Dielectric properties of upright carbon fiber filled poly(vinylidene fluoride) composite with low percolation threshold and weak temperature dependence

Abstract

Upright carbon fiber (CF) filled ferroelectric poly(vinylidene fluoride) (PVDF) composites were prepared via a simple blending and hot-molding technique. The dielectric properties of the CF/PVDF composites as a function of the volume fraction of CF, the temperature, and the frequency were studied. The dielectric constants decrease slowly with increasing frequency and rise gradually with increasing CF contents in the composites. As the volume fraction of the CF is up to 0.074, an abrupt increase in the dielectric constant occurs, which is attributed to the formation of the conductive network in the matrix. The percolation theory, the microcapacitor model, and the simple concept of polarization in the capacitors are employed to explain these experimental results.

Two percolation thresholds and remarkably high dielectric permittivity in pristine carbon nanotube/elastomer composites

“…1d), considering the percolation threshold at 0.07, also suggests a decrease in the dielectric permittivity of the composites with increase in filler concentration in the post-percolation threshold region. This theoretical outcome of post-percolation threshold trend of monotonic decrease in dielectric values of practical CNT/polymer composites has been reported in previous reports (Dang et al 2007a;Wang and Dang 2005). The mechanism of this decrease is that in the post-percolation region, composites become conductors and resultantly have a large leakage current that destroys the dielectric properties of the composites.…”

High Dielectric Permittivity and Low Percolation Threshold in Nanocomposites Based on Poly(vinylidene fluoride) and Exfoliated Graphite Nanoplates

“…[4,9,[11][12][13][14][15][16] For example, Dang et al [9] fabricated a new poly(vinylidene fluoride)/carbon-nanotube composite, with a percolation threshold of 8 vol%, possessing a dielectric constant of 600 (the dielectric loss value, tan d, is about 2) at 1000 Hz. For a P(VDF-TrFE-CFE)/carbon-nanotube system, the dielectric constant increased from 57 to 102 (tand % 0.36) at 100 Hz, by inclusion of only 2 wt% (1.2 vol%) carbon nanotubes.…”

“…[9] The significant increment in dielectric constant of PVDF/ xGnP nanocomposites can be mainly attributed to the homogenous dispersion of xGnPs in the PVDF polymer matrix and a gradual formation of the microcapacitor networks in the PVDF/ xGnP nanocomposites as the xGnP content increases. [9,12] The evolution process of the dielectric constant in PVDF/xGnP nanocomposites with the change of xGnP content can be divided into three stages (I, II, and III). Initially, as shown in part I of Figure 4, when a small amount of xGnPs is incorporated into the PVDF matrix, some microcapacitance structures are formed, resulting in a slight increase of dielectric constant relative to that of pure PVDF.…”

A Study of Radar Features of Wind Turbines in the Hf Band

“…The material is assumed to be carbon fiber and the real part of the relative permittivity is taken to be 20 while the imaginary part is 0.15 [24]. Figures 12(a) and (b) show the frequency responses for respectively the dielectric and PEC cases from 10 to 20 MHz.…”