Nanotribology of protic ionic liquids: Green lubricants for micro-/nano-electromechanical devices

The negligible vapor pressure and friction-reducing abilities of ionic liquids make them ideal candidates as green lubricants. Here we show that ethylammonium nitrate (EAN), a room-temperature ionic liquid, significantly alters energy dissipation between surfaces. Colloidal-probe atomic force microscopy was used to study nano-scale friction between silica, mica, alumina and teflon. Fundamental investigations in a model system imply that three friction regimes exist at low applied loads which correspond to structured EAN layers being sheared. The onset of the regimes is rate dependant and hydrodynamics play a dominant role. For industrially relevant material combinations in EAN, bringing the surfaces together quickly resulted in strong repulsive forces and eliminated attractive forces (electrostatic, capillary, van der Waals) and adhesion, responsible for stiction/wear in miniaturized devices. Moreover, at fast rates and high loads both the friction magnitude and the friction coefficient were decreased in EAN, compared to measurements in air and aqueous solutions.