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

Polyaniline (PANI) films deposited galvanostatically on gold electrode s precoated with self-assembled monolayers of p-aminothiophenol (PATP) exhibit significantly higher optical densities than similar polymer f ilms deposited on bare gold, as measured by in situ ellipsometry. At t he 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 microba lance measurements and by ex situ Rutherford backscattering results, r espectively. It is therefore concluded that PANI grown on Au/PATP is c onsiderably denser than PANI grown on bare Au. Failure of other self-a ssembled monolayers to produce a similar effect suggests that the chem ical resemblance of PATP to the aniline monomer is a key factor in its ability to alter the morphology of electrodeposited PANI. The ac-impe dance measurements indicate that the morphological change (i.e., densi fication) is accompanied by pronounced improvement in the electrochemi cal response of PANI. In particular, the insulator/conductor switching rate is enhanced for PANI grown on Au/PATP relative to PANI grown und er similar conditions on bare Au. Moreover, a substantial increase in the rate of discharge is observed for fresh PANI on Au/PATP when apply ing a cathodic bias to the electrode. It is suggested that morphologic al restructuring is the limiting step during initial discharge of PANI grown on bare Au.