Graphene Fillers Research Articles

Significantly improved interfacial shear strength in graphene/copper nanocomposite via wrinkles and functionalization: A molecular dynamics study

Graphene reinforced metal matrix composites (MMCs) have received extensive research interests as promising structural materials in developing lightweight structures. The mechanical performance of such composites, however, is considerably hindered by weak van der Waal (vdW) interaction between graphene and metal matrix. The present work shows that this challenging issue can be effectively alleviated by the use of chemically functionalized graphene fillers with mechanically induced wrinkles. Our extensive molecular dynamics (MD) simulations on graphene reinforced copper (Cu) composite manifest that the presence of shear-induced wrinkles and chemical modification of graphene using functional groups can significantly increase its surface roughness, enhance the vdW interaction and consequently lead to higher interfacial shear strength (IFSS) between graphene and Cu matrix. Compared with its counterpart functionalized with hydrogen, graphene functionalized with alkyl (methyl, ethyl, propyl, and butyl) offers better interfacial interactions with Cu matrix because these functional groups are longer than hydrogen functional group and can be embedded deeper into the matrix.

Bioactive, Ion‐Releasing PMMA Bone Cement Filled with Functional Graphenic Materials

Graphene oxide and functionalized graphenic materials (FGMs) have promise as platforms for imparting programmable bioactivity to poly(methyl methacrylate) (PMMA)-based bone cement. To date, however, graphenic fillers have only been feasible in PMMA cements at extremely low loadings, limiting the bioactive effects. At higher loadings, graphenic fillers decrease cement strength by aggregating and interfering with curing process. Here, these challenges are addressed by combining bioactive FGM fillers with a custom cement formulation. These cements contain an order of magnitude more graphenic filler than previous reports. Even at 1 wt% FGM, these cements have compressive strengths of 78- 88 MPa, flexural strengths of 74-81 MPa, and flexural stiffnesses of 1.8-1.9 GPa, surpassing the ASTM requirements for bone cement and competing with traditional PMMA cement. Further, by utilizing designer FGMs with programmed bioactivity, these cements demonstrate controlled release of osteogenic calcium ions (releasing a total of 5 ± 2 µmol of Ca2+ per gram of cement over 28 d) and stimulate a 290% increase in expression of alkaline phosphatase in human mesenchymal stem cells in vitro. Also, design criteria are described to guide creation of future generations of bone cements that utilize FGMs as platforms to achieve dynamic biological activity.

Facile green path to interconnected nano-graphite networks to overtake graphene as conductive fillers

Carbon nanomaterials are effective conductive fillers for permanent antistatic composites due to their long-term stability in electrical conductivity under ambient temperature and humidity. Where graphene or graphene-like materials have been demonstrated to be the most promising conductive fillers. However, the preparation of graphene and further dispersion into polymer matrices to obtain interconnected conductive networks is still a big challenge for conductive composites. A facile green path (all solid states), microsphere rolling transfer method, has been adopted to introduce nano-graphite conductive fillers for polyethylene. The nano-graphites were well dispersed into polyethylene matrices to give interconnected networks with low loading. The conductivity reinforcements of nano-graphite fillers even overtake those of complicated graphene fillers. The percolation threshold of the conductive composites with nano-graphite fillers for polyethylene has been demonstrated to be as low as 0.85 wt%. The electrical conductivity of the conductive composites was measured to increase by 13 orders of magnitude with 2.05 wt% nano-graphite fillers (0.02 S/m), much higher than traditional solid mixing methods and approaching to the best effects from complicated solution mixing of graphene fillers. The nano-graphite conductive networks are easily adjusted and the method is feasible to almost all conventional solid resins and industrial production.

Uncovering the glass-transition temperature and temperature-dependent storage modulus of graphene-polymer nanocomposites through irreversible thermodynamic processes

Several recent experiments have shown that the glass-transition temperature and temperature-dependent storage modulus of graphene-polymer nanocomposites are dependent on the graphene loading, but at present no theory exists to explain these observations. In this paper, we take the view that both issues are closely tied to the principle of irreversible thermodynamics, and that, by considering the phase transition from the glassy to the rubbery state in the polymer, and the temperature-affected degradation of the interphase, two independent state variables can be chosen and implemented into a two-scale homogenization scheme. In this approach, we also adopt the temperature-dependent complex modulus in the reduced frequency scale as the homogenization parameter. The developed theory is highlighted with a direct comparison with experiments. It is demonstrated that, with the addition of graphene fillers, both theory and experiments show an increase of glass-transition temperature and effective storage and loss moduli, but that, within the glass-transition range, the storage and loss moduli decrease drastically. The present research could provide the directions to tune the glass-transition temperature and storage modulus of graphene-polymer nanocomposite through graphene loading and temperature.

Effect of Graphene Additive on Flexural and Interlaminar Shear Strength Properties of Carbon Fiber-Reinforced Polymer Composite

Composite materials are widely used in various manufacturing fields from aeronautic and aerospace industries to the automotive industry. This is due to their outstanding mechanical properties with respect to their light weight. However, some studies showed that the major flaws of these materials are located at the fiber/matrix interface. Therefore, enhancing matrix adhesion properties could significantly improve the overall material characteristics. This study aims to analyze the effect of graphene particles on the adhesion properties of carbon fiber-reinforced polymer (CFRP) through interlaminar shear strength (ILSS) and flexural testing. Seven modified epoxy resins were prepared with different graphene contents. The CFRP laminates were next manufactured using a method that guarantees a repeatable and consistent fiber volume fraction with a low porosity level. Short beam shear and flexural tests were performed to compare the effect of graphene on the mechanical properties of the different laminates. It was found that 0.25 wt.% of graphene filler enhanced the flexural strength by 5%, whilst the higher concentrations (2 and 3 wt.%) decreased the flexural strength by about 7%. Regarding the ILSS, samples with low concentrations (0.25 and 0.5 wt.%) demonstrated a decent increase. Meanwhile, 3 wt.% slightly decreases the ILSS.

Endowing the sustainable antistatic properties to epoxy-based composites through adding graphene nanoplatelets

In order to explore the possibility of reducing the potential hazards caused by the accumulation of static charges in electronic components, graphene nanoplatelets with remarkable conductive property were added as functional fillers into epoxy matrix to enhance the antistatic property of composites used as the encapsulating materials. Optical microscope and scanning electron microscope were used to observe the dispersion of graphene fillers in the polymer to indicate the completeness of the establishment of the conductive network. The surface of the material was charged by corona discharge method, then the decay characteristics of the static charges was continuously measured. The accumulation and decay of the static charges on the surface of the sample were systematically analyzed by combining with water contact angle, resistivity and relevant permittivity parameters. Results showed that the antistatic ability of material had been constantly enhanced with the increase of graphene content. It was worth noting that when only 0.5 wt% graphene fillers were added, the surface and volume resistivity of composite could reach 5.38 × 1012 Ω/square, 2.37 × 1010 Ω.cm respectively, fully meeting the requirement standard of antistatic encapsulating material for electronic devices. It is forecasted that the prepared composites have considerable prospects in the antistatic encapsulation of electronic devices and aerospace fields.

Flexible Nanocomposites Based on Polydimethylsiloxane Matrices with DNA-Modified Graphene Filler: Curing Behavior by Differential Scanning Calorimetry.

Novel silicone-based nanocomposites with varied elastic properties were prepared by blending standard polydimethylsiloxane (PDMS) with a lower viscosity component (hydroxyl-terminated PDMS) and integrating a graphene nanoplatelets (GNP) filler modified by strands of deoxyribonucleic acid (DNA). The curing behavior of these nanocomposites was studied by dynamic and isothermal differential scanning calorimetry. The activation energies of the polymerization reactions were determined using the Kissinger method and two model-free isoconversional approaches, the Ozawa–Flynn–Wall and the Kissinger–Akahira–Sunose methods. Results show that the complex trend of the curing behavior can be described using the isoconversional methods, unveiling lower activation energies for the nanocomposites with standard PDMS matrices. The role of the DNA modification of graphene on the curing behavior is also demonstrated. The curing reactions of the nanocomposites with the PDMS matrix are favored by the presence of the GNP–DNA filler. PDMS/PDMS–OH blends generate softer nanocomposites with hardness and reduced elastic modulus that can be tuned by varying the amount of the filler.

Review of Recent Developments in the Formulation of Graphene-Based Coatings for the Corrosion Protection of Metals and Alloys

Corrosion is a naturally occurring phenomenon and there is continuous interest in the development of new and more protective coatings or films that can be employed to prevent or minimise corrosion. In this review the corrosion protection afforded by two-dimensional graphene is described and discussed. Following a short introduction to corrosion, the application of graphene in the formulation of coatings and films is introduced. Initially, reduced graphene oxide (rGO) and metallic like graphene layers are reviewed, highlighting the issues with galvanic corrosion. Then the more successful graphene oxide (GO), functionalised GO and polymer grafted GO-modified coatings are introduced, where the functionalisation and grafting are tailored to optimise dispersion of graphene fillers. This is followed by rGO coupled with zinc rich coatings or conducting polymers, GO combined with sol-gels, layered double hydroxides or metal organic frameworks as protective coatings, where again the dispersion of the graphene sheets becomes important in the design of protective coatings. The role of graphene in the photocathodic protection of metals and alloys is briefly introduced, while graphene-like emerging materials, such as hexagonal boron nitride, h-BN, and graphitic carbon nitride, g-C3N4, are then highlighted.

Tritium Effects on Aromatic Carbon–Loaded Polymers

By incorporating carbon nanotubes (CNTs) and graphene nanomaterials with aromatic sp2 carbon structures, we have specifically tuned filled ethylene propylene diene monomer elastomer (EPDM) seal and gasket composite materials for radiation resistance. Our results show that CNTs and graphene have an increased ability to stabilize the EPDM matrix compared to standard carbon black (CB) as a radiation-resistant filler. Graphene outperforms both CNT and CB fillers when considering surface damage under conditions where beta exposure is an issue. Both graphene and CNT fillers offer significantly reduced changes in glass transition temperature under prolonged exposure to tritium compared to CB-filled standards, with a 2.5-fold and almost 5-fold reduction, respectively. Thus, CNT- and graphene-filled O-ring materials could be designed that would maintain acceptable seals significantly longer than currently used composites.

Optimization of Thermal Conductivity of NanoPCM-Based Graphene by Response Surface Methodology

Common phase change materials (PCMs) possess very low thermal conductivity whilst hybrid PCM with graphene filler could be produced to achieve increased thermal conductivity. This research focuses on the effects of graphene flakes on the thermal conductivity of a PCM (paraffin wax). Three experimental parameters at different levels of average lateral sizes of graphene flakes (4.5, 5 and 7µm), mass fractions (0.1, 0.2 and 0.25 wt.%), and rising temperatures (25-75°C) are considered. For the first time in the literature, the impact of various parameters on the thermal conductivity performance of the nanoPCM-based graphene nano-composites is investigated extensively by adopting response surface methodology supported by central composite design. Thermal conductivity prediction is proposed by a new general correlation and a promising value of the coefficient of determination (R2) higher than 0.88. Amongst the investigated various variables in terms of impact on thermal conductivity, the temperature is identified as the most influential parameter on response variables. According to the implemented optimization technique, for the composite with the average graphene flake size of 4.5 µm, the optimum value of the thermal conductivity is found 0.275 W/m K at the mass fraction of 0.186 wt.% and temperature of 69.73°C.

Graphene and Polyethylene: A Strong Combination Towards Multifunctional Nanocomposites.

The key to the preparation of polymer nanocomposites with new or improved properties resides in the homogeneous dispersion of the filler and in the efficient load transfer between components through strong filler/polymer interfacial interactions. This paper reports on the preparation of a series of nanocomposites of graphene and a polyolefin using different experimental approaches, with the final goal of obtaining multifunctional materials. A high-density polyethylene (HDPE) is employed as the matrix, while unmodified and chemically modified graphene fillers are used. By selecting the correct combination as well as the adequate preparation process, the nanocomposites display optimized thermal and mechanical properties, while also conferring good gas barrier properties and significant levels of electrical conductivity.

Multifunctional Graphene Composites for Electromagnetic Shielding and Thermal Management at Elevated Temperatures

AbstractA method for scalable synthesis of epoxy composites with graphene and few‐layer graphene fillers is described, and the electromagnetic interference (EMI) shielding and thermal properties of such composites at elevated temperatures are reported. The tested materials reveal excellent total EMI shielding of SET ≈ 65 dB (≈ 105 dB) at a thickness of 1 mm (≈ 2 mm) in the X‐band frequency range. At higher filler loading fractions, composites reveal a room‐temperature cross‐plane thermal conductivity of 11.2 ± 0.9 Wm−1 K−1, which is a factor of ×41 larger than that of the pristine epoxy. Interestingly, the EMI shielding efficiency improves further as the temperature increases while the thermal conductivity remains approximately constant. The enhancement in the EMI shielding is explained by the temperature dependence of the two electrical conduction mechanisms, electronic band‐type conduction inside the fillers, and hopping conduction between the fillers. The excellent EMI shielding and heat conduction characteristics of such multifunctional graphene composites at high temperatures are promising for packaging applications of microwave components where EMI shielding and thermal management are important design considerations.

WITHDRAWN: Improving the De-Icing properties of wing structure by adding graphene filler into the composite structure

Abstract In this present work, we discuss about a promising technique where graphene is added into the composite structure as filler in order to improve its De-icing property. Graphene is known to have unique properties namely high thermal and electrical conductivity which will help with De-icing characteristics. Hand layup process was employed to fabricate the Glass fibre Reinforced Polymer (GFRP). Epoxy Resin was used along with Reduced Graphene Oxide (rGO) as Filler. Material Properties are studying using various tools like Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) .The Mechanical properties of the manufactured composite is studied using the Dynamic Testing Analysis (DMA) with the specification of DMA 242 E. Dynamic testing gives the mechanical properties of FRP composite specimens as a function of temperature and frequency. 2 wt% and 5 wt% of rGO were Incorporated to the epoxy and its various properties are compared.

Graphene/polyaniline nanocomposites: effect of in-situ polymerization and solvent blending methods with dodecylbenzene sulfonic acid surfactant

Polyaniline (PANI) has fascinated considerable interest from industrial and academic researchers due to their great potential in many electronic applications. The present study aims to enhance the electrical and thermal properties of the graphene/PANI nanocomposites using different fabrication methods and modifications in the nanocomposites formulation. Comparison on the properties of graphene/PANI nanocomposites produced by in-situ polymerization and solvent blending methods and also the effects of dodecylbenzene sulfonic acid (DBSA) surfactant are investigated. Electrical conductivity, thermal conductivity, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to characterize the sample. Results showed that graphene/PANI nanocomposites produced by the in-situ polymerization method have better electrical conductivity, thermal conductivity and thermal stability if compared to that of the solvent blending method. The in-situ polymerization method exhibits a smaller diameter size of PANI fiber and good dispersion of graphene filler. Furthermore, the addition of DBSA surfactant in the graphene/PANI nanocomposites developed homogeneity and uniform dispersion of the graphene filler within the PANI matrix. In conclusion, graphene/PANI with surfactant nanocomposites produced by the in-situ polymerization method showed higher electrical and thermal conductivity by 10% and 6%, respectively, if compared to the in-situ polymerization without surfactant. Thermal stability also showed improvement with the addition of surfactant.

Highly conductive polyimide nanocomposite prepared using a graphene oxide liquid crystal scaffold

High loading of aligned graphene filler is effective for fabricating polymer nanocomposites with drastically improved properties, while practical preparation of such composites remains elusive. This paper reports on a method of preparing polyimide (PI, BPDA/PDA) nanocomposites containing highly loaded graphene fillers that are uniformly aligned parallel to the coating substrate in the PI matrix. The highly aligned graphene/PI film was achieved by infiltrating water-soluble poly(amic acid) ammonium salt (PAAS) into the scaffold of the graphene oxide liquid crystal. After thermal treatment, a freestanding reduced graphene oxide/polyimide (rGO/PI) film was prepared with the imidization of PAAS and reduction of graphene oxide. Owing to the excellent mechanical properties of the infiltrated PI, the hardness and modulus of the rGO/PI film were as high as 0.9 GPa and 9.3 GPa, respectively. In addition, the rGO/PI film was highly conductive, with an electrical conductivity of 446 S/m, because of the well-connected electrical pathways of the highly loaded and aligned graphene sheets.

Enhancing mechanism of interfacial metal element on the thermal transport across Cu-graphene interfaces revealed by molecular dynamics simulations

Enhancing the interfacial thermal conductance (ITC) between graphene fillers and a metal matrix is critical for the practical application of metal matrix composites as thermal management materials. In this work, the interfacial metal element (M) is utilized to enhance the ITC in copper matrix composite filled with trilayer graphene (TLG) through non-equilibrium molecular dynamics (NEMD) simulations. The results show that different impacts are induced in enhancing the ITC of Cu-TLG interfaces. Specifically, a positive enhancing effect is introduced by interfacial elements (Ti and Co) chemically bonded with copper matrix and TLG. The positive enhancing mechanism of a metal interfacial element on the ITC is further illustrated in terms of the phonon density of states (PDOS) in the Cu-M-TLG interface region. It should be stressed that the ITC increases gradually with the increasing interfacial Ti layer thickness (from 1 to 5 layers). In contrast, a negative enhancing effect is introduced by interfacial elements (Au and Pd) physically and mixed bonded with copper and TLG because of Cu-M (M = Au/Pd) interface caused a strong phonon scattering. The enhancing mechanism on the ITC of Cu-TLG composite induced by the interfacial metal element is expected to provide a theoretical guideline for improving the overall thermal conductivity of metal matrix composite materials.

Graphenated Ceramic Particles as Functional Fillers for Nonisocyanate Polyhydroxyurethane Composites

AbstractGraphenation of corundum and silicon carbide filler particles simultaneously improves mechanical properties and electrical conductivity of nonisocyanate polyhydroxyurethanes (NIPU) composites prepared by amine cure of polyfunctional cyclic carbonates. Typically, the ceramic fillers coated with either glucose, polydopamine, or graphite oxide (GO) are thermolyzed to produce an ultrathin graphene shell around the ceramic core, as verified by transmission electron microscopy. As compared to a blend of corundum particles with the thermally reduced graphite oxide (TRGO) nanofiller, graphenation of corundum with GO at a similar total carbon content significantly improves the Young’s modulus (7000 MPa, +184%) of trimethylolpropane glycidylether carbonate (TMPGC) cured with diethylenetriamine (DETA). Moreover, up to 30 wt% of the graphenated corundum filler is uniformly dispersed, whereas a few percent of neat TRGO account for intolerable high viscosity. Furthermore, NIPU composites containing graphenated ceramic fillers exhibit electrical conductivities of up 2.58 × 10−5 S m−1 well below the percolation threshold of neat TRGO in the same NIPU matrix. Hence, the graphenation of inorganic particles represents a facile and universal synthetic route toward tailoring functional fillers and combines the two worlds of functionalized graphene and inorganic fillers in an economic way by eliminating the tedious syntheses and handling typical for graphene nanofillers.

Experimental and theoretical study of the evolution of fluid-suspended graphene morphology driven by an applied electric field and the attainment of ultra-low percolation threshold in graphene-polymer nanocomposites

We report on a coordinated experimental and theoretical investigation into the evolution of the morphology of fluid-suspended graphene driven by an electric field, and the attainment of ultra-low percolation threshold in graphene-polymer nanocomposites. A remarkable outcome is that, due to the field-driven graphene rotation and agglomerate chaining, the percolation threshold can be as low as 0.03 vol%, as opposed to the 0.75 vol% without the application of the field. This is likely to be the lowest ever reported for a graphene-polymer nanocomposite. To quantify this and other measured conductivity data, a two-scale effective-medium theory with highly aligned, agglomerated nanofillers is developed. In this process Cauchy's cumulative probability function is introduced to describe the increased level of electron tunneling near the percolation threshold, and a statistical approach based on the projection length of graphene fillers is developed to characterize the agglomerate shape. We also built a kinetic equation from the torque of the applied electric field to calculate the time- and field-dependent rotation of graphene nanoplatelet. The study is highlighted with a direct comparison between the theory and the experiment. It is concluded that the measured ultralow percolation threshold can indeed be achieved through the concurrent graphene rotation and elongation of agglomerate shape toward the field direction.

Nanocarbon and macrocarbonaceous filler–reinforced epoxy/polyamide: A review

Epoxy is a thermosetting polymer and an engineering material for structural and composite applications. However, pure epoxy has disadvantages of stiffness and low toughness properties, so limiting its practical uses. Polyamide is an important thermoplastic polymer for commercial uses. Epoxy has been blended with polyamide (thermoplastic polymer) to enhance the toughness and mechanical properties. Consequently, epoxy/polyamide blend matrix has been developed for composite applications. Incorporation of carbonaceous nanoparticles in epoxy/polyamide blend has been used to improve the morphological and physical properties of these materials. This review describes scientific development in the field of epoxy/polyamide-based nanocomposite and composites. Epoxy/polyamide materials have been reinforced with micro- and macroscale carbonaceous fillers such as graphene, carbon nanotube, nanodiamond, carbon black, carbon fiber, and hybrid fillers. The strength, modulus, toughness, electrical, conductivity, thermal conductivity, and thermal stability properties of epoxy/polyamide have been influenced through the incorporation of nanofillers. The fundamentals and applications (coatings, adhesives, electronics, radiation shielding, automotive/aerospace) of these materials have been discussed. Toward the end, applications, future, and challenges of epoxy/polyamide-based nanocomposites have been comprehended.

Graphene Epoxy-Based Composites as Efficient Electromagnetic Absorbers in the Extremely High-Frequency Band.

We report on the synthesis of the epoxy-based composites with graphene fillers and test their electromagnetic shielding efficiency by the quasi-optic free-space method in the extremely high-frequency (EHF) band (220-325 GHz). The curing adhesive composites were produced by a scalable technique with a mixture of single-layer and few-layer graphene layers of few-micrometer lateral dimensions. It was found that the electromagnetic transmission, T, is low even at small concentrations of graphene fillers: T<1% at a frequency of 300 GHz for a composite with only ϕ = 1 wt% graphene. The main shielding mechanism in composites with the low graphene loading is absorption. The composites of 1 mm in thickness and a graphene loading of 8 wt% provide an excellent electromagnetic shielding of 70 dB in the sub-terahertz EHF frequency band with negligible energy reflection to the environment. The developed lightweight adhesive composites with graphene fillers can be used as electromagnetic absorbers in the high-frequency microwave radio relays, microwave remote sensors, millimeter wave scanners, and wireless local area networks.