Surface viscoelasticity of a foam-forming solution

Surface light scattering has been used to study the propagation of thermally excited capillary waves on the surface of a complex solution of anionic surfactants. The data suggest that some process or processes act to reduce the damping of the dilatational waves coupled to the capillary waves. Various aspects of the results are inconsistent with the generally accepted model of free diffusional exchange of amphiphile molecules between the bulk solution and surface, a barrier to adsorption apparently playing a role in these effects. Furthermore, the transverse shear viscoelastic modulus of the absorbed surface film exhibits relaxation as a Maxwell fluid, in a similar manner to various insoluble monolayers.