Microstructure, dielectric response and electrical properties of polypyrrole modified (poly N-vinyl carbazole–Fe 3O 4) nanocomposites

Abstract

N-vinyl carbazole (NVC) was polymerized in the presence of nanodimensional Fe 3O 4 in solid state at ∼65 °C and a nanocomposite of poly N-vinyl carbazole with Fe 3O 4 (PNVC–Fe 3O 4) was isolated. This composite was further modified by encapsulation with polypyrrole (PPY) via oxidative polymerization of pyrrole in an aqueous dispersion of the PNVC–Fe 3O 4 composite in the presence of potassium persulfate (KPS). The presence of PNVC and of PPY in the PPY–PNVC–Fe 3O 4 composite was confirmed by FTIR spectroscopic analyses. TGA and DTA analyses showed the overall thermal stability trend as: Fe 3O 4 > PNVC–Fe 3O 4 > PPY–(PNVC–Fe 3O 4) > PNVC. HRTEM images revealed that the PPY–(PNVC–Fe 3O 4) nanocomposites have an average grain size of ≈37 nm in good agreement with the values estimated from XRD data. SEM analysis indicated the preponderance of spherical particles embedded in the matrix. The dielectric constants of PNVC–Fe 3O 4 and the PPY–Fe 3O 4 systems were low (110–400) whereas the PPY encapsulated PNVC–Fe 3O 4 nanocomposites showed significantly higher values of dielectric constant (>1000), suggested that the interfaces between grain and grain boundary of the composite play a dominant role for enhancing dielectric properties of the system. Relaxation behaviors for the nanocomposite system were explained considering Maxwell–Wagner two-layered dielectric models. The ac conductivity was found to be independent on frequency in the range 10 2–10 3 Hz for all the nanocomposites implying contribution of free charges and rise thereafter appreciably in the frequency range of 1–25 kHz due to trapped charges in the grain boundary.