Application of rheology for assessment and prediction of the long-term physical stability of emulsions

This review deals with the use of rheology for assessment and prediction of the long-term physical stability of emulsions. It starts with an introduction, highlighting the importance of having accelerated test to predict emulsion stability. This is followed by a section on the stability/instability of emulsion systems, giving a brief summary of the driving force of each instability process and its prevention. The classical techniques that can be applied for assessment of creaming or sedimentation, flocculation, Ostwald ripening, coalescence and phase inversion are briefly described. This is followed by several sections on the application of rheological techniques to assess and predict each of these instabilities. This involves the use of steady state shear stress-shear rate measurements, constant stress (creep) measurements and dynamic (oscillatory) techniques. The last section gives an example of model emulsions to illustrate the correlation between the various break-down processes with the rheological characteristics of the system.