Mechanistically, the hydrophilic units disrupt the dense packing of thermal-stiffening clusters, creating a high-entropy topological structure with a low energy barrier for rapid mass diffusion. This approach retains the impressive thermal-stiffening response with a 760-fold increase in storage modulus, while dramatically reducing the characteristic recovery time to merely 28 s. We anticipate this high-entropy strategy to be broadly applicable in designing modulus-adaptive materials with fast switching dynamics.