Effect of Surrounding Atmosphere on Friction Properties of Hydrophobic and Hydrophilic Ionic Liquids

Abstract

The properties of ionic liquids make them an appealing choice for use as lubricant oil. However, the effect of moisture on the friction properties of ionic liquids needs to be elucidated. Moisture affects the disappearance and growth of the lubricating layer of these liquids. To express the high friction reduction effect, the lubricating layer formed by the ionic liquids at the friction interface plays a very important role. Thus, it is necessary to evaluate the relationship between these liquid structures and moisture, for the development of design guidelines for new ionic liquid structures that can achieve very low friction. This investigation evaluated the friction properties and the friction mechanisms of hydrophobic ionic liquids (1-butyl-3-methylimidazolium dicyanamide [BMIM][DCN] and 1-butyl-3- methylimidazolium tetrafluoroborate [BMIM][BF4]), and a hydrophilic ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6]) under various atmospheres (vacuum, dry air, and air) to better understand the effect of moisture on the friction properties. The hydrophilic ionic liquid exhibited differences in the friction properties depending on the atmosphere, while the hydrophobic ionic liquid remained unaffected by the atmosphere. The adsorption layer formed by [BMIM][DCN] was anion-rich, both ion-rich, and cation-rich in vacuum, dry air, and air respectively. In air, [BMIM][BF4] developed corrosive wear and the reaction layer formed by [BMIM][PF6] increased with moisture.

Keywords

• ionic liquid
• water
• humidity
• hydrophobicity
• hydrophilicity
• tof-sims
• sem-eds