Ultra-Low Friction with a Protic Ionic Liquid Boundary Film at the Water-Lubricated Sapphire-Stainless Steel Interface

The sapphire/AISI 316L contact has been lubricated with water, with the protic ionic liquid (PIL) bis (2-hydroxyethylammonium) succinate (MSu), and with a 1 wt% solution of MSu in water. Neat water evaporates after the running-in period to give a transition to dry contact. Neat MSu reduces the running-in period, reducing the friction coefficient to 0.09, an 88 % lower than water. Water + 1 wt% MSu reduces the running-in period, and after water evaporation, a PIL boundary film is formed, with an ultralow minimum friction coefficient of 0.0001, and a mean friction value of 0.02, a 97 % lower than that of water, and a 78 % lower than that of neat MSu. Surface interactions have been studied by 3D profilometry, FTIR, SEM-EDX, and XPS analysis.