Effect of synthesis parameters on electrical conductivity and morphological characteristics of pristine PANI and polyaniline-MWCNT nanocomposites

Effect of synthesis parameters including oxidant to monomer molar ratio ([O]/[M]) and oxidant type on the conductivity and morphological characteristics of pristine polyaniline (PANI) and a polyaniline-multi walled carbon nanotube (PANI-MWCNT) nanocomposite were investigated. The samples were synthesized by chemical oxidative polymerization technique at a constant concentration of HCl (1 M) and structurally characterized by Fourier transform infrared, Ultraviolet–visible, and X-ray diffraction spectroscopies. The electrical conductivity of pristine PANIs and PANI-MWCNT nanocomposites were enhanced by increasing the [O]/[M] ratio from 0.2 to 0.4. However it was reduced by subsequent increasing of the [O]/[M] ratio from 0.4 to 0.8 for both ammonium persulfate (APS) and potassium persulfate (KPS) as oxidants. At a 0.4 [O]/[M] ratio, the highest conductivity was obtained as the optimal point in both pristine PANIs synthesized with APS and KPS with values of 4.82 × 10 –1 S/cm and 6.63 × 10 –1 S/cm, respectively. Moreover, at the same [O]/[M] ratio, PANI-MWCNT nanocomposites also displayed a maximum conductivity of 7.12 S/cm using APS and 9.77 S/cm using KPS as oxidants. Conductivity measurements showed higher values for the KPS than the APS group due to the different morphology and active nucleation centers. Field emission scanning electron microscopy showed a predominant elongated coral-like morphology for pristine PANIs and a granular core–shell morphology for PANI-MWCNT nanocomposites. When changing the [O]/[M] ratio and the oxidant from APS to KPS, some morphological changes also happened for PANI-MWCNT nanocomposites, leading to an interesting evolution in the control of conductivity using synthesis parameters.