Hydrodynamics of thin liquid films effect of the surfactant on the rate of thinning

Summary A theory of the effect of the surfactant on the rate of thinning of foam films is presented. The formulae obtained for the separately treated cases of low and high concentrations cover the whole concentration range. The effect of both bulk and surface diffusion is taken into consideration and it is demonstrated that the relative importance of the latter increases with the decrease of the film thickness. The role of the surface diffusion for the stability of foam films is discussed. It is shown that films stabilized with soluble surfactants never strictly obey Reynolds'eq. 19] so that the actual velocity of thinning can be substantially higher than that calculated by the quoted equation.