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This work studied few-layer graphene (FLG) dominant action mechanisms as a photo-stabilizer. High-density polyethylene (HDPE) containing 0-0.5 wt% FLG were exposed to UVA radiation in a QUV chamber, according to ASTM G154 for different exposure times, ranging from 0 to 672 h. The chemical, rheological, and mechanical properties were tracked using attenuated total reflection-Fourier transform infrared (ATR-FTIR), rheological measurements, and tensile tests. The experimental results showed that the addition of only 0.25 wt% FLG fully stabilized 1- to 3-mm thick HDPE for an exposure time of 672 h. Electron paramagnetic resonance (EPR) test was performed on the UV-exposed mixture of hydrogen peroxide ([H.sub.2][O.sub.2]) and the FLG aqueous suspensions (0, 0.2, 1, and 5 mg/mL), to study the FLG performance and mechanisms as a photo-stabilizer. The results showed that FLG effectively decreased the characteristic EPR signal intensity due to both UV absorption/reflection and free radical scavenging. Fifty-seven percent of the reduction was found to be due to UV absorption/ reflection and 43% due to free radical scavenging. It is demonstrated that UV absorption/reflection and free radical scavenging are the dominant ones among the three FLG photo-stabilizing mechanisms (UV absorption/reflection, free radical scavenging, and physical barrier to oxygen). Highlights * FLG showed potential as a photo-stabilizer for HDPE. * Addition of 0.25 wt% FLG fully stabilized HDPE for 672 h of UVA exposure. * FLG demonstrated UV absorption/reflection and free radical scavenging effects. KEYWORDS graphene, photo-oxidative degradation, photo-stabilizer, physical barrier, radical scavenger, UV absorption/reflection, 1 | INTRODUCTION Graphene, a two-dimensional carbon-based material, has attracted the attention of both academics and industrialists due to its exceptional chemical and physical properties. (1-3) In recent years, graphene [...]

The self-healing performance of epoxidized deproteinized natural rubber (EDPNR) and EDPNR/graphene oxide (GO) composites was investigated. Composites of EDPNR25 and EDPNR50 with GO contents of 0.5 and 1.0 phr were prepared by adding a GO dispersion into a EDPNR latex and the product was subsequently cast into films. Tensile strengths of the original samples and after self-healing were used to evaluate self-healing performance. The tensile strength of EDPNR25 after self-healing achieved about 65% of tensile strength of original EDPNR25. The recovery of tensile strength for the composite increased to 81% for EDPNR25/GO0.5 and 105% for EDPNR25/GO1.0 for self-healing at 25[degrees]C for 24 h. At 70[degrees]C, EDPNR25/GO0.5 and EDPNR25/GO1.0 composite achieved ~100% recovery after 24 h. On the other hand, the tensile strength recoveries of EDPNR50, EDPNR50/GO0.5, and EDPNR50/GO1.0 were relatively low (33%, 28%, and 24%, respectively) at 25[degrees]C. At 70[degrees]C, recoveries increased to 63%, 67%, and 52%, respectively. This result demonstrated that the interdiffusion of epoxidized natural rubber molecules plays a key role in the self-healing performance rather than hydrogen bonds between GO and functional groups on EDPNR molecules. KEYWORDS epoxidized deproteinized natural rubber, graphene oxide, hydrogen bonds, interdiffusion, self-healing, 1 | INTRODUCTION In recent years, humans have been facing environmental problems of discharging thermoset plastics and vulcanized natural rubber (VNR) products since these materials are difficult to be recycled [...]

This study investigates and predicts the tribological properties of an imidazolium ionic liquid modified graphene oxide (ILGO) with silicone rubber (QM) composite. The pin on the disc tribometer was utilized to conduct experimental tribological property analysis, with load, sliding velocity, and temperature as changing parameters. Coefficient of friction (COF) of QMILG01.5 was 42% lower than that of pure QM. Study found that ionic liquid serves as a self-lubricating layer for graphene, establishing a solid graphene-to-ionic liquid interface bond with the rubber matrix. The experimental data were utilized for training artificial neural networks (ANNs), which were then used to predict the COF of the nanocomposites for values for which the experiment was not performed. The produced composite's predictions of friction coefficient utilizing the ANN technique were quite close to experimental results. The work's fundamental goal is to buy experimentation verifies the COF of functionalized graphene oxide (ILGO) with silicone rubber composite, use the actual experimental values to train a deep neural network using Multilayer perceptron, and then use the trained network to predict the values of COF for which obtaining the values by experimentation was difficult. KEYWORDS graphene oxide, ionic liquids, multilayer perceptron, silicone rubber, tribology, 1 | INTRODUCTION Silicone rubber (QM) is a synthetic elastomer with a solid silicone-oxygen chemical structure that contributes to its excellent properties, high chemical and thermal stability, and biocompatibility. [1] [...]

The article explores viscoelastic and mechanical property analysis of graphene decorated with graphene quantum dots (GDGQD) reinforced epoxy composite. Tensile, nanoindentation, and nano-dynamic mechanical analysis (DMA) tests were conducted on the composite with 0 to 1 wt% filler variation (an interval of 0.25 wt% maintained). The hardness and elastic modulus for two different loading conditions under a frequency range of 10 to 250 Hz were performed. The viscoelastic properties described through loss tangent and storage modulus graphically and the various factors such as modulus and depth of penetration were influenced by force frequency and mobility of the molecular chain. The results revealed the role of GDGQDs as filler material for enhancing the nanomechanical and tensile properties of the epoxy matrix. The differences in the properties can be ascribed to the filler interfacial bonding with the polymer matrix at the molecular level. The macro-level properties like tensile properties following the same trend as that of the micro-level properties like nanoindentation and nano-DMA results. Further, with the GDGQD aspect ratio, and assuming three-dimensionally filled randomly orientation of filler, the Halpin-Tsai model was satisfied with the experimental tensile modulus values. KEYWORDS epoxy, graphene, nano-indentation and nano-DMA, tensile strength, 1 | INTRODUCTION Epoxy is an important grade of polymers used for diverse applications such as adhesives, anticorrosive coatings, insulations for electronic devices, and polymer matrix composites. The synthesis of [...]

The discovery of radiation-shielding materials remains a critical technology to enable long-term space travel and extraterrestrial colonization. Hydrocarbon polymers, such as high-density polyethylene (HDPE), are among the best radiation attenuators due to their rich H content and lightweight. Due to their simple chemical structure that lacks larger heteroatoms, HDPE is also resistant to numerous radiation-induced degradation pathways that often limit the applicability of more sophisticated polymers. One drawback of hydrocarbon polymers is their inferior mechanical properties, such as tensile strength and impact toughness, relative to metals and other high-performance polymer systems. In this report, we develop an alkylated reduced graphene oxide that is used as an additive to enhance the storage and tensile moduli of HDPE by 10-15% across the lunar temperature range. These additives outperform unmodified reduced graphene oxide by 30% due to better dispersion through the polymer matrix as observed by cross-sectional scanning electron microscopy., INTRODUCTION A major barrier to long-term space exploration is the development of technologies to protect astronauts and their equipment from harmful levels of radiation exposure [1, 2], which can lead [...]

Three-dimensional (3D) graphene aerogel (GA) with a spatial porous structure and network skeleton was facilely prepared via one-step self-assembly hydrothermal reduction. Such network structure is regarded as a critical advantage in resolving the dispersion of graphene in polymer matrix, thereby enhancing the damping property. Here, as-prepared GA was added to the carboxylated butadiene nitrile rubber/polyurethane blend (XNBR/PU) by melting/mechanical complex method. Their dynamic mechanical properties were investigated in detail, and the relationship between thermal aging and dynamic mechanical properties had also been studied. Finding that the storage modulus and loss modulus of XNBR/PU were continually improved with the increase in addition amount of high-performance GA, reaching 3,219 and 316 MPa with the content of 3 wt% GA, respectively. Loss factor (tano) of XNBR/PU with GA shows two sets of maximum values (0.22 and 0.61) at around -25 and 0.6[degrees]C, respectively. Results illustrate that GA can greatly improve the damping performance, damping temperature range, mechanical properties, and thermal aging resistance of XNBR/PU blend, mainly depending on the performance characteristics of GA and interface interaction between GA and XNBR/PU. Verifying that GA with 3D network structure holds a great prospect for damping materials., INTRODUCTION With the rapid development of modern industrial technology, the damage of vibration and noise has made severely negative influence on the reliability and safety of equipment [1, 2]. Vibrations [...]

Graphene oxide (GO) nanoparticles were introduced in the interlaminar region of carbon fiber-epoxy composites by dispersing it in a thermoplastic polymer carrier such as polyvinylpyrrolidone (PVP). Mode-I fracture toughness ([G.sub.IC]) was investigated using double cantilever beam testing to evaluate the effect of the GO on the delamination behavior of the composite. The GO content was varied from 0% to 7% by weight as a function of the PVP content. Improvement of ~100% in the Mode I fracture toughness ([G.sub.IC]) was observed compared to composites with no GO. The optimum amount of nanoparticles for improving the interlaminar fracture toughness was found to be ~0.007% by weight of the composite. The increase in the value of flexural strength value was also observed. Scanning electron microscopy of fracture surfaces, X-ray diffraction, and transmission electron microscopy, and reflectance Fourier transform infrared spectra, as well as Raman spectroscopy results, are presented to support the conclusions., INTRODUCTION Due to their high specific strength, carbon fiber reinforced composites find wide applications as lightweight and high strength materials, especially for aerospace applications. However, these composite materials are extremely [...]

In this work, the influence of graphene oxide (GO) doped poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin nanocomposite on an indium-tin-oxide (ITO) anode, as hole transport layer (HTL) in perovskite solar cells, was investigated. Different concentrations of GO were added into the PEDOT:PSS in order to enhance its conductivity. In particular, the influence of GO content on the rheological and thermal properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/ GO nanocomposites was initially examined. The GO filler was prepared by using modified Hummers method and dispersed into PEDOT:PSS in different quantity (ranging from 0.05 to 0.25%wt/wt). The obtained nanocomposite solutions were analyzed by rheological characterizations in order to evaluate the influence of the GO filler on the viscosity of the PEDOT:PSS matrix. The wettability of solutions was evaluated by Contact Angle (CA) measurements. The quality of GO dispersion into the polymer matrix was studied using Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Thermal characterizations (DSC and TGA) were, finally, applied on nanocomposite films in order to evaluate thermal stability of the films as well as to indirectly comprehend the GO influence on PEDOT:PSS-water links., INTRODUCTION Since the discovery of conductive polyacetylene in 1978 [1-3], conductive polymers have attracted the attention worldwide because they combine the properties of metals and polymers [4], However, application and [...]

pH- and temperature-responsive double network hydrogels (DN hydrogels) were prepared by using poly (N-isopropylacrylamide) (PNIPAM) as a tightly crosslinked network (1st network), polyacrylic acid (PAA) as a loosely crosslinked network (2nd network), with clay and graphene oxide as effective crosslinkers and reinforcing fillers. The structure and morphology of the hydrogels were characterized by SEM, FTIR, DSC, and TGA. The synergetic effects of clay, GO and DN structure on various physical properties were investigated. With the increasing of crosslinking densities, the swelling ratios of DN hydrogels gradually decreased by increasing the contents of graphene oxide and PAA. While the DN hydrogels had much better mechanical properties than that of the conventional chemically cross-linked PNIPAM hydrogels., INTRODUCTION Responsive hydrogels, with capability to respond to external stimuli, such as temperature, pH, and photons, have attracted great attention. Usually, such kind of hydrogel systems can be served as [...]

The objective of this study was to prepare chitosan and starch composite films by the addition of 0-3 wt% graphene nanosheets. The film's tensile strength (TS), tensile modulus (TM), elongation at break (E), moisture uptake (Mu), and water vapor transmission rate (WVTR) were investigated. The surface morphology of the composite films was studied using scanning electron microscopy (SEM). Regardless of biopolymer type, both the TS and TM of the composite films first increased and then decreased with graphene loading. Composite film made with native (unmodified) starch showed lower TS and TM than those with chitosan. Composite films exhibit lower E values than pure chitosan and starch; this is attributed to the increase in the hardness of the films. SEM micrographs indicated that, the surface roughness and phase separation increased with increasing graphene content. This is due to the aggregation of graphene nanosheets, leading to the reduced compatibility of biopolymers. The addition of graphene considerably decreased WVTR and Mu of the composite films. These results indicated that graphene is a promising reinforcing agent for biopolymer composite films., INTRODUCTION Ecological concerns and the impending depletion of fossil fuels are driving the development of new biocomposites as green products [l]. Bio-composites are a new generation of composite materials that [...]

The physical properties of Afunctional epoxies would be improved by adding nanofillers and multifunctional epoxies. Therefore, in this study, a tetrafunctional epoxy was added to difunctional epoxy GNPs nanocomposites. An [...]

Dislocations represent one of the most fascinating and fundamental concepts in materials science (1-3). Most importantly, dislocations are the main carriers of plastic deformation in crystalline materials (4-6). Furthermore, they can strongly affect the local electronic and optical properties of semiconductors and ionic crystals (7,8). In materials with small dimensions, they experience extensive image forces, which attract them to the surface to release strain energy (9). However, in layered crystals such as graphite, dislocation movement is mainly restricted to the basal plane. Thus, the dislocations cannot escape, enabling their confinement in crystals as thin as only two monolayers. To explore the nature of dislocations under such extreme boundary conditions, the material of choice is bilayer graphene, the thinnest possible quasi-two-dimensional crystal in which such linear defects can be confined. Homogeneous and robust graphene membranes derived from high-quality epitaxial graphene on silicon carbide (10) provide an ideal platform for their investigation. Here we report the direct observation of basal-plane dislocations in freestanding bilayer graphene using transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. Our investigation reveals two striking size effects. First, the absence of stacking-fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern that corresponds to an alternating AB ↔ AC change of the stacking order. Second, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane that results directly from accommodation of strain. In fact, the buckling changes the strain state of the bilayer graphene and is of key importance for its electronic properties (11-14). Our findings will contribute to the understanding of dislocations and of their role in the structural, mechanical and electronic properties of bilayer and few-layer graphene., In graphite, the bulk material most closely related to graphene, basalplane dislocations have been well known since the early 1960s (15). The dissociation of perfect basal-plane dislocations into pairs of [...]

Using friction force microscopy, we compared the nanoscale frictional characteristics of atomically thin sheets of graphene, molybdenum disulfide (Mo[S.sub.2]), niobium diselenide, and hexagonal boron nitride exfoliated onto a weakly adherent substrate (silicon oxide) to those of their bulk counterparts. Measurements down to single atomic sheets revealed that friction monotonically increased as the number of layers decreased for all four materials. Suspended graphene membranes showed the same trend, but binding the graphene strongly to a mica surface suppressed the trend. Tip-sample adhesion forces were indistinguishable for all thicknesses and substrate arrangements. Both graphene and Mo[S.sub.2] exhibited atomic lattice stick-slip friction, with the thinnest sheets possessing a sliding-length--dependent increase in static friction. These observations, coupled with finite element modeling, suggest that the trend arises from the thinner sheets' increased susceptibility to out-of-plane elastic deformation. The generality of the results indicates that this may be a universal characteristic of nanoscale friction for atomically thin materials weakly bound to substrates. 10.1126/science.1184167

Author(s): Astrid S. de Wijn (corresponding author) [1] As anyone who has slipped on wet autumn leaves might realize, friction in layered materials can behave in peculiar ways. Such friction [...]

The effects of atomic hydrogen chemisorption on the structure and morphology of graphene layers and single-walled carbon nanotubes (SWCNTs) are studied. The structural analysis of the relaxed hydrogenated surfaces has shown a tendency for clustering of hydrogenated and of nonhydrogenated sites, leading to surface morphologies characterized by ripples.

The inhomogeneities are examined in the charge density of unintentionally doped graphene on Si[O.sub.2] prepared by mechanical exfoliation. The results have shown how graphene levels have varied within the same flake depending on the distance between graphene and the substrate.

The scope of various types of two-dimensional carbon nanostructures including graphene and free-standing carbon nanowalls/nanosheets are discussed. The synthesis, characterization and potential applications of the carbon nanostructures are presented.

Several molecular dynamics simulations are conducted to determine the effects of temperature and strain-rate on the variations observed in the fracture strength of graphene. The results demonstrate that the any kind of changes do not affect the strength of the material, as it always remains strong.

The gradient approximation approach is employed to explain the different optical properties of the various deformed few-layer AB-stacked graphenes. The optical properties are shown to be highly dependent on the number of the layers.

The atomic force microscopy technique is employed to explain the various mechanical properties of the suspended graphene layers exhibiting a completely rippled structure. The results demonstrate that at the concave region, the local spring constant exhibits an extremely large value.

The morphological stability of a graphene monolayer on an oxide substrate, subject to van der Waals interactions and in-plane mismatch strains, is analyzed. The theoretical results have suggested some ways to control the morphology of supported graphene monolayers by substrate surface patterning and strain engineering.

An oxidized form of graphene -- single-atom-thick layers of carbon -- is extremely flexible, despite also being very resistant to stretching. Cécile Zakri at the University of Bordeaux in France [...]

A composite thread with a structure inspired by nacre--the iridescent material found inside many seashells--is the strongest graphene-based fibre ever made. Such fibres are typically produced by spinning together nanometre-thick [...]