The effect of the C/O ratio of graphene oxide materials on the reinforcement and rheological percolation of epoxy-based nanocomposites has been studied. As-prepared graphene oxide (GO) and thermally-reduced graphene oxide (TRGO) with higher C/O ratios were incorporated into an epoxy resin matrix at loadings from 0.5 to 5 wt %. Tensile testing revealed good reinforcement of the polymer up to optimal loadings of 1 wt %, whereas agglomeration of the flakes at higher loadings caused the mechanical properties of the composites to deteriorate. The level of reduction (C/O) of the graphene oxide filler was found to influence the mechanical and rheological properties of the epoxy composites. Higher oxygen contents were found to lead to stronger interfaces between graphene and epoxy, giving rise to higher effective Young's moduli of the filler and thus to superior mechanical properties of the composite. The effective modulus of the GO in the nanocomposites was found to be up to 170 GPa. Furthermore, rheological analysis showed that highly oxidized graphene flakes did not raise the viscosity of the epoxy resin significantly, facilitating the processing considerably, of great importance for the development of these functional polymeric materials.

Electromagnetic interference (EMI) shielding coating materials with thicknesses in the microscale are required in many sectors, including communications, medical, aerospace and electronics, to isolate the electromagnetic radiation emitted from electronic equipment. We report a spray, layer-by-layer (LbL) coating approach to fabricate micron thick, highly-ordered and electrically-conductive coatings with exceptional EMI shielding effectiveness (EMI SE ≥4830 dB/mm), through the alternating self-assembly of negatively-charged reduced graphene oxide (RGO) and a positively-charged polyelectrolyte (PEI). The microstructure and resulting electrical properties of the (PEI/RGO) n LbL structures are studied as function of increasing mass of graphene deposited per cycle (keeping the PEI content constant), number of deposited layers (n), flake diameter and type of RGO. A strong effect of the lateral flake dimensions on the electrical properties is observed, which also influences the EMI SE. A maximum EMI SE of 29 dB is obtained for a 6 μm thick (PEI/RGO) 10 coating with 19 vol.% loading of reduced electrochemically-exfoliated graphene oxide flakes with diameters ~3µm. This SE performance exceeds those previously reported for thicker graphene papers and bulk graphene/polymer composite films with higher RGO or graphene nanoplatelets contents, which represents an important step towards the fabrication of thin and light-weight high-performance EMI shielding structures.performance. 6, 7, 9,12,13 Carbon-based materials have been investigated as conductive fillers to fabricate composite materials for EMI shielding because they offer a combination of high electrical conductivity, excellent mechanical properties, light weight, flexibility and large aspect ratios. [6][7][8][9][10][11][12][13][14][15][16][17] In particular, graphene emerges as highly promising for EMI shielding applications due to its excellent in-plane electrical conductivity (∼4.5 × 10 4 S/cm) 14, 18-20 and easy processability. 21 Graphene-based polymer composites, foam structures, aerogels, thin films and papers have already been investigated as light-weight EMI shielding materials. 2, 22-30 An EMI SE ~500 dB·cm 3 /g was reported for a graphene foam composite with a density ~0.06 g/cm 3 , 2 and ~33780 dB·cm 2 /g for ultralight cellulose fiber/thermally reduced GO hybrid aerogels, with a density as low as 2.83 mg/cm 3 . 22 More recently, EMI SE of 21.8 dB have been reported for thermoplastic polyurethane/reduced graphene oxide composite foams with only 3.17 vol.% of RGO 27 , whereas EMI SE of 48.56 dB has been found for 3D-interconnected graphene aerogels decorated with cobalt ferrite nanoparticles and ZnO nanorods 28 . Graphene papers with thicknesses between 12.5 and 470 µm 23, 24 and ~30-60 µm thick graphene/polymer composites 25,26 were also investigated as EMI shielding materials. Wan et al. reported EMI SE of up to ~52.2 dB for iodine doped and ~47 dB for 12.5 µm thick undoped reduced GO papers 23 , whereas EMI SE ~55.2 dB was reported for 0.47 mm thick multila...

Metal-fluoride nanoparticles, (MFx-NPs) with M = Fe, Co, Pr, Eu, supported on different types of thermally reduced graphite oxide (TRGO) were obtained by microwave-assisted thermal decomposition of transition-metal amidinates, (M{MeC[N(iPr)]2}n) or [M(AMD)n] with M = Fe(II), Co(II), Pr(III), and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium, Eu(dpm)3, in the presence of TRGO in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]). The crystalline phases of the metal fluorides synthesized in [BMIm][BF4] were identified by powder X-ray diffraction (PXRD) to be MF2 for M = Fe, Co and MF3 for M = Eu, Pr. The diameters and size distributions of MFx@TRGO were from (6 ± 2) to (102 ± 41) nm. Energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used for further characterization of the MFx-NPs. Electrochemical investigations of the FeF2-NPs@TRGO as cathode material for lithium-ion batteries were evaluated by galvanostatic charge/discharge profiles. The results indicate that the FeF2-NPs@TRGO as cathode material can present a specific capacity of 500 mAh/g at a current density of 50 mA/g, including a significant interfacial charge storage contribution. The obtained nanomaterials show a good rate capacity as well (220 mAh/g and 130 mAh/g) at a current density of 200 and 500 mA/g, respectively.

Dry ball milling of graphite under carbon dioxide pressure affords multilayer-functionalized graphene (MFG) with carboxylic groups as nanofiller for composites of carbon and acrylonitrile–butadiene–styrene copolymers (ABSs). Produced in a single-step process without requiring purification, MFG nanoplatelets are uniformly dispersed in ABS even in the absence of compatibilizers. As compared to few-layer graphene oxide, much larger amounts of MFG are tolerated in ABS melt processing. Unparalleled by other carbon nanofillers and non-functionalized micronized graphite, the addition of 15 wt % MFG simultaneously results in a Young’s modulus of 2550 MPa (+68%), a thermal conductivity of 0.321 W∙m−1∙K−1 (+200%), and a heat distortion temperature of 99 °C (+9%) with respect to neat ABS, without encountering massive embrittlement and melt-viscosity build-up typical of few-layer graphene oxide. With carbon filler at 5 wt %, the Young’s modulus increases with increasing aspect ratio of the carbon filler and is superior to spherical hydroxyl-functionalized MFG, which forms large agglomerates. Both MFG and micronized graphite hold promise for designing carbon/ABS compounds with improved thermal management in lightweight engineering applications.

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Graphite exfoliation by shear‐induced dry and wet processes and especially mechanochemistry represent attractive routes to carbon nanofillers. Dry ball‐milling of graphite in a planetary mill under gas pressure is a scalable and environmentally benign one‐step process, which requires neither hazardous solvents nor tedious separate functionalization and purification steps. Gas type, pressure, and milling duration govern average particle size, shape, and functionalization. Ball‐milling under Ar yields hydroxylated spherical carbon particle agglomerates, whereas ball‐milling under CO2 affords functionalized nanoplatelets without encountering agglomeration problems and highly exothermic post‐milling reactions with air. The carboxylation of graphene nanoplatelets enhances their dispersibility in various media including polypropylene (PP) even in the absence of compatibilizers. Large amounts of carboxylated nanoplatelets are dispersed in PP without massive viscosity build‐up. Functionalized carbon nanoplatelet fillers enable tailoring of recyclable lightweight carbon/hydrocarbon composites exhibiting an improved balance of stiffness, strength, toughness, electrical, and thermal conductivity.

The two-stage mechanochemical amination of graphite by dry ball milling of graphite in a planetary ball mill under Ar followed by NH 3 yields aminated multilayer graphene (AMFG) as intermediates for carbon/polymer hybrids and nanocomposites. Opposite to efficient edge-selective graphene functionalization under Ar, CO 2 and N 2 pressure, the onestage ball milling under NH 3 pressure affords rather low N content (<0.5 wt%) and fails to reduce the graphite platelet size. According to DFT (Density Functional Theory) calculations NH 3 exhibits low mobility between graphene layers and forms weak bonds to carbon which impair breakage of carbon bonds. In the two-stage ball-milling of graphite under Ar affords reactive carbon nanoparticles which react with NH 3 in the second stage. With increasing milling duration of the second stage the nitrogen content increases to 3.2 wt%. As verified by XPS (X-ray photoelectron spectroscopy) measurements primary amine groups are formed which couple with various dicarboxylic anhydride groups including maleated PP to produce imidefunctionalized graphene. This is of interest to produce compatibilizers and dispersing agents for carbon/PP nanocomposites exhibiting improved mechanical properties. Two-stage mechanochemistry holds promise for carbon nanoparticle functionalization well beyond amination.

Dry ball milling of graphite under CO2 pressure in a planetary ball mill affords carboxylated multilayer graphene nanoplatelets as carbon nanofillers (MFG‐CO2) for carbon/epoxy spray coatings combining electrical conductivity up to 0.09 S cm−1 with excellent adhesion and improved toughness. As confirmed by µCT‐imaging, the two‐stage homogenization by means of a speed mixer with subsequent shearing in a three‐roll mill uniformly disperses up to 60 wt% MFG‐CO2 in aqueous emulsions of epoxy resins and hardener without impairing spray coating. The MFG‐CO2 content governs surface roughness, as determined by 3D laser microscopy, gloss, electrical conductivity, and toughness without adversely affecting excellent adhesion. Mechanochemical tailoring MFG nanofillers holds great promise for the development of advanced epoxy spray coatings exhibiting an improved balance of thermooxidative, chemical and environmental stability, electrical and thermal conductivity, toughness, corrosion, and barrier resistance.