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Application of emulsion theory to complex and real systems
Author(s) -
ECCLESTON G. M.,
FLORENCE A. T.
Publication year - 1985
Publication title -
international journal of cosmetic science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 62
eISSN - 1468-2494
pISSN - 0142-5463
DOI - 10.1111/j.1467-2494.1985.tb00414.x
Subject(s) - flocculation , emulsion , coalescence (physics) , colloid , dispersity , chemical engineering , pulmonary surfactant , pickering emulsion , materials science , metastability , chemistry , physics , polymer chemistry , organic chemistry , astrobiology , engineering
Synopsis Theories of emulsion stability are discussed in relation to dilute, concentrated and semisolid emulsions. It is shown that whilst a unified theory cannot be applied quantitatively to emulsion systems, a better understanding of the various mechanisms of stabilization and breakdown is emerging. Established concepts, eg, the HLB concept, are now given a less empirical gloss. The application of colloid stability theory, even to very dilute emulsions, is difficult. This is because of the polydispersity of the systems and because surfactant and stabilizers may be free to move on the globule surfaces, as well as dissolve in the dispersed or continuous phases. Further difficulties arise because flocculation is not necessarily a sign of emulsion instability in the practical sense, as creamed or flocculated emulsions often may be redispersed by shaking. Crucial to emulsion stability is the prevention of coalescence, and this is governed by the nature of the adsorbed emulsifier film. The flocculation and coalescence that can be understood in dilute emulsions from the DVLO theory and the metastability of thin films against rupture do not address themselves to flocculation and coalescence in concentrated, structured or semi‐solid emulsions. These may possess surfactant multilayers rather than monolayers at the oil/water interfaces and the bulk phases are frequently structured. Some emulsions invert at critical temperatures. In semi‐solid emulsions, stability is controlled by the phase behaviour of the emulsifier components, rather than by the forces governing stability in dilute colloids and thin films. Stability is usually considered to be product stability during storage. The stability of an emulsion in use, eg, during and after application to the skin, is a topic of equal importance but little documented. This related problem is also discussed. Application de la theorie des emulsions aux systemes complexes et reels On discute les théories de la stabilité des émsions diluées. concentrées et semi solides. Bien qu'une théorie unique ne puisse s'appliquer de façon quantitative á tous les systemes d'emulsions, il ne s'en dégage pas moins une meilleure compréhension des mécanismes de stabilisation et de rupture. Les concepts établis, tels que la valeur HLB apparaîssent maintenant moins empirique. L'application de la théorie de la stabilité des colloïdes est difficile même pour les émulsions diluées. Cela est dûá la diversité des systèmes et au fait que les surfactifs et les agents de stabilisation sont libres de se mouvoir sur la surface des globules comme de se dissoudre dans les phases dispersée et continue. Des difficultés supplémentaires surviennent du fait que la floculation n'est pas obligatoirement synonyme de l'instabilité de l'émulsion et que des émulsions eremeuses ou floculées peuvent souvent être redispersées par agitation. Le paramétre important pour la stabilité des émulsions est la prévention de la coalescence ce qui est liéà la nature du film d'émulsif adsorbé.