Dynamic scaling analysis of scanning force microscopy images of electrochemically formed polyaniline films in the oxidized form scale-dependent roughening kinetics

Abstract

The morphology of the oxidized form of electrodeposited polyaniline films (PANI) grown on platinum under potentiodynamic cycling has been studied by scanning force microscopy (SFM). For average film height 〈h〉 < 100 nm, the nucleation and growth of PANI without a change in the surface roughness was observed. For the range 100 < 〈h〉/nm < 1000 a granular and compact polymer film was formed and for 〈h〉 > 1000 nm, a highly branched deposit was produced. The dynamic scaling analysis of the granular-deposit SFM image scans revealed the characteristic features of a self-affine fractal surface with two sets of roughness exponents α and β, depending whether the length of the SFM scan, L_s, involved in the analysis was smaller or larger than the average grain size d_s of the polymer film. For L_s < d_s, α(I)= 0.90 and β(I)= 0.4, whereas for d_s⩽L_s⩽ 1000 nm, α(II)= 0.4 and β(II)= 0.6 were obtained. Both high values of β are consistent with the contribution to the growth process of a directional electric field, which at advanced stages of growth leads to the development of the highly branched deposit. A correlation between the analysis of PANI morphology and potentiostatic PANI electroformation current transient data is also presented.