Multiple emulsions

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Final Project for AP225 Fall 2011, written by Hyerim Hwang

Definition

Multiple emulsions are complex systems where both oil in water and water in oil emulsion exists simultaneously which are stabilized by surfactants respectively. Among water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) type emulsions, the first one is much more widely used in many applications. Various factors affect the stability of these emulsions. Wide range of applications in controlled or sustained drug delivery, targeted delivery, bioavailability enhancement, and enzyme immobilization are found and these are promising research areas. Multiple emulsions can be employed as an intermediate step in the microencapsulation process and those are used in oral drug delivery. We can expect that a novel carrier system for drugs, cosmetics, and pharmaceutical agents is provided with the advancement in techniques for preparation, stabilization, and rheological characterization of multiple emulsions.

Figure 1. Multiple Emulsions Formed with Microfluidic Devices.

Multiple Emulsion Systems

Multiple emulsions are emulsions of emulsions. In these emulsions, the internal and external phases are alike and an intermediate phase separates the two like phases. The intermediate phase is immiscible with the two like phases. For instance, in w/o/w multiple emulsions, a w/o emulsion is dispersed in a water-continuous phase. An emulsifier is present to stabilize the emulsions and various ionic and nonionic surfactants are available for this purpose. Oil-soluble surfactants stabilizes w/o emulsions, whereas water-soluble surfactants stabilizes o/w systems. As referred, applications for multiple emulsions are well-documented and many of these applications have been patented. Applications in cosmetics are promising. For example, in cosmetics they have a fine texture and a smooth touch upon application, and they are aimed for slow and sustained release of active matter from an internal reservoir into the continuous phase. They can serve as an internal reservoir to entrap matter from the outer diluted continuous phase into the inner confined space. 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. We can expect many more applications to emerge in the near future.

References

1. Kim, S. H., Shim, J. W., Yang, S.-M. (2008). "Microfluidic Multicolor Encoding of Microspheres with Nanoscopic Surface Complexity for Multiplex Immunoassays". Angewandte Chemie International Edition, 50, 1171-1174.

2. Kim, S. H., Jeon, S.-J., Yang, S.-M. (2008). "Optofluidic Encapsulation of Crystalline Colloidal Arrays into Spherical Membrane”. Journal of the American Chemical Society, 130, 6040-6046.

Additional Readings

1. Aserin, A. (2007). Multiple Emulsion: Technology and Applications. Wiley Series on Surface and Interfacial Chemistry. ISBN 9780470170939.

2. Leal-Calderon, F., Schmitt, V., Bibette, J., Caruso, Frank. (2010). Emulsion Science: Basic Principles. Springer Second Edition. ISBN 9781441922908

3. See also: Multiple emulsions in Emulsions and foams from Lectures for AP225.

Keyword in references:

Controllable Monodisperse Multiple Emulsions

Double Emulsions Using a Microcapillary Device

Synthesis of Monodisperse Microparticles from Non-Newtonian Polymer Solutions