Stretchable Sponge-like Hydrogels with a Unique Colloidal Network Produced by Polymerization-Induced Microphase Separation

We report a series of sponge-like hydrogels prepared by polymerizing an aqueous solution of methacrylic acid (MAAc) in the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA), which results in hydrogen bond complexation, microphase separation, and formation of a unique colloidal network. The microstructure of the gels is determined by the coupling of microphase separation and gelation, which are influenced by the feeding concentrations of MAAc and TMEDA. Colloidal gels are only obtained at a relatively low concentration of MAAc in the presence of a certain amount of TMEDA. The structural evolution during the polymerization and the formation mechanism for the colloidal network are revealed by a combination of dynamic light scattering measurements and optical microscopy. It reveals that hydrogen bond complexes are formed between poly(methacrylic acid) (PMAAc) and TMEDA, leading to the formation of colloidal particles that assemble into clusters and then the interconnected colloidal network. The physical hydrogels with a colloidal network are stable in water and possess high stretchability and good self-recovery ability due to the robustness of colloidal particles joined by adhesive PMAAc chains. These sponge-like hydrogels are applied to remove dye molecules for water purification and devised into a solar vapor generation device to produce clean water. The strategy by harnessing reaction-induced phase separation should be applicable for other systems to engineering the microstructure and properties of functional materials toward specific applications.