[article]
| Titre : |
Science and technology of emulsions - From nanoemulsions to multiple emulsions |
| Type de document : |
texte imprimé |
| Auteurs : |
Tharwat F. Tadros, Auteur |
| Année de publication : |
2000 |
| Article en page(s) : |
p. 31-38 |
| Note générale : |
Bibliogr. |
| Langues : |
Anglais (eng) |
| Index. décimale : |
668.5 Parfums et cosmétiques |
| Résumé : |
This overview deals with the important aspects of emulsion science and technology. It starts with a section on the basic principles of emulsion formation and stability. The thermodynamics of emulsion formation and breakdown are briefly described to illustrate the kinetic stability of emulsions which requires the presence of an energy barrier (repulsive energy) to reduce flocculation and coalescence. The basic stabilization mechanisms that can be applied to produce such repulsion are briefly described. This is followed by a section o the main breakdown processes of emulsions, namely creaming and sedimentation, flocculation, Ostwald ripening, coalescence and phase inversion. The various methods that can be applied to control such processes are briefly described. The second section deals with the subject of nanoemulsions (with size range in the region of 100-200 nm) which attracted considerable attention in recent years for application in personal and health care. The problem of formation of small droplets is described in terms of the high Laplace pressure produced on deformation of small drops. This requires the application of high energy (e.g by application of high pressure homogenisers) and high surfactant concentration. The high stability of nanoemulsions stems from their small size which reduces an creaming or sedimentation as well as the lack of flocculation and/or coalescence. The latter is prevented as a result of the lack of fluctuation of the interface and the high steric repulsion between the droplets. However, nanoemulsions suffer from the problem of Ostwald ripening that arises from the difference in solubility between small and large droplets. The higher the oil solubility the the higher the rate of Ostwald ripening. The procedures that may be applied to reduce Ostwald ripening are briefly described. One of these methods is to incorporate a second highly insoluble oil component. Alternatively, one may incorporate a polymeric surfactant that is strongly adsorbed at the 0/W interface and which does not desorb during the process of ripening. Such polymeric surfactant should be highly insoluble in the continuous phase. The last section of this overview deals with multiple emulsions which offer some advantages for application in personal care. The main criteria for production of stable W/0/W multiple emulsions are briefly described. These are: two polymeric surfactants with low and high HLB numbers and optimum osmotic balance between the internal water droplets and the external continuous phase. Examples of such polymeric surfactants are given. This is followed by a brief description of the method of preparation of multiple emulsions (a two or one-stage process could be applied). Finally a description of the multiple emulsion drop is given and a brief account of the use of gelling agents to reduce creaming or sedimentation. The methods that can be applied to follow the stability of multiple emulsion are briefly described. |
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https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=10798 |
in IFSCC MAGAZINE > Vol. 3, N° 4 (10-11-12/2000) . - p. 31-38
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Science and technology of emulsions - From nanoemulsions to multiple emulsions in IFSCC MAGAZINE, Vol. 3, N° 4 (10-11-12/2000)
