13C CPMAS NMR, XRD, d.c. and a.c. electrical conductivity of aromatic acids doped polyaniline

Abstract

Aromatic acids, para-toluene sulfonic acid (PTSA) and sulfosalicylic acid (SSA), doped polyanilines at different dopant levels and prepared by chemical and electrochemical methods are characterized by the high-resolution solid-state 13C CPMAS NMR technique. X-ray diffraction (XRD) patterns of highly protonated samples show a peak around 24 °. There is increase in crystallinity as the dopant concentration is increased. Temperature dependence of d.c. electrical conductivity measurements suggests that conduction takes place in an inhomogeneous medium consisting of ‘metallic’ polymer particles embedded in an insulating matrix. A.c. electrical conductivity measured on some of these samples shows that σ ac ∝ ω s in the frequency range 10 Hz to 100 kHz, and s is found to decrease as the dopant concentration and the temperature are increased. For higher dopant concentration samples, σ ac is found to be temperature independent in the frequency range 10 Hz–100 kHz. The real part of the dielectric constant showed a steep increase at low frequencies. The results of a.c. transport are discussed in terms of hopping of charges among defect states.