Modulation of the Mechanical Properties of Hydrophobically Modified Supramolecular Hydrogels by Surfactant-Driven Structural Rearrangement

Abstract

A combination of rheology and small-angle neutron scattering (SANS) experiments revealed the mechanism by which a surfactant can stiffen or soften physically cross-linked hydrogels. Here, the structure and rheological properties of a supramolecular hydrogel based on a random copolymer of N,N-dimethylacrylamide (DMA) and 2-(N-ethylperfluorooctane-sulfonamido)ethyl methacrylate (FOSM) were modified by the addition of sodium dodecyl sulfate (SDS). The effect of SDS concentration on the microstructure and properties of the hydrogel was determined by two types of experiments: (1) adding SDS by time-dependent, radial diffusion and (2) using samples where uniform loadings, i.e., no concentration gradient, of the SDS were achieved. Nanodomains consisting of FOSM aggregates were responsible for the physical cross-links in the hydrogel, but the formation of an equilibrium supramolecular network of the hydrogel was limited by conformational pinning of the water-swollen polymer segments by the relatively immobile FOS...