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5. Multiple emulsions

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Volume 2 Basic Principles of Dispersions
This chapter is in the book Volume 2 Basic Principles of Dispersions
5 Multiple emulsions5.1 IntroductionMultiple emulsions are complex systems of “emulsions of emulsions”. Both the water-in-oil-in-water (W/O/W) and oil-in-water-in-oil (O/W/O) multiple emulsions have po-tential applications in various fields. The W/O/W multiple emulsion may be consid-ered a water/water emulsion in which the internal water droplets are separated byan “oily layer” (membrane). The internal droplets could also consist of a polar solventsuch as glycol or glycerol which may contain a dissolved or dispersed active ingredient(AI). The O/W/O multiple emulsion can be considered an oil/oil emulsion separatedby an “aqueous layer” (membrane).Multiple emulsions are ideal systems for applications in several industrial sys-tems, e.g. pharmaceuticals, cosmetics, the food industry and agrochemicals. Due tothe oily liquid or aqueous membrane formed, multiple emulsions ensure completeprotection of the entrapped drug, controlled release of the drug from the internal tothe external phase and possible drug targeting due to the vesicular character of thesesystems. In the cosmetics field, multiple emulsions offer several advantages such asprotection of fragile ingredients, separation of incompatible ingredients, prolongedhydration of the skin and in some cases formation of a firm gelled structure. In addi-tion, a pleasant skin feel like that of an O/W emulsion combined with the well-knownmoisturizing properties of W/O emulsions are obtained with W/O/W multiple emul-sions. In the food industry, the existence of an encapsulated water (or oil) phase ina W/O/W (or O/W/O) multiple emulsion facilitates the protection of reactive food in-gredients or volatile flavours as well as control of their release. Since less oil phase isrequired to make a W/O/W multiple emulsion compared to an O/W emulsion withthe same disperse volume fraction, multiple emulsions can be used in developinglow calorie, reduced-fat food products, e.g. dressings, mayonnaise or spreads. In theagrochemical industry, multiple emulsions allow one to have three active ingredients(AIs) in one formulation and one can incorporate adjuvants in three compartments.Multiple emulsions can be usefully applied for controlled release by controlling therate of the breakdown process of the multiple emulsion on application. Initially, oneprepares a stable multiple emulsion (with a shelf life of two years) which on dilutionbreaks down in a controlled manner thus releasing the AI also in a controlled manner(slow or sustained release). As will be discussed later, the formulated W/O/W multipleemulsion is osmotically balanced but on dilution the system breaks down as a resultof the lack of this balance.https://doi.org/10.1515/9783110541953-006
© 2017 Walter de Gruyter GmbH, Berlin/Munich/Boston

5 Multiple emulsions5.1 IntroductionMultiple emulsions are complex systems of “emulsions of emulsions”. Both the water-in-oil-in-water (W/O/W) and oil-in-water-in-oil (O/W/O) multiple emulsions have po-tential applications in various fields. The W/O/W multiple emulsion may be consid-ered a water/water emulsion in which the internal water droplets are separated byan “oily layer” (membrane). The internal droplets could also consist of a polar solventsuch as glycol or glycerol which may contain a dissolved or dispersed active ingredient(AI). The O/W/O multiple emulsion can be considered an oil/oil emulsion separatedby an “aqueous layer” (membrane).Multiple emulsions are ideal systems for applications in several industrial sys-tems, e.g. pharmaceuticals, cosmetics, the food industry and agrochemicals. Due tothe oily liquid or aqueous membrane formed, multiple emulsions ensure completeprotection of the entrapped drug, controlled release of the drug from the internal tothe external phase and possible drug targeting due to the vesicular character of thesesystems. In the cosmetics field, multiple emulsions offer several advantages such asprotection of fragile ingredients, separation of incompatible ingredients, prolongedhydration of the skin and in some cases formation of a firm gelled structure. In addi-tion, a pleasant skin feel like that of an O/W emulsion combined with the well-knownmoisturizing properties of W/O emulsions are obtained with W/O/W multiple emul-sions. In the food industry, the existence of an encapsulated water (or oil) phase ina W/O/W (or O/W/O) multiple emulsion facilitates the protection of reactive food in-gredients or volatile flavours as well as control of their release. Since less oil phase isrequired to make a W/O/W multiple emulsion compared to an O/W emulsion withthe same disperse volume fraction, multiple emulsions can be used in developinglow calorie, reduced-fat food products, e.g. dressings, mayonnaise or spreads. In theagrochemical industry, multiple emulsions allow one to have three active ingredients(AIs) in one formulation and one can incorporate adjuvants in three compartments.Multiple emulsions can be usefully applied for controlled release by controlling therate of the breakdown process of the multiple emulsion on application. Initially, oneprepares a stable multiple emulsion (with a shelf life of two years) which on dilutionbreaks down in a controlled manner thus releasing the AI also in a controlled manner(slow or sustained release). As will be discussed later, the formulated W/O/W multipleemulsion is osmotically balanced but on dilution the system breaks down as a resultof the lack of this balance.https://doi.org/10.1515/9783110541953-006
© 2017 Walter de Gruyter GmbH, Berlin/Munich/Boston
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