The effect of concentration on the bulk adsorption of bovine, lipid extract surfactant

The film adsorption of bovine lipid extract surfactant (BLES) onto the air-liquid interface was examined using axisymmetric drop shape analysis. In combination with a pendant drop constellation, BLES concentrations as high as 10 mg/ml were studied, i.e. concentrations far higher than those accessible with the captive bubble set-ups. 'Adsorption clicks', i.e. dynamic processes in which the interfacial tension of surfactant films decreases quickly in a stepwise fashion, were studied at concentrations below 1 mg/ml. Adsorption clicks with high magnitudes up to approximately 35 mJ/m(2) (within 0.2 s) were observed. The rate of adsorption was investigated as a function of surfactant concentration. At concentrations below 1 mg/ml, the rate of adsorption is highly concentration dependent. Surfactant films formed on I mg/ml BLES solutions reached a surface tension of about 25 mJ/m(2) in approximately 10 s, while 0.1 mg/ml BLES required more than 100 s to reach a similar value. (C) 2002 Elsevier Science B.V. All rights reserved.