GRAPHENE NANOPLATELETS- OR GRAPHITE NANOPLATELETS-BASED NANOCOMPOSITES FOR REDUCING ELECTROMAGNETIC INTERFERENCES

• US 20150305212A1
• Filed: 10/16/2013
• Published: 10/22/2015
• Est. Priority Date: 10/16/2012
• Status: Active Grant

• Current Assignee: Universita' Degli Studi Di Roma La Sapienza (Repubblica Italiana)
• Original Assignee: Universita' Degli Studi Di Roma La Sapienza (Repubblica Italiana)
• Inventors: SARTO, Maria Sabrina, DE BELLIS, Giovanni, TAMBURRANO, Alessio, D'ALOIA, Alessandro Giuseppe
• Granted Patent: US 9,717,170 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: B82Y 99/00 Subject matter not provided for in other groups of this subclass
• CPC Class Codes: C01B 32/182 Graphene
• CPC Class Codes: H01B 1/24 the conductive material comprising carbon-silicon compounds, carbon or silicon
• CPC Class Codes: H01Q 17/00 Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
• CPC Class Codes: H05K 9/0083 comprising electro-conductive non-fibrous particles embedded in an electrically insulating supporting structure, e.g. powder, flakes, whiskers H05K9/0086 takes precedence
• CPC Class Codes: Y10S 977/734 Fullerenes, i.e. graphene-based structures, such as nanohorns, nanococoons, nanoscrolls or fullerene-like structures, e.g. WS2 or MoS2 chalcogenide nanotubes, planar C3N4, etc.

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.

Claims

1-24. -24. (canceled)

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:

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.

26. The process for producing polymeric nanocomposites as per claim 25, characterized in that said GNPs are constituted by thin lamellae of graphene sheets set on top of one another in a number ranging from 1 to 70 with thicknesses comprised between 0.335 nm and 25 nm with lateral dimensions ranging from 0.5 μ

m to 25 μ

m, and in that said GNPs are present in the polymeric matrix at a variable concentration, typically lower than 20 wt %.

27. The process for producing polymeric nanocomposites as per the claim 25, characterized in that GNPs are produced by thermochemical exfoliation of graphite intercalated compound (GIC), which involves liquid-phase exfoliation of thermally expanded graphite using as solvent acetone or DMF, or an appropriate mixture of the two in amounts indicatively ranging between 5 and 15 parts out of 100 of DMF, and accordingly between 95 and 85 parts out of 100 of acetone, and preferably in the ratio DMF:

Acetone of 1;

9.

28. The process for producing polymeric nanocomposites as per claim 25, characterized in that the polymeric matrices that can be used for the formulations are thermosetting polymers, such as epoxy resins, phenolic resins, amide resins, polyurethane resins, unsaturated polyester resins, silicone resins, alkyl resins, and vinyl ester resins, or thermoplastic polymers, such as polyolefin polymers, amongst which polypropylene, polyethylene, polystyrene, and polyurethanes, or thermoplastic resins, amongst which acrylic resins, polycarbonates, and fluoropolymers.

29. The process as per claim 25, characterized in that the choice of the expansion temperature of GIC on the basis of the desired electrical properties of the GNPs is made using the regression line

R=−

0.0002 T+0.3357

where T is expressed in degrees centigrade and R in ohms, said regression line expressing analytically, as a function of the expansion temperature, the resistance of the GNP films measured using the four-tip technique;

said regression line being obtained by interpolation of experimental data.

30. The process as per claim 25, characterized in that the choice of the rate of expansion of GIC on the basis of the desired electrical properties of the GNPs, is made using the regression line

R=−

4.10<sup>−

6</sup> r+0.1646

where r is expressed in degrees centigrade per minute and R in ohms;

said regression line being obtained by interpolation of experimental data.