Adsorption des tensio-actifs à l'interface solide-liquide : thermodynamique et influence de l'hétérogénéité des adsorbants

Abstract

A model for the adsorption of amphiphiles on solids is presented. It takes into account all of the potential energies in the adsorbed layer, the variation of entropic terms during adsorption and the superficial heterogeneity of minerals. This model explains the trends of experimental isotherms, the superposition in (θ, Δμ) plane (when bidimensionnal condensation is possible) of isotherms when the number of methylen groups of the aliphatic chain changes. The distribution of active centers has been determined and the variation of desorption free energy for one group CH2, has been calculated (1, 15 kT). It is possible to show the influence of strong grinding and the influence of amphiphiles with hydrophilic neutral head like alcohol, in adsorbed layer. Some of these results have been obtained by comparing the structure of the adsorbed layer with that of the reticular plane of the lamellar phase of the same adsorbate choosen as a reference phase.