EFFECTS OF SURFACE FINISH AND MOLECULAR STRUCTURE ON THE LUBRICATING ABILITY OF BORATE-BASED PROTIC IONIC LIQUIDS

Friction and wear are inherent problems in mechanical systems, leading to about 23% world's total energy usage. However, energy losses could be reduced by up to 40% using high-performance lubricants. In order to meet these objectives, Ionic liquids have been studied for more than two decades. Ionic liquids are a class of synthetic salts with melting points below 100 degrees C due to their asymmetric chemical structure. This feature confers them remarkably interesting physicochemical properties. Moreover, the delocalized charge in their functional groups enables them to react with metal surfaces through the formation of protective layers that prevent them against contact. Ionic liquids are generally categorized based on the nature of their cation into aprotic ionic liquids and protic ionic liquids. Even though aprotic ionic liquids have been proved as neat lubricants and additives with great performance, their applicability is limited as a consequence of the complexity of their synthesis. On the contrary, protic ionic liquids can be easily obtained through proton transfer from a Bronsted acid to a Bronsted base. In this study, two borate-based PILs, N-methylethanolamine 1,2-dodecanediolborate and N'N-dimethylethanolamine 1,2-dodecanediolborate, were synthesized, with same anion and different ammonium cation. Their lubricating abilities were investigated as neat lubricants on steel-steel contact at room temperature, using a custom-designed ball-on-flat reciprocating tribometer. Each protic ionic liquid was tested using ground and polished steel disks and two levels of normal force and frequency. Results showed that the surface finish have an important influence on the lubricating performance of these ordered fluids. In addition, frequency was found to have an influence on the wear mechanisms on steel surfaces.