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Issue 13, 2016

Is the boundary layer of an ionic liquid equally lubricating at higher temperature?

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Abstract

Atomic force microscopy has been used to study the effect of temperature on normal forces and friction for the room temperature ionic liquid (IL) ethylammonium nitrate (EAN), confined between mica and a silica colloid probe at 25 °C, 50 °C, and 80 °C. Force curves revealed a strong fluid dynamic influence at room temperature, which was greatly reduced at elevated temperatures due to the reduced liquid viscosity. A fluid dynamic analysis reveals that bulk viscosity is manifested at large separation but that EAN displays a nonzero slip, indicating a region of different viscosity near the surface. At high temperatures, the reduction in fluid dynamic force reveals step-like force curves, similar to those found at room temperature using much lower scan rates. The ionic liquid boundary layer remains adsorbed to the solid surface even at high temperature, which provides a mechanism for lubrication when fluid dynamic lubrication is strongly reduced. The friction data reveals a decrease in absolute friction force with increasing temperature, which is associated with increased thermal motion and reduced viscosity of the near surface layers but, consistent with the normal force data, boundary layer lubrication was unaffected. The implications for ILs as lubricants are discussed in terms of the behaviour of this well characterised system.

Graphical abstract: Is the boundary layer of an ionic liquid equally lubricating at higher temperature?

Supplementary files

Article information


Submitted
29 Sep 2015
Accepted
03 Mar 2016
First published
04 Mar 2016

This article is Open Access

Phys. Chem. Chem. Phys., 2016,18, 9232-9239
Article type
Paper
Author version available

Is the boundary layer of an ionic liquid equally lubricating at higher temperature?

N. Hjalmarsson, R. Atkin and M. W. Rutland, Phys. Chem. Chem. Phys., 2016, 18, 9232 DOI: 10.1039/C5CP05837F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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