Reaction between stearic acid and calcium ions at the air-water interface using surface viscometry

Abstract

Using a sensitive surface viscometer, a study has been made of a slow reaction between stearic acid and calcium ions at the air/water interface. The reaction varies with the experimental conditions but is of kinetic order ⅔ when the acid has been spread at 30 Ų per molecule, the pH is 5.2 and the concentration of calcium in the substrate is M/2000. The energy of activation of the reaction is 8 kcal mole^–1, and the free energy of activation of viscous flow of the resulting film is about 11 kcal mole^–1.