DYNAMIC SURFACE TENSIONS OF SURFACTANT MIXTURES AT THE WATER-AIR INTERFACE

Studies of dynamic surface tensions gamma(t) using an automated maximum bubble pressure method in the time interval from 1 ms to 30 s are performed with mixtures of non-ionic surfactants (Triton X-45, X-100, X-114, X-165, X-305 and X-405) and sodium alkyl sulphates (decyl, dodecyl, tetradecyl and hexadecyl). In the range of longer times t the dependencies gamma(1/root t) of the single components show linear behaviour, giving evidence for a diffusion controlled adsorption in the absence of disturbing amounts of surface active impurities. Similar results are obtained on the addition of a second component with a sufficiently high surface activity. The adsorbed amount calculated from the (gamma(1/root t) dependences using a modified Hansen-Joos approximate relation agree well with those obtained from equilibrium surface tension data. The experimental gamma(1/root t) curves of some surfactant mixtures show small jumps in the range over which displacement of the lower component by the stronger surface active molecules is introduced. These surface tension jumps are used to calculate the rate constants of desorption of sodium decyl and dodecyl sulphate. The obtained value of k(ad) = 50 s(-1) is in good agreement with earlier published data for these surfactants.