Rupture of common black films: Experimental study

Abstract

The dependence of the mean lifetime of microscopic horizontal common black foam films from sodium dodecyl sulphate (SDS) on the surfactant concentration C is studied at various electrolyte concentrations C el by the thin liquid film microinterferometric technique. These data are used for determination of the surfactant concentration C τ at which the common black films have a constant mean lifetime. Thus the parameter C τ is proposed as a new characteristic of the black foam film stability at different electrolyte concentrations. The C τ ( C el) dependence is obtained within the range 0.1–0.5 mol dm −3 NaCl. The results for the stability of the common black films are compared with those for the Newton black films (foam bilayers). It is shown that the two parameters τ and C τ characterising the stability of the black films are constant above 0.2 mol dm −3 NaCl. This fact allows us to hypothesise that the thinner common black films (thickness below 8.4 nm) rupture by the hole nucleation mechanism analogously to the Newton black films. The statistical analysis of the data for the lifetimes of the SDS black foam films shows that this hypothesis can be adopted for the rupture mechanism of all common black films studied.