Oil-soluble deep eutectic solvent as high-performance green lubricant additives for PAO 40 and PEG 200

Developing green, cost-effective and controllably oil-soluble lubricants additives to enhance the tribological properties of different base oils furnishes great social and economic benefits. Although deep eutectic solvents (DESs) have shown extraordinary lubrication properties, they are scarcely reported as lubricant additives. Herein, oil-soluble DES composited of menthol and dodecanoic acid was synthesized successfully. The as-prepared DES presented splendid compatibility with polyethylene glycol (PEG 200) due to the existence of polar groups. Meanwhile, DES showed excellent oil solubility in non-polar poly-alpha-olefin (PAO 40) lube oil because of its oleophilic groups. Under 1200 rpm and 392 N, 0.5 wt% DES as an additive to PEG 200 decreased friction (31%∼40%) and wear (44%∼59%) owing to their synergistic lubrication by strong adsorption and formed protective tribo-chemical film. In PAO 40, the friction and wear reduced by (25%∼51%) and (50%∼63%) due to the collaboration of preferential adsorption of DES on the tribo-interfaces, PAO 40-induced thick oil film and DES-derived tribo-chemical film. This work pushes designable DESs into wide application prospects and guides the development of next-generation green lubrication additives.