CALORIMETRIC STUDIES OF THE SURFACE AGGREGATION OF ADSORBED MOLECULESIN IONIC SURFACTANT ADSORPTION ONTO THE HETEROGENEOUS OXIDE SURFACES

A review is given of our extensive experimental studies of the calorim etric effects accompanying ionic surfactant adsorption on the heteroge neous surfaces of some oxides. Then equations are developed for the he ats of surfactant adsorption, corresponding to two models of surfactan t adsorption: one of them assuming that the surface aggregation of ads orbed surfactant molecules is a two-dimensional condensation and the s econd one assuming that this is a two-dimensional micellization. The o btained experimental data for heats of adsorption are compared next wi th the theoretical predictions arising from these two models. There ar e systems where the assumption of two-dimensional condensation, along with the model of perfect random topography seems to explain the behav ior of the experimental heats of adsorption. There are also systems wh ere it is difficult to discriminate one aggregation mechanism in favor of the other one. A simultaneous analysis of experimental isotherms a nd heats of adsorption seems to suggest that the hydrophobic phase for med at lower surface coverage is a noncondensed 'swelling'' phase.