Adhesion of lubricant on aluminium through adsorption of additive head-groups on γ-alumina: A DFT study

To improve lubricant formulation, a better understanding of the wettability properties and hence of the interactions between the surface and the lubricant additives is a key parameter. Herein, we use density functional theory calculations to characterize 32 typical head groups, classified into four categories: protic, aprotic, aromatic and phosphorus-containing molecules. By comparing their adsorption energies on gamma-alumina, used as a surface model of aluminium sheets, and their salvation energies in a model lubricant base oil, we found that the salvation energy was not a discriminant parameter while the adsorption energy was critical. Phosphates and carboxylic acids are the most strongly adsorbed, and thus more likely to yield to improved wettability properties of the lubricant through film formation.