ABSTRACT
This chapter reviews methods to measure foams that provide fundamental information on their stability. It identifies two types of foams: dynamic foams and static foams. Dynamic foam is one that has reached a state of dynamic equilibrium between rates of formation and decay. A static foam is one in which the rate of foam formation is zero; the foam, once formed, is allowed to collapse without regeneration by further agitation or input of gas. Dynamic foam measurement is applicable to evanescent or transient foams; static foam measurement is applicable to foams of high stability, such as are generated from solutions of detergents or proteins. An optical fiber-based method was introduced for measuring size distributions in foam. The optical fiber probe method is attractive in offering a straightforward experimental and theoretical method for determining cell size distributions. A variety of other techniques have been introduced to obtain fundamental information relating to foam stability.
