Analytical Sciences

Abstract − Analytical Sciences, 17(5), 613 (2001).

A Comparative Study on the Viscoelasticity and Morphology of Polyaniline Films Galvanostatically Grown on Bare and 4-Aminothiophenol-Modified Gold Electrodes Using an Electrochemical Quartz Crystal Impedance System and SEM
Qingji XIE,  Youyu ZHANG, Canhui XIANG, Jianxin TANG, Yunlong LI, Qiuxiang ZHAO, and Shouzhuo YAO
Chemical Research Institute, Hunan Normal University, Changsha 410081, P. R. China
The equivalent-circuit parameters of the 9-MHz piezoelectric quartz crystal (PQC) resonance were measured in situ during the galvanostatic polymerization of aniline on 4-aminothiophenol(4-ATP)-modified and bare Au electrodes for ca. 2000 s, respectively. Two polymerization media, 0.100 mol L-1 aniline in 1.0 mol L-1 H2SO4 and in 2.0 mol L-1 HClO4 aqueous solutions, and two values of the current density, 12 and 36 uA cm-2, were used. At identical levels of the resonant frequency shifts in the solutions, obviously greater increases in the motional resistance (R1) were found after aniline polymerization on bare Au electrodes, though the absolute values of deltaf0/deltaR1 were all large; also, the resonant frequency shifts in air (deltaf0g) were considerably smaller for PANI films grown on bare Au electrodes. It is thus concluded that, under identical polymerization conditions, (1) the PANI film grown on a bare gold electrode is rougher, less compact, and can entrap solution more notably; (2) the deposition efficiency of PANI is higher on a 4-ATP-modified Au electrode, owing to a significantly greater observed "dry" frequency shift, and thus a greater "net" mass value of the polyaniline backbone. SEM observations have confirmed that PANI films on 4-ATP-modified Au electrodes were smoother and more compact than those grown on bare Au ones under identical polymerization conditions. In addition, a technique of simultaneous measurements of the electroacoustic admittance of the PQC resonance and the electrochemical impedance was used to monitor the adsorption of 4-ATP onto a PQC gold electrode.