Friction of Rubber with Surfaces Patterned with Rigid Spherical Asperities

Abstract

This paper reports on the frictional properties of smooth rubber substrates sliding against rigid surfaces covered with various densities of colloidal nano-particles (average diameter 77 nm). Friction experiments were carried out using a transparent Poly(dimethyl siloxane) (PDMS) rubber contacting a silica lens with silica nano-particles sintered onto its surface. Using a previously described methodology (Nguyen et al., J. of Adhesion 87 (2011) 235-250 ), surface shear stress and contactpressure distribution within the contact were determined from a measurement of the displacement field at the surface of the PDMS elastomer. Addition of silica nano-particles results in a strong, pressure-independent enhancement of the frictional shear stress as compared to the smooth lens. The contribution of viscoelastic losses to these increased frictional properties is analyzed in the light of a numerical model that solves the contact problem between the rubber and the rough surface. An order-of-magnitude agreement is obtained between experimental and theoretical results, the latter showing that the calculation of viscoelastic dissipation within the contact is very sensitive to the details of the topography of the rigid asperities.

Adhesion: role of bulk viscoelasticity and surface roughness

“…The results for Re E(ω) and Im E(ω) are shown (without smoothing) in figure 1. In the same figure we show the results obtained by Nguyen et al in a narrower frequency range [17]. The corresponding shift function a T is shown in figure 2 (red line).…”

“…In a classical study Fuller and Tabor [7] studied the adhesion between rubber balls and hard rough substrate surfaces with different root-mean-square Figure 1. (a) The real and imaginary part of the viscoelastic modulus, and (b) tan δ for PDMS as a function of frequency at room temperature T = 20 • C. The curves denoted Jülich and Paris were obtained by us and by the authors of [17], respectively.…”

Effects of stretching on the frictional stress of rubber

“…For the contact conditions under consideration, a weak, logarithmic, dependence of the frictional stress on velocity has previously been reported. [14] As a consequence, one cannot explain the observed changes in the local frictional stress from a consideration of the variations in local sliding velocity which result from the non-homogeneous deformation of the PDMS substrate: as a result of compressive (resp. tensile) surface strains at the leading (resp.…”

“…They can neither be explained from a simple viscoelastic effect which would induce a stress gradient in the opposite direction: shear stress would be higher in the less relaxed state encountered at the leading contact edge than in the more relaxed regions at the trailing edge. In addition, one can also mention that the frequency of the glass transition of the selected PDMS substrate at room temperature is about 10 8 Hz, [14] while the characteristic strain frequency of the contact, v/a (where v is the sliding velocity and a the contact radius) is no more than 10 Hz.…”

Comparing Surface Roughness and Texture Concepts

“…But until now there is a problem with using such parameters in the theoretical problems. The progress in this direction results to define optimal textures for different operation conditions and making them by laser or patterning methods with rigid asperities [14][15][16].…”