FEBRUARY 2014 • Vol. 20 No. 2
New York Society of Cosmetic Chemists
www.nyscc.org
Recent Developments Related to the Formulation of Water-in-Oil-in-Water (W/O/W) Emulsions with Improved Emulsion Stability …Paul Thau
F
or over fifty years, numerous publications have been written and patents issued related to multiple emulsions, particularly W/O/W emulsions. This interest stems from the significant applications of these complex emulsion systems to entrap watersoluble materials, particularly as topical delivery systems for controlled and sustained release of active ingredients. These emulsions are of practical use to formulators working in the areas of pharmaceuticals, cosmetics, food chemistry, and agriculture. Despite numerous attempts, cosmetic chemists were unsuccessful in formulating multiple emulsions with acceptable stability at room temperature and 40 ºC until the last twenty years. A major factor for this achievement has been the synthesis and commercial availability of a group of lipophilic polymeric emulsifiers, most of which have molecular weights in excess of 5000. The objective of this review article is to document the progression of advances for the use of these new emulsifiers, in conjunction with our understanding for the use of specific stabilizing additives, associated with improved understanding of colloid chemistry and knowledge about processing techniques to produce a W/O/W emulsion with acceptable stability at all standard temperature conditions.
Background information Multiple W/O/W emulsions are composed of aqueous droplets, which are dispersed inside oil drops. These oil droplets are themselves dispersed in an external aqueous phase. There are two interfaces in these complex systems. A hydrophobic emulsifier with a low HLB value stabilizes the first one and a hydrophilic emulsifier with a high HLB is present at the second interface.1 Potential applications for multiple emulsions include uses for cosmetic, pharmaceutical, and food products. Most of these uses
are aimed for slow and sustained release of active ingredients from an internal reservoir into the continuous aqueous phase. They can also improve dissolutions or solubilization of insoluble materials. Due to these properties, multiple emulsions find applications related to protecting sensitive and active molecules such as vitamins C and E from the external phase. Numerous patents related to the use of multiple emulsions for special applications, including protecting
2014 NYSCC RHEOLOGY SYMPOSIUM March 19-20 • Princeton University
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