The adsorption of C 14-labeled stearic acid on iron

Abstract

Stearic-1-C 14 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 these two kinds of monolayer-covered surfaces showed that the surface-packing density of stearic acid molecules was 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 the roughness factor of the iron surface. Desorption and exchange experiments indicated that about 60% of a complete monolayer was rather weakly adsorbed on iron while the remainder was probably chemically adsorbed. A rectilinear relationship was found between the measured contact angle and the extent of surface coverage. Surface-active impurities, which may occur in radioactive stearic acid solutions as a result of radiation damage, can be eliminated by treatment with activated adsorption alumina.