Emulsion phase matching (EPM) technique for predicting optimal emulsifers

The formation of a ‘stable’ emulsion is more of an art than a science. Emulsions are inherently unstable heterogenous systems such that a truly stable emulsion is not feasible. However, commercial emulsions are very common indicating that it is possible to achieve a ‘commercially stable’ emulsion. A commercially stable emulsion can be defined as one that remains homogenous throughout its commercial life. Emulsions provide an aesthetically pleasing and practical method of forming a homogenous mixture of oil and water. This type of product is very common with examples including milk, mayonnaise, cosmetic creams and paints. Despite the very many emulsion products available and the considerable time and effort spent on research, there is still no definitive technique available that can pinpoint an emulsifier or emulsifier combination that will form a guaranteed ‘commercially stable’ emulsion. Trial and error is still required in emulsion formulation. The techniques that are available to help reduce the number of emulsifier options that should be considered have been outlined in this thesis. One, the Hydrophile-Lipophile Balance (HLB) is well known to the emulsification industry and very popular. The benefits and the limitations of this technique are reviewed along with the modifications and extensions of the technique that have been proposed throughout its 50 year life. It is important to note that the HLB technique is over 50 years old. The commercial demands of emulsion products have developed considerably in this time and emulsion systems tend to be somewhat more complex with more ingredients required than when this technique was first formulated. A fresh approach to emulsifier selection is desirable and this work proposes a new concept called the Emulsion Phase Matching or EPM technique. The name arises from the fact that, in this technique, each phase of the emulsion is considered independently of the other, although with all auxiliary ingredients included. A quantitative measure of the ‘difference’ between the two phases to be emulsified (in this case interfacial tension) is ‘matched’ to the difference between the hydrophobic and hydrophilic moieties of the emulsifier to be used. A good match should correlate to a ‘stable’ emulsion. The data should ultimately be listed in a database to make this task simpler. However, the scope of the current work was to test the concept, in general, and the use of interfacial tension, in specific, as the measure of difference. Interfacial tension was, indeed, found to be linked to emulsion stability. Test emulsions were designed to test the proposed EPM technique and to compare the results with those emulsions that would be achieved if the HLB technique was used. Results for both ‘ideal’ and ‘commercial’ emulsions (refer Chapter 6) did show superior results for the EPM proposed emulsion, both in terms of initial droplet size of the emulsion as well as its longer term stability. Although the work completed in this thesis only touches the surface of a full validation of the proposed method, it does show encouraging signs and raises some interesting questions regarding emulsion formation, resulting stability and the mechanisms involved with each process. This is an area where further work is justified in the quest to remove the trial and error approach to emulsifier selection.