Abstract
Reducing friction and wear in moving mechanical systems is essential for their intended functionality. This is currently accomplished using a large variety of anti-friction and anti-wear additives, that usually contain sulfur and phosphorous both of which cause harmful emission. Here, we introduce a series of diesters, typically dioctyl malate (DOM), as green and effective anti-friction and anti-wear additives which reduce wear by factors of 5–7 and friction by over 50% compared to conventional additives when tested under extreme pressures (up to 2.78 GPa). Surface studies show that these impressive properties are primarily due to the formation of a 30 nm graphitic tribofilm that protects rubbing surfaces against wear and hence provides low shear stress at nanoscale. This graphitic tribofilm is prone to form from diesters dereived from short-chain carboxylic acid due to their lone pair effect, which stabilizes the carbon free radicals. Furthermore, the formation of this tribofilm was catalyzed by nascent iron single atoms, which were in-situ generated due to the mechanochemical effects during sliding contact. Computational simulations provided additional insights into the steps involved in the catalytic decomposition of DOM by iron and the formation of a graphitic carbon tribofilm. Due to its superior anti-friction and wear properties, DOM holds promise to replace conventional additives, and thus provide a green and more effective alternative for next-generation lubricant formulations.