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Graphene production has been widely explored and developed in the past decade. Most research has aimed at developing scalable, environmentally friendly and cheap procedures to produce defect-free graphene that can be used in a variety of applications such as mechanical properties enhancement and energy storage. Top-down graphene production approaches (from graphite) in liquid, which include high-shear mixing and sonication, were recently scaled up. Nevertheless, their production yields have remained low (

The loading of individual carbon nanotubes (CNTs) in matrices provides state-of-the-art nanocomposite reinforcement at low CNT concentrations. The dispersion of the CNTs in the matrix is often assisted by surfactants (termed also dispersants), which de-bundle the CNT agglomerates. Despite the critical role of the dispersants in this process, their effect on the properties of the nanocomposite has not been sufficiently studied. In the current study, we elucidate the influence of freeze-dried dispersant-CNT on the performance of polymeric and cementitious nanocomposites. We show that the dispersant (Pluronic) is crucial for exfoliating the CNTs in both types of nanocomposite, whereas it also acts as a plasticizer – thus lowering the mixture's effective viscosity – in cementitious matrices. We identify the optimal nanomaterial concentration (ONC) in each nanocomposite system, namely, the critical filler concentration in which optimal mechanical properties are obtained, and above which they degrade dramatically due to the formation of air voids that can initiate mechanical failure. Importantly, the effect of the dispersant on the nanocomposite system – and, accordingly, the origin of the resulting air voids – is different between polymeric and cementitious matrices. In polymers, a high filler concentration increases the viscosity, and, consequently, entraps air voids in the matrix during mixing. In cement, by contrast, the dispersant stabilizes the air and leads to the formation of foam in the matrix. Taken together, our findings indicate that the behavior of the dispersant throughout the composite preparation process – both in the fresh mixture and in the hardened state – should be considered when employing dispersants for use in applicative composite systems.

The growing availability of nanotubes and the increased knowledge about their loading in polymers have prompted the incorporation of nanotubes in cementitious matrices. The effects of loading straight tungsten di-sulfide nanotubes (WS2NT) or waved carbon nanotubes (CNT) in cementitious matrices was explored. Their inclusion in these composites at exceptionally low concentrations (0.063 vol% and 0.15 vol% for WS2NT and CNT, respectively) enhanced the composite’s mechanical properties, including compressive and flexural strengths (25–38%). Thermal analysis and electron microscopy indicated that nanotube incorporation in cementitious matrices also accelerated hydration reaction kinetics. It was shown that straight WS2NTs bridged pores and cracks more effectively than the waved CNTs, which resist crack propagation via an anchoring mechanism. A comparison to representative cement nanocomposite systems shows that nanotubes (aspect ratio≫1), offer better reinforcement efficiencies than particulate nanomaterials, yielding high mechanical properties enhancement at low concentration.

The extraordinary mechanical properties of graphene prompt its incorporation into a wide range of polymeric nanocomposite materials (NCMs). However, similar to other nanomaterials (NMs), the reinforcement efficiency of graphene and its derivatives is hindered by their agglomeration and poor compatibility with the polymer matrix. In this paper, edge-functionalized graphene nanoribbons (EF-GNR) are incorporated in brittle epoxy polymer matrix. The functionalization process by polyvinylamine (PVAM) chains occurs only at the edges, preserving the in-plane sp 2 of the graphene; thereby the PVAM EF-GNRs are both compatible and strong. The produced NCMs exhibit a wide range of enhanced mechanical properties including fracture toughness, flexural strength and shear strength at low EF-GNR loading (0.15 wt%). The effect of the edge functionalization is indeed critical, demonstrating superior mechanical properties by the EF-GNR loaded NCMs compared to pristine-GNR loaded composites. Finally, a comparative overview of various carbon NM-loaded NCMs indicates that EF-GNR possess high reinforcement efficiency (enhancement % per NM loading %) making it an attractive filler for polymer systems.

Nanotubes are considered as promising nano-reinforcement in cement-based materials. The main challenge towards achieving a significant enhancement in cement properties is an effective dispersion of the agglomerated nanotubes. In this paper, we demonstrate a novel dispersion method of Tungsten di-Sulfide NanoTubes (WS 2 NTs) that results in substantial flexural and compressive strength enhancements at optimal nanotube concentration as low as 0.15 wt%. The reinforcement by WS 2 NTs remains significant after a variety of curing processes, suggesting a genuine nanoscale reinforcing effect. Finally, by employing a comprehensive fractography we found that the WS 2 NTs inhibit crack propagation by bridging with a pullout failure mechanism.

The rapidly increasing device densities in electronics dictate the need for efficient thermal management. If successfully exploited, graphene, which possesses extraordinary thermal properties, can be commercially utilized in polymer composites with ultrahigh thermal conductivity (TC). The total potential of graphene to enhance TC, however, is restricted by the large interfacial thermal resistance between the polymer mediated graphene boundaries. We report a facile and scalable dispersion of commercially available graphene nanoplatelets (GnPs) in a polymer matrix, which formed composite with an ultrahigh TC of 12.4 W/m K (vs 0.2 W/m K for neat polymer). This ultrahigh TC was achieved by applying high compression forces during the dispersion that resulted in the closure of gaps between adjacent GnPs with large lateral dimensions and low defect densities. We also found strong evidence for the existence of a thermal percolation threshold. Finally, the addition of electrically insulating boron-nitride nanopart...

A major challenge in nanocomposite research is to predict the optimal nanomaterial concentration (ONC) yielding a maximal reinforcement in a given property. We present a simple approach to identify the ONC based on our finding that it is typically located in close proximity to an abrupt increase in polymer matrix viscosity, termed the rheological percolation threshold, and thus may be used as an indicator of the ONC. This premise was validated by rheological and fractography studies of composites loaded by nanomaterials including graphene nanoribbons or carbon or tungsten disulfide nanotubes. The correlation between in situ viscosity, the rheological percolation threshold concentration and the nanocomposite fractography demonstrates the utility of the method.

The utilization of highly branched polymer (e.g., epoxy resins) in engineering applications is often limited by their brittle nature (low fracture toughness). Loading the polymer matrix by fillers such as individual nanotubes is a promising alternative to enhance fracture toughness without compromising other mechanical properties. However, to fully understand the nanotubes toughening role and correctly characterize the nanocomposite failure mechanisms, a complete exfoliation of the nanotubes aggregates into individual nanotubes is essential. In this work, we embed only individual nanotubes in the polymer matrix using a novel dispersion method. The individual nanotube concentration in the composite is accurately determined. We achieve a record fracture toughness enhancement and, for the first time, demonstrate a coherent quantitative correlation between the fracture toughness and the surface roughness. Finally, comprehensive statistical investigation of the nanotube failure mechanisms shows that carbon nanotubes fail via fracture mechanism, while tungsten di-sulfide nanotubes via pullout mechanism. The failure mechanism could be predicted by the slope of the surface roughness vs. fracture toughness curve.

International audience; The binding of block copolymer Pluronic F-127 in aqueous dispersions of single- (SWCNT) and multiwalled (MWCNT) carbon nanotubes has been studied by pulsed-field-gradient (PFG) 1H NMR spectroscopy. We show that a major fraction of polymers exist as a free species while a minor fraction is bound to the carbon nanotubes (CNT). The polymers exchange between these two states with residence times on the nanotube surface of 24 ± 5 ms for SWCNT and of 54 ± 11 ms for MWCNT. The CNT concentration in the solution was determined by improved thermal gravimetric analysis (TGA) indicating that the concentration of SWCNT dispersed by F-127 was significantly higher than that for MWCNT. For SWCNT, the area per adsorbed Pluronic F-127 molecule is estimated to be about 40 nm2.

Thermal management has become a critical aspect in next-generation miniaturized electronic devices. Efficient heat dissipation reduces their operating temperatures and insures optimal performance, service life, and efficacy. Shielding against shocks, vibrations, and moisture is also imperative when the electronic circuits are located outdoors. Potting (or encapsulating) them in polymer-based composites with enhanced thermal conductivity (TC) may provide a solution for both thermal management and shielding challenges. In the current study, graphene is employed as a filler to fabricate composites with isotropic ultrahigh TC (12 W m(-1) K(-1)) and good mechanical properties (30 MPa flexural and compressive strength). To avoid short-circuiting the electronic assemblies, a dispersion of secondary ceramic-based filler reduces the electrical conductivity and synergistically enhances the TC of composites. When utilized as potting materials, these novel hybrid composites effectively dissipate the heat from electronic devices; their operating temperatures decrease from 110 to 37 °C, and their effective thermal resistances are drastically reduced, by up to 90%. The simple filler dispersion method and the precise manipulation of the composite transport properties via hybrid filling offer a universal approach to the large-scale production of novel materials for thermal management and other applications.

The rapid increase in graphene-based applications has been accompanied by novel top-down manufacturing methods for graphene and its derivatives (e.g., graphene nanoplatelets (GnPs)). The characterization of the bulk properties of these materials by imaging and surface techniques (e.g., electron microscopy and Raman spectroscopy) is only possible through laborious and time-consuming statistical analysis, which precludes simple and efficient quality control during GnP production. We report that thermogravimetry (TG) may be utilized, beyond its conventional applications (e.g., quantification of impurities or surfactants, or labile functional groups) to characterize bulk GnP properties. We characterize the structural parameters of GnP (i.e., defect density, mean lateral dimension, and polydispersity) by imaging and surface techniques, on one hand, and by a systematic TG, on the other. The combined data demonstrate that the combustion temperature of commercially available and laboratory-prepared GnPs is correlated with their mean lateral dimension and defect density, while the combustion temperature range is proportional to their polydispersity index. Mapping all these parameters allows one to evaluate the GnPs' structure following a simple thermogravimetric experiment (without necessitating further statistical analysis). Finally, TG is also used to detect and quantify different GnP constituents in powder and to conduct rapid quality-control tests during GnP production.

Loading a matrix with nano-sized particles such as nanotubes (carbon or tungsten di-sulfide) is expected to improve the mechanical properties of composite materials better than traditional (macroscopic) fillers due to extra-ordinary mechanical properties accompanied by high surface area. One of the major challenges towards achieving this goal is an effective dispersion of the as-produced aggregated nanotubes. In this work we demonstrate a novel dispersion method, facilitating the integration of individual nanotubes in cement paste matrix. We demonstrate the effectiveness of our nanotubes dispersion method by enhancing both flexural strength and compressive strength of cement paste using carbon and tungsten di-sulfide nanotubes. Finally, a comprehensive fractography study indicates that both types of nanotubes fail via pull-out mechanism with an intermediate state of bridging mechanism.

Upon dispersant-assisted exfoliation, pristine carbon nanotubes (CNTs) are divided between the supernatant and precipitate, which makes the determination of dispersant concentration a challenging task. We have developed a thermogravimetric-spectroscopy-based approach to accurately determine the dispersant-assisted CNT (or nanoparticles, in general) concentration in dispersion. A thermogravimetric analysis of the filtered and washed precipitate, that is usually discarded after centrifugation, is used here to accurately calculate the CNT mass in the precipitate and (through mass-balance) its mass in the supernatant. Once the true CNT concentration has been determined, a conventional spectroscopy-based concentration calibration plot is constructed for simple and swift use in further concentration measurements. Such true concentration analysis is crucial for studying the concentration-property relationship.

Dispersing graphite into few-layers graphene sheets (GS) in water is very appealing as an environmental-friendly, low-cost, low-energy method of obtaining graphene. Very high GS concentrations in water (0.7 mg mL(-1)) were obtained by optimizing the nature of dispersant and the type of ultra-sonic generator. We find that a multi-step sonication procedure involving both tip and bath sources considerably enhances the yield of exfoliated GS. Raman and transmission electron microscopy indicate few-layers graphene patches with typical size of ∼0.65 μm in one dimension and ∼0.35 μm in the other. These were further employed in combination with water-dispersed CNTs to fabricate conductive transparent electrodes for a molecularly-controlled solar-cell with an open-circuit voltage of 0.53 V.