The structure of the water–propane interface investigated by x-ray reflectivity measurements

We present an x-ray reflectivity study of the water–propane interface. The vertical structure of the interface is analyzed and the adsorption of thin layers of propane on the water surface is observed. An increase of layer thickness with rising pressure is found. The electron density of the thin films is identical with the corresponding value of bulk liquid propane. From the adsorption isotherm we determine the Hamaker constant of the system, which shows a considerably higher value compared to calculations based on the Lifshitz theory. The surface tension of the molecularly thin layer is reduced in comparison to the bulk value. The measured surface roughness is in good agreement with a modified model based on capillary wave fluctuations of the water-propane–gas interfaces. Copyright © 2008 John Wiley & Sons, Ltd.