Contact angle between black film and bulk liquid

Abstract

The contact angles between black film and bulk liquid from aqueous solutions of NaLS are measured at different NaCl concentrations both by topographical and expansion methods. The contact angles increase about 10 times during the transition from first to second black films. The rate of expansion of the black films is studied; the critical thickness of the films by which black spots are formed coincide with the critical thickness of rupture. The data for the contact angles and for the kinetics of expansion of the black films are interpreted with the aid of the concept for the film tension.