EFFECT OF MAGNESIUM-IONS ON THE PROPERTIES OF FOAM FILMS STABILIZED WITH SODIUM DODECYL-SULFATE

Unstable and equilibrium foam films and foams formed from solutions of sodium dodecyl sulfate and bivalent electrolyte, MgCl2 or MgSO4, are experimentally investigated. It was found that at low ionic strength a nd low surfactant concentration the films with magnesium ions are more stable than films with sodium ions. At higher surfactant concentratio n the films containing MgCl2 become stable while the films with MgSO4 remain unstable. The unstable films exhibit at least five types of rup ture which are documented by photographs and frequency distribution cu rves of the film lifetimes. In the case when magnesium ions are presen t the formation of lenses inside the him was observed; the lenses cont ribute to a longer lifetime of the films. With the stable films the tr ansition from common to Newton black film occurs at magnesium concentr ations between 0.01 and 0.015 M. The results for the stability of sing le microscopic films are found to correlate with the results for the f oam drainage. (C) 1997 Academic Press.