Morphology Control in Electrochemically Grown Conducting Polymer Films. 3. A Comparative Study of Polyaniline Films on Bare Gold and on Gold Pretreated with p-Aminothiophenol

Abstract

Polyaniline (PANI) films deposited galvanostatically on gold electrodes precoated with self-assembled monolayers of p-aminothiophenol (PATP) exhibit significantly higher optical densities than similar polymer films deposited on bare gold, as measured by in situ ellipsometry. At the same time there is no change in the total mass of the deposit or in the amount of polymer, as indicated by in situ quartz crystal microbalance measurements and by ex situ Rutherford backscattering results, respectively. It is therefore concluded that PANI grown on Au/PATP is considerably denser than PANI grown on bare Au. Failure of other self-assembled monolayers to produce a similar effect suggests that the chemical resemblance of P A P to the aniline monomer is a key factor in its ability to alter the morphology of electrodeposited PANI. The ac-impedance measurements indicate that the morphological change (i.e., densification) is accompanied by pronounced improvement in the electrochemical response of PANI. In particular, the insulator/conductor switching rate is enhanced for PANI grown on Au/PAP relative to PANI grown under similar conditions on bare Au. Moreover, a substantial increase in the rate of discharge is observed for fresh PANI on AuRATP when applying a cathodic bias to the electrode. It is suggested that morphological restructuring is the limiting step during initial discharge of PANI grown on bare Au.