Abstract
Nano-object additives are used in tribological applications as well as in various applications in liquids requiring controlled manipulation and targeting. On the macroscale, nanoparticles in solids and liquids have been shown to reduce friction and wear. On the nanoscale, atomic force microscopy (AFM) studies have been performed in single- and multiple-nanoparticle contact, in dry environments, to characterize friction forces and wear. However, limited studies in submerged liquid environments have been performed and further studies are needed. In this paper, spherical Au nanoparticles were studied for their effect on friction and wear under dry conditions and submerged in water. In single-nanoparticle contact, individual nanoparticles, deposited on silicon, were manipulated with a sharp tip and the friction force was determined. Multiple-nanoparticle contact sliding experiments were performed on nanoparticle-coated silicon with a glass sphere. Wear tests were performed on the nanoscale with AFM as well as on the macroscale by using a ball-on-flat tribometer to relate friction and wear reduction on the nanoscale and macroscale. Results indicate that the addition of Au nanoparticles reduces friction and wear.
Highlights
Nano-objects are continually studied in tribological applications and increasingly in other applications that require controlled manipulation and targeting in liquid environments
The manipulation technique is first described for each condition, and the friction forces for both Au 30 and Au 90 nanoparticles are compared and discussed for both dry conditions and submerged in water
Since the adhesive force is dependent on surface area, it is expected that the larger Au 90 nanoparticles will display higher changes in friction force compared to the smaller Au 30 nanoparticles, and this is confirmed from the results shown in Figure 8a–b for both dry and submerged-in-water conditions
Summary
Nano-objects are continually studied in tribological applications and increasingly in other applications that require controlled manipulation and targeting in liquid environments. To characterize friction forces associated with controlled manipulation and to understand the nature of the mechanism of friction and wear reduction of nanoparticles in MEMS/NEMS devices, studies have been carried out in both single-nanoparticle contact and multiple-nanoparticle contact with the aid of an AFM. In multiple-nanoparticle contact, a glass sphere attached to an AFM cantilever, as shown in Figure 2b as an example, was used to slide over several nanoparticles This type of study simulates the contacts experienced by MEMS/NEMS devices when nanoparticles are introduced for the purpose of friction and wear reduction. These studies are crucial to determine the added advantage of dispersing nanoparticles in liquids, in cases where the entire MEMS/NEMS system is submerged in a liquid environment This has the ability to eliminate the adhesive effects of meniscus forces associated with the formation of capillary bridges due to adsorbed moisture on a surface
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