INSITU CONDUCTANCE MEASUREMENT DURING ELECTROPOLYMERIZATION

A mathematical model for the conductance of a growing conductive polymer layer on a double-band electrode has been developed. The model, which is based on the theories of conformal mapping and elliptic integrals, predicts that conductance is linearly related to the conductivity and approximately to the logarithm of the thickness of the polymer layer. A new type of ac conductimeter based on a double current follower has been constructed in order to monitor conductance during the electrochemical polymerization on a double-band microelectrode. By recording conductance during the galvanostatic polymerization of pyrrole and 3-methylthiophene the conductivities were obtained from the slope of the linear section of the graph vs logarithm of time and the growth rate from its intercept. The conductivity of polypyrrole-dodecylsulfate was in accordance with the reported values. The conductance of poly(3-methylthiophene) showed a catastrophic decline after a prolonged electropolymerization, presumably as a result of the known "polythiophene paradox", i.e. polymerization potential being outside the stability range of the polymer. The method allows a facile measurement of the specific conductivity of a polymer without the need for calibration with materials of known conductivity and thickness.