Rheology of Adsorbed Surfactant Monolayers at Fluid Surfaces

When surfactants adsorb at liquid surfaces, they not only decrease the surface tension, they also confer rheological properties to the surfaces. The most common rheological parameters are the surface compression elasticity and viscosity and the surface shear viscosity. These parameters usually depend on the timescale of the deformation, owing to surface relaxations, and on its amplitude, owing to nonlinear responses. In addition, surfactants can exchange between the bulk and surface, in a way that depends on the amount of bulk surfactant locally available. This complexity explains why the topic has progressed slowly over the years. This review describes the current knowledge, focusing on recent advances, and gives examples of phenomena in which surface rheology plays an important role.