Phase inversion is usually triggered by some alteration in the composition or environmental conditions of an emulsion (e.g., dispersed-phase volume fraction, emulsifier type, emulsifier concentration, solvent conditions, temperature, or mechanical agitation) (Shinoda and Friberg 1986, Dickinson 1992, Campbell et al. 1996). Only certain types of emulsion are capable of
FIGURE 7.25 Phase inversion involves the conversion of an oil-in-water emulsion to a water-in-oil emulsion or vice versa.
undergoing phase inversion, rather than being completely broken down into their component phases. These emulsions are capable of existing in a kinetically stable state after the phase inversion has taken place. It is usually necessary to agitate an emulsion during the phase inversion process; otherwise it will separate into its component phases.
The physicochemical basis of phase inversion is believed to be extremely complex, involving aspects of flocculation, coalescence, partial coalescence, and emulsion formation. At the point where phase inversion occurs, which is often referred to as the "balance point," the system may contain regions of oil-in-water emulsion, water-in-oil emulsion, multiple emulsion, and bicontinuous phases. Phase inversion in food emulsions can be conveniently divided into two different categories according to its origin.
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