Reduction of the Coefficient of Friction of Steel-Steel Tribological Contacts by Novel Graphene-Deep Eutectic Solvents (DESs) Lubricants

Abstract

Deep eutectic ionic liquids (DES) possess similar properties to conventional ionic liquids (ILs). However, ILs cannot be considered as environmentally friendly compounds due to both its processing and synthesis, which could have significant polluting effects. On the contrary, deep eutectic solvents (DESs) can be biodegradable, non-toxic, and have a lower price than most ILs, making them potentially useful in a wide variety of advanced technological applications, such as tribology. On the other hand, graphene has recently been proposed as an extremely promising lubricant due to its combination of mechanical properties and chemical stability as well as its “green” character. In the present paper, graphene flakes (≈250 nm) have been used as an additive to DES composed of choline chloride (ChCl)-urea, ChCl-ethylene glycol, and ChCl-malic acid. According to the results, the addition of 1 wt% graphene reduces friction coefficient (COF) and, notably, prevents adhesive wear, reducing wear rate on steel-steel sliding contacts.

Nanolubrication in deep eutectic solvents

“…By applying a negative normal force we can access sliding before the surfaces jump out, yielding a friction coefficient of m = 3.0 AE 1.0. As with pure ethaline, the coefficient of friction measured for ethaline with added water compares favourably to the values reported previously, 19,20 supporting the assertion that DESs could have application as marine lubricants. 21 3.2.3 Structural origin of lubrication.…”

“…19 More recent work reported better lubrication performance from choline chloride-based DES, and found that adding graphene further reduced the coefficient of friction. 20 Abbott et al 21 reported superior lubrication performance from DESs and from ionic liquids than from base oil for steel-steel contacts. Intriguingly they also reported outstanding corrosion resistance from DESs compared to base oil, when the lubricant had become contaminated with aqueous salt solution, and noted a potential application for DESs as marine lubricants.…”

Deep Eutectic Solvent Reline at 2D Nanomaterial Interfaces

“…A new promising field for DESs rises for the design and development of new and functional materials, , with attention to the materials at a nanoscale level . DESs have been considered for the development of 2D nanomaterials such as graphene (GRA), for exfoliation of GRA layers, , for functionalization, or for improving materials performance such as lubrication . Additional systems formed by DESs and other 2D nanomaterials have been scarcely studied in the literature, and thus although some applications have been reported for the preparation of materials based on boron nitride (BN) or MoS 2 (MOS) 2D nanosheets, studies on other 2D materials such as silicene (SIL) or germanene (GER) are absent.…”

Machine Learning Approach for Application-Tailored Nanolubricants’ Design

“…Here, (i) sp -carbons, that is layer-structure carbons with the most eminent graphite and its structural component graphene, (ii) sp diamond-like, onion-like, and fullerene-like carbons, carbon nanotubes (CNTs), and (iii) sp -carbons, that is nanocrystalline diamonds, served as the solid lubricants [ 8 , 9 , 10 ]. Importantly, numerous carbon nanoparticles can be amalgamated with functional liquids to obtain novel nanofluids, that is stable nanodispersions of synergetic, thus exceptional, characteristics upon friction [ 11 , 12 , 13 , 14 , 15 ]. As for graphene, graphite, and CNTs themselves, superlubricity is attributed to the formation of atomically incommensurate contact between (variously separated) carbon nanolayers attached to the tribo-pairs.…”