J. Rafiee

Bio: J. Rafiee is an academic researcher from Rensselaer Polytechnic Institute. The author has contributed to research in topics: Graphene & Wavelet. The author has an hindex of 20, co-authored 29 publications receiving 6842 citations. Previous affiliations of J. Rafiee include University of Tabriz & Beijing University of Chemical Technology.

Enhanced mechanical properties of nanocomposites at low graphene content.

Abstract: In this study, the mechanical properties of epoxy nanocomposites with graphene platelets, single-walled carbon nanotubes, and multi-walled carbon nanotube additives were compared at a nanofiller weight fraction of 0.1 ± 0.002%. The mechanical properties measured were the Young’s modulus, ultimate tensile strength, fracture toughness, fracture energy, and the material’s resistance to fatigue crack propagation. The results indicate that graphene platelets significantly out-perform carbon nanotube additives. The Young’s modulus of the graphene nanocomposite was ∼31% greater than the pristine epoxy as compared to ∼3% increase for single-walled carbon nanotubes. The tensile strength of the baseline epoxy was enhanced by ∼40% with graphene platelets compared to ∼14% improvement for multi-walled carbon nanotubes. The mode I fracture toughness of the nanocomposite with graphene platelets showed ∼53% increase over the epoxy compared to ∼20% improvement for multi-walled carbon nanotubes. The fatigue resistance resu...

Wetting transparency of graphene

Abstract: It is demonstrated that graphene coatings do not alter the wetting behaviour of copper, gold or silicon surfaces Such wetting transparency—shown to occur only for surfaces where surface–water interactions are dominated by van der Waals forces—and graphene’s ability to suppress copper oxidation result in a 30–40% increase in condensation heat transfer on copper The findings have implications for graphene-based coatings with independently tunable electronic and wetting properties

Fracture and fatigue in graphene nanocomposites

Abstract: Graphene, a single-atom-thick sheet of sp-bonded carbon atoms, has generatedmuch interest due to its high specific area and novel mechanical, electrical, and thermal properties. Recent advances in the production of bulk quantities of exfoliated graphene sheets from graphite have enabled the fabrication of graphene–polymer composites. Such composites show tremendous potential for mechanical-property enhancement due to their combination of high specific surface area, strong nanofiller–matrix adhesion and the outstanding mechanical properties of the sp carbon bonding network in graphene. Graphene fillers have been successfully dispersed in poly(styrene), poly(acrylonitrile) and poly(methyl methacrylate) matrices and the responses of their Young’s modulus, ultimate tensile strength, andglass-transition temperaturehave been characterized. However, to the best of our knowledge there is no report on the fracture toughness and fatigue properties of graphene–polymer composites. Fracture toughness describes the ability of a material containing a crack to resist fracture and it is a critically important material property for design applications. Fatigue involves dynamic propagation of cracks under cyclic loading and it is one of the primary causes of catastrophic failure in structural materials. Consequently, the material’s resistance to fracture and fatigue crack propagation are of paramount importance to prevent failure. Herein we report the fracture toughness, fracture energy, and fatigue properties of an epoxy polymer reinforced with various weight fractions of functionalized graphene sheets. Remarkably, only 0.125% weight of functionalized graphene sheets was observed to increase the fracture toughness of the pristine (unfilled) epoxy by 65% and the fracture energy by 115%.Toachievecomparableenhancement,carbonnanotube (CNT) and nanoparticle epoxy composites require one to two orders of magnitude larger weight fraction of nanofillers. Under fatigue conditions, incorporation of 0.125% weight of functionalized graphene sheets drastically reduced the rate of crack propagation in the epoxy 25-fold. Fractography analysis

Graphene–aluminum nanocomposites

Abstract: Composites of graphene platelets and powdered aluminum were made using ball milling, hot isostatic pressing and extrusion. The mechanical properties and microstructure were studied using hardness and tensile tests, as well as electron microscopy, X-ray diffraction and differential scanning calorimetry. Compared to the pure aluminum and multi-walled carbon nanotube composites, the graphene–aluminum composite showed decreased strength and hardness. This is explained in the context of enhanced aluminum carbide formation with the graphene filler.

Superhydrophobic to superhydrophilic wetting control in graphene films.

Abstract: Adv. Mater. 2010, 22, 2151–2154 2010 WILEY-VCH Verlag G T IO N Superhydrophobic materials with water contact angles above 1508 are the key enabler for antisticking, anticontamination, and self-cleaning technologies. Similarly, superhydrophilic materials with water contact angles below 108 have many important applications; for example, as a wicking material in heat pipes and for enhanced boiling heat transfer. In general, the wettability of a solid surface is strongly influenced both by its chemical composition and by its geometric structure (or surface roughness). Several experimental and modeling studies have focused on exploiting surface roughness to engineer superhydrophobicity or superhydrophilicity. Both microscale roughness features (e.g., micromachined silicon pillars) as well as nanoscale features (e.g., aligned arrays of carbon nanotubes) have been investigated. However, so far the wetting properties of graphene-based coatings have not been studied in detail. Graphene is a single-atom-thick sheet of sp hybridized carbon atoms. When deposited on a planer substrate, the individual graphene sheets form an interconnected film, which increases the surface roughness of the substrate by one to two orders of magnitude. We demonstrate here that this roughness effect in conjunction with the surface chemistry of the graphene sheets can be used to dramatically alter the wettability of the substrate. If hydrophilic graphene sheets are used (for example, by sonicating the as-produced graphene in water), the substrate acquires a superhydrophilic character. Conversely if hydrophobic graphene sheets are used (by sonicating the as-produced graphene in acetone) then the roughness effect imparts superhydrophobicity to the underlying substrate. By controlling the relative proportion of acetone and water in the solvent, the contact angle of the resulting graphene film can be tailored over a wide range (from superhydrophobic to superhydrophilic). Such graphene-based coatings with controllable wetting properties provide a facile and effective means to modify the wettability of a variety of surfaces. The graphene sheets used in this study were extracted from graphite using the method developed in Reference [19,20]. In this method, partially oxygenated graphene sheets are generated by the rapid thermal expansion (>2000 8C min ) of completely oxidized graphite oxide. The protocols used to oxidize graphite to graphite oxide and then generate graphene sheets (Fig. 1a) by the thermal exfoliation of graphite oxide are provided in the Experimental section. Figure 1b illustrates a transmission electron microscopy (TEM) image of a typical graphene flake synthesized by the above method and deposited on a standard TEM grid for imaging. The flake is several micrometers in dimension; note the wrinkled (rough) surface texture of the graphene flake. Figure 1c displays a high-resolution TEM (HRTEM) image of the edge of a typical graphene flake, indicating that each flake is comprised of 3 individual graphene sheets. The electron diffraction pattern (shown in inset) confirms the signature of few-layered graphene.

Graphene and Graphene Oxide: Synthesis, Properties, and Applications

Abstract: There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.

Graphene-based composites

Abstract: Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

Two-dimensional transition metal carbides.

Abstract: Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti2AlC, Ta4AlC3, (Ti0.5,Nb0.5)2AlC, (V0.5,Cr0.5)3AlC2, and Ti3AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the “A” group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.

Graphene/Polymer Nanocomposites

Abstract: Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent- and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives f...