The Influence of Packing Densities and Surface Order on the Frictional Properties of Alkanethiol Self-Assembled Monolayers (SAMs) on Gold:  A Comparison of SAMs Derived from Normal and Spiroalkanedithiols

Abstract

We report a comparative study of the structure and frictional properties of self-assembled monolayers (SAMs) generated by the adsorption of three homologous 17-carbon alkanethiolssheptadecanethiol, 2,2dipentadecyl-1,3-propanedithiol, and 2-pentadecyl-1,3-propanedithiolsonto the surface of Au(111). The structural properties of these SAMs were characterized by atomic force microscopy, surface infrared spectroscopy, X-ray photoelectron spectroscopy, spectral ellipsometry, and wettability by water and hexadecane. The frictional properties of the SAMs were examined by friction force microscopy. The results demonstrate that the packing density and the related crystalline order of the hydrocarbon chains influence the frictional properties of organic thin films. The origins of the frictional differences measured from these films are discussed in terms of the structure of the films.

Friction Modifier Additives

“…Clearly the last of these is most relevant to understanding OFMs but the first two provide bettercharacterised, close-packed monolayers. These studies have confirmed the important influence of chain length and packing density on friction and also provided some estimates of film strength [79][80][81]. Most AFM work has studied films on substrates withdrawn from the liquid phase (i.e.…”

The influence of surface lubricity on the adhesion of Navicula perminuta and Ulva linza to alkanethiol self-assembled monolayers

“…The chemical and physical properties of a surface will affect the interaction of this adhesive with the surface. Lee et al (2000) reported that shorter, less ordered SAMs The influence of surface lubricity J. Bowen et al 475 exhibit greater frictional forces, as measured using AFM, than crystalline, ordered SAMs, discussing the effect of intermolecular packing on the modulus of the SAM.…”

Influence of chain ordering on frictional properties of self-assembled monolayers (SAMs) in nano-lubrication

“…Lee et al examined the frictional properties of SAMs composed of spiroalkanedithiols, which had the same packing of the anchor group but different packing densities at the sliding interface, and showed that the relative frictional properties of the monolayer films mirrored the trends in packing density and crystalline order of the films [137]. Perry et al also measured the frictional properties of SAMs formed from a series of spiroalkanedithiols and a single structurally related normal alkanethiol, and observed that less densely packed monolayers exhibited higher friction [138].…”