Ionic conductivity in polypyrrole–poly (vinyl acetate) films synthesized by chemical oxidative polymerization method

Abstract

Polypyrrole (PPy) and poly (vinyl acetate) (PVAc) composite thin films were synthesized by chemical oxidative polymerization method with the solution of ferric chloride (FeCl3) oxidant in methanol. Their dc conductivities as a function of temperature (308–383K) were measured. The ionic transference numbers for the PPy–PVAc films, synthesized with different concentration of FeCl3, were determined by dc polarization technique. The transference number for the films prepared with 0.1M and 0.2M concentration of FeCl3 are 0.49 and 0.55, respectively. While for the films prepared with 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1M concentration of FeCl3, the transference number lies between 0.78 and 0.99. The dc electrical conductivity of the films, at room temperature, first increases with concentration of FeCl3 and attains the maximum value (σ=6.17×10−10S/cm) at 0.5M of FeCl3. This increase in ionic conductivity of PPy–PVAc film with FeCl3 may be due to increased the mobility of FeCl4- ions promoted by coordination of FeCl2+ with nitrogen of PPy. However, further increase in concentration of FeCl3, decreases the conductivity of the films. The decreased conductivity may be due to reduced segmental motion of polymer. Conductivity variation with FeCl3 shows the percolative behavior. The temperature dependence of conductivity shows clear cross over from Vogel–Tamman–Fulcher (VTF) to Arrhenius behavior. The cross over from VTF to Arrhenius takes place at different temperatures for the films synthesized with different concentration of FeCl3.