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The microscopic molecular motion behavior between graphene and the liquid lubricant oil affects the rheological and frictional behavior of the nano-lubricant. However, the effect of graphene on the rheological behavior of industrial #3 lubricant oil has not been revealed. Thus, molecular dynamics (MD) and experimental study are used to investigate the effect of graphene concentration, size, temperature, and shear rate on the viscosity, mean square displacement (MSD), and density of graphene lubricant oil are investigated. The results show that the viscosity of GLO increases with the increase of graphene concentration and decreases with the increase of temperature (293 K–330 K). The MSD of graphene lubricant oil decreases with the increase of graphene size and increases with the increase of temperature. It is worth noting that graphene lubricant oil with 3G has the maximum value of MSD, which means the graphene has the best diffusion performance at this concentration. Compared to the base oil, the simulation and experiment viscosity values of the GOL with 3G increased by 22.9 % and 47.6 %, respectively. The GOL has the characteristics of a Newtonian fluid. This study can provide a reference for the application of graphene lubricant oil in industry. [Display omitted] • Molecular dynamics simulation of rheological behavior of graphene lubricant oil • The viscosity of the graphene lubricating oil is higher than the base oil. • Effect of temperature on the rheological behavior of graphene lubricant oil • Effect of size on the rheological behavior of graphene lubricating oil [ABSTRACT FROM AUTHOR]

Carbon dots (CDs), a kind of burgeoning carbon-based nanomaterial, were widely used as high-efficiency lubricant additives for promoting the friction-reduction and anti-wear behaviors of green PEG-based lubricating oils. Undoubtedly, advances in CDs-based lubricant additives play a crucial role in enhancing their application prospect and utility value. Recent studies suggest that doping CDs with heteroatoms, especially multiple heteroatoms could remarkably promote their tribological performance. Therefore, the state-of-the-art N, B, and P-co-doped CDs (N,B,P-CDs) with a diameter of approximately 3.8 nm and composed of amorphous structures were synthesized by conveniently "one-step" pyrolyzing the corresponding carbon sources and dopants. Noticeably, the synthetic procedures of N,B,P-CDs were uninvolved in any pre-processing and post-processing techniques, showing favorable large-scale preparation potential. Adding suitable concentrations of N,B,P-CDs, the friction-reduction, anti-wear, and load-supporting functions of PEG200 base oil can be maximally increased by 38.1 %, 86.2 %, and 66.7 %, respectively, showing outstanding tribological performances. In addition, the tribological behaviors of N,B,P-CDs are evidently better than that of N,B-CDs and P-CDs under identical test conditions, exhibiting a multiatomic synergistic lubrication effect. According to the wear track surface analysis results and previous reports, the excellent tribological performance of N,B,P-CDs attributes to their favorable film-forming ability and nano-lubrication effect in the different friction stages. [Display omitted] • Novel N,B,P-CDs-based lubricant additives for PEG200 base oil were synthesized. • N,B,P-CDs as additives showed great anti-friction and anti-wear functions. • N,B,P-CDs possessed good multiatomic synergistic lubrication effect. • N,B,P-CDs have outstanding film-forming and nano-lubrication effects. [ABSTRACT FROM AUTHOR]

The present work investigates the thermo-physical and tribological properties of acidic functionalized graphene dispersed viscosity grade-68 (VG-68) hydraulic oil nanolubricant and their potential of reducing friction in a mechanical system. The prepared nanolubricant possesses a zeta potential value of −48 mV at pH 7 which shows its high dispersion stability. The thermal conductivity and viscosity index of the nanolubricant enhances with an increase in nanoparticle concentration. A maximum of 67.4 % enhancement in thermal conductivity was observed for 0.4 wt% nanolubricant compared to the base lubricating oil. The viscosity index of 0.4 wt% nanolubricant was enhanced about 2.2 times of the base lubricant. The tribological properties of the nanolubricants were measured using a rotating disc tribometer with an attachment to measure the coefficient of friction. The nanolubricant (0.4 wt%) reduces the frictional coefficient by a maximum of 21.8 % compared to pure hydraulic oil. The wear rate of the rotating disc also decreases with an increase in the nanoparticle concentration in hydraulic oil. A maximum decrease of 35.51 % in wear rate was observed by using 0.4 wt% nanolubricant compared to pure hydraulic oil. The acidic functionalized graphene nanoparticles were identified as a potential additive to protect surfaces against wear by reducing the frictional coefficient and enhancing the load-carrying capability of the lubricant. [Display omitted] • Acidic functionalized graphene dispersed hydraulic oil based nanolubricant was prepared. • Nanolubricant exhibits good dispersion stability and enhanced thermal properties. • Viscosity index and lubricity of nanolubricant enhances with the addition of functionalized graphene. • Significant decrease in the frictional coefficient shows its ability to protect surfaces against wear. [ABSTRACT FROM AUTHOR]

In the field of tribology, graphene has become a potential candidate material for lubricating oil and lubricant additives at multiple scales due to their high thermal conductivity and impermeability. In order to further improve the anti-wear and anti-friction properties of graphene, Ni/polydopamine-functionalized graphene composites (Ni/pDA/GR) were successfully prepared by a wet chemical reduction method. In this paper, The GR, pDA/GR, Ni/GR and Ni/pDA/GR were added into the base oil as lubricant additives respectively to explore their lubrication properties. The results showed that the friction coefficient of Ni/pDA/GR group is the lowest, which is about 15 % lower than base oil. Ni/pDA/GR also exhibited good wear resistance in wear tests. At the same time, the optimal concentration of the composite is 0.1 wt% in base oil, and the optimal lubrication load is 5 N. [Display omitted] • Polydopamine was used to modify graphene which is facile and environmental. • Spherical Ni NPs can improve the load-bearing capacity of base oil. • The composite can improve the anti-wear and anti-friction performance of base oil. • We report a facile method to prepare metal-nanomaterial composites. [ABSTRACT FROM AUTHOR]

Spheroidal carbon particles are touted as excellent additives in lubricants for reduction in friction and wear. Herein 50–100 nm-sized spheroidal carbon soot particles with heliocentric graphitic layers are prepared by controlled decomposition of wasted rubber and subsequent heat-treatment of wasted rubber derived soot. Thermogravimetric analysis showed that the on-set degradation temperature of the soot particles was representative of a material constituted by amorphous and crystalline phases complementing well with x-ray diffraction studies. The soot particles are dispersed in an additive-free base oil (BO), and the soot particles added oil was used as a lubricant. At room temperature, a reduction in coefficient of friction (CoF) and wear scar diameter (WSD) of ~9% and 16.55% were recorded. At a higher temperature of 70 °C, a reduction in CoF and WSD of as high as 48.93% and 28.12% were recorded. Based on the observations, it is theorized that the soot particles acted like nano-bearings between the contacting surfaces producing a rolling effect that efficiently reduced friction and wear concerning the contacting surfaces. Also, the dispersion of soot particles improved the viscosity retention of BO at higher temperatures indicating its multifunctional ability. [Display omitted] • 50–100 nm-sized carbon soot particles with sphere-like morphology are prepared from wasted rubber. • Heliocentric graphitic layers constituted the soot particles. • The carbon soot particles had a mixture of crystalline and amorphous characteristics. • The carbon soot particles are dispersed in an additive-free Group-2 dewaxed lubricating oil. • Carbon soot particles are an excellent additive in lubricating oil for considerable friction and wear reduction. [ABSTRACT FROM AUTHOR]