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The adsorption at the air/water interface of hydrophobically modified poly(acrylic acid) sodium salt (HMPAANa) with various degrees of grafting and lengths of graft has been investigated using both tensiometry and X-ray reflectivity techniques. Tensiometry has provided the Gibbs adsorption isotherms and has revealed that HMPAANa associating copolymers behave like low molecular weight surfactants with surface tensions leveling off at the critical aggregate concentrations (cac) determined from viscosity measurements. However, very long times (up to 2 days) were required to achieve equilibrium. X-ray reflectivity measurements have permitted us to detect a monomer units-rich zone at the air/water interface, corresponding to the proximal zone of the adsorbed polymer layer. This zone thickens with increasing either the bulk polymer concentration or the salt concentration but remains unchanged with varying the polymer backbone molecular weight. The polymer concentration within the zone is 40% in volume fraction with a bulk concentration equal to cac. By coupling both techniques, we show that the Gibbs adsorption theory is valid for HMPAANa copolymers and that the longest polymer loops and tails extending into the sublayer do not contribute to the surface activity. As a matter of fact, a good agreement between the values of the excess surface concentration Γ is obtained using both techniques.

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The permeability coefficients K for permeation of air through Newton black foam films (bilayer films) from sodium dodecyl sulfate plus sodium chloride aqueous solutions have been measured. The dependencies of the permeability coefficienta on surfactant concentration C at temperatures 23,25,27, and 30 O C have been obtained. The K values strongly depend on C at low concentrations, but they remain constant at higher C. The permeability increases with increasing temperature. The experimental data have been discussed on the basis of the nucleation theory of fluctuational formation of holes in amphiphile bilayers. The results are in favor of an essential contribution of hole-mediated permeability at low surfactant concentrations and higher temperatures.

The gas permeability of Newtonian black foam films, formed on the top of a small bubble at the solution surface, was studied experimentally. The aqueous solutions contained sodium dodecylsulphate with concentrations in the range 1.5 x 10 -4 to 3 • 10 -3 mol/dm 3 and sodium chloride (constant concentration of 0.5 mol/dm3). A dependence of the gas permeability coefficient on the surfactant concentration was obtained. The experimental results are discussed on the basis of a theory assuming the presence of clusters of molecule vacancies (holes) in the bilayer foam film, their number and size depending on the surfactant concentration. The experimental results are in agreement with this film structure and confirm the existence of flow through both the hole-free bilayer film and the holes. It was found that the holes of three molecule vacandes make the main contribution to gas permeability at low surfactant concentration. The diffusion coefficients through the hole-free film and through the three-vacancy holes are calculated.

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