Friction mechanism of individual multilayered nanoparticles

Abstract

Inorganic nanoparticles of layered [two-dimensional (2D)] compounds with hollow polyhedral structure, known as fullerenelike nanoparticles (IF), were found to have excellent lubricating properties. This behavior can be explained by superposition of three main mechanisms: rolling, sliding, and exfoliation-material transfer (third body). In order to elucidate the tribological mechanism of individual nanoparticles in different regimes, in situ axial nanocompression and shearing forces were applied to individual nanoparticles using a high resolution scanning electron microscope. Gold nanoparticles deposited onto the IF nanoparticles surface served as markers, delineating the motion of individual IF nanoparticle. It can be concluded from these experiments that rolling is an important lubrication mechanism for IF-WS 2 in the relatively low range of normal stress (0.96±0.38 GPa). Sliding is shown to be relevant under slightly higher normal stress, where the spacing between the two mating surfaces does not permit free rolling of the nanoparticles. Exfoliation of the IF nanoparticles becomes the dominant mechanism at the high end of normal stress; above 1.2 GPa and (slow) shear; i.e., boundary lubrication conditions. It is argued that the modus operandi of the nanoparticles depends on their degree of crystallinity (defects); sizes; shape, and their mechanical characteristics. This study suggests that the rolling mechanism, which leads to low friction and wear, could be attained by improving the sphericity of the IF nanoparticle, the dispersion (deagglomeration) of the nanoparticles, and the smoothness of the mating surfaces.fullerene-like nanoparticles | tribology | rolling friction | nanotribology F riction causes wear and energy dissipation, and is responsible (directly or indirectly) for about one-third of the world's energy resource consumption (1,2). Therefore, friction and wear reduction are key factors in any future energy conservation plan. Similar in many ways to carbon fullerenes and nanotubes; hollow polyhedral nanoparticles (NP) of the inorganic compounds WS 2 , MoS 2 , were first reported in 1992 (3). These NP, known as inorganic fullerene-like (IF) structures and inorganic nanotubes, were shown to reduce friction and wear either as a pure solid lubricant; as additives to various fluid lubricants, or as part of self-lubricating coatings (4, 5). The seamless-hollow nanostructures were shown to be inherent to the layered structure of the material. The IF nanoparticles are common to layered metal dichalcogenides, MX 2 (M ¼ W , Mo, Ti, Nb, Hf; X ¼ S, Se) compounds as well as to numerous other inorganic compounds with layered two-dimensional (2D) structure. Each layer in the MX 2 material consists of three covalently bonded sheets with the metal atoms sandwiched between two chalcogenide sheets. In WS 2 (MoS 2 ) each tungsten (molybdenum) atom is bonded to six sulfur atoms in a trigonal prismatic coordination mode. Weak van der Waals forces are responsible for stacking the planar X-M-X layers together. Both graphi...

Tribological Properties of Carbon Nanocapsule Particles as Lubricant Additive

“…5, it shows that the lubricants with CNC nanoparticle addition have a lower friction coefficient than the pure oil lubricant, In fact, the main favorable benefit of the nanoparticle as oil additives is attributed decidedly to the following two effects, namely, ball bearing mechanism [26,27] and third body materials forming mechanism [28]. Specifically, the present frictionless phenomenon can be most likely attributed to the fact that a ball bearing effect induced by the spherelike multilayered structure of the CNC particles [29][30][31][32]. As shown in Fig.…”

Probing biomechanical properties with a centrifugal force quartz crystal microbalance

“…Objects such as microparticles attached or tethered to a biopolymer on the QCM surface become inertial transducers through which one can extract mechanical and thermodynamic properties of the macromolecules. Furthermore, the technique is applicable to microscopic biological objects such as viruses, bacteria and cells where measurements of mechanical properties and their changes have been directly linked to disease [44][45][46] .…”

Friction of low-dimensional nanomaterial systems

“…Tevet et al explored the friction mechanism of fullerene-like nanoparticles with high-resolution transmission electron microscopy (TEM; see results in Fig. 1) [18]. The three main mechanisms causing friction for nanoparticles are rolling, sliding, and exfoliation, and low friction and wear may be achieved with these fullerene-like nanoparticles by improving their sphericity, dispersion (de-agglomeration), and the smoothness of the mating surfaces.…”