Quantitative analysis of surface morphology: characterization of polypyrrole films aging

The structure and properties of polypyrrole have been studied intensively in the past decade. Polypyrrole microstructure and morphology are quite well described, nevertheless they remain roughly characterized from a quantitative point of view. In a previous work, one of the authors has underlined changes in some physical and microstructural properties which are linked to molecular mobility but the influence of aging on morphology has not been studied. To fill this gap, SEM and AFM observations have been performed. The surface morphology of polypyrrole films looks like 'cauliflowers' that are made of clusters aggregated on a large range of scales. Fractal methods have been used to treat quantitatively the pictures: the fractal dimension D (estimated from Minkowski) has a tendency to decrease for the aged material viewed by SEM as well as by AFM. Pseudo Fractality Graphs (the variation of D along the scales) show that the difference between virgin and aged polypyrrole is higher for the largest scales. The topography analysis is compared by using AFM and SEM pictures. (C) 1999 Elsevier Science Ltd. All rights reserved.