Europhys. Lett, 48 (1), pp. 86-92 (1999)
Two-dimensional emulsions at the air-water interface.
Macroscopic and mesoscopic
scales experimental studies
V. Duprés, S. Cantin, F. Benhabib and F. Perrot
Laboratoire de Physique des Matériaux et des Surfaces, Université de Cergy-Pontoise
5 mail Gay-Lussac - Neuville sur Oise, 95 031 Cergy-Pontoise Cedex, France
(received 19 April 1999; accepted in final form 3 August 1999)
PACS. 78.66 - Optical properties of specific thin
films, surfaces, and low-dimensional structures.
PACS. 68.35Md - Surface energy; thermodynamic properties.
PACS. 64.75 - Solubility, segregation, and mixing; phase separation.
We report on the study of mixed monolayers consisting of two amphiphilic molecules spread at the air/water interface, one with a hydrocarbon chain, the other with a partially fluorinated chain. The mixing behaviour of this system is deduced from a thermodynamic analysis correlated to a direct observation of the monolayers with fluorescence microscopy and Brewster angle microscopy. We show that this mixture presents a complete phase separation over the entire range of molar fractions and surface pressures. Two-dimensional circular domains displaying an optical anisotropy related to the tilt of the molecules are observed. The domains are identified as being exclusively occupied by the hydrocarbon amphiphile, regardless of the molecular density and the mixture composition.
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