Hitherto Unexplored Three-Membered Heterocyclic Rings Favorably Alter Tribological Properties of Fatty Acid Linear Esters

Abstract

Esters of linear long-chain unsaturated fatty acids with a variety of alcohols, both linear and branched, are extensively used in the lubricant industry. Extending the generally accepted principle that disruptions to linearity may favorably enhance tribological properties, this article presents a combined experimental and molecular dynamic simulation study to explore the influence of polar ring strain-inducing heterocyclic moieties on the lubrication behavior of such long-chain unsaturated fatty acid esters. The introduction of these disruptive structural features has been achieved by synthesizing the smallest possible three-membered heterocyclic rings (epoxy and thiirane) containing oxygen and sulfur, respectively, in the backbone of oleic acid esters, creating hitherto unexplored derivatives of such esters. The epoxy ester (EE) and thiirane ester (TE) show significant reduction in friction (40%) and wear (30%) with respect to the linear ester (LE), including in elliptical contact experiments at different interfacial contact stresses. Molecular dynamic simulation studies offer valuable insights into the orientation, adsorption, and diffusion behavior of such atomic changes on the lubricant’s physicochemical and tribological characteristics.