Lubrication of Si-Based Tribopairs with a Hydrophobic Ionic Liquid: The Multiscale Influence of Water

Abstract

This work aims to elucidate the role of water on the tribological behavior of silicon-based surfaces lubricated with a hydrophobic ionic liquid (IL), by means of a multitechnique, multiscale approach. At the nanoscale, the presence of water at the interface was found to promote adhesion between a sharp silicon tip and a silicon substrate, when submerged in the IL. In line with this finding, in the case of samples that had been exposed to humid air, lateral force microscopy at low loads revealed a significant contribution of adhesion to friction. Under dry conditions, a low-to-high friction-regime transition is observed at low loads, which is reminiscent of the behavior already observed at the nanoscale in previous studies on IL-mediated lubrication. The comparison of friction-vs-load curves from tests carried out under both humid and dry conditions suggests that a similar mechanism of energy dissipation, presumably involving solid–solid contact between sliding counterparts, is established when applied loa...