Flexural fatigue behavior of synthesized graphene/carbon-nanofiber/epoxy hybrid nanocomposites

In the present research, effects of adding a combination of synthesized graphene nanosheets and carbon nanofibers (CNFs) on the flexural fatigue behavior of epoxy polymer have been investigated. Graphene nanosheets are synthesized based on a changing magnetic field. The flexural bending fatigue life of 0.5 wt.% of graphene/CNF/epoxy hybrid nanocomposites has been considered at room temperature. The samples were subjected to different displacement amplitudes fatigue loadings. Due to the addition of hybrid nanoparticles, a remarkable improvement in fatigue life of epoxy resin was observed in comparison with results obtained by adding 0.25 wt.% graphene or 0.25 wt.% CNF into the resin. Experimental observations show that at a strength ratio equal to 43% by using 0.5 wt.% of hybrid nanoparticles; 37.3-fold improvement in flexural bending fatigue life of the neat epoxy was observed. While, enhancement of adding only graphene or CNF was 27.4 and 24-fold, respectively.     

Effects of functional groups on the graphene sheet for improving the thermomechanical properties of polyurethane nanocomposites

Dispersibility of graphene sheets in polymer matrices and interfacial interaction are challenging for producing graphene-based high performance polymer nanocomposites. In this study, three kinds nanofillers; pristine graphene nanoplatelets (GNPs), graphene oxide (GO), and functionalized graphene sheet (FGS) were used to prepare polyurethane (PU) composite by in-situ polymerization. To evaluate the efficacy of functional groups on the graphene sheets, PU reinforced with GNPs, GO, and FGS were compared through tensile testing and dynamic mechanical thermal analysis. The Young's moduli of 2 wt% GO and FGS based PU nanocomposites were found significantly higher than that of same amount of GNPs loading as an evidence of the effect of functional groups on graphene sheets for the mechanical reinforcement. The strong interaction of FGS with PU was responsible to exhibit notably high modulus (25.8 MPa) of 2 wt% FGS/PU composite than the same amount of GNPs and GO loading even at elevated temperature (100 °C).     

Ultrasound-assisted fabrication of dispersed two-dimensional copper/reduced graphene oxide nanosheets nanocomposites

Graphene oxide nanosheets (GOS) were employed as template and hydrazine hydrate was used as reductant for GOS and cupric ion. Highly dispersed two-dimensional (2D) copper/reduced graphene oxide nanosheets (Cu/RGOS) nanocomposites were effectively fabricated by ultrasound-assisted electroless copper plating process. Sandwich-like 2D Cu/RGOS nanocomposites consist of uniform Cu layer on the both side of centric RGOS. The Cu layer with thickness of about 60 nm exhibits almost single-crystalline with (1 1 1) preferred crystalline direction and have tight binding with RGOS. The effect of ultrasound on electroless Cu plating includes: accelerating deposition rate, enhancing interfacial bonding and preventing 2D Cu/RGOS nanocomposites from aggregating.     

Enhanced electrochemical capacitance of polyaniline/graphene hybrid nanosheets with graphene as templates

Polyaniline/graphene nanocomposites (PANi/GR) were prepared via PANi covalent grafting from the surface of GR. The unique structure of hybrid nanosheets was formed with uniform PANi layer coating GR without phase separation appearing when the weight ratio of aniline-to-graphene was 1:1. The unique PANi/GR hybrid nanosheets as electrode material for supercapacitors have a specific capacitance as high as 922 F/g at 10 mV/s and still retain a specific capacitance of 106 F/g at a high scan rate of 1 V/s due to synergistic effect between PANi and GR. The capacitance retention was ∼90% after 1000 cycles, which is much better than that of pure PANi or other PANi nanocomposites. The enhanced capacitive performance of PANi/GR hybrid nanosheets makes them have potential application in developing high performance energy storage devices.     

3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance

High-performance electromagnetic absorbers with wide absorption band, strong absorption and lightweight are necessary for industry and military application. To obtain the desired materials, two-dimensional (2D) atomic layers structure nanosheets, such as graphene and graphene-like, were adopted due to its unique structure and properties. Here, 3D architecture reduced graphene oxide-molybdenum disulfide (RGO-MoS₂) composite was prepared by one-pot hydrothermal reaction. MoS₂ generated on graphene oxide intercalation through hydrothermal process and rGO is obtained in the meanwhile. 3D architecture RGO-MoS₂ composite can effectively prevent two-dimensional nanosheets re-stacked and can be applied in electromagnetic wave absorption field. In this paper, composites consist of RGO and various MoS₂ were prepared and their electromagnetic performances were investigated for the first time. Maximum absorption bandwidth (R_L < −10 dB) is 5.92 GHz with thickness of 2.5 mm. We may reasonably conclude that RGO-MoS₂ composite can serve as excellent light-weight electromagnetic wave absorbers and can be widely used in practice.     

Facile preparation,characterization and performance of noncovalently functionalized graphene/epoxy nanocomposites with poly(sodium 4-styrenesulfonate)

Graphene was noncovalently functionalized with poly(sodium 4-styrenesulfonate) (PSS) and then successfully incorporated into the epoxy resin via in situ polymerization to form functional and structural nanocomposites. The morphology and structure of PSS modified graphene (PSS-g) were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The effects of PSS-g additions on tensile, electrical and thermal properties of the epoxy/graphene nanocomposites were studied. Noncovalent functionalization improved interfacial bonding between the epoxy matrix and graphene, leading to enhanced tensile strength and modulus of resultant nanocomposites. The PSS-g additions also enhanced electrical properties of the epoxy/PSS-g nanocomposites, resulting in a lower percolation threshold of 1.2 wt%. Thermogravimetric and differential scanning calorimetric results showed the occurrence of a two-step decomposition process for the epoxy/PSS-g nanocomposites.     

Thermal,mechanical and electrical properties of polyurethane/(3-aminopropyl) triethoxysilane functionalized graphene/epoxy resin interpenetrating shape memory polymer composites

Functionalized graphene (FG) was successfully synthesized by treating graphene oxide with (3-aminopropyl) triethoxysilane (KH-550) and then reduced by hydrazine hydrate. Subsequently, significant reinforcement of polyurethane/epoxy resin (PU/EP) composites in situ synthesized on the FG is prepared. Morphologic study shows that, due to the formation of chemical bonding, the FG was dispersed well in the PU/EP matrix and the mechanical performance is improved. Meanwhile, the thermal degradation temperature was enhanced almost 50 °C higher than that of PU/EP. The conductivity of PU/FG/EP nanocomposites was 82.713 × 10⁻⁶ S/m at 2.0 wt% loadings. The resulting composites exhibited 96% shape fixity, 94% shape recovery, enhanced shape recovery force to realize thermo-electric dual-responsive property. Comparing with the results in literature, the composites used in this study have shown a progress between electrical conductivity and shape memory property.     

In situ thermal preparation of polyimide nanocomposite films containing functionalized graphene sheets

Graphene oxides (GO) were exfoliated in N,N-dimethylformamide by simple sonication treatment of the as-prepared high quality graphite oxides. By high-speed mixing of the pristine poly(amic acid) (PAA) solution with graphene oxide suspension, PAA solutions containing uniformly dispersed GO can be obtained. Polyimide (PI) nanocomposite films with different loadings of functionalized graphene sheets (FGS) can be prepared by in situ partial reduction and imidization of the as-prepared GO/PAA composites. Transmission electron microscopy observations showed that the FGS were well exfoliated and uniformly dispersed in the PI matrix. It is interesting to find that the FGS were highly aligned along the surface direction for the nanocomposite film with 2 wt % FGS. Tensile tests indicated that the mechanical properties of polyimide were significantly enhanced by the incorporation of FGS, due to the fine dispersion of high specific surface area of functionalized graphene nanosheets and the good adhesion and interlocking between the FGS and the matrix.     

Combination effect of carbon nanotubes with graphene on intumescent flame-retardant polypropylene nanocomposites

A novel polypropylene (PP) nanocomposite was fabricated by the incorporation of intumescent flame retardant (IFR), carbon nanotubes (CNTs) and graphene into the PP matrix. Results from TEM indicate that IFR, CNTs and exfoliated graphene nanosheets are dispersed finely in the PP matrix, which is supported by the XRD analysis results. Thermogravimetric (TGA) results show that the addition of IFR, CNTs and graphene improved the thermal stability and the char yields of PP. The PP/IFR/CNTs/RGO nanocomposites, filled with 18 wt% IFR, 1 wt% CNTs and 1 wt% graphene, achieve the limiting oxygen index value of 31.4% and UL-94 V0 grade. Cone calorimeter data reveal that combustion behavior, heat release rate peak (PHRR) and average specific extinction area (ASEA) of PP decrease substantially when combination effects of IFR, CNTs and graphene intervene. For the PP/IFR/CNTs/RGO nanocomposites, the PHRR exhibits an 83% reduction and the time of ignition is delayed 40 s compared with neat PP.     

Hydrolytic dehydrogenation of ammonia borane catalyzed by poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets supported Ag0.3Co0.7 nanoparticles

Poly(amidoamine) dendrimers-modified reduced graphene oxide nanosheets (PAMAM/rGO) composite was selected as a carrier of heterogeneous Ag_0.3Co_0.7 nanoparticles in order to obtain an excellent catalyst for ammonia borane (AB) hydrolysis. During the synthetic processes, GO could easily assembled with PAMAM by the electrostatic and hydrogen-bonding interactions. Structural characterization revealed that Ag_0.3Co_0.7 bimetallic nanoparticles with uniform size distribution of 5 nm are well dispersed on PAMAM/rGO composite architecture. Ag_0.3Co_0.7@PAMAM/rGO was found to be a highly active and reusable catalyst in hydrogen generation from the hydrolysis of AB with a turnover frequency value (TOF) of 19.79 mol_H2 min^–1 mol_M^–1 at 25.0 ± 0.1 °C and retained 75.4% of their initial activity with a complete release of hydrogen in five runs. The relatively high TOF value and low apparent activation energy (34.21 kJ mol^–1) make these Ag_0.3Co_0.7@PAMAM/rGO NPs as a high-efficient catalyst for catalytic dehydrogenation of AB facilitating the development of practically applicable energy storage materials.     

An investigation on post-fire behavior of hybrid nanocomposites under bending loads

This work focuses on residual bending properties of hybrid nanocomposites after intense heat conditions. Carbon fiber/epoxy-nanoclay and carbon fiber/epoxy-graphene nanosheets were manufactured. The nanoparticles employed were Cloisite 30B nanoclay and surface modified graphene nanosheets. The epoxy system was RemLam M/HY956. For short beam samples exposed to 800 KW/m² heat flux, for a various period of time up to 120 s, the addition of nanoparticles (nanoclay and graphene nanosheets) increased the unburned thickness from 0.16 mm (original) to 2.63 mm and 2.74 mm, respectively. When the two-dimensional (plates) samples were tested, the improvement on heat performance was reduced. The unburned thickness improved close to 10% with the presence of nanoclay. The addition of graphene nanosheets leads to a decrease in unburned thickness of 12.8%. This result can be due to the good thermal protection properties of the graphene nanosheets. Using SEM analysis, it was observed that when the hybrid nanocomposites were subjected to a large heat flux, nanoparticles remained trapped inside the char layers. Finally, the proposed model seems to overestimate the residual bending response by 8%.     

Free-standing functional graphene reinforced carbon films with excellent mechanical properties and superhydrophobic characteristic

In this work, we reported a simple method to fabricate novel free-standing stiff carbon-based composite films with excellent mechanical properties and superhydrophobic behaviors. The free-standing stiff carbon composite films based on reduced graphene oxide/glassy carbon (rGO/GC) were prepared by the combination of in-situ polymerization and carbonization process. The obtained composite films exhibited excellent mechanical properties by the addition of rGO nanosheets. It was found that incorporating 0.5 wt.% of rGO sheets in GC precursors resulted in enhancements of 99% in strength (202.6 MPa) and 184% in modulus (33.8 GPa), respectively. More interestingly, carbon nanoarrays were uniformly grown on the surface of composite films by the incorporation of rGO sheets. Superhydrophobic surfaces of carbon films were subsequently formed through functionalizing carbon nanoarrays with Trichloro(1H, 1H, 2H, 2H-perfluorodecyl)silane. Contact angle (CA) analysis suggested that superhydrophobic surfaces with a CA as high as 155° could be formed through optimizing the fabrication process.     

Preparation,mechanical and thermal properties of functionalized graphene/polyimide nanocomposites

Graphene oxide sheets with isocyanate functional groups (GONCO) were firstly synthesized and functionalized graphene/polyimide (FGS/PI) nanocomposites were subsequently prepared by typical solution casting and thermal imidization. The chemical changes of GONCO during the preparation of FGS/PI nanocomposites were carefully characterized by Fourier transfer infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. As a result, the morphology analysis indicated that the FGS were dispersed in the PI matrix and were aligned more orderly with increasing the FGS contents. The tensile strength and the modulus of FGS/PI nanocomposites were significantly increased by 60% with a small quantity of 0.75 wt% FGS incorporated and decreased beyond that dosage. Moreover, the thermogravimetric analysis (TGA) results revealed that the thermal stability of PI was slightly improved by the incorporation of FGS.     

Enhanced microwave absorption properties of flake-shaped FePCB metallic glass/graphene composites

A novel kind of composite absorber, i.e. FePCB/graphene composite, with excellent microwave absorption properties was successfully fabricated by a simple and scalable ball milling method. After being milled, the FePCB particles displayed flaky morphology with large aspect ratio. The complex permittivity and permeability of the flaky FePCB distinctly increased compared with those before milling. Furthermore, with the introduction of graphene, the flaky FePCB/graphene composite exhibited excellent microwave absorption performance with strong absorption and wide absorption band. In particular, for FePCB/graphene composite with an absorber thickness of 2 mm, the reflection loss (RL) reached a minimum of −45.3 dB at 12.6 GHz and the effective absorption bandwidth (RL < −10 dB) covered 5.4 GHz. The enhanced microwave absorption performance of the FePCB/graphene composite was attributed to the high magnetic loss and improved impedance matching which were closely related to the flake-shaped FePCB particles and the introduction of graphene sheets.     

Effects of graphene nanoplatelets and graphene nanosheets on fracture toughness of epoxy nanocomposites

The effects of graphene nanoplatelets (GPLs) and graphene nanosheets (GNSs) on fracture toughness and tensile properties of epoxy resin have been studied. A new technique for synthesis of GPLs based on changing magnetic field is developed. The transmission‐electron microscopy and the Raman spectroscopy were employed to characterize the size and chemical structure of the synthesized graphene platelets. The critical stress intensity factor and tensile properties of epoxy matrix filled with GPL and GNS particles were measured. Influence of filler content, filler size and dispersion state was examined. It was found that the GPLs have greater impact on both fracture toughness and tensile strength of nanocomposites compared with the GNSs. For instance, fracture toughness increased by 39% using 0.5 wt% GPLs and 16% for 0.5 wt% GNSs.     

Functionalizing graphene decorated with phosphorus-nitrogen containing dendrimer for high-performance polymer nanocomposites

In this paper, we demonstrate a novel strategy for fabricating advanced polymer composites based on functionalized graphene oxide decorated with phosphorus-nitrogen-containing dendrimers (PND-GO). Both X-ray diffraction and transmission electron microscopy results show that reduced PND-GO uniformly disperses within polymer matrix and is exfoliated in polyurethane (PU) via in situ polymerization. Cone calorimetry results show that incorporating 2 wt% reduced PND-GO into PU decreases the peak heat release rate by 53% and prolongs the time to ignition by 28 s as compared with the PU bulk. Besides, the tensile strength and Young’s modulus are remarkably enhanced by about 2 times and 5 times, respectively.     

Graphene-enhanced microwave absorption properties of Fe3O4/SiO2 nanorods

Fe₃O₄/SiO₂/graphene composite composed of Fe₃O₄/SiO₂ core–shell nanorods and graphene nanosheets were synthesized by a facile wet chemical method. Structure and morphology studies reveal that the Fe₃O₄/SiO₂ nanorods with porous structure and large aspect ratio are densely wrapped by the graphene nanosheets. By changing the graphene content, the electromagnetic properties of the Fe₃O₄/SiO₂/graphene composite can be well tuned. When the weight ratio of Fe₃O₄/SiO₂ to graphene reaches an appropriate value, excellent microwave absorption performance is achieved due to the large electromagnetic losses and good impedance matching. The Fe₃O₄/SiO₂/graphene composite with graphene content of 5 wt.% shows the minimum reflection loss of −27.1 dB at 12.2 GHz when the coating layer thickness is only 1.5 mm.     

Starch/polylactide sustainable composites: Interface tailoring with graphene oxide

The high production cost of polylactide (PLA) can be effectively reduced by simply mixing with starch, unfortunately a trade-off of its mechanical properties. In this paper, we reported a new strategy in which graphene oxide (GO) was used as a compatibilizer to bridge PLA and starch. The native starch was first cationized and then encapsulated with GO by electrostatic force between the negatively charged GO and the positively charged cationic starch. The encapsulating GO was reduced by the quaternary ammonium ions on the cationic starch, which converted the surface of the starch from hydrophilic to hydrophobic. Due to the amphipathicity approximation between PLA and starch, a good dispersion as well as a strong interfacial adhesion was achieved. The PLA composite reinforced with GO encapsulated starch exhibited much higher yield strength than that of pure PLA, increasing from 36.64 MPa up to 41.40 MPa.     

Defective graphene as a high-efficiency Raman enhancement substrate

Pristine graphene (PG) has been demonstrated to be an excellent substrate for Raman enhancement, which is called graphene-enhanced Raman scattering. However, the chemically inert and hydrophobic surface of PG hinders the adsorption of molecules especially in aqueous solutions, and consequently limits the Raman enhanced efficiency. Here, we synthesized defective graphene (DG) films by chemical vapor deposition on Au, which has a defect density of ∼2.0 × 10¹¹ cm⁻². The DG shows a much better wettability than PG towards dye solution. Combining with the strong adsorption ability of defects to molecules, DG shows greatly enhanced efficiency than PG with perfect lattice. For example, the detection limit for rhodamine B can reach 2 × 10⁻⁹ M for DG while it is on the order of 10⁻⁷ M for PG. In addition, DG has high enhancement uniformity and the Au substrate can be reused after electrochemical bubbling transfer. These advantages suggest the great potential of the DG grown on Au for practical applications in environmental monitoring.     

氰酸酯树脂/氧化石墨烯纳米复合材料的制备及表征

通过溶液插层的方法制备氰酸酯树脂/氧化石墨烯纳米复合材料,采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和热重分析(TGA)研究纳米复合材料的结构和性能,采用电子万能试验机研究纳米复合材料的力学性能。研究表明,异氰酸苯酯改性氧化石墨在二甲基甲酰胺中经超声处理后剥离形成氧化石墨烯薄片;添加氧化石墨烯后纳米复合材料的力学性能和耐热性显著改善。当氧化石墨烯的含量为基体树脂的1%时,纳米复合材料的拉伸强度、弯曲强度和冲击强度分别为82.9 MPa、148.6 MPa和12.9 kJ/m2,1000℃时的残炭率达45.1%。