APPLICATION OF A NEW METHOD BASED ON CONDUCTIVITY MEASUREMENTS TO DETERMINE THE CREAMING STABILITY OF O W EMULSIONS/

A kinetic model, based on equations used in biological population dyna mics, is proposed to describe the creaming profile of oil-in-water emu lsions at the top of a storage cell. The creaming profile itself is de termined by conductivity measurements through the emulsion at differen t heights, and conversion of conductivities into volume fraction value s of the dispersed phase in terms of dispersion dielectric theory. The reliability of the proposed model was successfully verified. This met hodology (conductivity method and kinetic model) was applied to model emulsions, to analyze the most reliable test scheme for stability asse ssment (room temperature storage, temperature stress test, and low cen trifugational stress test), The conductivity method is sensitive to sm all changes in the volume fraction of dispersed phase observed at room temperature. The creaming profile can then be analyzed with the kinet ic model allowing extrapolations for long-term predictions and shorten ing the time needed for stability assessments. Additionally, an Arrhen ius-type equation relating the creaming rate constants with the corres ponding storage temperatures can principally be employed. With regard to centrifugation stress testing, if under centrifugation no creaming can be observed, it is normally correct to assume that the emulsion wi ll be stable at normal gravitational condition. However, the reverse a rgument does not always apply.