Rupture of common black films - Experimental study

The dependence of the mean lifetime of microscopic horizontal common black foam films from sodium dodecyl sulphate (SDS) on the surfactant concentrati on C is studied at various electrolyte concentrations C-el by the thin liqu id film microinterferometric technique. These data are used for determinati on of the surfactant concentration C-tau at which the common black films ha ve a constant mean lifetime. Thus the parameter C(tau)is proposed as a new characteristic of the black foam film stability at different electrolyte co ncentrations. The C-tau(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 tau and C-tau characterising the stability of the black films are constant above 0.2 mol dm(-3) NaCl. This fact allows u s to hypothesise that the thinner common black films (thickness below 8.4 n m) rupture by the hole nucleation mechanism analogously to the Newton black films. The statistical analysis of the data for the lifetimes of the SDS b lack foam films shows that this hypothesis can be adopted for the rupture m echanism of all common black films studied. (C) 1999 Elsevier Science B.V. All rights reserved.