Lubricity and mechanism of catechol-based biomimetic lubricant in water-based drilling fluid

Abstract

In this study, the lubrication performance and underlying mechanism of catechol-based biomimetic lubricants in water-based drilling fluids were investigated. A catechol-based biomimetic lubricant, L3,4, was synthesized by acid and oleyl alcohol utilizing the strong underwater adhesion of DOPA. Besides, the significant influence of phenolic hydroxyl group positioning on the adhesion performance, and consequently, the lubrication and wear resistance properties of the lubricants were revealed. Lubrication performance and wear resistance were evaluated through extreme pressure lubrication testers, four-ball friction machines, and scanning electron microscopy. In bentonite, L3,4 exhibited the best lubrication performance, with a low coefficient of friction (COF) of 0.06 at a 1% addition, a wear scar diameter of 0.365 mm, and a temperature resistance of 210 ℃. In contrast, L3,5 showed moderate lubricity with a COF of 0.16, while L2,5 showed no lubrication capabilities. X-ray photoelectron spectroscopy was used to analyze the composition and thickness of the surface lubrication film, revealing that the phenolic hydroxyl structure enhances the adhesion ability of lubricants on metal surfaces. L3,4, containing a catechol structure, formed a dense organic film of thickness exceeding 100 nm on the metal surface through bidentate metal-ligand bonds; L3,5, with a meta-hydroxy structure, formed a lubrication film of thickness lower than 80 nm through hydrogen bond adsorption; and L2,5, with a para-hydroxy structure, formed a lubrication film of thickness lower than 20 nm. L3,4 addressed the inadequate lubrication exhibited by ester-based lubricants in water, attributed to their insufficient adhesion, which prevented the formation of an effective lubrication film on the surface of drilling pipe.