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Thin-Film Lubrication in the water/octyl ß-D-glucopyranoside system: macroscopic and nanoscopic tribological behavior Wei Chen, Tobias Amann, Andreas Kailer, and Jürgen Rühe Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.9b00383 • Publication Date (Web): 06 May 2019 Downloaded from http://pubs.acs.org on May 6, 2019
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Langmuir
Thin-Film Lubrication in the water/octyl ß-D-glucopyranoside system: macroscopic and nanoscopic tribological behavior Wei Chen†, Tobias Amann, ‡ Andreas Kailer‡ and Jürgen Rühe*,† †University
Germany
of Freiburg, IMTEK – Department of Microsystems Engineering, Georges-Köhler-Allee 103, Freiburg,
‡Fraunhofer
Institute for Mechanics of Materials IWM, Wöhlerstraße 11, Freiburg, Germany
KEYWORDS: Thin Film Lubrication, Water-based lubricant, Atomic force microscopy, Tribochemistry, Surfactant
ABSTRACT: The friction properties of the water-based surfactant system C8 (octyl ß-D-glucopyranoside) are investigated both at the macro and nanoscale in ring-on-plate and AFM friction experiments, respectively. Surface characterization and measurement of the friction gap during sliding, together with the tribological behavior show a strong shear rate dependence of the friction behavior. High shear rates of approximately 106 s-1 in the macroscopic friction experiments induce a molecular alignment of the surfactants in the friction gap. This generates an anisotropic viscosity which allows to carry a high load, but exhibits low viscosity in shear direction. When the nanoscale and macroscale friction experiments are normalized to the same shear rate, almost identical frictional behavior is observed in the two regimes.
INTRODUCTION Worldwide, tribological contacts between moving surfaces account for approx. 23 % of the total energy consumption. In this respect, 20 % of the energy is used to overcome friction and 3 % to refurbish wearing parts. [1] For example, in 2009, 0.28 million cubic kilometers of fuel were used worldwide alone to prevent friction in passenger cars. [2] Water-based tribological systems seem to be an attractive solution to this as they allow overcoming friction and increase the energy efficiency without the danger of environmental pollution which is inherent to oil based systems. As water has only a very low viscosity and is easily squeezed out from the friction gap, the lubricant components must be adapted to the technological application to allow favorable interactions between the lubricant and the materials in tribological contact. [3, 4] "Superlubricity", the tribological regime in which friction almost disappears and the coefficient of friction COF reaches a value of almost COF≈0 [5], was reported in various experimental lubrication systems [5-8], but has remained elusive in technical applications so far. It should be noted that the term is used sometimes in a strict sense i.e COF ≈ 0 and sometimes in a wider sense, COF
