Microstructure, dielectric response and electrical properties of polypyrrole modified (poly N-vinyl carbazole–Fe3O4) nanocomposites

N-vinyl carbazole (NVC) was polymerized in the presence of nanodimensional Fe3O4 in solid state at ∼65 °C and a nanocomposite of poly N-vinyl carbazole with Fe3O4 (PNVC–Fe3O4) was isolated. This composite was further modified by encapsulation with polypyrrole (PPY) via oxidative polymerization of pyrrole in an aqueous dispersion of the PNVC–Fe3O4 composite in the presence of potassium persulfate (KPS). The presence of PNVC and of PPY in the PPY–PNVC–Fe3O4 composite was confirmed by FTIR spectroscopic analyses. TGA and DTA analyses showed the overall thermal stability trend as: Fe3O4 > PNVC–Fe3O4 > PPY–(PNVC–Fe3O4) > PNVC. HRTEM images revealed that the PPY–(PNVC–Fe3O4) 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–Fe3O4 and the PPY–Fe3O4 systems were low (110–400) whereas the PPY encapsulated PNVC–Fe3O4 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 102–103 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.

► PNVC–Fe3O4 nanocomposites are prepared by in situ solid state polymerization.
► Encapsulated nanocomposite with polypyrrole shows enhanced dielectric constants.
► Fe3O4 nanoparticles are fairly well-dispersed in the composite matrix.
► Grain boundary contribution of dielectric properties is dominant in nanocomposite.