Enhanced Lubricity of SnO₂ Nanoparticles Dispersed Polyolester Nanofluid

Nanofluid lubrication is a novel approach for enhancing energy efficiency of the sliding interfaces which is useful for reducing friction and wear of the machine elements. The SnO₂ nanoparticles (NPs) of 25 nm size and concentration 0.03 mg mL^–1 dispersed in polyolester (POE) oil is found to exhibit significant reduction in friction coefficient and wear up to 38 and 42%, respectively, in comparison to neat POE oil. It is also found that the lubrication efficiency depends on size of the NPs, dispersion stability, and concentration. Fourier transform infrared red spectroscopy confirmed that the chemical stability of the POE was preserved after the tribology test and there was no product due to oxidation reaction. Formation of low shear strength tribofilm containing organic compounds and SnO₂ nanoparticles was key factor in reduction of the friction and protection against wear and deformation

Effective Noncovalent Functionalization of Poly(ethylene glycol) to Reduced Graphene Oxide Nanosheets through γ‑Radiolysis for Enhanced Lubrication

High-quality reduced graphene oxide (rGO) nanosheets (NSs) were synthesized by the oxidation of graphite followed by hydrazine treatment for the reduction of the oxygen functionalities. γ-Radiolysis was then used for the functionalization of the rGO-NSs with poly­(ethylene glycol) 200 (PEG200). The functionalization resulted in the intercalation of PEG200 molecules in rGO through hydrogen bonding between the hydroxyl groups of rGO and the oxygen atoms of PEG200 molecules. This resulted in an increase in the <i>d</i> spacing of the graphene sheets and a decrease in the defect density of the carbon network in the rGO. The friction coefficient and wear of sliding steel surfaces were reduced by 38% and 55%, respectively, when 0.03 mg mL^–1 PEG200-functionalized rGO dispersed in PEG200 was used. The lubrication properties can be described by bipolar interactions between PEG200 and rGO, leading to effective dispersion. Chemical analysis of wear particles showed decomposition of rGO into nanosized graphite domains, as exhibited by mechanical energy produced in tribo-contact. Moreover, these domains formed effective and stable tribofilms on the steel wear tracks that easily sheared under the action of contact stress. This significantly enhanced the antifriction and antiwear properties, resulting in improved oxidation resistance of PEG200 under the tribo-contact. It was found that, at high rGO concentrations, the lubrication efficiency decreased as a result of graphene–graphene intersheet collisions, producing mechanical energy and chemical defects at contact interfaces