X-ray surface scattering investigation of Langmuir films: Phase transitions and elastic properties

¹ LURE, CNRS/CEA/MENJR, Centre Universitaire Paris-sud, Bât. 209D B.P. 34, F-91898 Orsay cedex, France
² Lions, Service de Chimie Moléculaire, CEA Saclay F-91191 Gif-sur-Yvette Cedex, France
³ European Synchrotron Radiation Facility - B.P. 220, F-38043 Grenoble Cedex, France

Received: 9 December 2003
Accepted: 30 March 2004

Abstract

We have investigated Langmuir films at the water surface using grazing-incidence diffuse X-ray scattering. We show that beyond structural parameters like the film thickness and density, diffuse scattering also gives access to phase transitions and elastic properties (surface tension and bending rigidity). We find that the surface tension measured with X-rays is consistent with the Wilhelmy plate measurements, at least for tilted phases. The bending rigidity is found to be on the order of 20– whatever the phase. The underlying molecular mechanisms are discussed using different models.