Role of Roughness Parameters on the Tribology of Randomly Nano-Textured Silicon Surface

Abstract

This experimental work is oriented to give a contribution to the knowledge of the relationship among surface roughness parameters and tribological properties of lubricated surfaces; it is well known that these surface properties are strictly related, but a complete comprehension of such correlations is still far to be reached. For this purpose, a mechanical polishing procedure was optimized in order to induce different, but well controlled, morphologies on Si(100) surfaces. The use of different abrasive papers and slurries enabled the formation of a wide spectrum of topographical irregularities (from the submicro- to the nano-scale) and a broad range of surface profiles. An AFM-based morphological and topographical campaign was carried out to characterize each silicon rough surface through a set of parameters. Samples were subsequently water lubricated and tribologically characterized through ball-on-disk tribometer measurements. Indeed, the wettability of each surface was investigated by measuring the water droplet contact angle, that revealed a hydrophilic character for all the surfaces, even if no clear correlation with roughness emerged. Nevertheless, this observation brings input to the purpose, as it allows to exclude that the differences in surface profile affect lubrication. So it is possible to link the dynamic friction coefficient of rough Si samples exclusively to the opportune set of surface roughness parameters that can exhaustively describe both height amplitude variations (Ra, Rdq) and profile periodicity (Rsk, Rku, Ic) that influence asperity-asperity interactions and hydrodynamic lift in different ways. For this main reason they cannot be treated separately, but with dependent approach through which it was possible to explain even counter intuitive results: the unexpected decreasing of friction coefficient with increasing Ra is justifiable by a more consistent increasing of kurtosis Rku.

Transparent Pullulan/Mica Nanocomposite Coatings with Outstanding Oxygen Barrier Properties

“…Reversely, the fact that concentrations of the filler below 0.2 wt% had no effect on the friction performance is plausibly explained by considering that the tribological behavior of the coatings surface is influenced by the surface morphology and topography at a macro-scale level (i.e., when filler aggregates form on the coating surface). As already reported, differences at the nanoscale level do not seem to have any significant effect [24,25].…”

Transparent Pullulan/Mica Nanocomposite Coatings with Outstanding Oxygen Barrier Properties

“…Reversely, the fact that concentrations of the filler below 0.2 wt % had no effect on the friction performance is plausibly explained by considering that the tribological behavior of the coatings surface is influenced by the surface morphology and topography at a macro-scale level (i.e., when filler aggregates form on the coating surface). As already reported, differences at the nano-scale level do not seem to have any significant effect [ 24 , 25 ].…”

Effect of Surface Grooves on the Static Friction of an Elastic Slider

“…Many experimental and numerical studies demonstrate the effectiveness of surface patterning in reducing friction both at macro and nanoscale [13][14][15][16][17], but the generality of this claim remains controversial. In fact, the patterned pads of many insects and reptiles show an extraordinary ability to stick to surfaces with no loss of traction.…”