A CRITICAL COMPARISON OF ADSORPTION MODELS FOR SOLUBLE SURFACTANTS

The adsorption isotherm of a soluble anionic surfactant was measured a nd discussed within the framework of established thermodynamical model s. The adsorbed amount derived by these models was compared with the r esults obtained by second harmonic generation, SHG. SHG can be used as a highly surface specific probe which allows the determination of ori entation and number density. Since no thermodynamic quantities are inv olved in the interpretation of SHG measurements, the data can be used to assess the validity and underlying assumptions of thermodynamic ads orption models. The SHG experiments reveal a good agreement with the F rumkin model. No indication of a subsurface layer can be found.