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

Yuhong Liu,Pengxiao Liu,Yuqi Xiao

doi:10.1007/s11434-012-5106-2

Yuhong Liu, Pengxiao Liu + Show 1 more

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https://doi.org/10.1007/s11434-012-5106-2

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Journal: Science Bulletin	Publication Date: May 1, 2012
Citations: 3	License type: CC BY 2.0

Affiliation: Tsinghua University

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.

Highlights

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
Considering the hydrophobic properties of decorated surfaces and their interactions with water molecules, the aim of our present work is to study the tribological properties of SAM films, made using a series of alkylsilanes with different chain-lengths and fluorinated substituents on the surface of the Si wafers, under water lubrication conditions
The low-intensity C1s peak in the X-ray photoelectron spectroscopy (XPS) spectrum of the Si surface is probably caused by organic contaminants adsorbed from the atmosphere during specimen preparation for the XPS measurements

Summary

Introduction

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. Nanometer-thick organic self-assembled molecular (SAM) films are potential candidates as lubricants for improving the performance of MEMS and NEMS. The introduction of fluorine could lead to enhanced intra- and inter-molecular steric interactions for bulky CF3-terminated films, and the corresponding lateral steric interactions can plausibly occur over distances sufficiently long to permit the propagation of surface phonons [14]. These properties make them good candidates for use in micro/nano devices.

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