Adhesion of lubricant on aluminium through adsorption of additive head-groups on γ-alumina: A DFT study. (May 2020)

• Record Type: Journal Article
• Authors: Blanck, Sarah; Loehlé, Sophie; Steinmann, Stephan N.; Michel, Carine
• Is Part Of: Tribology international. Volume 145(2020)
• Publication Date: 2020-05
• Subjects: Lubricant -- Wettability -- DFT -- Alumina; Tribology -- Periodicals; 621.89
• DOI: 10.1016/j.triboint.2019.106140
• Languages: English
• ISSNs: 0301-679X

Abstract

Abstract: 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 γ-alumina, used as a surface model of aluminium sheets, and their solvation energies in a model lubricant base oil, we found that the solvation 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. Graphical abstract: Image 1 Highlights: Ab initio modelling unravels the wettability related competition between solvation and adsorption for lubricant additives. For lubricants in apolar base oils, the solvation is not critical while the adsorption strength discriminates the additives. A linear correlation is obtained between the dissociative adsorption energy and the pKa of the head group of the additive. Phosphates and carboxylic acids are the most adsorbed functional groups and should improve the wettability properties.