Morphology control in electrochemically grown conducting polymer films. Part 2.—Effects of cathodic bias on anodically grown films studied by spectroscopic ellipsometry and quartz-crystal microbalance

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Abstract
We describe studies of effects of electrochemical growth conditions on the morphology of films of polyaniline (PANI). From single-wavelength ellipsometric measurements during film growth at constant anodic current, we have concluded that the temporary application of a cathodic bias during such an anodic growth process brings about an effect of (electrochemical) film annealing. This conclusion is further supported by a spectroscopic ellipsometric study. The spectroscopic study shows that, following temporary application of a cathodic bias during the galvanostatic growth of PANI films, the absorption peak in the near-infrared, associated with polarons in doped PANI, is shifted to lower photon energies. Such a shift is expected as a result of higher long-range order. The film annealing effect induced by temporary application of a cathodic bias is corraborated by further experimental evidence from quartz-crystal microbalance and electrode potential measurements. This beneficial morphological effect explains, at least in part, why potential multicycling has become a preferred mode of electrochemical growth of conducting polymer films. We suggest a possible interpretation for such annealing effects in an anodically grown conducting-polymer film brought about by interruption of the anodic growth current and temporary application of a cathodic bias. Elucidation of this phenomenon could be also valuable in the clarification of effects of undoping–redoping cycles applied to conducting-polymer membranes to achieve optimized gas-separation characteristics.