Control over the Self-Assembly of Supramolecular Hydrogels Using Hofmeister Effect.

Supramolecular hydrogels are usually prepared in aqueous media containing diverse ions, for instance, buffer solutions, yet the influences of ions, especially the Hofmeister effect, on their self-assembly are often overlooked. Here, we systematically investigate the impacts of different anions in the Hofmeister series on the self-assembly of supramolecular hydrogels. On the basis of a hydrazone formation-mediated supramolecular gelation system, we found that the addition of kosmotropic anions can accelerate the self-assembly of gelators as determined by rheology and critical gelation concentration tests. Confocal microscopy observations and rheological measurements demonstrate that the resultant hydrogels have denser fibrous networks and higher stiffness relative to the samples without additional kosmotropic anions. In contrast, chaotropic anions effectively impede the self-assembly process. These impacts of ions on the self-assembly of supramolecular hydrogels are in line with the specific ion effect. This work suggests that the Hofmeister effect can serve as an effective approach to control the self-assembly and the properties of supramolecular hydrogels, and the effects of ions should be considered in the studies of supramolecular hydrogels.