CHARGE REVERSAL AT THE AIR-WATER-INTERFACE AS INFERRED FROM THE THICKNESS OF FOAM FILMS

Experiments are reported with foam films from aqueous solutions with i ncreasing concentration of a cationic surfactant. A correlation is est ablished between the foam film thickness and the possible variation of diffuse electric layer potential at the air/water interface from a ne gative value in absence of surfactant to positive values at higher sur factant concentrations. It is concluded that a charge reversal at the air/water interface is expected to occur under increasing concentratio n of cationic surfactants in aqueous solutions.