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).

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Graphene-based composites

Graphene based materials: Past, present and future

Carbon nanotubes (CNTs) hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. Ever-increasing interest in applying CNTs in many different fields has led to continued efforts to develop dispersion and functionalization techniques. To employ CNTs as effective reinforcement in polymer nanocomposites, proper dispersion and appropriate interfacial adhesion between the CNTs and polymer matrix have to be guaranteed. This paper reviews the current understanding of CNTs and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT dispersion and functionalization on the properties of CNT/polymer nanocomposites. The fabrication techniques and potential applications of CNT/polymer nanocomposites are also highlighted.

Dispersion and functionalization of carbon nanotubes for polymer-based nanocomposites: a review

http://staff.ulsu.ru/moliver/ref/polymers/pott11.pdf

Graphene-based polymer nanocomposites

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...

Enhanced mechanical properties of nanocomposites at low graphene content.

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

Fracture and fatigue in graphene nanocomposites

Crazing is a failure mode of bulk polymers and occurs under predominant uniaxial tensile load when the bulk eventually forms denser ligaments (or fibrils) while preserving its continuity. [1‐2] The bridging of cracks by such fibrils is an importantmechanismforenergydissipationandtougheningin thermoplastic polymers. However, craze phenomena are not observed [3‐5] in thermosetting polymers such as epoxies due to the high crosslinking density of the epoxy chains, which limits molecular mobility and inhibits craze fibril formation. Such thermosetting epoxies typically display a brittle failure. [6‐7] We demonstrate here that thermosetting epoxies reinforced with amido-amine-functionalized multiwalled carbon nanotubes (A-MWNTs) exhibit crazing. We show order of magnitude reduction in fatigue crack growth rates as a result of the crazing. The fracture toughness and ductility of the brittle epoxy is also significantly enhanced by the crazing. Importantly these enhancements in fatigue resistance and toughness are achieved without any softening of the material. In fact, the Young’s modulus of the nanocomposite is � 30% greater and the average hardness of the nanocomposite is � 45% higher than the baseline (pristine) epoxy. We show that this effect is related to heterogeneous curing of the epoxy, which results in localized pockets of uncrosslinked epoxy that are trapped (or frozen) at the nanotube‐matrix interfaces. Under mechanical loading, these localized regions of high molecular mobility can evolve (or coalesce) to generate conditions that are favorable for crazing. Recently, in a very interesting study, [8] crazing has been reported for a poly(lactide

Heterogeneity in epoxy nanocomposites initiates crazing: significant improvements in fatigue resistance and toughening.

We tracked the strain-sensitive characteristic Raman G-band shift of graphene platelets in polydimethyl-siloxane (PDMS) nanocomposites revealing the filler-to-matrix interactions. We obtained large debonding strains of ∼7% for graphene in PDMS, with the peak shift rate with strain being ∼2.4 cm−1/composite strain % in comparison to single-walled carbon nanotube composites, where a relatively low rate of ∼0.1 cm−1/composite strain % was obtained, suggesting enhanced load-transfer effectiveness for graphene. A surprising observation was that for large strains (>1.5%) the graphene fillers went into compression under uniaxial tensile deformation and vice versa. We propose that this effect is related to the high mobility of the PDMS chains at room temperature.

Raman study of interfacial load transfer in graphene nanocomposites

The fatigue and failure mechanisms of epoxy composites have been researched extensively because of their commercial importance in fields demanding materials with high specific strength. Particulate, sheets, short and long fibers with dimensions in the micrometer and nanometer range are the major fillers which have been studied for enhancing the fatigue resistance of epoxies. The nano and micro scale dimensions of the fillers give rise to unexpected and fascinating mechanical properties, often superior to the matrix including fracture toughness and fatigue crack propagation resistance. Such properties are dependent on each other (e.g., the fatigue properties of the polymer composites have been found to be strongly influenced by its toughness). This article is a review of the various developments in this field and the underlying mechanisms which are responsible for performance improvements in such composites.

Fatigue and fracture toughness of epoxy nanocomposites

We demonstrate that aligned carbon-nanotube arrays are efficient transporters of laser-generated megaampere electron currents over distances as large as a millimeter. A direct polarimetric measurement of the temporal and the spatial evolution of the megagauss magnetic fields (as high as 120 MG) at the target rear at an intensity of (10(18)-10(19)) W/cm(2) was corroborated by the rear-side hot electron spectra. Simulations show that such high magnetic flux densities can only be generated by a very well collimated fast electron bunch.

https://link.aps.org/accepted/10.1103/PhysRevLett.108.235005

Iti Srivastava

Papers

Fracture and fatigue in graphene nanocomposites

Heterogeneity in epoxy nanocomposites initiates crazing: significant improvements in fatigue resistance and toughening.

Raman study of interfacial load transfer in graphene nanocomposites

Fatigue and fracture toughness of epoxy nanocomposites

Macroscopic transport of mega-ampere electron currents in aligned carbon-nanotube arrays.