Preferential Adsorption of Compounds with Long Methylene Chains on Cast Iron, Graphite, Boron Nitride, and Molybdenum Disulfide

Several layered solids, which are effective solid lubricants, have a strong affinity for methylene groups. This leads to preferential adsorption on the solids of those paraffinic molecules that can form the maximum number of contacts with the surface and with each other. Thus the strength of adsorption of mineral oils increases with their average molecular weight. The strong affinity of the surfaces of the solid lubricants and cast iron for paraffinic hydrocarbon is expected to influence their load-carrying capacity, in that it should be higher for the oleophilic sliding surfaces than for surfaces such as those of plain steel, which are devoid of this property. So far, however, this has not been confirmed experimentally. For MoS2 dispersed in mineral oils, indications have been obtained that the strong attachment of oil molecules to the surfaces of the dispersed solid reduces its EP effectiveness.