Separation of Formulation Syneresis

Another problem encountered with many dispersions is that of syneresis that is, the appearance of a clear liquid film at the bottom (if creaming is the case) 

Syneresis may he predicted from measurement of the yield value (using steady-state measurements of shear stress as a function of shear rate) as a function of time, or hy using oscillatory techniques whereby the storage and loss modulus are measured as a function of strain amphtude and frequency of oscillation. 

The oscillatory measurements are perhaps more useful, since to prevent separation the bulk modulus of the system should balance the gravity forces that is given by hpAg, where h is the height of the disperse phase, Ap is the density difference, and g is acceleration due to gravity. 

The bulk modulus is related to the storage modulus G. A more useful predictive test is to calculate the cohesive energy density of the structure E, which is given by the following equation (see Chapter 20)  

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