Self-assembled monolayers (SAMs) were prepared by the adsorption of a series of 2,2-dialkylpropane-1,3-dithiols (
1-
5) and 2-pentadecylpropane-1,3-dithiol (
6) onto the surface of gold. These SAMs werecharacterized by ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy (XPS), polarizationmodulation infrared reflection absorption spectroscopy (PM-IRRAS), and atomic force microscopy (AFM).The studies demonstrate that a systematic variation in the structure of R'RC(CH
2SH)
2 from symmetrical (
1; R'= R) to progressively more unsymmetrical (
2-
6; R'
![](/images/entities/ne.gif)
R) can be used to provide control over the conformationalorder and interchain packing of the hydrocarbon tail group assembly. The tail group conformation and packingwere found to influence profoundly both the wettability and the tribological properties of the SAMs. Assembliesof well-ordered, well-packed hydrocarbon tail groups yielded interfaces that exhibited low wettabilities andlow frictional responses when compared to assemblies of disordered, loosely packed hydrocarbon tail groups.The trends in wettability and friction were rationalized by considering the magnitude of the van der Waalsinteractions between the hydrocarbon film and the contacting probe liquid and AFM tip, respectively.