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 g razing incidence diffraction at three distinct temperatures near room tempe rature and in the region of high surface pressures in the vicinity of the t ilting transition and of the transition reported by Lawrie and Barnes (J. C olloid 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 incline d 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 Barne s.