Interferometric and x-ray diffraction study of "Built-up" molecular films of some long chain compounds

By using the Blodgett and Langmuir technique, monomolecular films of barium palmitate, barium margarate, barium stearate and barium behenate have been built-up to films of 2, 4 and 7 mono-molecular layer thicknesses, on a silver substrate. The metrical thickness has been determined by multiple-beam interferometry. The c-spacings measured by X-rays are found to be twice the molecular chain length. A correlation between the interferometric measurement of the thickness and the lattice spacing normal to the film, is established. The correlation between the unimolecular film thickness and the chain length of the corresponding fatty acid leads to the conclusion that the fatty acids spread on a water surface mono-molecularly, oriented with their hydrocarbon chains almost at right angles to the substrate