Properties of thin polystyrene films prepared on gold electrodes by the dip-coating method

The characterization of thin, polystyrene (PS) coatings (molecular weight c a. 90 000, up to SO nm in thickness), deposited on polycrystalline Au surfa ces, was carried out by using ellipsometry, mass measurements using the qua rtz crystal microbalance (QCMB) technique, and various electrochemical meth ods. The PS coatings were reproducibly deposited using a dip-coating techni que, involving the immersion of the Au substrate for times ranging from 5 s to 2 h in 0.6-10 g of PS/(L of cyclopentane (CP)). The coverage of the Au substrates by PS in aqueous solutions, determined from the extent of suppre ssion of the cyclic voltammetric (CV) response vs at bare electrodes, as we ll as from ac impedance measurements in pH 7 phosphate buffer and in pH 7 K 4Fe(CN)(6) (1 mM) solutions, could be controllably varied from ca. 0.1 to 0 .99 by the deposition conditions employed. With the time of potential cycli ng in aqueous solutions, the degree of blockage of the Au surfaces by these PS films decreases, likely due to the development of an increasing number of defects in the coating and the consequent uptake of solution into the fi lm. Evidence for the presence of both an inner and outer PS layer has been found, based on the observed dependence of the coating density, thickness, and degree of Au coverage on the PS deposition time.