Thinning of Nonionic Detergent Films

The effect of added electrolytes on the thinning of single vertical film formed from nonionic detergent solution has been studied. Addition of the electrolytes did not show an appreciable effect on the thinning of the film in the region of interference fringes. Specific effects of anions upon the “blackening time” (the time necessary for turning the total film area completely into a black film) were observed similarly to those on the cloud point. The order of magnitude of these effects followed the lyotropic series, which may be explained qualitatively by the effects on the dehydration of detergent molecules and on the electrical double layer of the film. The effect of the electrolytes on aqueous ionic detergent film was also examined. It was mainly explained by their influence on the electrical double layer.