The structure of surface films. Part XVI.—Surface potential measurements on fatty acids on dilute hydrochloric acid

Abstract

Guyot, Frumkin, and Schulman and Rideal have shown that it is possible, by means of an air electrode covered with a small amount of a radioactive deposit, which ionises the air in its neighbourhood, to measure changes in the contact potential at an air-liquid interface caused by spreading a film over the surface. It is now clear that this change in contact potential is caused by the dipoles of the film molecules, the magnitude of the change in potential depending on the vertical component of the dipole moment of the molecules in the film, and on the extent to which the water molecules and the ions in the solution are re-arranged near the surface under the influence of these dipoles. In combination with surface pressure measurements, which have already given a great deal of information as to the orientation of the molecules in the surface, and their shapes, sizes, and adhesive fields of force, this method, which indicates the orientation of the dipoles of the film molecules to the surface, is a valuable addition to our methods of investigating the structure of surface films.