Electrochemical polymerization of 3-dodecylthiophene: Effect of current density and film thickness

Abstract

Poly(3-dodecylthiophene) (PDDT) films are electrochemically prepared and their conductivities examined. At a constant charge density, the conductivities of PDDT films are dependent on the current density, but in fact its effect should be attributable to a change in film thickness. At a constant current density, the conductivity of films decreases with an increase in charge density below 1.2 C/cm 2. Above this, it is nearly independent of the charge density. There is a similar tendency in the relationship between conductivity and thickness. The molecular weight increases with an increase in the current density and crosslinking reactions take place at high current densities. In the scanning electron micrographs (SEM) of freestanding films, projections are observed on the film surfaces, and grow as the electrochemical polymerization proceeds. The surface of a 0.1 μm thick film on a substrate is smooth, but at high magnification there are many bumps, due to nucleus-centred growth. A scheme that explains the processes of film growth and dependence of conductivity on film thickness is proposed.