Influence of electrostatic interactions on the history dependent rheology of surfactant hexagonal phases

The time-dependent response of hexagonal phases of nonionic and anionic surfactant systems to stepped strain has been investigated. It was found that the rheology of the anionic system is very sensitive to the degree of the surfactant charge screening. Two types of transitions were detected: strain-induced, i.e. transitions associated with the yielding of most of the domains of the system when their energy becomes close to the yield energy, and noise-induced, i.e. yielding of most of the domains of the system due to domain coupling. It was found that the transitions in the nonionic system are mostly associated with strain-induced yielding events, while noise-induced yielding plays an important role in the process of domain rearrangement/fusion in anionic systems. Consequently only long-range forces provide a sufficient domain coupling for noise-induced yielding to take place.