Assessment of creaming or sedimentation

Several methods may be applied to assess the creaming or sedimentation of 

Centrifugation may be applied to accelerate the rate of creaming or sedimentation, but one should be careful in the amount of g force that may be apphed (g should not exceed the critical g force that causes deformation of the emulsion droplets and oil separation). 

For dilute emulsions (which may be obtained by careftdly diluting the concentrate in the supernatant liquid), the rate of flocculation can be determined by measuring turbidity, r, as a function of time 

a plot of r versus t gives a straight line, in the initial time of flocculation, and k can be calculated from the slope of the line. Flocculation of emulsions can also be assessed by direct droplet counting using optical microscopy (with image analysis), using the Coulter counter and Photosedimentation methods. 

As mentioned above, the best procedure to follow Ostwald ripening is to plot versus time, following Eq. (6.68). This gives a straight line, from which the rate of Ostwald ripening can be calculated. In this way one can assess the effect of the various additives that may reduce Ostwald ripening, e.g. addition of highly insoluble oil and/or an oil-soluble polymeric surfactant. 

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