Amontonian frictional behaviour of nanostructured surfaces

Abstract

With nanotextured surfaces and interfaces increasingly being encountered in technological and biomedical applications, there is a need for a better understanding of frictional properties involving such surfaces. Here we report friction measurements of several nanostructured surfaces using an Atomic Force Microscope (AFM). These nanostructured surfaces provide well defined model systems on which we have tested the applicability of Amontons' laws of friction. Our results show that Amontonian behaviour is observed with each of the surfaces studied. However, no correlation has been found between measured friction and various surface roughness parameters such as average surface roughness (R(a)) and root mean squared (rms) roughness. Instead, we propose that the friction coefficient may be decomposed into two contributions, i.e., μ = μ(0) + μ(g), with the intrinsic friction coefficient μ(0) accounting for the chemical nature of the surfaces and the geometric friction coefficient μ(g) for the presence of nanotextures. We have found a possible correlation between μ(g) and the average local slope of the surface nanotextures.

Sustained Frictional Instabilities on Nanodomed Surfaces: Stick–Slip Amplitude Coefficient

“…In addition, the longer pillars exhibited a higher friction coe cient than the shorter ones, as the longer pillars underwent more elastic deformation which led to an increase in the contact area. Thormann The oscillations in the shear traces observed by Pilkington et al 19 are similar to the stick-slip behaviour between two sliding surfaces under certain conditions. Stick-slip motion can be found at all length scales, ranging from the atomic scale up to the macroscale where stick-slip is responsible for common-life phenomena such as the noise of squeaking doors and car brakes' squeal.…”

“…A nite friction force f 0 extrapolated at zero load can be attributed to the contributions by the adhesive force which can be considered as an e ective load, as shown in the equation derived by Derjaguin: The apparent linear relationship between f s and L exhibited here is consistent with previous frictional studies on nanostructured surfaces. For instance, such a behaviour has previously been reported by Pilkington et al 19 on surfaces bearing nanoseeds, nanodiamonds, nanodomes and nanorods and in that study the linear relationship was discussed using various existing models. At the microscale, the linear nature of the friction-load relationship is commonly explained using models based on the Bowden and Tabor theory, 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 However, such a linear relationship between f s and L has not always been observed for surfaces with nanotextures.…”

“…The presence of such characteristics has previously been reported in the literature on a wide range of nanostructured surfaces. 19 Weilandt et al studied friction at an highly orientated pyrolite graphite (HOPG) surface in a NaClO 4 electrolyte medium liquid and observed friction peaks corresponding to HOPG steps whilst scanning the step upwards and downwards. They 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 attributed the friction peaks to both topographic and frictional contributions.…”

“…This μ g was calculated by taking into account both lateral and vertical nano-features of the sample under investigation and the size of the AFM tip used during the experiments to include contributions to the friction coe cient from the average local slope of the nanotextures. 19 Although this correlation was not straightforward, it was…”

Tuning the Friction of Silicon Surfaces Using Nanopatterns at the Nanoscale

“…The result revealed that the friction force varied linearly with the normal load, but the magnitude of the friction force was high relative to that on a smooth nickel surface. Pilkington et al [20] reported that the friction behavior of nanopatterned surfaces, including ZnO nanorods, ZnO nanograins, Al 2 O 3 nanodomes and nanodiamonds, obeys Amontons' law. Conversely, other authors reported that Amontons' law is no longer valid for a nanopatterned surface.…”