Advanced water-based biolubricants from fatty acid-derived protic ionic liquids

• Protic ionic liquids diethanolammonium octanoate and 10-undecenoate were synthesized. • Novel water-based biolubricants were prepared with concentrations of DC8 and DC11. • The critical micellar concentration (CMC) was found through conductivity measurements. • CMC biolubricants provided friction & wear that was up to 87.9 % and 97.5 % lower. • Tribofilm formation ability of CMC biolubricants yielded good tribological performance. Novel water-based biolubricants that used protic ionic liquids containing the octanoic and 10-undecenoic fatty-acids as additives were synthesized and investigated. Neat protic ionic liquids and the biolubricants at different concentrations were evaluated using a stainless steel-sapphire tribopair in a pin-on-disc configuration. The critical micelle concentrations of each protic ionic liquid were established through the specific conductivity of the solutions as a function of molality. The tribological evaluation revealed that the biolubricants formulated at their critical micelle concentration exhibited superior performance, as evidenced by significant reductions in both friction coefficient and wear rate. Specifically, friction coefficients decreased by 86.8 % and 87.9 %, respectively, compared to water. Furthermore, the wear rates were reduced by up to one order of magnitude, with the most pronounced improvements being observed in biolubricants at critical micelle concentration, highlighting their potential for high-efficiency and environmentally friendly lubricant. The presence of a fatty-acid tribofilm on the wear tracks was confirmed using X-ray spectroscopy techniques. These results underline the potential use of protic ionic liquids containing fatty acids as effective additives in the development of water-based biolubricants.