F. Carmona

Bio: F. Carmona is an academic researcher from University of Bordeaux. The author has contributed to research in topics: Dielectric & Epoxy. The author has an hindex of 2, co-authored 2 publications receiving 9 citations.

Microwave Propagation in Random Particulate Composites

Abstract: Etude du materiau composite noir de carbone-resine epoxy. Mesure de la constante dielectrique a 35 GHz. La theorie originale de la percolation n'est pas applicable aux hyperfrequences. Le concept d'une permittivite complexe effective est peut-etre sans signification pour ces materiaux

Microwave properties of carbon black–epoxy resin composites and their simulation by means of mixture laws

Abstract: This article reports on a study of the dielectric properties of carbon black dispersions in an insulating epoxy matrix at microwave frequencies. Measurements showed that the complex permittivity of the composites depends strongly on the nature and concentrations of the conducting medium. The experimental values of the complex permittivity were compared to those obtained by using different mixing laws. We show that effective medium theories correctly account for the experimental results at low conducting particle concentrations. At concentrations higher than a few percent, these laws fail to interpret experimental results and all tentative results must take into account parameters such as the particle size, their distribution, and the existence of agglomerates. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 969–973, 1999

Microwave propagation through carbon black-epoxy resin composites

Abstract: Research that has been recently carried out on t h e dielectric behaviour of conductor-insulator composite systems in the microwave domain has shown that the complex permivitty e* = e ' j e " depends strongly on the nature and the concentration of the conducting medium [1-4]. The dielectric permittivity of the samples has been calculated from the experimental determination of reflection and transmission coefficients of electromagnetic waves. The experimental values of complex permittivity in these media are in disagreement with the provisions of effective medium theory [5]. This is due to the fact that this theory does not take into account the formation of clusters of particles in contact which is revealed by d.c. electrical conductivity measurements [6-8]. This disagreement has also been observed for high volumetric concentrations of conducting medium in the visible and infrared regions [9-11]. Measurements performed as a function of sample thickness of carbon black (Monarch 700)--epoxy for different concentrations of conducting medium show that the measured reflection coefficient agrees with that calculated for an equivalent homogeneous medium. However, the calculated transmission coefficient differs significantly from the calculated value [12]. Such anomalies lead us to wonder about the validity of the concept of effective permittivity, which is supposed to represent, as is generally admitted, heterogeneous medium behaviour when particle size is much smaller than sample size and wavelength. The electrical properties of heterogeneous media, which are constituted of pure dielectrics or conductors, are perfectly defined by mixture formulae [13-16]. In the case of conductor-insulator composite systems, these properties are strongly related to the inclusion size and to their shape [17, 18]. Accordingly, propagation laws which intervene in diffraction of the incident wave by the medium, answer some of the questions relating to mixtures by defining a complex propagation constant but not an equivalent permittivity [19-21]. This work is particularly interested in the different

Temperature effect on dielectric properties of carbon black filled epoxy polymer composites

Abstract: The complex permittivity of carbon black/epoxy composites containing different amounts of conductive carbon black particles was reported in the frequency range 100 Hz-15 MHz and over the temperature range 23-80◦C. The shape of experimental spectra of these heterogeneous media gives evidence of a typical dielectric relaxation process below the threshold percolation. The temperature dependence of the dielectric response has been analysed below and at near the epoxy glass transition temperature (Tg∼=80◦C), for various carbon concentrations. Jonscher's phenomenological model has been used for modelling this relaxation process. The activation energy, deduced from Arrhenius equation, is found to be insensitive to the carbon black concentration. This behavior is discussed in term of the interfacial interaction between the carbon particles and the polymer. Besides, the increase of both parts of the complex permittivity with increasing the carbon black concentration and the temperature is compared to the recently proposed Shin's mixture law.

Dielectric Properties of Carbon Black–Epoxy Resin Composites Studied with Impedance Spectroscopy*

Abstract: Dielectric properties of carbon black-epoxy resin composites were studied in the frequency range between 100 Hz and 15 MHz and over a temperature range 23-98°C. The results show that the composites exhibit, below the critical concentration, a dielectric relaxation phenomenon due to dipolar groups of expoxy resin and to interfacial polarization. This relaxation phenomenon was modeled by the Cole-Cole model.

Modeling microwave dielectric properties of polymer composites using the interphase approach

Abstract: The electrical properties of heterogeneous materials are closely related to the composition of its constituents. Several theoretical approaches have been developed to predict the complex permittivity of composites materials, such as the mixture laws and the effective medium theories. However, these laws fail to interpret experimental data at high concentrations of filler, because the morphological parameters such as particle size, their distribution, and mostly the interphase region between the components are not taken into account. A new model for predicting the complex permittivity of composite materials is presented, taking into account the interaction between the filler and the matrix. We report a study on the dielectric properties of the epoxy polymer/carbon black nanocomposites, with different concentrations of the dispersed conducting particles, at 35 GHz, using the interphase model. The experimental results of the complex permittivity are compared to those obtained by the proposed theoreti...