GRAPHENE NANOPLATELETS- OR GRAPHITE NANOPLATELETS-BASED NANOCOMPOSITES FOR REDUCING ELECTROMAGNETIC INTERFERENCES
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Abstract
A process for producing GNP-based polymeric nanocomposites for electromagnetic applications such as shielding and/or absorption of the energy associated to electromagnetic fields envisages a plurality of steps that include: controlled synthesis, for optimizing the morphological and electrical properties thereof, of graphene nanoplatelets (GNPs) to be used as nanofillers in a polymeric matrix; selection of the polymeric matrix so as to optimize its chemical compatibility with the type of GNPs thus obtained; production via the solution-processing technique of GNP-based polymeric nanocomposites with dielectric permittivity and electric conductivity controlled and predictable via the equivalent-effective-medium model by calibrating the parameters of the model for the specific type of polymeric matrix and GNPs used.
16 Citations
30 Claims
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1-24. -24. (canceled)
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25. A process for producing a polymeric nanocomposite with electrical and electromagnetic properties controlled and predictable by applying the equivalent-effective-medium model, for electromagnetic applications such as shielding and/or absorption of the energy associated to electromagnetic fields, characterized in that it envisages the following steps:
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a) carrying out a controlled synthesis of graphene nanoplatelets (GNPs) through liquid phase exfoliation of thermally expanded graphite (TEGO), modifying, through the parameters of the production process, the morphological and electrical properties thereof, said parameters of the production being; i) temperature-to-time expansion rate higher than 2000 °
C./min and up to 45000 °
C./min;ii) dispersion of TEGO in organic solvents or their appropriate mixture matching Hansen'"'"'s solubility parameters of graphite; iii) Sonication with ultrasound tip at controlled power (in the range 20%-100%, and preferably 70%), in pulse mode (between is ON-2 s OFF and 4 s ON-is OFF, and preferably 2s ON-is OFF with total ON time of 20 min), at controlled temperature (well below the boiling point of the solvent, typically in the range 14°
C.-20°
C., and preferably at 15°
C.) in order to keep the ultrasound tip in conditions of resonance throughout the duration of the process.b) using said graphene nanoplateletes (GNPs) as nanofillers in a polymeric matrix selected on the basis of its chemical compatibility with the GNPs themselves, distributing them evenly and dispersing them finely in the entire mass of the matrix in a specific weight percentage through an appropriate process of mixing consisting of a particular magnetic stirring technique which imparts on the magnetic anchor a motion of revolution in addition to a rotation around its own axis so as to prevent formation of GNP aggregates in the mixture during the complete solvent evaporation, envisaging; i) the control of the solvent evaporation rate (in the range 0.05-0.2 ml/min depending on GNPs concentration, and corresponding to a total duration between 0.5 and 24 h) in order to avoid formation of GNP aggregates and trapping of molecules of solvent in the nanocomposite ii) the use of an appropriate device designed to impart on the magnetic anchor a motion of revolution in addition to the rotation around its own axis in order to avoid formation of GNP aggregates and to obtain finely dispersion of the nanofiller in the polymer matrix. wherein said mixing process, preventing aggregate formation, allows to obtain a nanocomposite in which the imaginary part of the effective permittivity is controlled independently of the real part through the nanometric thickness of the filler, which activates the electron transport between filler and polymer matrix, whereas the real part of the effective permittivity is controlled independently of the imaginary part through the micrometer surface extension of the GNPs themselves, which affects the properties of polarization of the material but not its electrical conductivity. - View Dependent Claims (26, 27, 28, 29, 30)
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