Tunable tribological properties in water-based lubrication of water-soluble fullerene derivatives via varying terminal groups

Abstract

In this paper, three kinds of water-soluble fullerene derivatives were synthesized via electrophilic addition reaction and cycloaddition reaction, respectively. The chemical composition characterizations of these derivatives indicated the successful preparation of C 60 (OH) x , C 60 (C(COOH) 2 ) x and C 60 (OH) x (NHCH 2 COOH) y fullerene derivatives. The aggregation and morphology characterizations showed that the three kinds of derivatives had an ideal spherical aggregating structures and excellent dispersibility in water, especially C 60 (OH) x and C 60 (C(COOH) 2 ) x . The lubrication performance of the fullerene derivatives acted as lubricant additives were investigated at different concentrations in the range of 0-1 wt%. The results indicated that the addition of polyhydroxyl and carboxylic derivatives could improve the lubrication properties, which led to the reduction of wear to about 40% at most. It is attributed that the optimized substitutions of fullerene molecules may be of benefit to their distribution properties and lubricating behaviors in water based lubrication. The discovery [1] and large scale preparation [2] of fullerene C 60 are one of the most important achievements in the 20th century. Since then, much attention has been paid to fullerene C 60 for its potential applications in physics, chemistry and material science [3][4][5][6][7][8][9][10]. The lubricating properties of fullerene C 60 [1,11] have been predicted because of its unique spherical shape, high load-bearing capacity, strong intramolecular forces, weak intermolecular forces, low surface energy and so on. Some researchers predicate that C 60 could be used as microsphere ball lubricant [12,13]. It has been found that hexagonal close packed structure of fullerene molecules have obliterated phase transition, and the theoretical study find that fullerene molecules can scroll on the surface of graphite and diamond under low pressure [14]. Therefore, fullerene C 60 is regarded as a good solid lubricant.So far, researches on the friction properties of C 60 can be classified into two categories. One is solid lubrication system focusing on the C 60 films, such as sublimation deposition film [15][16][17] and Langmuir-Blodgett film [18][19][20][21]. In 1993, Bhushan et al.[17] got fullerene thin film using sublimation deposition method on polished silicon and studied its tribological properties under a serial of conditions. All the results showed that the friction coefficient decreased in the presence of fullerene thin film. The author attributed this result to the unique crystal structure and chemical bond of fullerene. Other researchers focused on fullerene LB film found that fullerene LB thin film had higher bearing capacity compared with C 60 powder [18]. For instance, the C 60 monolayer film formed by evaporation of a BN crucible on highly oriented pyrolytic graphite (HOPG) exhibited a low frictional force of 2 mN [22]. The other studies are fluid lubrication system using fullerene as lubricating additive [23]. All the results indicat...

Mechanism of Solubilizing Fullerene C60in Presence of Poly(Vinyl pyrrolidone) Molecules in Water

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