Structural changes during the overoxidation of electro-chemically deposited poly(3,4-ethylenedioxythiophene) films

Electrochemical, mechanical and morphological properties of thin poly(3,4-ethyl-enedioxy-thiophene) (PEDOT) films deposited on gold were investigated in aqueous sulfuric acid and sodium sulphate solutions. At sufficiently positive electrode potentials overoxidation of the polymer took place and resulted in morphological changes and structure evolution. These effects were monitored by electrochemical impedance spec-troscopy (EIS), scanning electron microscopy (SEM) and X-ray diffraction. Significant changes in the film stress caused by overoxidation were detected by using the electro-chemical bending beam method. Results of the EIS measurements proved that the charge transfer process at the metal/film interface is more hindered in case of the degraded film. According to SEM images the overoxidation/degradation of PEDOT films can result in random-like but quite well-ordered arrays of islands and trench-like structures. The diffraction peaks of PEDOT became sharper and more intensive during the subsequent oxidation cycles indicating an increase in the degree of crystallinity of the polymer

Experimental methods for the determination of stress changes at electrified solid-liquid interfaces

Abstract In the present study some of the methods developed for the experimental determination of (interfacial or film) stress changes in electrochemical systems containing solid-liquid interfaces are briefly reviewed, as well as the kind and quality of information that can be obtained using these methods are discussed. The “bending beam” (“bending cantilever”, “laser beam deflection”, “wafer curvature”) method and related techniques, the piezoelectric method, the extensometer method, and the method based on the measurement of contact angle are discussed in detail. Special attention has been paid to problems related to the use of optical methods for position sensing.</jats:p