Adsorption kinetics and exchange of matter at liquid interfaces and microgravity

The oscillating bubble set-up allows accurate measurements of relaxation processes of surfactant, protein and mixed surfactant/protein adsorption layers in a frequency interval from few Hz up to several hundred Hz. Experimental dependencies of dilational elasticity as a function of oscillation frequency obtained for some surfactant solutions are in good agreement with a diffusional exchange of matter theory. The relaxation behaviour of gelatin adsorption layers show no significant dependence in the studied frequency interval as remarkable changes are expected at much lower frequencies. However, in presence of a surfactant the mixed protein/surfactant adsorption layer shows a linear dependence E(f) which would be in line with a dilational viscosity effect. The instrument has the capacity to be used also for adsorption kinetics studies by enlarging the bubble surface several times of its initial area at the beginning of the experiment and then recording the pressure change with time. Moreover, transient relaxation studies can be performed setting in after generating small-amplitude step-type or square pulse changes of the bubble area.