A review on alternative lubricants: Ionic liquids as additives and deep eutectic solvents

The growing concern with environmental issues and the rapid development of new engines accentuated the need for more efficient and green lubricants. Ionic liquids (ILs) have emerged as promising alternatives to the conventional lubricants due to their interesting properties. However, the manufacturing costs of ILs are usually high, making their application as neat lubricants impracticable. A viable solution to overcome this drawback is the application of ILs as additives to commonly used base oils. Another very attractive alternative is related to the deep eutectic solvents (DES), which have similar properties to ILs but are much cheaper and simple to prepare. This paper aims at reviewing the most relevant research done in the field of lubrication using IL additives and DES in the last 10 years (from 2011 to 2020).