Supramolecular Crosslinked Hydrogels: Similarities and Differences with Chemically Crosslinked Hydrogels

The specific design of a water-soluble supramolecular cross-linker based on a terpyridine–iron(II) bis-complex is reported. Copolymerization of this cross-linker with acrylamide monomers in water allows a novel one-step synthesis of metallo-supramolecular hydrogels. The synthesized hydrogels were characterized by rheology, dynamic light scattering, and 1H double-quantum nuclear magnetic resonance experiments. They reveal great similarities with the rheological behavior of a chemically crosslinked acrylamide network but differences in the structure at low length scales. Characterization also shows that the supramolecular cross-linker behaves similarly to a permanent bond at the observed time scales (from 10–6 to almost 1000 s), thanks to its relatively high binding energy. However, unlike their chemical counterparts, supramolecular gels show polyelectrolyte swelling behavior and stimulus responsiveness when put in contact with an oxidant. A controlled tuning of the physical–chemical properties of the final gel, ranging from the initial supramolecular gel properties to those of a polymer solution, is then achievable.