Adsorption of Thiol-Containing Copolymers onto Gold

Polystyrene and poly(styrenesulfonate) copolymers bearing (mercaptomethyl)styrene units have been synthesized via an amidinothio intermediate which allows for quantitative hydrolysis to the thiol. The kinetics of adsorption of these polymers to gold has been determined in situ using the quartz crystal microbalance. The introduction of a few percent of thiol groups causes polystyrene to adsorb to gold from a good solvent (THF). Poly(styrenesulfonate) can also be induced to adsorb at a negatively charged (repulsive) gold/water interface when heavily loaded with (mercaptomethyl)styrene. Copolymers adsorb relatively rapidly, attaining stable surface coverages within 1 h. Steady-state adsorbance for copolymers of wide molecular-weight distribution is taken as indirect evidence for adsorption in the nonequilibrium regime. Electron spectroscopy of adsorbed poly(styrenesulfonate) copolymers suggests that sulfonate groups are expelled from the metal/polymer interface. The kinetics of octadecanethiol chemisorbing to gold was studied to provide a well-characterized, small-molecule comparison.