Foaming behaviour and dynamic surface properties of liquids

A growing interest has occurred in the physical mechanisms that are involved in the the various aspects of foaming behaviour such as foam making (overrun and bubble size distribution) and foam keeping (drainage, coalescence and Ostwald ripening). It has recently been shown that dynamic surface properties, both close and far from equilibrium, play an important role in these physical mechanisms. Recently, well-defined physical methods have also been made available to measure these surface properties. With regard to foaming behaviour, further investigations have to be encouraged in order to develop experimental techniques which are able to distinguish between the different physical aspects of foaming behaviour. As yet, however, a dynamic surface property that fulfils all the requirements for a good foaming behaviour such as a high overrun, a small bubble size, a slow drainage, no coalescence and no Ostwald ripening still does not exist. Further knowledge of the physical background of foaming behaviour can help to find a compromise between the formulation of foaming liquids and the way of foam making to realise the required foaming behaviour.