Plastic-Like Supramolecular Hydrogels with Polyelectrolyte/Surfactant Complexes as Physical Cross-links

Developing hydrogels with new structures and extraordinary performances is fundamental and mission-critical for the advancements of gel materials. Here, we report a class of tough supramolecular hydrogels facilely prepared by polymerizing methacrylic acid precursor solution in the presence of hexadecyltrimethylammonium chloride micelles. After swelling the as-prepared hydrogels in water, strong polyelectrolyte/surfactant complexes (PESCs) are formed between the weakly charged polymer chains and oppositely charged surfactants, serving as the physical cross-links of the gel matrix. The equilibrated hydrogels are transparent with a water content of 50–85 wt % and possess excellent mechanical properties, with a tensile breaking stress of 0.1–5 MPa, a breaking strain of 600–1200%, and Young's modulus of 1–70 MPa. Typical yielding is observed at a small tensile strain of ∼10%, followed by forced elastic deformation of the hydrogels, which are in a glassy state due to the reduced segmental mobility of the matrix highly cross-linked by PESCs. The plastic-like mechanical properties of hydrogels could be well tuned by pH, temperature, and ionic strength that influence the ionization of polymer chains and the strength of PESCs. These dynamic behaviors render the hydrogels with self-recovery and shape-memory properties. Furthermore, the nanosized hydrophobic pockets within the hydrogels afford the capacity of loading functional hydrophobic molecules with promising applications as fluorescent materials and drug delivery systems. The design principle and strategy should be extended to other systems, including biomacromolecules and lipids, toward broad applications in biomedical and engineering fields.