Graphite nanoplatelets (GNPs) are bidimensional carbon nanostructures consisting of stacks of graphene sheets, having thickness in the range from one up to a few tens of nanometers, and lateral linear dimension in the micrometer range. These nanostructures represent a good candidate to replace carbon nanotubes in composites for electromagnetic applications. This paper proposes a new model based on the Maxwell-Garnett approach to compute the effective complex permittivity of GNP-filled nanocomposites. The effect of the dimensional probabilistic distribution of the nanofiller is investigated. To this purpose, an extensive experimental characterization of the morphological and physical properties of the GNPs after synthesis is performed. The proposed model is validated by comparison with the measured effective permittivity of GNP-composites with different concentrations, and it is used for the design of radar-absorbing materials in the frequency range 1-18 GHz

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The strain-dependent electrical resistance of polyvinyl ester-based composites filled with different weight fractions of graphene nanoplatelets (GNPs) has been experimentally investigated. The GNP synthesis and nanocomposite fabrication process have been optimized in order to obtain highly homogeneous filler dispersion and outstanding electrical properties. The produced nanocomposites showed a low percolation threshold of 0.226 wt% and electrical conductivity of nearly 10 S m(-1) at only 4 wt% of GNPs. The piezoresistive response of thin nanocomposite laminae has been assessed by measuring the variation of the electrical resistance as a function of the flexural strain in three-point bending tests under both quasi-static monotonic and dynamic cyclic loading conditions. The obtained results showed higher strain sensitivity than traditional metal foil strain gauges or recently investigated carbon-based nanocomposite films.

Development of epoxy or epoxy-based vinyl ester composites with improved mechanical and electromagnetic properties, filled with carbon-based nanomaterials, is of crucial interest for use in aerospace applications as radar absorbing materials at radio frequency. Numerous studies have highlighted the fact that the effective functional properties of this class of polymer composites are strongly dependent on the production process, which affects the dispersion of the nanofiller in the polymer matrix and the formation of micro-sized aggregations, degrading the final properties of the composite. The assessment of the presence of nanofiller aggregation in a composite through microscopy investigations is quite inefficient in the case of large scale applications, and in general provides local information about the aggregation state of the nanofiller rather than an effective representation of the degradation of the functional properties of the composite due to the presence of the aggregates. In this paper, we investigate the mechanical, electrical, and electromagnetic properties of thermosetting polymer composites filled with graphene nanoplatelets (GNPs). Moreover, we propose a novel approach based on measurements of the dielectric permittivity of the composite in the 8-12 GHz range in order to assess the presence of nanofiller aggregates and to estimate their average size and dimensions.

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In recent years, several studies have demonstrated\ud the strong cytotoxicity toward bacteria of graphene-based\ud materials, suggesting their use as antimicrobial agents. The\ud objective of this study was to evaluate the antibacterial activity\ud against Streptococcus mutans, the principal microbiological agent\ud in the etiology of dental caries, of two types of graphene\ud nanoplatelets (GNPs), characterized by different thickness and\ud lateral dimensions of the flakes. The antimicrobial properties of\ud GNPs were valued on some plaque and saliva samples extracted\ud from children with dental caries. Our results show that the\ud killing effect of GNPs on S. mutans cells is both lateral size and\ud thickness dependent. In fact, lower thickness and smaller size\ud GNPs exhibit stronger antibacterial activity than larger and\ud thicker ones. Scanning electron microscopy analysis revealed that\ud GNPs interact strongly with cells. This study suggests that GNPs\ud may be highly effective against S.mutans and therefore caries

This paper investigates the shielding effectiveness properties of different types of carbon fiber reinforced composites (CFRC), typically used aboard air-vehicles, in the frequency range from 100 kHz up to 18 GHz. Both single-layer and multilayer, unidirectional or woven, CFRCs are analyzed, and the critical issue concerning sample preparation is addressed. The study is aimed at defining an effective single layer model of the CFRC laminate, characterized by an effective frequency-dependent electrical conductivity, which is extracted from the measured shielding effectiveness. © 2012 IEEE

A bundle of single wall carbon nanotubes (SWCNTs) with circular cross-section is treated as a homogeneous material with a.c. effective conductivity σ( ω), which is evaluated by using the Drude's complex expression. The effective d.c. conductivity of the homogeneous bundle is obtained from the total d.c. resistance. The frequency-domain distribution of current density along radial direction of the bundle is utilized to obtain the expressions of the skin depth and the effective impedance. Applications of the proposed formulation to SWCNT bundles of different configurations are carried out. The obtained results show the saturation behaviour of the effective resistance and inductance above a critical frequency, which depends on the momentum relaxation time of the CNTs. ©2010 IEEE