Room-temperature ionic liquids (RTILs) have properties such as high thermal stability, low volatility, non-flammability, low melting point, and broad liquid range, which are applicable to superior lubricants and additives. Previous researches on RTILs as a lubricant have mainly focused on the characterization of various types of RTILs and synthesizing novel functionalized RTILs. Tetrafluoro-borate (BF4) and hexafluoro-phosphate (PF6) are the two of the most commonly used anions and RTILs based on the 1-n-alkyl-3-methylimidazolium cation with either the BF4 or PF6 anion are known to be effective lubricants. However, both BF4 and PF6 have been found to undergo complex tribo-chemical reactions and to produce corrosive acid in the presence of water, which is inevitably present in practical use . To understand lubrication mechanism and design RTILs suited for lubricants, it is important to clarify the molecular behavior of water which mixed into RTILs under lubricating condition.
