Tribochemistry of Ionic Liquid Lubricant on Magnetic Media

Abstract

The newly synthesized perfluoropolyether (PFPE) ionic liquid whose terminal group is an ammonium salt with a carboxylic acid has better frictional properties when compared to the conventional PFPEs. Stick-slip motion was not observed even for the smooth surface for the modified PFPE tape. The friction is almost independent of the PFPE structure, but depends on the amine structures. The ammonium salt being tightly anchored to the rubbing surface covers uniformly, which leads to better lubricity. The higher dispersive interaction of the hydrophobic group of the amine is endowed with a compensating friction reduction. Steric hindrance of the hydrophilic group causes a high friction. Based on these findings, a saturated long chain ammonium salt is the best selection. Moreover, the modified PFPEs are dissolved in alcohol and hexane, which makes practical use convenient without any environmental problems. These ionic lubricants invented around 1987 have been used for magnetic tapes for about a quarter century because of their good lubricity and are reviewed in this paper.

Behavior of Ionic Liquids Under Nanoconfinement Greatly Affects Actual Friction

“…This consideration is also supported by the results of the crystallization temperature measurement using differential thermal calorimetry (DSC) [28]. As indicated by the DSC measurements, [DEME][BF 4 ], for which the viscosity increases at a relatively long distance, shows a distinct crystallization temperature, whereas the TFSI salt only shows a glass transition temperature but not a crystallization temperature. The same trend is found for aromatic ILs.…”

“…Therefore, the difference in boundary lubrication under the measurement conditions between [ 4 ] is better than that of [DEME][TFSI] under such confined conditions. The inversion of the order of IL viscosities under confinement from the order of bulk viscosity values appears to be due to the differences in the layering structure of the ILs due to the differences in their anion structure.…”

“…This means that [DEME][TFSI] remained between the silica surfaces at the separation of 2.5 nm, and the coupling of the upper and lower surfaces became stronger with the increased applied load. 4 ] confined between the silica surfaces at various separation distances under an applied load N. Resonance curves for AS and SC are also shown [22]. Solid lines denote the best fit curves to a physical model [27].…”

“…The details of the analytical procedure are described in the literature [21,27]. Figure 6 plots the effective viscosity (η eff ) obtained for the ILs using the model versus the separation distance between the silica surfa- 4 ] confined between the silica surfaces [21], even though the cations used in this study are different from those used in Ref. [21].…”

“…Ionic liquids (ILs) are expected to be promising candidate materials for new lubricants [1][2][3][4][5]. In particular, their stability under severe conditions, such as ultrahigh vacuum [6,7] and high temperatures [8], has attracted increasing interest.…”