THE DOWELL EFFECT OF (PERFLUOROALKYL)ALKENES AT THE FLUOROCARBON WATER INTERFACE - INCREASED ADSORPTION OF SODIUM LAURATE

The addition of small quantities of mixed fluorocarbon-hydrocarbon com pounds ((perfluoroalkyl)alkanes or alkenes, FmHn(E)) to fluorocarbon-i n-water emulsions results in remarkably stable systems. The contributi on that such ''molecular dowels'' have upon the lowering of the interf acial tension at a fluorocarbon/water interface was investigated using a sodium laurate (NaL) model. It was found that, when these compounds were added to the fluorocarbon C8F17Br (PFOB), the gamma(min) at the PFOB/saline interface was not, or only very slightly, modified. On the other hand, the adsorption of sodium laurate at the same interface wa s found to depend significantly upon the presence and nature of FmHn(E ): there appears to be a direct correlation between the m/n ratio and the surface excess concentration of sodium laurate at the (PFOB/FmHn(E ))/saline interface. The stabilizing effect of the FmHn(E) compounds o n fluorocarbon emulsions is, therefore, to be attributed to a better s tructuration of the interfacial film (i.e., to the so-called dowel eff ect). The Lifshitz-Slyozov-Wagner theory, which does not take into acc ount the presence and structure of the interfacial film, fails in pred icting or interpreting the observed stabilization. (C) 1994 Academic P ress, Inc.