Tribometric Comparison of n-Alkanethiolate and n-Alkyl Trichlorosilane Monolayers

In this presentation we offer a quantitative comparison of the frictional performance for monolayers derived from n-alkanethiolates on gold and n-alkyl trichlorosilanes on silicon. Pin-on-disk microtribometry provided frictional analysis at applied normal loads from 10 to 1,000 mN at a speed of 0.1 mm/s. For monolayers prepared from both n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon, a critical chain length of at least 8 carbons is required for beneficial tribological performance at an applied load of 9.8 mN. The direct comparison between the tribological stability of alkanethiolate and silane monolayers shows that monolayers prepared from n-octadecyl dimethylchlorosilane and n-octadecyl trichlorosilane withstood normal loads at least 30 times larger than those that damaged octadecanethiolate SAMs. Collectively, our results show that the tribological properties of monolayer films are dependent on their internal stabilities, which are influenced by cohesive chain interactions (van der Waals) and the adsorbate-substrate bond.