ISSN:
1435-1536
Schlagwort(e):
Winsor IV Systems
;
microemulsions
;
electrical properties
;
structural transitions
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
Notizen:
Abstract A comparative study of phase diagram features and electrical properties of Winsor IV phases (so-called microemulsions) led to define two types of quaternary systems involving water, a hydrocarbon, and an ionic surfactant/alcohol combination defined byk, the surfactant/alcohol mass ratio. Systems of the first type exhibit a Winsor IV domain consisting of two disjointed areas corresponding to water-in-oil (w/o) and oil-in-water (o/w) monophasic fluid transparent isotropic media. The w/o and o/w areas are separated by a composition zone over which exist viscous turbid long-range organized structures related to the o/w ↔ w/o phase inversion mechanism. In that case, over the w/o area, the low frequency electrical conductivity and permittivity undergo non-monotonous changes as the composition varies. From conductivity maxima and minima, it is possible to define in the general case two lines Γ1 and Γ2 separating three adjacent sub-areas to which can be assigned compositions representing pre-micellar entities, inverted swollen spherical micelles and micelles clusters. For systems of the second type, the w/o and o/w sub-areas merge so as to form a unique monophasic area, which implies that the w/o ↔ o/w phase inversion occurs through a progressive diffuse mechanism. In that case the conductivity exhibits much higher values than in the preceding situation, and its variations with composition allow to define two linesC d andC m partitioning the Winsor IV domain into three adjacent areas. AboveC d , that is for low and medium water contents, the conductivity variations with water content follow equations derived from the Percolation and Effective Medium theories, which indicates that the w/o swollen spherical micelles are submitted to attractive interactions. Below Cm, i. e. in the water rich region, the conductivity decrease with water content results from the progressive dilution of the external aqueous phase of the o/w Winsor IV media. BetweenC d andC m , the Winsor IV media exhibit an anomalous conductive behaviour which suggests that they are neither w/o nor o/w systems. This region can be considered as the diffuse phase inversion zone over which the systems are in a hybrid state that could be depicted tentatively as resulting from the formation of equilibrium bicontinuous structures.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01447681
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