AN INVESTIGATION OF THE BEHAVIOR OF AMMONIUM PERFLUORO-OCTANOATE AT THE AIR/WATER INTERFACE IN THE ABSENCE AND PRESENCE OF SALTS

The use of the Gibbs adsorption equation for ionised surfactants in the absence and presence of added salt, in the latter case both with and without a common ion, has been reviewed. The equations obtained were applied to experimental data obtained using aqueous solutions of ammonium perfluoro-octanoate; the added salts were ammonium chloride and sodium chloride. The area per molecule occupied by a perfluoro-octanoate ion, at concentrations just below the critical micelle concentration, was estimated. The results obtained from the Gibbs analysis were then compared with those obtained under similar conditions by neutron reflection from the monolayer at an air/water interface.