ELECTROCHEMICAL DEPOSITION OF A CONDUCTING POLYMER, POLY(THIOPHENE-3-ACETIC ACID) - THE 1ST OBSERVATION OF INDIVIDUAL EVENTS OF POLYMER NUCLEATION AND 2-DIMENSIONAL LAYER-BY-LAYER GROWTH

Cyclic voltammetric and chronoamperometric studies reveal that the electrochemical deposition of a conducting polymer, poly(thiophene-3-acetic acid) (poly(TPAA)), proceeds via a mechanism of two-dimensional (2-D) layer-by-layer nucleation and growth, following the first monolayer deposited through oxidative adsorption of the TPAA monomer on a bare Pt surface. This finding is to be compared with previous investigations of conducting polymer deposition which have reported consistently a mechanism of three-dimensional nucleation and growth. The 2-D layer-by-layer mechanism is embodied in a variety of phenomena observed under various experimental conditions. The most striking evidence arises from the unique features of the cyclic voltammograms (CVs), in which multipeaks resulting from oxidative monomer adsorption, and single events of polymer nucleation and successive monolayer spreading, respectively, have been observed for the first time. The nucleation peaks in the CVs are characterized by a linearly rising edge as expected theoretically and the amount of charge involved, ca. 200-mu-C/cm2, in agreement with the deposition of a poly(TPAA) monomolecular layer. The initial propagation rate of a poly(TPAA) monolayer is between ca. 0.08 and 0.14 cm/s. The new mechanism indicates the possibility of preparing conducting polymer films with a more uniform and smooth morphology for use, e.g., as electronic materials.