LAUSR

Three ecofriendly protic ionic liquids (PILs), 2-hydroxyethylammonium 2-ethylhexanoate, 2-hydroxymethylammonium 2-ethylhexanoate, and 2-hydroxydimethylammonium 2-ethylhexanoate, with different extents of hydrogen bonding and ionicities, were synthesized and examined as neat lubricants and lubricant additives to a mineral oil (MO) under steel/steel and steel/aluminum contacts. The stability of each PIL–MO blend was observed and correlated to their individual structural features; their physicochemical and tribological properties were investigated and compared to a commercial mineral oil-based lubricant. The addition of any PIL to the mineral oil improved lubricity in steel/steel contact. In aluminum/steel contact, the PILs were studied as neat lubricants and additives showing different effects. The PIL with lower extent of hydrogen bonding but higher ionicity presented poor friction and led to higher wear as neat lubricant. However, as additive, this PIL prevented the intense tribo-corrosion reactions and generated a stable lubrication film that reduced friction; and was capable to form a protective layer on aluminum surface to avoid severe wear.