A grazing-incidence X-ray diffraction study of octadecanol monolayers at high surface pressures

The structure of water-surface monolayers of octadecanol is studied using grazing incidence diffraction at three distinct temperatures near room temperature and in the region of high surface pressures in the vicinity of the tilting transition and of the transition reported by Lawrie and Barnes (J. Colloid Interface Sci. 1994, 162, 36). The data mere obtained in independent experiments by different groups at two different synchrotrons. The tilting transition between a low-pressure phase in which the molecules are inclined to the substrate normal and a high-pressure upright phase was observed at surface conditions reported by other authors. We conclude that the grazing incidence technique is not sensitive to the transition of Lawrie and Barnes.