Raman spectroscopy and AC conductivity of polyaniline montmorillonite (PANI–MMT) nanocomposites

A series of polyaniline/montmorillonite clay (PANI–MMT) nanocomposites were synthesised by in situ polymerisation of aniline in acidic medium in the presence of varying amounts (from 1 to 30 wt%) of MMT and a substoichiometric amount of ammonium persulfate (APS). For a preferred molar ratio of monomer to oxidant of 2:1, the aniline was polymerised and largely incorporated into the MMT. The PANI–MMT nanocomposites were characterised and compared by wide-angle powder X-ray diffraction and UV–Vis spectroscopy. Raman spectroscopy was used to investigate the interaction between clay layers and the intercalated polymer chains. Room temperature AC conductivity was measured in the frequency range 30 Hz to 1 MHz. Pure PANI and all the composites exhibited a low frequency region of frequency independent AC conductivity followed by a high frequency dispersive region where the AC conductivity obeyed a fractional power law of frequency dependence. The fractional exponent n for all the nanocomposites is significantly high as compared to that of pure PANI; n = 0.9 for all the composites whereas for pure PANI n = 0.2. In pristine PANI the onset of the dispersive region ωc is at a much higher frequency (at 300 kHz) as compared to the nanocomposites in which ωc is about 10 kHz.