Friction Manipulation of Ionic Liquids under Boundary Lubrication by Controlling the Surface Potential

Abstract

This study attempted to manipulate the friction coefficient of ionic liquids at contact pressures on the order of several hundred MPa (maximum Hertzian pressure) via the surface potential. Because the manipulation of the friction coefficient requires the adsorption and desorption of ionic liquids, the tests were conducted at potentials where electrolysis does not occur. The friction coefficients at negative potentials were different for the same cationic ionic liquid at a constant friction potential. This indicates that the ionic liquid was not a monolayer film but a multilayer film in which anions also exist. The friction coefficient was reduced by lengthening the cationic alkyl chains. These results suggest that the conductivity has a significant effect on the frictional response of ionic liquids. Moreover, the friction coefficient remained constant after the surface potential was removed. The adsorption layer at the surface potential was considered stable, and it was difficult to overcome the energy barrier to change the adsorption structure of the ionic liquids.