Page 192 - Handbook of Surface Improvement and Modification

11.1 Methods and mechanisms of improvement of the coefficient of friction 187

Figure 11.30. (a) SEM (the inserted picture at top right corner: image at lower magnification) (b) TEM images of
hollow MoS microspheres. [Adapted, by permission, from Liu, L; Zhou, W, Tribology Intl., 114, 315-21, 2017.]
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The silver nanoparticles significantly increased the micro-hardness, reduced the friction
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coefficient, and enhanced the wear resistance of the lubricating coating. The coating
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filled with 5% Ag nanoparticles exhibited the lowest friction coefficient.
The smaller the size of PTFE particles and the more important is their presence in
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lubricating oil, the smaller the coefficient of friction.
Acrylic latex containing variable amounts of sodium dodecyl sulfate was dried to
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form film. Friction coefficient dramatically decreased with increased surfactant concen-
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tration, especially at high strain rates. Surface shear stress was strongly decreased
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because of lubrication by surfactant which was migrating to the film surface. The organi-
zation of surfactant on surface in a form of layers had more impact on lubrication than its
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concentration.
The polymer brushes grafted on solid substrates reduce friction between surfaces as
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known from plastic bag production. The addition of free chains (e.g., erucamide) helps
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in stabilization of the film formed by the brushes and the solvent.
Molybdenum disulfide hollow microspheres (Figure 11.30), prepared via a hydro-
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thermal method, were added as lubricating additive to liquid paraffin. The results indi-

Figure 11.31. Schematic diagrams of lubrication-wear mechanisms of MoS 2 hollow microspheres. [Adapted, by
permission, from Liu, L; Zhou, W, Tribology Intl., 114, 315-21, 2017.]