Novel method and parameters for testing and characterization of foam stability

The paper presents novel parameters which can be used for a swift characterization of all kinds of liquid foams. The procedure of the automated method developed consists of introducing a predefined volume of gas into the test solution contained in a cylindrical glass column at constant flow rate. The levels of the foam and of the solution are recorded simultaneously in dependence on time using a photosensor system. Two novel parameters, called time of deviation and time of transition, have been derived on the basis of simultaneous measurements of the changes in the foam volume (DeltaV(F)) and the corresponding volume of the drained solution (DeltaV(S)). These parameters enable one to distinguish three different stages of the foam decay, and on their basis the foam stability can be predicted, irrespective of whether constituting an unstable (wet) or a (meta)stable (dry) foam system. The validity of the method elaborated is demonstrated by applying various unstable and stable foam systems, including biological surfactants such as sugar and lung surfactants.