Dielectric and microstructure properties of polymer carbon black composites

Abstract

Dielectric and physicochemical properties of a composite material prepared by incorporating carbon black particles into a polymer matrix were investigated. Two types of carbon blacks, having very different structures of aggregates, were used. The volume fraction of the carbon blacks ranged from 0.2% to 7%, i.e. below and above the percolation threshold concentration observed from the measurements of dc conductivity. The composite samples were characterized in terms of: swelling by a compatible solvent, electron paramagnetic resonance (EPR) response, and frequency variation of permittivity. First, the article attempts to evaluate the diffusion coefficient of an appropriate solvent in these materials. Sorption kinetics experiments with toluene indicate that the initial uptake of solvent exhibits a square root dependence in time as a consequence of Fick’s law and permit to evaluate the effective diffusion coefficient in the range 10−11–10−12 m2 s−1 depending on the volume fraction of the carbon black in the sample. Second, the analysis of the carbon black concentration dependence of the intensity and linewidth of the EPR signals indicates that EPR is an important experimental probe of the structure of the elasticity network. The most notable feature of the present work is that we find a correlation of the percolation threshold concentration which is detected from the dc electrical conductivity with moments of the EPR lines. The conclusions on the elasticity networks deduced from swelling measurements are confirmed by EPR data carried out on swollen samples. On qualitative grounds the role of the specific surface of carbon black is further analyzed. It is suggested that the elasticity network is mainly controlled by secondary (respectively primary) aggregates for samples containing low (respectively high) specific surface carbon blacks. Last, the article reports precise experimental data on the permittivity of these composite materials as a function of frequency. Thanks to a sensitive measurement technique using an impedance analyzer, we are able to measure the complex permittivity and permeability values of the samples in the frequency range from 108 to 1010 Hz. It is found that the real part of the permittivity is a function of frequency f, via a power law expression ε′=af−b, where a and b are two parameters depending upon carbon black concentration, in the range of frequency investigated. The data analysis reaffirms the result that percolation threshold is a key parameter for characterizing the topological arrangement in these structures.

Flexible microwave absorbers based on barium hexaferrite, carbon black, and nitrile rubber for 2–12 GHz applications

“…39 There are numerous reports in the context of CB and polymer composite with very good absorbing properties. [14][15][16][17][18][19][20][21][22][40][41][42][43] Here, the enhancement of impedance matching, absorption bandwidth, and mechanical properties by incorporating an optimum amount of barium hexaferrite along with CB is examined.…”

“…For example, Brosseau et al carried out systematic investigations on composite materials by impregnating CB and other carbonaceous material in various matrices. [14][15][16][17][18][19][20][21][22] They also evaluated the microwave absorbing properties of composite materials by incorporating magnetic fillers in non magnetic matrices. [23][24][25] We carried out extensive investigation on composites containing magnetic and nonmagnetic fillers in various rubber matrices [26][27][28][29][30][31][32] and very recently on rubber-hexaferrite-carbon black (CB) composite with strontium hexaferrite (SrF) as the magnetic component.…”

Dielectric and magnetic properties of YIG/PMMA nanocomposites

“…Interfacial polarization is the result of the heterogeneity of the system, such as mobile charges accumulated at the fillers-polymer matrix interface, form large dipoles. Recently, adding conductive fillers (with infinitively large ε) into polymer was reported on preparation of high ε composites [12][13][14][15][16][17], but the insulating properties of the composites will be reduced in this case. So, the inorganic fillers with super high ε should be the key consideration in obtaining higher ε composites with integrative properties needed in practical applications.…”

Induced displacive transition in heterogeneous materials

“…On one hand, these materials have a wide range of applications, such as shielding enclosures, electromagnetic absorbants, antistatic devices, capacitive memory disks, etc. [10]. On the other hand, there are many theoretical investigations devoted to the effective electric susceptibility of such materials [11][12][13][14][15][16].…”