Foams and Thin Films
Foams are normally characterized by determination of the foam number and the foam average lifetime.
The foam number is identical to the expansion coefficient of the foaming liquid, i.e. the volume of the foam divided by the volume of the original foaming liquid. The lifetime of a foam can be characterized by the Ross-Miles method or by the Bikerman method.
Ross miles
In the Ross-Miles method the foaming liquid is poured into a container also containing the original foaming liquid. The immediate foam height is determined as well as at certain time intervals after the formation. Electrodes can determine the conductance across the foam at certain heights hence giving a characterization of the drainage.
Bikerman
In the Bikerman method the gas is allowed to flow through the foam liquid and the foam volume is determined as a function of the gas flow rate, giving the average lifetime of the foam. This method is suitable for transient, short-lived, foams.