ADSORPTION AT THE AIR WATER INTERFACE IN DODECYLAMMONIUM CHLORIDE SODIUM DODECYL-SULFATE MIXTURES/

The composition and properties of the adsorption films of dodecylammon ium chloride/sodium dodecyl sulfate at the air/water interface depend on interactions between the film molecules and equilibria in the bulk phase (monomer-micelle and/or monomer-precipitate equilibria). The neg ative value of surface molecular interaction parameter beta(mon) calcu lated using the regular solution theory indicates strong attractive in teractions between adsorbed molecules. Electrostatic interactions betw een oppositely charged ionic head groups enhance the adsorption of sur factants and decrease the minimum molar area of surfactant molecules a t the air/water interface. The addition of an oppositely charged surfa ctant enhances packing at the air/water interface and transition from a liquid expanded to a liquid condensed state. Surface potential measu rements reveal positive values for the mixtures investigated, implying the cationic surfactant ions are closer to the surface than the anion ic ones.