KINETICS OF ADSORPTION OF IONIC SURFACTANTS AT THE SOLUTION AIR INTERFACE AND THE NATURE OF THE ADSORPTION BARRIER

The surface tension of the sodium decyl-, dodecyl- and tetradecylsulphate solutions was investigated by the maximum bubble pressure method within the surface lifetime interval 0.001-100 s over wide ranges of solution temperature and concentration of surfactant and inorganic electrolyte additives. The comparison of the experimental results with the diffusive theory has shown that, with rare exceptions, the adsorption mechanism of these surfactants is non-diffusive. Values of the adsorption rate constant beta are calculated and relationships of beta-versus dilatational surface deformation rate are presnted. The adsorption kinetics model based upon the exchange mechanism is also suggested. Besides, in this paper there are numerical evaluations of the adsorption entropy barrier resulting from the suggested model. Such known experimental facts as non-diffusive mechanism of adsorption in the concentrated solutions of the low-molecular surfactants and diffusive mechanism of adsorption at the liquid phases interface are explained. It is also shown that the processes of the surfactant molecule reorientation which probably take place in the surface layer do not influence the dynamic surface tension of the sodium alkylsulphate solutions.