Thickness and Refractive Index of Fatty Acid, Alcohol, Amine and Amide Retracted Monolayers

摘要

Ellipsometric measurements of film thickness and refractive index were made on retracted monolayers of fatty acids, alcohols, amines and amides on chrome surfaces. Compounds studied had carbon chain lengths in the range of 4 to 26 carbon atoms. The purpose of this work is to provide information on molecular conformations of adsorbed molecules for use in development phases of projects on preservatives and weapons cleaner formulations. A linear relationship was found between film thickness and number of carbon atoms, or molecular weight, for the compounds studied. It is concluded from this result that molecules in these films are oriented vertically to the surface. This conclusion agrees with published results of electron diffraction measurements on similar films. Film thicknesses are somewhat lower, and refractive indexes higher, than expected from published data on multilayer films. These differences are explained by incomplete packing and/or roughness of the substrate surface. It was also found in this study that stearic acid desorbs from chrome in the temperature range 73 to 240C to a limiting average film thickness about one-half the initial thickness. (Author)