Temperature-regulated flexibility of polymer chains in rapidly self-healing hydrogels

Abstract Without the introduction of new functional groups, altering the properties of a substance, such as by changing from a non-self-healing to a rapidly self-healing material, is often difficult. In this work, we report that the properties of 2-hydroxyethyl methacrylate and acrylamide (HEMA/AAm) hydrogels can be easily altered from non-self-healing to rapidly self-healing by simply tuning the reaction temperature. Notably, the hydrogels that are prepared at room temperature do not exhibit self-healing behavior, while those treated at an elevated temperature show automatic self-healing performance within ~15 s. Interestingly, in contrast with the previous self-healing HEMA-based polymeric hydrogels, which function only above their glass transition temperatures (T_g), the hydrogels prepared herein exhibit rapid self-healing properties at room temperature, which is below their T_g. In addition, the stretching capabilities of the hydrogels can be greatly enhanced by up to 30-fold. The hydrogels also exhibit good adhesive performance and can adhere strongly onto various substrates, such as wood, glass, fabric, paper, leather, porcelain, and steel. For example, a 10 kg weight could be suspended from a wooden substrate with the aid of these hydrogels. These results may provide valuable insight regarding the design of self-healing hydrogels and their large-scale production.