Mixed monolayers of polyelectrolytes and surfactants at the air-water interface

Dilute mixed solutions of non surface active anionic polymers (polyacrylami de and polystyrene sulfonate) and various surfactants have been studied wit h several methods: surface tension, ellipsometry, surface and bulk rheology . A strong synergistic lowering of the surface tension is found with cation ic surfactants in the concentration range where no appreciable complexation of surfactant and polymer occurs in the bulk solution (as seen from viscos ity measurements). A simple adsorption model, in which it is assumed that b oth polymer and surfactant counterions are expelled away from the surface, is in good agreement with the observations on polyacrylamide sulfonate. The behaviour of the more hydrophobic polystyrene sulfonate is very different and still not understood. The behaviour of this polymer with nonionic surfa ctants is also different. The connection of foam stability with surface and bulk complexation is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.