Understanding the role of tungsten species in diamond-like carbon coatings for enhanced interaction with ionic liquids

This study investigated the impact of tungsten species in tungsten-doped diamond-like carbon (WDLC) coatings on their interactions with ionic liquids (ILs). Using analytical techniques such as in-situ neutron reflectometry, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy, we examined the adsorption mechanism of tributylmethylphosphonium dimethylphosphate on WDLC and undoped hydrogenated DLC (hDLC) coatings. These techniques provide high-resolution insights into the molecular interactions, revealing that tungsten doping enhances the formation of tungsten carbide and tungsten oxides. These species facilitate the dissociation of dimethylphosphate anions, forming a robust 0.75 nm-thick tungsten phosphate layer on the WDLC surfaces. This layer, which adheres strongly even after cleaning, underscores the role of tungsten in enhancing the effectiveness and lubrication properties of WDLC coatings with ILs. Adsorption layer of ionic liquid on the WDLC coatings. • W-doped coatings enhance ionic liquid adsorption, forming a stable 0.75 nm layer. • W promotes surface defects, enhancing ionic liquid reactivity, unlike inert hDLC. • Surface defects catalyze dimethylphosphate anion dissociation. • Electrostatic and chemical interactions form a heterogeneous, patchy adsorbed layer. • Strongly adhered adsorbed layer on WDLC stays intact after rigorous cleaning.