Isolated polymer chains via mixed self-assembled monolayers: Morphology and friction studied by scanning force microscopy

In this paper, we describe a system of mixed self-assembled monolayers of alkanethiols and thiol-terminated polystyrene (PS-SH) chemisorbed on a gold surface from mixed toluene solutions. Topography and friction images were obtained with a scanning force microscope (SFM) under bad-solvent conditions. We observed randomly distributed single polystyrene coils. We found that the polymer grafting density increases when the molar ratio of polymer to alkanethiol in solution increases. The local friction coefficient on a collapsed polystyrene chain was found to be about 0.3, a value that compares with a macroscopic one of 0.515. X-ray photoelectron spectroscopy and ellipsometry were employed to verify and supplement the SFM measurements.