Grazing incidence X-ray diffraction study of the tilted phases of Langmuir films: Determination of molecular conformations using simulated annealing

We have analyzed grazing incidence X-ray diffraction (GIXD) data from condensed phases of Langmuir films of long-chain fatty acids at the air–water using a new method consisting in a careful extraction of the structure factors followed by fitting of molecular parameters using simulated annealing. We show that the information contained in GIXD spectra is enough to obtain near-atomic structural information. In particular, we directly determine the orientation of the chain backbone planes and of the carboxylic headgroups, and we evaluate chain conformation defects.