The ionization characteristics of monolayers of weak acids and bases

The variation with pH of the surface potentials of spread monolayers of weak acids or bases may be used to calculate the intrinsic ionization constants of the film-forming molecules. The method is valid for condensed monolayers at the air/water interface for regions of a low degree of ionization only. The intrinsic constants for stearic acid and nonadecylamine monolayers are similar to the ionization constants for short-chain fatty acids and amines in aqueous solution. The relations between this and other methods of treating the ionization of a weak acid or base in a surface are discussed.