Phase equilibria involving microemulsions (Remarks on the Talmon-Prager model)

J. Jouffroy , P. Levinson , P.-G. de Gennes (1)

1 LPMC - Laboratoire de Physique de la Matière Condensée

We discuss a statistical model for microemulsions, inspired by an idea of Talmon and Prager (but with certain modifications). The surfactant is assumed to be insoluble in both oil and water, and to be distributed in thin sheets, separating oil and water regions. The sheet has a persistence length ξ K. Consecutive pieces (of area ξ2K) have independent orientations. This gives a certain entropy S to the film. The free energy includes : a) the interfacial tension y; b) the entropy S ; c) a curvature term whose sign is defined by the Bancroft rule. Interaction effects between droplets (or other shapes) appear simply as a renormalization of γ. We show that in this model all equilibria of interest take place for very low γ ∼ kT/ξ2K, i.e. very close to a particular line (the « Schulman line ») corresponding to γ = 0 in the ternary phase diagram. The detailed structure of the tie lines depends sensitively on the structure of the curvature term. But for plausible forms of this term we are able to generate only 2-phase equilibria, and we do not reproduce 3-phase equilibria. We conclude that more complex effects (involving the vicinity of a cloud point or strong attraction between droplets) are requested to explain the observed 3-phase equilibria.

Mots clés: emulsions; phase equilibrium

Domaines: Articles anciens

J. Jouffroy, P. Levinson, P.-G. de Gennes. Phase equilibria involving microemulsions (Remarks on the Talmon-Prager model). Journal de Physique, 1982, 43 (8), pp.1241-1248. ⟨10.1051/jphys:019820043080124100⟩. ⟨jpa-00209502⟩