Influence of surfactant type and concentration on the drainage of liquid films

Measurements of drainage are reported of films drawn from surfactant solns. in a vertical frame. The drainage was measured either by interference or by the downward velocity of polystyrene particles. The latter can be obsd. by light extinction. The drainage time of films of 1.5 mm thickness (measured with polystyrene particles) is independent of the film height within the investigated range (13-17 mm) and proportional to the bulk viscosity for solns. contg. water/glycerol and CTAB. The drainage rate is independent of concn. above the crit. micelle concn. (cmc), and films drain faster below the cmc. Liq. films drawn from CTAB solns. are mobile below the cmc. Thicker and thinner regions at the film/Plateau border transition alternate; the corresponding wavelength does not vary strongly with the bulk viscosity. From the drainage time of films drawn from solns. with a complicated rheol. behavior, the effective shear stress and shear rate in the dominant process of film thinning can be estd. [on SciFinder (R)]