Ionic liquids–based magnetic nanofluids as lubricants

Abstract

In this paper, a kind of ionic liquid–based ferrofluid, which may be suitable as a prospective lubricant was synthesised. The nanosized magnetic particles dispersing in the ionic liquid were coated with a layer of designed surfactant containing ionic liquid unit with carboxylic acid group. Three ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate (C2MIMBF4), 1-butyl-3-methylimidazolium tetrafluoroborate (C4MIMBF4), and 1-hexyl-3-methylimidazolium tetrafluoroborate (C6MIMBF4), with the same anionic structure and cationic backbone were used as carrier liquid. The effect of cation alkyl chain length on the colloidal stability was checked qualitatively by direct observation and magnetic sedimentation. The lubrication performances of the stable ferrofluid were evaluated. Experiment result shows that stable ferrofluid can only be achieved for the ionic liquid C6MIMBF4 with the longest alkyl chain. Lubrication tests first evidence the benefits of ionic liquid–based ferrofluid as a new kind of magnetic lubricant, whose lubrication behaviour can be actively controlled by the application of magnetic field.