EFFECT OF THE SURFACTANT CONCENTRATION ON THE KINETIC STABILITY OF THIN FOAM AND EMULSION FILMS

The thinning and the lifetime of foam and emulsion films formed in a m odel experimental cell have been investigated. The foam films were sta bilised by either sodium dodecyl sulfate or sodium dodecyl polyoxyethy lene-2 sulfate. The emulsion films contained either Tween 20 or Span 2 0. The time of hydrodynamic drainage of the films increased linearly a s the logarithm of the surfactant concentration. This linear dependenc e was valid whatever the type of him or surfactant and not only below the critical micelle concentration (c.m.c.) but also much above this c oncentration threshold. The experimental results are relevant to the h ydrodynamic basis of foam and emulsion stabilisation. They are compare d with the earlier hydrodynamic theories of film drainage. A reasonabl e, but not excellent, agreement between the experimental data and the theory could be achieved in the region below the c.m.c. of the surfact ant. The data about the complex system above the c.m.c. still remain u nexplained by an adequate theory. The investigation provides some guid elines for choosing the optimal type and concentration of surfactant i n colloid systems of practical importance.