Effect of the pH on the Collapse Pressure of Fatty Acid Monolayers Evaluation of the Surface Dissociation Constant

The collapse pressures of stearic and cholanic acid monolayers were measured as a function of pH. The surface phase was treated as a mixture containing acid and soap, and our previously outlined theory concerning the collapse of a mixed monolayer was applied to it. From this results, a surface dissociation constant, different from the bulk value, can be obtained. The experimental data are in good agreement with the outlined theory.