ON DIMPLE FORMATION IN FOAM FILMS

Dimple formation has been studied numerically in foam films formed in the conventional Scheludko-Exerowa cell and in a miniature cell recent ly developed by O. D. Velev et al. (J. Colloid Interface Sci. 175, 68 (1995)). Results of the simulations provide a criterion for dimple for mation in the conventional cell in the absence of disjoining pressure, Because the films in the miniature cell are very thin, disjoining pre ssure effects are important even during the liquid withdrawal step whe n the film is initially formed, If the disjoining pressure is repulsiv e, film thickness remains nearly uniform and constant as observed expe rimentally by the above authors. In other cases the simulations predic t that dimple formation will occur in the miniature cell but that it w ill not be detectable by the usual interference techniques because fil m thickness is less than one-fourth the wavelength of visible light. ( C) 1997 Academic Press.