Determination of fractal rough surface of polypyrrole film: AFM and electrochemical analysis

Physico-chemical properties of conductive polymers depend on the morphology and characteristic of the synthesized film which emerge from synthesis conditions. For example, conductivity of polypyrrole is related to the fractal dimension of surface. Atomic force microscopy (AFM) is a powerful technique in revealing characteristic of surfaces. In the present research electrochemical techniques and atomic force microscopy are employed to analyze the surface morphology and parameters of surface such as interface width, kurtosis, Hurst exponent, fractal dimension and lateral correlation length for polypyrrole electrodeposited on glassy carbon (GC) electrode and relation between skewness and kurtosis were investigated. Height–height correlation function shows the correlation of heights in different points on the surface and can be calculated by analyzing AFM data and surface profile. Scanning electron microscopy (SEM) analysis carried out to confirm the AFM results. Cyclic voltammetry and electrochemical impedance spectroscopy methods are used to compare the electrochemical capacitance of films with different roughness. AFM images were used to estimate the surface area and results showed that the films synthesized in higher temperatures are rougher and have a larger surface area and according to the results of electrochemical experiments rougher surfaces with higher skews have larger electrochemical capacitance. The study of surface morphology and physico-chemical properties of polypyrrole film can provide suitable methods of synthesis of films with required properties.