Multiple emulsions primary emulsion breakdown

These natural or spontaneous mechanisms of emulsion breakdown, as well as others, must be addressed in the formulation stage in order to understand and control a particular multiple emulsion system of interest. In all cases, the final stability of the system will depend on the nature of the oil phase of interest, the characteristics of the primary and secondary emulsifier systems, and the relationship between the internal and continuous phases. 

Florence and Whitehill [14] distinguished between three types of multiple emulsions, (W/O/W) that were prepared using isopropyl myristate as the oil phase, 5% Span 80 to prepare the primary W/O emulsion and various surfactants to prepare the secondary emulsion (see Chapter 12 for details). A schematic representation of some breakdown pathways that may occur in W/O/W multiple emulsions is shown in Figure 13.26. 

Florence and Whitehill [38] distinguished between three types of multiple emulsions (W/O/W) that were prepared using isopropyl myristate as the oil phase, 5 % Span 80 to prepare the primary W/0 emulsion and various surfactants to prepare the secondary emulsion (a) Brij 30 (polyoxyethylene 4 Lauryl ether) 2%. (b) Triton X-165 (polyoxyethylene 16.5 nonyl phenyl ether (2%). (c) 3 1 Span 80 Tween 80 mixtures. A schematic picture of the three structures is shown in Fig. 1.34. The most common structure is that represented by (b) whereby the large size multiple emulsion droplets (10-100 pm) contain water droplets 1 pm. A schematic representation of some breakdown pathways that may occur in W/O/W multiple emulsions is shown in Fig. 1.35. 

Figure 9.17. Some possible pathways for the breakdown of multiple emulsions (a) coalescence of secondary emulsion drops (b) coalescence of primary emulsion drops (c) loss of primary emulsion dispersed phase to external phase.

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