| Abstract
| - We report a grazing incidence X-ray diffraction (GIXD) study of mixed Langmuir monolayers of stearicacid (ST) and a fluorinated amphiphilic molecule (FEP). The mixing behavior of the two components wasinvestigated at two different surface pressures, 5 and 30 mN/m. The ST molecules are found to be in theL2 mesophase at 5 mN/m and in the LS mesophase at 30 mN/m, whereas the FEP molecules appeardisordered. In the mixture, the GIXD measurements, associated with previous thermodynamical andoptical microscopy results, show that in the whole range of molar ratio, the two molecules are completelyphase-separated. Also, we observed at 5 mN/m, relaxation in the pure ST monolayer and in the mixturesrich in ST; the tilt angle of the molecules and the rectangular distortion of the 2D-lattice decrease. Bycomparing mixed films and pure ST films, this relaxation could be correlated to the size of the domains.
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