Dielectric spectroscopy of melt-extruded polypropylene and as-grown carbon nanofiber composites.

In this work, different weight contents of as-grown carbon nanofibers (CNFs), produced by chemical vapor deposition, were melt-extruded with polypropylene (PP) and their morphologic, structure and dielectric properties examined. The morphologic analysis reveals that the CNFs are randomly distributed in the form of agglomerates within the PP matrix, whereas the structural results depicted by Raman analysis suggest that the degree of disorder of the as-received CNFs was not affected in the PP/CNF composites. The AC conductivity of PP/CNF composites at room temperature evidenced an insulator-conductor transition in the vicinity of 2 wt.%, corresponding to a remarkable rise of the dielectric permittivity up to [Formula: see text] 12 at 400 Hz, with respect to the neat PP ([Formula: see text] 2.5). Accordingly, the AC conductivity and dielectric permittivity of PP/CNF 2 wt.% composites were evaluated by using power laws and discussed in the framework of the intercluster polarization model. Finally, the complex impedance and Nyquist plots of the PP/CNF composites are analyzed by using equivalent circuit models, consisting of a constant phase element (CPE). The analysis gathered in here aims at contributing to the better understanding of the enhanced dielectric properties of low-conducting polymer composites filled with carbon nanofibers.

Analysis of the dielectric relaxation in reduced graphene oxide/epoxy composites materials using the modulus formalism.

This work reports an analysis of the dielectric properties of reduced graphene oxide mixed into epoxy resin, diglycidyl ether of bisphenol A, in the frequency range 10[Formula: see text]-10[Formula: see text] Hz and over the temperature range of 300-400 K, using impedance spectroscopy. For this study, a series of samples were prepared with various filler contents. Using the electric modulus formalism, it has been found that these composites exhibit below and above the percolation threshold [Formula: see text] a critical behavior of the dielectric relaxation phenomenon due to the single [Formula: see text]-relaxation, which is associated with the glass-rubbery transition of the epoxy matrix above the glass transition temperature. The Cole-Cole model of dielectric relaxation was used for modeling the relaxation processes from which we extract the relaxation parameters. The obtained relaxation parameters suggest a behavior close to single relaxation time.