Dispersion and spatial distribution of graphene sheets play crucial roles in tailoring mechanical and functional properties of their polymer composites. Anisotropic graphene aerogels (AGAs) with highly aligned graphene networks are prepared by a directional-freezing followed by freeze-drying process and exhibit different microstructures and performances along the axial (freezing direction) and radial (perpendicular to the axial direction) directions. Thermal annealing at 1300 °C significantly enhances the quality of both AGAs and conventional graphene aerogels (GAs). The aligned graphene/epoxy composites show highly anisotropic mechanical and electrical properties and excellent electromagnetic interference (EMI) shielding efficiencies at very low graphene loadings. Compared to the epoxy composite with 0.8 wt % thermally annealed GAs (TGAs) with an EMI shielding effectiveness of 27 dB, the aligned graphene/epoxy composite with 0.8 wt % thermally treated AGAs (TAGAs) has an enhanced EMI shielding effectiveness of 32 dB along the radial direction with a slightly decreased shielding effectiveness of 25 dB along the axial direction. With 0.2 wt % TAGA, its epoxy composite exhibits a shielding effectiveness of 25 dB along the radial direction, which meets the requirement of ∼20 dB for practical EMI shielding applications.Keywords: anisotropic graphene aerogel; directional freezing; electrical conductivity; electromagnetic interference shielding; epoxy;

To enhance the mechanical properties of three-dimensional graphene aerogels with aramid fibers, graphene/organic fiber aerogels are prepared by chemical reduction of graphene oxide in the presence of organic fibers of poly(p-phenylene terephthalamide) (PPTA) and followed by freeze-drying. Thermal annealing of the composite aerogels at 1300 °C is adopted not only to restore the conductivity of the reduced graphene oxide component but also to convert the insulating PPTA organic fibers to conductive carbon fibers by the carbonization. The resultant graphene/carbon fiber aerogels (GCFAs) exhibit high electrical conductivities and enhanced compressive properties, which are highly efficient in improving both mechanical and electrical performances of epoxy composites. Compared to those of neat epoxy, the compressive modulus, compressive strength and energy absorption of the electrically conductive GCFA/epoxy composite are significantly increased by 60%, 59% and 131%, respectively.

Three dimensional reduced graphene oxide (RGO)/Ni foam composites are prepared by a facile approach without using harmful reducing agents. Graphene oxide is reduced by Ni foam directly in its aqueous suspension at pH 2 at room temperature, and the resultant RGO sheets simultaneously assemble around the pillars of the Ni foam. The RGO/Ni foam composite is used as a binder-free supercapacitor electrode and exhibits high electrochemical properties. Its areal capacitance is easily tuned by varying the reduction time for different RGO loadings. When the reduction time increases from 3 to 15 days, the areal capacitance of the composite increases from 26.0 to 136.8 mF cm–2 at 0.5 mA cm–2. Temperature is proven to be a key factor in influencing the reduction efficiency. The composite prepared by 5 h reduction at 70 °C exhibits even better electrochemical properties than its counterpart prepared by 15 day reduction at ambient temperature. The 5 h RGO/Ni foam composite shows an areal capacitance of 206.7 mF cm–2 at 0.5 mA cm–2 and good rate performance and cycling stability with areal capacitance retention of 97.4% after 10000 cycles at 3 mA cm–2. Further extending the reduction time to 9 h at 70 °C, the composite shows a high areal capacitance of 323 mF cm–2 at 0.5 mA cm–2. Moreover, the good rate performance and cycling stability are still maintained.Keywords: binder-free; electrochemical performance; graphene oxide; Ni foam; supercapacitor electrode

•Phase change composites show high thermal conductivity, good shape stability and large latent heat of fusion.•Cellulose/graphene nanoplatelet (GNP) aerogel benefits the encapsulation of polyethylene glycol and prevents its leakage.•Highly porous cellulose network and low loading of defect-free GNPs are responsible for the high latent heat of fusion.As phase change composites, high thermal conductivity, large latent heat of fusion and good shape stability are all required for practical applications. By combining defect-free graphene nanoplatelets (GNPs) and microcrystalline cellulose, lightweight cellulose/GNP aerogels are fabricated and their highly porous but strong three-dimensional networks benefit the encapsulation of polyethylene glycol (PEG) and prevent the leakage of PEG above its melting point. Phase change composites are prepared by vacuum-assisted impregnating of PEG into the cellulose/GNP aerogels, which exhibit high thermal conductivity, good shape stability and high latent heat of fusion. Even compressed upon the melting point of PEG, the phase change composites keep their shapes stable without any leakage. With only 5.3 wt% of GNPs, the composite exhibits a high thermal conductivity of 1.35 W m−1 K−1, 463% higher than that of the composite without GNPs. The highly porous cellulose network and the low loading of highly thermally conductive GNPs are responsible for the high loading of PEG in the composite with a satisfactory latent heat of fusion of 156.1 J g−1.

Three dimensional (3D) graphene aerogel was prepared by in situ reduction-assembly method. Paraphenylene diamine (PPD) was used as reducing and functionalizing agent of graphene oxide in an aqueous medium with ammonia. The synthesized 3D graphene-PPD aerogel has highly porous structure, low density, high electrical conductivity and good mechanical properties. Further, epoxy/aerogel composites were prepared by vacuum-assisted impregnation process, which exhibited good electrical conductivity and compressive properties.

Graphene oxide was reduced and functionalized simultaneously by reacting with 3-aminopropyltriethoxysilane (APTES) without the use of conventional reducing agents. Silica was subsequently formed in situ on APTES functionalized graphene (A-graphene) sheets by a sol–gel approach using tetraethyl orthosilicate as the precursor of silica. The covalently bonded APTES on A-graphene enhances the compatibility between A-graphene and silica nanoparticles. The silica-coated A-graphene (S-graphene) sheets were incorporated to improve the thermal conductivity of epoxy. The presence of silica nanoparticles not only enhances the interfacial interaction between S-graphene and the epoxy matrix, but also alleviates the modulus mismatch between the fillers and the matrix and thus benefits the interfacial thermal conductance. The thermal conductivity of the epoxy nanocomposite with 8 wt% S-graphene is improved by 72% in comparison with that of neat epoxy, while the electrically insulating feature of the nanocomposite is retained.

To simultaneously improve electrical conductivity and toughness of polyamide 6 (PA 6), carbon black (CB) nanoparticles and maleic anhydride grafted polyethylene–octene copolymer (POE-g-MA) were compounded with PA 6 by melt compounding, and the influences of CB and POE-g-MA components on the electrical conductivity and mechanical properties of PA 6 nanocomposites were investigated. The addition of CB improves the electrical conductivity and Young’s modulus of PA 6. With 40 wt % POE-g-MA and 15 wt % CB, the nanocomposite exhibits a high notched impact energy of 73.9 kJ/m2 and an electrical conductivity of 7.1 × 10–6 S/m. Interestingly, the presence of POE-g-MA reduces the electrical percolation threshold of the PA 6 nanocomposites due to the selective localization of CB in the PA 6 matrix. Compared to PA 6/CB binary nanocomposites, the ternary nanocomposites exhibit both higher electrical conductivity and supertoughness.

Simultaneous reduction and surface functionalization of graphene oxide (GO) was achieved by refluxing GO with a diamine, polyetheramine (D230) at 95 °C followed by thermal treatment at 120 °C. The D230-treated GO (GO-D230) exhibits a high electrical conductivity of 1.0 S/m, much higher than that of GO, due to the chemical and thermal reduction. The incorporation of GO-D230 significantly improves the electrical conductivity of epoxy, exhibiting a sharp transition from electrically insulating to conducting with a low percolation threshold of 0.78 vol%. With 2.7 vol% of GO-D230, the electrical conductivity of its epoxy nanocomposite is 1.0 × 10−4 S/m, nearly 11 orders of magnitude higher than that of neat epoxy; meanwhile, compared to the low Young’s modulus and tensile strength of the rubbery epoxy, those of the nanocomposite are increased by 536% and 269%, respectively.