Surfactants and foam stability control

A number of fundamental works are dedicated to the investigation of foam stability [6, 17] but the interest of the investigators in this problem is persistent, which is evidenced by recent review papers, e.g. [20]. In this section data are given which can be of interest for the practical application of foams. First of all, several processes take place simultaneously in real foams, which lead to foam collapse. The main processes are redistribution of the disperse medium in differently high foam column layers and the change of the mean radius of the foam cells [12]. 

The result of these processes is a gradual decrease in the foam column height (H) in a layer-wise foam collapse or a avalanche -like decay of the foam volume when reaching a critical size of the polyhedral foam cells. 

When this condition is met, the liquid in the foam is redistributed due to its drainage from the films and disappearance of a part of the Gibbs-Plateau channels. 

The aggregative foam stability is manifested in changes of the foam dispersity. There are two main causes of aggregative foam stability disturbances a) coalescence of foam cells due to the rupture of bilateral films separating them b) disappearance of foam cells due to gas penetration from small cells into larger ones (Ostwald ripening). 

The change of foam expansion with time depends on the initial expansion of the foam obtained (Fig. 6.5, Curves 1 and 2). The foams of initially higher expansion than the equilibrium expansion are characterized by the presence of a horizontal initial area on the Ig K(t) curves, while those of lower expansion than the equilibrium expansion exhibit an initial range 

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