J. Phys. II France
Volume 3, Numéro 12, December 1993
Page(s) 1747 - 1757
DOI: 10.1051/jp2:1993228
J. Phys. II France 3 (1993) 1747-1757

Local properties of an AOT monolayer at the oil-water interface : neutron scattering experiments

H. Kellay1, T. Hendrikx2, J. Meunier1, B. P. Binks3 and L. T. Lee4

1  Laboratoire de Physique Statistique de l'ENS, 24 rue Lhomond, 75231 Paris Cedex 05, France
2  Laboratoire de Physique des Solides associé au CNRS, Université Paris XI, Bât. 510, 91405 Orsay Cedex, France
3  School of Chemistry, University of Hull, Hull HU6 7RX, North Humberside, England
4  Laboratoire Léon Brillouin, C. E. de Saclay, 91191 Gif-sur-Yvette Cedex, France

(Received 27 May 1993, accepted 7 September 1993)

The structures of the AOT-rich phases obtained in mixtures of AOT-alkane-brine at low AOT concentrations and close to the optimal salinity (i.e. the salinity at which the spontaneous curvature of the AOT monolayer is zero) have been investigated by neutron scattering together with a precise study of the phase diagrams. In the case of octane and decane, the phases are lamellar. A detailed study of the local structure of the film shows that for octane, the lamellar phase is constituted of AOT monolayers separated by thick oil and brine films. In the case of decane, it is constituted of AOT bilayers swollen by decane. The thickness of these bilayers has large fluctuations due to fluctuations of the oil film. For dodecane, a succession of three phases was observed with increasing the salinity. At a low salinity it is probably an L 3 phase. As for decane, the film is a bilayer swollen by dodecane. The thickness of the oil film is smaller than that obtained with decane but also exhibits large fluctuations. The other two phases are viscous. At the highest salinity it is probably an oil/brine bicontinuous phase. This difference in phase structure and type correlates well with values of the monolayer bending elastic modulus K and of the saddle-splay modulus $\bar{K}$.

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