A Study of the Adsorption of Carbon-14 Labeled Stearic Acid on Iron

摘要

Stearic-1-C14 acid was adsorbed as a close-packed monomolecular layer on mechanically polished iron and fire-polished glass by the method of solution retraction. Measurements of the adsorbed radioactivity were made which allowed the determination of the number of adsorbed molecules per apparent unit area. Measurements of the methylene iodide contact angle on the two monolayer-covered surfaces showed that the surface packing density of stearic acid molecules was essentially the same in both cases. This conclusion, together with the assumption that the fire-polished glass surface had a roughness factor of unity, allowed the calculation of the area occupied per stearic acid molecule and of the roughness factor of the iron surface. The stearic acid molecule was found to occupy about 18.9 A2 on both iron and glass, and the roughness factor for the polished iron surface was 1.33. Desorption and exchange experiments indicated that about 60% of the monolayer on iron was rather weakly adsorbed and the remainder was probably chemically adsorbed. A rectilinear relationship was found between the measured contact angle and the extent of surface coverage. Additional studies of the temperature coefficients of the removal processes should permit determination of their activation energies and further clarification of the nature of the adsorption bond. (Author)