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Drops within a drop without surfactants

Emulsions within emulsions enable compartmentalised storage of active ingredients.

Multiple emulsions stabilised by cellulose fibrils partially fused under the effect of centrifugation at 2500g. The interfaces are dyed with a fluorescent dye. © INRA, Gisela Cunha
Updated on 01/13/2015
Published on 12/19/2014

Multiple emulsions are emulsions within emulsions: this means that internal drops are stabilised within larger drops (globules).

These types of emulsions are a means to achieve compartmentalised storage used, for example, with active ingredients. This compartmentalisation creates complex systems which are difficult to stabilise. As with single emulsions, multiple emulsions are subject to coalescence (the fusion of drops) that can affect globules, internal drops or an internal drop and a globule. Nevertheless, multiple emulsions have been shown to have interesting applications in the controlled release in a number of fields, such as pharmaceuticals, cosmetics and the food industry.

The Biopolymers, Interactions and Assemblies Research Unit in Nantes has already demonstrated that the crystallised particles in cellulose can stabilise oil-in-water (o/w) emulsions over the long term. Called Pickering emulsions – which are stabilised by solid submicrometre-sized particles – are extremely stable [1] and can be used to replace petroleum-derived chemical surfactants.

A hydrophobic modification of the surface of these nanocelluloses via alkyl chains enables the formation of inverse water-in-oil (w/o) emulsions. By combining the two types of stabilisers, it is now possible to create more complex emulsions such as oil-in-water-in-oil (o/w/o) emulsions, which can fuse under the effect of a constraint such as centrifugation (see figure below) [2].

  Simple direct emulsions (o/w) and inverse emulsions (w/o) stabilised using only cellulose particles to create multiple emulsions. The water is dyed with fluorescein.. © INRA, Gisela Cunha
Simple direct emulsions (o/w) and inverse emulsions (w/o) stabilised using only cellulose particles to create multiple emulsions. The water is dyed with fluorescein. © INRA, Gisela Cunha

This study, carried out in cooperation with a Swedish laboratory (Royal Institute of Technology, KTH – Stockholm), showed that stabilization by biodegradable colloidal particles like cellulose creates emulsions without the need for surfactants which are stable and whose salting out can be controlled by applied shear stress.

 

References

  1. Kalashnikova, I., H. Bizot, Cathala B. and Capron I. (2012). "Modulation of Cellulose Nanocrystals Amphiphilic Properties to Stabilize Oil/Water Interface." Biomacromolecules 13(1): 267-275.
  2. Cunha, A. G., J.-B. Mougel, Bizot H., Cathala B., Berglund L. and Capron I (2014). "Preparation of Double Pickering Emulsions Stabilized by Chemically Tailored Nanocelluloses." Langmuir 30(31): 9327-9335.
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