Tunable water-based lubrication behavior of alkyl- and fluoroalkyl-silanes

Abstract

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...

Mass-Scalable Molecular Monolayer for Ni-Rich Cathode Powder: Solution for Microcrack Failure in Lithium-Ion Batteries

“…It has been confirmed that a 1.2 nm thin layer with a different contrast in the image is found on the surface of the OTS-treated material. When the OTS precursor delivers a deposited molecular layer on the surface of the material, the thickness of the OTS layer is reported as 1.2 nm. , Therefore, the presence of a 1.2 nm layer on the surface strongly supports that OTS reacts with the Ni-rich cathode material and that the OTS is polymerized with same adjacent molecules. To date, in a conventional coating method, it is difficult to control the coating at the nanoscale because they are usually prepared by precipitation methods, which deliver thick coatings from hundreds of nanometers to several micrometers.…”