Application of Vogel-Tamman-Fulcher (VTF) model to polythiophene composite thin films

Synthesis of polymer composites poly (vinyl acetate) (PVAc) and polythiophene (PTh) was done by chemical oxidative method using FeCl3oxidant in methanol. Thin films with PTh-PVAc polymer composite were prepared for 5.5, 10.4, 14.9, 18.9 and 22.5 wt% of iodine as a dopant. Direct current (DC) conductivity as a function of temperature (313–363 K) was measured by the two probe method. Characterization of the sample was done via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG)/differential thermal analysis (DTA). The maximum value for DC electrical conductivity was found for 10.4 wt% (σ=9.78×10-10S cm-1). The decrease in conductivity for greater iodine concentrations may be due to reduced segmental motion. The temperature dependence conductivity shows percolative behavior and a clear cross over from Vogel-Tamman-Fulcher (VTF) to Arrhenius behavior. Ionic conduction decreased with increase in the concentration of iodine, which shows ionic charge transport. XRD of the samples showed an amorphous nature. FTIR spectra showed absorption in the range 550–3600 cm-1, which indicates various bands involved in the PTh-PVAc polymer composite with iodine doping. From TG/DTA studies, it was observed that all the samples with a different wt% of iodine showed degradation in a range 75–81% when heated up to 888 K.