Effect of electrolyte on adsorption of polyallyl amine hydrochloride/sodium dodecyl sulphate at water/tetradecane interface

The adsorption from mixed aqueous solutions of polyallyl amine hydrochloride (PAH)/sodium dodecyl sulphate (SDS), both in absence and presence of the inorganic electrolyte NaCl, at the solution/tetradecane interface is studied experimentally by drop profile analysis tensiometry. The results are discussed in terms of a competitive adsorption of PAH + SDS complexes and unbound SDS molecules. A thermodynamic model, developed originally for the adsorption of protein/surfactant mixtures, is modified such that it takes into account the formation of PAH + SDS complexes and the influence of the SDS concentration on their surface activity. It is shown that at low SDS concentrations the properties of the adsorbed monolayer are determined mostly by the adsorption of complexes, while at high SDS concentrations the properties are determined mostly by the SDS adsorption and the effect of the PAH + SDS complexes is negligibly small. The proposed modified model demonstrates good agreement with the experimental data.