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Polymer-Brush Lubrication in Oil: Sliding Beyond the Stribeck Curve

Bielecki, Robert ; Crobu, Maura ; Spencer, Nicholas

In: Tribology Letters, 2013, vol. 49, no. 1, p. 263-272

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    Title
    • Polymer-Brush Lubrication in Oil: Sliding Beyond the Stribeck Curve
    Author
    • Bielecki, Robert. Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    • Crobu, Maura. Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    • Spencer, Nicholas. Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Tribology Letters, 2013, vol. 49, no. 1, p. 263-272. Springer US; http://www.springer-ny.com
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:319360
    Summary
    We report a highly effective macroscopic, non-aqueous lubrication strategy, employing polymer-brush-based surface modification. Poly(alkyl methacrylates) with hexyl, dodecyl and octadecyl side chains have been prepared on both silicon and iron substrates by means of surface-initiated atom-transfer radical polymerisation. Frictional properties of the three polymers have been evaluated in hexadecane, ethanol and toluene. For the case of the poly(dodecyl methacrylate), the study additionally involved nine base lubricating fluids of different chemical natures, with viscosities ranging from 4 to 2,200cSt at 20°C. By constructing a set of Stribeck curves at low values of speed×viscosity (at constant load), it was possible to identify an extended hydrodynamic lubrication regime and, for P12MA-based coatings, a low-friction, brush-lubrication regime, reinforced by time-dependant effects, which appeared to replace the mixed and boundary regimes observed for conventional lubricants. Self-mated poly(dodecyl methacrylate) brushes maintained low coefficient-of-friction values (e.g. 0.012 in hexadecane) over thousands of reciprocating cycles (>100m total distance) under low speed×viscosity conditions (0.1cm/s and 4cSt)