3.2. AFM analysis
The AFM studies Fig. 2(a) showed that in the absence of ammonia exposure, the HCl doped polyaniline nanofibers had diameters of around 72.46 nm, with the surface contours being less developed [39]. After ammonia exposure Fig. 2(b) significant changes in the size and morphological distribution of the polyaniline nanoparticles was observed. The nanofibers became more compact and rounded, with average diameter around 43.56 nm.
The observations may be attributed to the probable restructuring of molecular structure so as to be able to accommodate the ions diffusing into the polymer. This may be applied to the dissolution of ammonia and the subsequent diffusion of ammonium ions. In an earlier study significant changes in the surface morphology of PANI films has been observed over repeated doping and dedoping cycles. The observation that the extent of effect on the surface morphology depended a great deal on the size of the anions from the acid corroborated the importance of diffusion on the phenomenon [47].
Alternatively it may be surmised that with exposure to ammonia, as it gets absorbed into the PANI film, the structural changes due to de doping are thought to cause the generation of a repulsive force between the polyaniline chains. This further causes the rearrangement of the PANI chains and hence a visible change in the surface morphology occurs [48].