Structure optimization of self-healing hydrogels formed via hydrophobic interactions

In an attempt to mimic self-healing functions in biological systems, we investigate here the optimum design parameters of self-healing hydrogels formed by hydrophobic associations in aqueous solutions of wormlike sodium dodecyl sulfate (SDS) micelles. n-alkyl (meth)acrylates were used as the hydrophobic comonomer (2 mol %) of acrylamide in the gel preparation. Two structural parameters are crucial for obtaining self-healing gels via hydrophobic interactions. One is the length of the alkyl side chain of the hydrophobe, and the other is the surfactant concentration. In addition, hydrophobic methacrylates generate gels with a higher healing efficiency than the corresponding acrylates due to the limited flexibility of the methacrylate backbones, leading to a greater number of non-associated hydrophobic blocks. These free blocks locating near the fracture surface of the gel samples link each other to self-heal the broken hydrogel. The physical gels without SDS are very tough due to their sacrificial bonds that are broken under force and preventing the fracture of the molecular backbone.