Critical thickness of thin liquid films: comparison of theory and experiment

Values for the critical thickness of rupture (or 'black spot formation') of aqueous and non-aqueous (aniline and nitrobenzene) foam films were computed by the Vrij (1966) and Radoev-Scheludko-Manev (1983) theories. The 'critical thickness versus film radius' dependences were derived, using different formulae for the rate of film thinning. The theoretical values were compared to the available - from the literature, as well as the investigations conducted here - experimental data for the critical thickness determined in the thinnest domains of the investigated microscopic horizontal foam films. It has been established that in all cases the agreement between theory and experiment is largely enhanced when the formula of Manev et al. (1997) is employed to describe the rate of film thinning, instead of the classical Stefan-Reynolds equation.