Influence of the Structure of Salicylic Acid Analogue Molecules on the Formation of Tribofilms in Di(2-ethylhexyl) sebacate

The formation of carbon deposits on friction surfaces, called “friction polymers”, increases the antifriction properties of the lubricant and reduces wear on metal bodies. However, it is still not known what features of the chemical structure of additive molecules contribute to the formation of tribofilms. It was found that the addition of salicylic acid and some of its analogues to di(2-ethylhexyl) sebacate (DEHS) makes it possible to increase the maximum load capacity and antifriction properties of the oil. The main feature of the structure of the additive molecules, which determines their effectiveness in the formation of tribofilms, is their ability to chemically interact with the metal. A study of the boundary films by ATR IR spectroscopy and XPS showed that they are formed from molecules of the base of the lubricant on the surface of an unoxidized metal. No absorption bands of atomic groups present only in the molecules of additives were found in tribofilms. The role of complexing additives is to dissolve the oxide layer on the metal surface. It was found that the process of tribofilm formation is influenced by the following structural features of the additive molecules: the presence of a group of atoms capable of forming complex compounds with iron; solubility of additives and products of their interaction with metal in base oil; the presence of a mobile hydrogen atom with acidic properties.