High lubricity induced by structural regulation from green ester lubricants: Ultra-short running-in period and long-term stability

High-performance lubricants have always been an urgent need for high-end equipment lubrication and service stability. In this work, citric acid-based ester oils with different alkyl chain lengths were synthesized, and their physicochemical properties and tribological performance were compared with commercial ester oils (5750). The synthesized ester oil behaves the characteristics of green source, further also show strong adsorption and ultra-short running-in period during friction, as well as long-term lubrication stability in harsh environments. Structurally speaking, the longer carbon chains is more conducive to the improvement of lubricity, which may be related to the molecular orientation and interaction of ester oil molecules at the sliding asperity. In term of mechanism, the efficient adsorption of ester oil molecules, molecular self-assembly behavior and the formation of carbon layer are the key to the film formation on the metal sliding asperity, of course, which also shows a certain positive correlation with the molecular chain length. This work provides guidance for the molecular design strategy of high-performance ester oils.