Experimental Assessment of Foam Stability

Foam stability is usually tested by one of three methods [4,6,13]  

The first method is quite difficult to reproduce due to the strong influence on the results that small contaminations or vibrations can have. The latter two are also difficult to reproduce since the foam generation and collapse is not always uniform, yet these methods are very commonly used. The dynamic foam tests are most suitable for evanescent foams since their lifetimes are transient. For more stable foams the static foam tests are more commonly used. 

In either the dynamic or static foam tests, but especially the static tests, one should bear in mind the many changes in a foam that may occur over time, including gas diffusion and changing bubble size distribution. 

Other methods of determining foam stability include monitoring physical properties related to the foam. For example, several researchers discuss the use of NMR spectroscopic or MRI imaging monitoring of foam stability [109,124]. 

In the static foam test, it is also usually fairly easy to measure the volume of bulk hquid that has separated after a specified interval. The separated volume, expressed as a percentage of the original volume of liquid foamed, is termed the foam number. 

---

Experimental Assessment of Foam Stability. Usually foam stability has been tested by one of three methods (4, 6, 13) (1) the lifetime of single bubbles (2) the steady-state (dynamic) foam volume under given conditions of gas flow, shaking, or shearing or (3) the rate of collapse of a (static) column of foam generated as described. 

---