Polyelectrolyte and surfactant mixed solutions. Behavior at surfaces and in thin films

Dilute mixed solutions of non-surface active anionic polymers (polyacrylami de and polystyrene sulfonate, xanthan) and various surfactants have been st udied with several methods: surface tension, ellipsometry, X-ray and neutro n reflectivity, thin film balance, surface and bulk rheology. A strong syne rgistic lowering of the surface tension is found with cationic surfactants in the concentration range where no appreciable complexation of surfactant and polymer occurs in the bulk solution (as seen from viscosity measurement s). Despite appreciable differences between surface tension behaviour, the adsorbed layer is very similar for all the polymers: their thickness is sma ll and the polymer chains are stretched along the surface. The surface tens ion behaviour of these polymers with non-ionic surfactants is also differen t. When the polymers are confined in thin films, the forces between surface s are similar, and independent of surfactant nature: oscillatory forces are measured, which reflect the existence of a polymer network with a well def ined mesh size. The connection of foam stability with surface and bulk comp lexation is far from clear. (C) 2001 Elsevier Science B.V. All rights reser ved.