STRUCTURE DEVELOPMENT IN POLYANILINE FILMS DURING ELECTROCHEMICAL POLYMERIZATION - II - STRUCTURE AND PROPERTIES OF POLYANILINE FILMS PREPARED VIA ELECTROCHEMICAL POLYMERIZATION

Structure development in polyaniline (PAn) films was followed during t he electrochemical polymerization in 1 M HCl solution via a constant p otential mode at + 0.76 +/- 0.03 V and pH = 0.2 by using several in si tu and/or out of situ techniques including UV-visible spectrometry, ch ronoamperometry, cyclic voltammetry, Rayleigh scattering and atomic fo rce- and optical microscopy. As the polymerization proceeded from the initial nucleation stage I (where the polymerization current density v aries as I proportional to t(0)) to the intermediate stages IIa and II b (I proportional to t(3) --> t(2)) and the final stage III (I proport ional to t(4)), the gross morphology changed from grainy to fibrillar texture. The fibrils were aggregates of the grains with the size uncha nged from that formed in the early stage. This difference between the grainy and fibrillar structures is due to the difference in the state of aggregation of the initially formed grains. In the later stages, ho wever, the fibrils began to form branches, accelerating the rate of po lymerization. The branched fibrils grew toward the vertical direction, keeping their horizontal structural size virtually unchanged. (C) 199 8 Elsevier Science Ltd. All rights reserved.