Foam stability column decay

The kinetics of foam collapse, i.e. the process of gas and liquid separation, is characterised by the rate of reduction of foam volume with time or by the rate of decline in its height, if the cross-sectional area is equal along the whole foam column. The stability of the foam as a whole can be characterised quantitatively at any moment by the reciprocal quantity of the rate of foam column destruction. Most often, however, the estimation of the stability of the foam column, is expressed by an integral characteristic time of decay of the whole foam column or a part of it. The relation between the internal foam collapse and the destruction of the foam column is discussed in Section 6.5. Sometimes foam stability is considered in terms of foaming ability of the solution. In general the latter characteristic involves the easiness of foam formation, foam volume and stability. Such an interpretation, however, makes this characteristic rather indefinite. For example, Abramson [12] indicates that for the estimation of the foaming ability of surfactants it is necessary to know the quantity and stability of the foam obtained from a particular surfactant as well as the conditions under which the surfactant acts as a foam stabiliser. That is why it has been repeatedly emphasised that foaming ability... 

Characteristics of Stability Related to the Foam Column Decay... 

When the foam is stable and the time for the process is short, the accumulation caused by internal collapse is not substantial. For foams of low stability and prolonged process, the accumulation resulting from internal foam collapse and foam column decay is comparable with that occurring in the adsorption layers. In addition, if accumulation is carried out with increase in the expansion ratio in the course of gravitational drainage or by the method of capillary foam drying, then the excess of the substance that accumulates in the bulk sections... 

For a 10 cm foam column, = 628 min. In order to compare the stability of foams decaying in gravitational field at a capillary pressure corresponding to the particular layer... 

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