Electrical transport properties of graphite sheets doped polyvinylidene fluoride nanocomposites
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Graphite nanosheets (GNs) were introduced into polyvinylidene fluoride (PVDF) via the solution mixing technique. The nanocomposites were then subjected to compression molding for electrical measurements. Solution mixing enabled homogeneous dispersion of GN within the PVDF matrix. The electrical transport behavior of such nanocomposites was studied by means of the impedance spectroscopy in a wide frequency range from 102 to 107 Hz. The results showed that the permittivity and conductivity of the composites are frequency dependent and well obeyed with the scaling law (e0 / ou and s0 / ov) in the vicinity of percolation threshold (Fc 2.5 wt%). A large dielectric constant of 173 was observed in the PVDF/GN 2.5 wt% composites at 1 kHz.
I. INTRODUCTION
Electrical percolation in mixtures of insulating polymers with conducting components has received considerable attention of materials scientists.1,2 One of the attractive properties is the unusual electrical transport behavior near the percolation threshold (Fc). A great enhancement in electrical conductivity and permittivity is observed near the insulator–conductor transition. In general, the sharp increase in conductivity is either caused by the formation of conducting path network or by the tunneling conduction.3,4 The abrupt enhancement in permittivity can be interpreted in terms of minicapacitor effect in which many charge carriers are trapped at the interfaces of composites.5,6 Recently, polymer nanocomposites filled with conducting components for embedded capacitor applications have triggered worldwide attention due to their good processability, low cost, and low-dielectric loss.7,8 Polyvinylidene fluoride (PVDF) is generally known to possess high piezoelectric coefficient, excellent thermal stability, and chemical resistance. Graphite nanosheet (GN), a kind of two-dimensional material with large aspect-ratio, maintains good electrical conductivity of 104 S/cm at room temperature. As a novel conducting filler, GNs have been successfully introduced into various polymer matrixes at low threshold concentrations.3,9 For instance, a low percolation threshold of 0.31 vol% can be achieved in the polymethyl methacrylate (PMMA)/ NanoG composites prepared by in situ polymerization.9 It is believed that GN additions are also beneficial in enhancing the permittivity of polymers. Accordingly, we
prepared the PVDF/GN nanocomposites via the solution mixing technique. The structure and electrical properties of the resulting composites were studied. II. EXPERIMENTAL
PVDF (Kynar 740) was purchased from Atofina Chemicals Inc., Philadelphia, PA. Graphite nanosheets with a large aspect ratio of 250 was supplied from Chen’s Lab and its fabrication procedure was described elsewhere.9 The mixture of N,N-Dimethylformaide (DMF; SigmaAldrich, St. Louis, MO, 99%) and acetone (ACS reagent, Sigma-Aldrich, 99.5%) with a ratio of 2:1 (v/v) was used as solvent. PVDF/GN nanocomposites containing different GN contents were prepared via the solution casting method. Briefly, PVDF was initiall
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