Experimental methods for assessment of emulsion stability

Understanding emulsion breakdown processes at a molecular level is far from being achieved at present. It is thus necessary to develop methods for assessing each pro- 

Modern analytical ultracentrifuges allow one to follow the separation of emulsions in a quantitative manner. With typical 0/W emulsions, three layers are generally observed A clear aqueous phase an opaque phase consisting of distorted polyhedral oil droplets and a clear separated oil phase, resulting from coalescence of the poly-hedra. The degree of emulsion stability may be taken as the volume of the opaque phase remaining after time t. Alternatively, one may use the volume of oil separated at infinite time as an index for stability. 

A simple expression may be used to treat the data in a quantitative manner. 

The flocculation of emulsions can be assessed using turbidity measurements. For dilute emulsions (which may be obtained by carefully diluting the concentrate in the supernatant liquid), the rate of flocculation can be determined by measuring turbidity, T, as a function of time, 

As mentioned above, the best procedure to follow Ostwald ripening is to plot r versus time, following equation (3.53). 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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