Author/Editor     Rebolj, N; Kozjek, F; Kristl, J
Title     Fizikalno-kemične osnove nestabilnosti emulzij
Translated title     Physico-chemical principles of emulsions instability
Type     članek
Source     Farm Vestn
Vol. and No.     Letnik 48, št. 3
Publication year     1997
Volume     str. 473-91
Language     slo
Abstract     In the article the forms of physical instability (creaming and sedimentation, flocculation, coalescence, Ostwald ripening and phase inversion) in emulsions are discussed. The forces, acting between droplets, as well as the mechanism of steric stabilization with polymers and stabilisation through monomolecular surfactant film, are explained. Details of local molecular structure are not of primary importance in describing sedimentation, flotation and flocculation. lt is sufficient to know the size, density and surface potencial of the droplets, density, viscosity, dielectric constant as well as the bulk electrolyte concentration of the external phase. On the other hand, in considering processes such as coalescence, phase inversion and Ostwald ripening, in addition to knowledge of droplet geometry and concentration, it is essential to have details of local molecular structure and composition both in the droplets and at the interface. In the last part of the article the recently developed theory of coalescence, called "Oriented Wedge Theory", is described. Both the phase behavior and emulsion stability are argued to be dependant on the bending constant and spontaneous curvature of the surfactant monolayer at the oilwater interface. At positive spontaneous curvature, O/W emulsions are stable, whereas, in the balanced state of surfactant film, an emulsion break usually occurs for a wide variety of systems. The extended DLVO theory in the combination with theory of coalescence represent new, efficient tool for the prediction and interpretation of emulsion stability.
Descriptors     EMULSIONS
DRUG STABILITY
FLOCCULATION
TECHNOLOGY, PHARMACEUTICAL