(534h) Tribological Behaviors of Ionic Liquids Nanoconfined between Hydrophilic and Hydrophobic Surfaces

The ionic liquids (ILs) are known to exhibit unique physical and chemical properties such as low vapor pressure, wide liquid temperature range, low flammability, and extraordinary chemical and thermal stability, all of which evoke extensive interests for a wide range of practical applications including active lubrication. While, in the past decade, the feasibility of using ILs as lubricant additives has been explored, their lubrication performance has not been precisely evaluated under given degrees of confinement in conjunction with molecular structuring events thereof. Surface Force Apparatus (SFA) was utilized to investigate film structures and molecular orientations of 1-methyl-3-octylimidazolium tetrafluoroborate ([C₈MIM]⁺[BF₄]^-, C8) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄MIM]⁺[BF₄]^-, C4) confined between hydrophilic (mica) and hydrophobic (PDMS) surfaces. Kinetic frictional behaviors of C8 and C4 under various normal load and sliding velocity values were quantified at 1^st and 2^nd repulsive hard walls where one and three layers of ions are confined, respectively. We anticipate our findings obtained from sophisticated interfacial science techniques would provide fundamental insights into the wear protection mechanism as well as identify crucial operation parameters for industrial applications such as nanoelectromechanical system, engine oil and turbine lubricant.