The Dissolving-Rates of Spread Monolayer of Palmitic Acid into Aqueous Sodium Tetradecyl Sulfate Solution at Constant Surface Area

Abstract

Rates and process of dissolution of tritium labelled palmitic acid monolayer into a solution of sodium tetradecyl sulfate (STS) were studied by means of a radiotracer method. The plots of the logarithm of the surface concentration of the monolayer against the square root of the time elapsed showed a linear relationship. The rate constant of dissolution at the concentration below the critical micellar concentration (cmc) was nearly zero. These constants began to increase suddenly at the cmc and continued to rise linearly above at 4.0×10-3mol/dm3. The mechanism of dissolution was explained on the basis of the solubilization of palmitic acid into STS micelles. The diffusion constants of the micelles were calculated from the rates of dissolution and the equilibrium distributions of palmitic acid between the monolayer and the micelles.