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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...

In this paper, we report the tribological properties of self-assembled molecular (SAM) films of fluoroalkylsilanes and non-fluoroalkylsilanes, with different chain-lengths, adsorbed on Si substrate surfaces by covalent bonds. The SAM films were characterized using a universal ball-disk experimental tester in aqueous solutions. The substrate surface was examined by X-ray photoelectron spectroscopy (XPS), and the SAM films adsorbed on the Si surfaces were inspected by contact angle measurements and XPS. Lubrication studies revealed that several kinds of fluoroalkylsilanes had similar friction coefficients; the small differences were attributed to the chain flexibility. In contrast, differences in the aqueous lubrication properties of SAM films of non-fluoroalkylsilanes were clearly identified. It is suggested that substitution with fluorine atoms and the surface affinities of fluoroalkylsilanes contributed to redistribution of surface changes, causing variations in lubrication behaviors. water-based lubrication, wettability, self-assmebled molecular films Citation:Liu Y H, Liu P X, Xiao Y Q. Tunable water-based lubrication behavior of alkyl-and fluoroalkyl-silanes. Chin Sci Bull, 2012, 57: 18791885, doi: 10.1007/s11434-012-5106-2Friction is a common phenomenon in engineering, and much energy is wasted because of serious friction or wear between moving parts. Much effort has been devoted to controlling energy dissipation during surface interactions. Also, micro/nano-electromechanical systems (MEMS/ NEMS), the use of which has increased in recent decades, have many other tribological problems [1][2][3][4]. As the dimensions of a system decrease, the surface area/volume ratio increases. This could cause surface forces such as adhesion and friction to predominate over inertial forces [5]. Tribological limitations such as stiction, friction, and wear are major problems that limit the efficiency, power output, and reliability of these devices [6][7][8].Although Si is the material most used in MEMS/NEMS components, the tribological performance of Si is very poor . Nanometer-thick organic self-assembled molecular (SAM) films are potential candidates as lubricants for improving the performance of MEMS and NEMS. Recently, much attention has been paid to self-assembled monolayers because they are easy to prepare, and they have excellent properties such as low thickness, stable physical and chemical properties, and good covalent bonding with substrates [9]. Moreover, the properties of SAM films can be extended by changing the lengths of the molecules, the type of terminal group, and the degree of cross-linking within the layer. In particular, fluorinated organic thin-films have been much studied because of their unique chemical stabilities and anti-adhesive properties [10][11][12]. Organosilane ultrathin films have been identified as promising boundary lubricants. This is because organosilane molecules interact strongly with substrates and their thicknesses are commensurate with the dimensions of the structures in these appl...