Page 185 - Handbook of Surface Improvement and Modification

180 The Coefficient of Friction

Figure 11.21. Schematic diagrams showing the influence of sliding distance on (a) positive and (b) negative tex-
tured surfaces on friction force. [Adapted, by permission, from Grewal, HS; Pendyala, P; Shin, H; Cho, I-J; Yoon,
E-S, Wear, 384-385, 151-8, 2017.]

like carbon using plasma-enhanced chemi-
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cal vapor deposition technique. Both wet-
tability and friction were influenced by the
shape, orientation, and a surface chemistry
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of the textured structures. The increase in
aspect ratio of the textured geometry
enhanced directional wettability and fric-
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tion. The wetting was controlled by the
contact-line pinning phenomenon modu-
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lated by the texture geometry. The friction
behavior of the textured geometry varied
with the direct correlation to the contact
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area (Figure 11.21). The edge-effect
Figure 11.22. Typical phases of friction stir spot weld- showed prominent influence leading to an
ing process: pre-heating, joining, consolidation, and
tool retraction. [Adapted, by permission, from Paoletti, increase in the friction force in the lateral
A; Lambiase, F; Ili, AD, Procedia CIRP, 33, 562-7, direction. The butterfly-inspired cavity-
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2015.]
shaped patterns can regulate the wetting
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and frictional properties of the surfaces. The fabricated patterns can be used in develop-
22
ment of smart surfaces requiring directional friction characteristics.
Friction stir spot welding of thermoplastic materials (polycarbonate) allows achiev-
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ing high quality joints over conventional welding processes. Figure 11.22 shows typical
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phases of welding process.
The unformulated latex film (random copolymer of n-butyl acrylate, methyl-
methacrylate, and acrylic acid) was significantly plasticized by humidity because of the
presence of hydrophilic monomer (acrylic acid), resulting in an increase of the friction
24
coefficient. The plasticizing effect of a coalescing agent (Texanol™) had even stronger
effect in further increase of the friction coefficient, which eventually decreased upon film
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aging (drying). Several additives were used to decrease friction with different effect,
namely ethanol, added to aqueous phase to increase evaporation, increased friction coeffi-