Abstract
Understanding the mechanism of precision sliding contacts with thin, adherent solid nano lubricating particle films is important to improve friction and wear behavior and ensure mechanical devices have long service lifetimes. Herein, a facile and multistep approach for the preparation of graphene oxide (GO) is presented. Subsequently, surface modification of as-synthesized GO with octadecyl amine (ODA) is performed to prepare hydrophobic GO-ODA and with 6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS) to prepare amphoteric GO-ANS through a nucleophilic addition reaction. X-ray diffraction and ultraviolet-visible, Fourier transform infrared, and Raman spectroscopy provide significant information about the reduction of oxygen functionalities on GO and the introduction of new functionalities in GO-ODA and GO-ANS. The effects of particle functionalization for the improved control of particle adhesion to the tribocontact have been studied. Wettability and thermal stability were determined using the water contact angle, and atomic force microscopy and differential scanning calorimetry (DSC) were used to characterize particle adhesion to the tribocontact. The tribological performances of the particles have been investigated using macro- and micro-tribometry using pin/ball-on-disc contact geometries. The influence of particle functionalization on the contact pressure and sliding velocity was also studied under rotating and reciprocating tribo-contact in ambient conditions. With an increase in the contact pressure, the functionalized particles are pushed down into the contact, and they adhere to the substrate to form a continuous film that eventually reduces friction. Amphoteric GO-ANS provides the lowest and most steady coefficient of friction (COF) under all tested conditions along with low wear depth and minimal plastic deformation. This is because particles with superior wetting and thermal properties can have better adherence to and stability on the surface. GO-ANS has a superior ability to adhere on the track to form a thicker and more continuous film at the interface, which is investigated by field emission scanning electron microscopy, energy dispersive spectroscopy, and Raman analysis.
Highlights
Ultra-precision mechanical assemblies like nano-electromechanical systems (NEMS) and micro-electromechanical systems (MEMS) involve micro-dynamical parts that have performances that are highly controlled by tribology [1,2,3]
Spectroscopic analyses of the worn tracks on the disc were investigated by Raman spectroscopy and electron dispersive spectroscopy (EDS) with Sigma (Zeiss, Germany) scanning electron microscope equipped with an X Flash Detector 4010 (Bruker, USA)
The π→π* peak red shifted towards the restoration of the π→π* conjugation in the graphene oxide (GO)-octadecyl amine (ODA) sample
Summary
Ultra-precision mechanical assemblies like nano-electromechanical systems (NEMS) and micro-electromechanical systems (MEMS) involve micro-dynamical parts that have performances that are highly controlled by tribology [1,2,3]. Saravanan et al [42] prepared multilayer polyethyleneimine/graphene coatings for macroscale superlubricity in different gas environments via layer-by-layer deposition techniques They reported that multilayer GO/polymer composite matrix has excellent adhesion properties via electrostatic attraction, and they provide better friction and wear reduction in N2 gas environments. We report here how the chemical functionalization on GO sheets can control the wetting behavior of the functionalized particles that controls their adhesion to the contacting steel surfaces for the reduction of macro to micro scale friction and wear in a variable pressure regime We address this issue of adhesion assisted lubrication mechanism by examining the microstructural and spectroscopic properties of the functionalized particles and further characterize the particle tribofilms on the steel contacts and relate with the wetting behavior of the particles and their ability to form a transfer film under traction
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