Spectroscopic ellipsometry investigation of the redox process of polypyrrole in several aqueous solutions

In this work, the properties of polypyrrole films electrochemically grown on platinum substrates from different aqueous solutions were studied using a spectroscopic ellipsometry technique at several electrode potentials. The electrolytes were: NaCl 0.5 M, CsCl 0.5 M, Na2SO4 0.5 M with pH = 4.5, and H2SO4 0.5 M (pH = 0.4). In all electrolytes with pH 4.5, for electrode potentials above 0.0 V vs. SCE, the polymer chains are in the highest state of oxidation, indicating that polarons are not present to a large extent. In a more acidic electrolyte, the film properties and oxidation mechanism are different from those under higher pH conditions. In all electrolytes, there is an increase in the thickness and degree of hydration of the film with polymer oxidation. (C) 1998 Elsevier Science B.V. All rights reserved.