Eutectic systems containing an ionic liquid and PEG200 as lubricants for silicon surfaces: Effect of the mixture's molar ratio

The tribological behavior of eutectic systems (ESs) composed by the hydrogen bond donor polyethylene glycol (MW 200), PEG200, and the hydrogen bond acceptor 1-hexyl-4-picolinium trifluoromethanesulfonate, [C₆-4-pic][TfO], with molar ratios 1:2, 1:4, 1:8 and 1:16, was investigated. In a previous work, this ionic liquid (IL) demonstrated good lubrication capacity of the pair steel ball/silicon substrate, which was attributed to the formation of adsorbed ordered layers that support the load together with the liquid film retained among the asperities of the opposing surfaces. The ESs were characterized by DSC, FTIR and NMR. All mixtures led to lower friction coefficients than the model lubricant, PEG200. The ES with molar ratio 1:2 was the most effective in the wear reduction, mainly at the highest applied load. This behavior was attributed to the preferential interactions existent between PEG200 and the IL for this composition, which ensured a higher stability of the adsorbed layer and a better protection of the sliding surfaces.