This work deals with the tribological properties of recently described mixtures of nanoparticles (NPs) and ionic liquids (ILs), specifically mixtures of SiO2 (silica) nanoparticles and 1-butyl-3-methylimidazolium (trifluoromethysulfony)imide. Friction force profiles, kinetic friction coefficients, friction traces, rheological properties, and wear behavior of these mixtures were compared with that of the pristine ionic liquids at various concentrations of nanoparticles for a tribo-pair of stainless steel ball and a steel surface. It was shown that NP concentration significantly influences the tribological properties of the NP-IL mixtures: the friction coefficient for the optimum NP concentration (0.05wt%) was ~35% less than that for high NP concentrations (>3wt%) and 25% less than that for low NP concentrations (<0.01wt%). At the optimum NP concentration, while the friction force was slightly lower for NP-IL mixture at low loads, the friction force was about 28% lower for NP-IL mixture at high loads, compared to the pristine ionic liquid. In addition, the wear volume was found to decrease by 24% upon the addition of the optimum amount of nanoparticles into ionic liquid. Overall, this study concludes that promising tribological properties of ionic liquids can be further enhanced by incorporating nanoparticles into ionic liquids. 2013 Elsevier B.V.
