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/m2 (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 1 mg/ml BLES solutions reached a surface tension of about 25 mJ/m2 in approximately 10 s, while 0.1 mg/ml BLES required more than 100 s to reach a similar value.