Graphene Nanoplatelets Particles Research Articles

Flammability, Smoke, Mechanical Behaviours and Morphology of Flame Retarded Natural Fibre/Elium® Composite.

The work involves fabrication of natural fibre/Elium® composites using resin infusion technique. The jute fabrics were treated using phosphorus-carbon based flame retardant (FR) agent, a phosphonate solution and graphene nano-platelet (GnP), followed by resin infusion, to produce FR and graphene-based composites. The properties of these composites were compared with those of the Control (jute fabric/Elium®). As obtained from the cone calorimeter and Fourier transform infrared spectroscopy, the peak heat release rate reduced significantly after the FR and GnP treatments of fabrics whereas total smoke release and quantity of carbon monoxide increased with the incorporation of FR. The addition of GnP had almost no effect on carbon monoxide and carbon dioxide yield. Dynamic mechanical analysis demonstrated that coating jute fabrics with GnP particles led to an enhanced glass transition temperature by 14%. Scanning electron microscopy showed fibre pull-out locations in the tensile fracture surface of the laminates after incorporation of both fillers, which resulted in reduced tensile properties.

Thermal enhancement of paraffin/hydrophobic expanded perlite granular phase change composite using graphene nanoplatelets

Thermal performance of latent heat thermal energy storage (LHTES) systems is often limited by low thermal conductivity of phase change materials (PCMs), which reduces the heat transfer rate and energy storage efficiency. This study investigates the development of a thermally enhanced paraffin/hydrophobic expanded perlite (EPOP) form-stable PCM seeded with graphene nanoplatelets (GNP) as a heat transfer promoter. Experimental research was carried out on fabrication, characterization and heat transfer performance analysis of EPOP–GNP composite. It was shown that the GNP particles were partially immersed into the paraffin occupied in the pores of EPO, which remarkably improved the thermal properties and heat transfer performance of composite PCM. In comparison with EPOP, the addition of 0.5 wt% GNP increased the thermal conductivity by up to 49%. Heat transfer performance test also showed that the EPOP–GNP composite reduced the heat storage/release duration by up to 20%, compared to EPOP. Moreover, prototype test room experiment conducted on cement mortars containing EPOP–GNP revealed that the introduction GNP into form-stable PCM significantly enhanced the thermal energy storage performance of cement mortars. This is particularly demonstrated by the reduction in peak inner surface temperature of 0.8 °C and the increase in inner surface convective heat gain energy by 78%, compared to cement mortars containing EPOP only. It can be said, therefore, the integration of GNP into form-stable PCMs is a promising way to achieve high energy storage efficiency for numerous LHTES applications such as solar energy storage and energy conversation in buildings.

Evaluation of multi-layered graphene nano-platelet composite coatings for corrosion control part I - contact potentials and gas permeability

The electronic and diffusion-blocking properties of graphene nano-platelets (GNPs) are quantified with a view to understanding their action as (possible) additives to anti-corrosion coatings. Platelet size and thickness are determined by SEM and BET specific surface area measurements. A Scanning Kelvin probe is used to show that a contact potential of up to 1.2V develops between GNP particles and various metal substrates: silver, copper, iron and zinc. A novel photochemical method is used to show that oxygen permeation rates through a PVB-GNP (polyvinylbutyral) composite coating decrease by over an order of magnitude as GNP volume fraction increases to 0.056.

Controlling dispersion of graphene nanoplatelets in aqueous solution by ultrasonic technique

The homogenous graphene nanoplatelets (GNP) suspension had been prepared through ultrasonic exfoliation in the presence of methylcellulose (MC) as dispersant. The influence of different sonication times on dispersing of aqueous GNP suspension was monitored by UV–Vis absorbance, sedimentation test, optical microscope and transmission electron microscope (TEM). The study of UV–Vis absorbance verifies that the minimum sonication time to break the 0.1 g/L concentration of bundled GNPs is 20 min; furthermore, the GNP suspension achieved the best dispersion, when sonication time increased up to 80 min. From optical microscope images of GNPs, the agglomeration of GNPs was broken by enough sonication energy, and the distribution of GNPs particles became more uniform. The dispersing mechanism had been discussed and simulated by HRTEM image. The bundled GNPs were exfoliated by cavitation effect of ultrasonic irradiation, meanwhile, the dispersant adsorbed on the surface of GNPs prevented re-entanglement by forming steric hindrance.

Graphene nanoplatelets enhanced myo-inositol for solar thermal energy storage

Thermal behavior of nanocomposite phase change materials, Myo-inostol (MI) (a sugar alcohol) added with graphene nanoplatelets (GNN) as a solar thermal energy storage system, for use in the temperature range of 100–260°C was studied. GNN is added to MI with mass fraction of 1.0, 2.0 and 3.0wt%. Thermal and chemical stability of MI and MI-GNN were investigated before and after 50 thermal cycles. Results showed that the dispersion of GNN into pure MI was effective, no crystal change and chemical reaction had taken place between GNN and MI before and after thermal cycling, only physical interaction between them had taken place. GNN particles were dispersed throughout the MI with small aggregates. The heat of fusion was found to decrease by 14.13%, 15.06% and 17.63% and heat of solidification by 13.02%, 23.12% and 29.68% for MI-GNN with 1.0, 2.0 and 3.0wt% of GNN added to MI respectively.

Effect of channel angle of pin-fin heat sink on heat transfer performance using water based graphene nanoplatelets nanofluids

This study reports an experimental work to examine the angle effect of pin fin heat sink channel in terms of convective heat transfer coefficient, log mean temperature difference and thermal resistance using water based graphene nanoplatelets (GNPs) nanofluids in a flow rate range of 0.25–0.75 LPM. Three heat sinks having channel angles, measured from positive x-axis, 22.5 degree, 45 degree and 90 degree are used. The volumetric concentration of GNPs particles is 9.5% and these particles consist of overlapped two-dimensional graphene layers. All heat sinks are fabricated with copper substrate, which is maintained at uniform heat flux during experimentation. Heat sink with 22.5 degree channel angle shows better thermal performance as compared to other tested heat sinks. For the same flow rate, 22.5 degree heat sink shows lowest convective thermal resistance as compared to other tested heat sinks.

Mechanical and thermal properties of tungsten carbide – graphite nanoparticles nanocomposites

Abstract Previous studies concerning pure tungsten carbide polycrystalline materials revealed that nanolayers of graphite located between WC grains improve its thermal properties. What is more, pressure-induced orientation of graphene nano platelets (GNP) in hot pressed silicon nitride-graphene composites results in anisotropy of thermal conductivity. Aim of this study was to investigate if addition of GNP to WC will improve its thermal properties. For this purpose, tungsten carbide with 0.5–6 wt.% of GNP(12)-additive underwent hot pressing. The microstructure observations performed by SEM microscopy. The anisotropy was determined via ultrasonic measurements. The following mechanical properties were evaluated: Vickers hardness, bending strength, fracture toughness KIc. The influence of GNP(12) addition on oxidation resistance and thermal conductivity was examined. It was possible to manufacture hot-pressed WC-graphene composites with oriented GNP(12) particles, however, the addition of graphene decreased both thermal and mechanical properties of the material.

Experimental modal analysis of masonry arches strengthened with graphene nanoplatelets reinforced prepreg composites

Strengthening of masonry structures with different engineering materials has become a challenge for civil engineers with the advancements in engineering technology. This study mainly focused on dynamic parameters of masonry arches, which were strengthened with nanoparticle reinforced prepreg composites. For this purpose, the prepreg composites were produced with carbon fiber and epoxy system which was reinforced with graphene nanoplatelets particles that was 1wt% of the epoxy system. Afterwards, four different strengthening alternatives were performed at the extrados and intrados of the masonry arches. Finally, dynamic characteristics such as mode shapes and modal frequencies of unstrengthened and strengthened arches were determined through experimental modal analysis (EMA) and numerical analysis.

Electrical and mechanical properties of graphene/carbon nanotube hybrid nanocomposites

Polymer nanocomposites with improved electrical and mechanical properties can be formulated by proper dispersion of conductive high aspect ratio nanofiller within the host polymer matrix. In this work, the microstructure, processing behavior, electrical and mechanical properties of melt-mixed graphene nanoplatelets (GNP)/polypropylene (PP) nanocomposites were investigated. In addition, the influence of processing conditions on the electrical properties of GNP/PP nanocomposites was evaluated. Moreover, GNP: carbon nanotube (CNT)/PP hybrids were prepared aiming at formulating nanostructured material with synergistic properties. The electrical percolation threshold of GNP/PP nanocomposite was found to be ∼4vol%. However, upon the introduction of only 1wt% (0.52vol%) CNT, significant improvement in the electrical properties was obtained. The CNT was found to bridge the distance between the GNP particles. At constant overall nanofiller concentration, GNP:CNT/PP hybrids exhibited improved properties with the increase in CNT volume fraction due to the better dispersion of nanotubes and strong adhesion at the nanotube/PP interface.

In Situ Synthesis of Carbon Nanotubes/Graphene Nanoplatelets Hybrid Materials with Excellent Mechanical Performance

A two-step method for the preparation of hybrid materials consisting of multi-walled carbon nanotubes (MWCNTs) attached to graphene nanoplatelets (GNPs) was proposed. Firstly, poly (acryloyl chloride) was grafted in situ onto the surface of MWCNTs. Secondly, the obtained MWCNTs (MWCNTs-PACl) were reacted with acid-treated GNPs to form a nanotube–polymer–graphene hybrid. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA) were used to investigate the forming of the hybrid materials. FTIR results showed that MWCNTs/PACl and GNPs were successfully bridged by chemical bonds like O – C = O and C – O – C . Raman spectroscopy furthermore revealed that acryloyl chloride can be used to connect the MWCNTs and GNPs due to the defects of MWCNTs, and consequently the defects of the hybrid materials were limited. Meanwhile, TEM observation demonstrated the nanostructure clearly in which the MWCNTs with a polymer layer were attached successfully on the surface of GNPs. And TGA curves reflected that the content of MWCNTs and GNPs was about 46.5% in the hybrid materials. In addition, the tensile tests results showed that MWCNTs/GNPs hybrid materials can improve the mechanical performance of epoxy composites in higher degree, compared with MWCNTs or GNPs particles alone.

Investigation on the use of graphene oxide as novel surfactant to stabilize weakly charged graphene nanoplatelets.

This paper presents a unique synergistic behavior between a graphene oxide (GO) and graphene nanoplatelet (GnP) composite in an aqueous medium. The results showed that GO stabilized GnP colloid near its isoelectric point and prevented rapid agglomeration and sedimentation. It was considered that a rarely encountered charge-dependent electrostatic interaction between the highly charged GO and weakly charged GnP particles kept GnP suspended at its rapid coagulation and phase separation pH. Sedimentation and transmission electron microscope (TEM) micrograph images revealed the evidence of highly stable colloidal mixtures while zeta potential measurement provided semi-quantitative explanation on the mechanism of stabilization. GnP suspension was confirmed via UV-vis spectral data while contact angle measurement elucidated the close resemblance to an aqueous solution indicating the ability of GO to mediate the flocculation prone GnP colloids. About a tenfold increase in viscosity was recorded at a low shear rate in comparison to an individual GO solution due to a strong interaction manifested between participating colloids. An optimum level of mixing ratio between the two constituents was also obtained. These new findings related to an interaction between charge-based graphitic carbon materials would open new avenues for further exploration on the enhancement of both GO and GnP functionalities particularly in mechanical and electrical domains.

Graphene nanoplatelets and fullerene in polypropylene matrix as nanosized dielectric probe

Composite materials of polypropylene, graphene nanoplatelets (GNP) or fullerene C60 were synthesized by in situ polymerization. GNP particles consist of 3–5 graphene layers and have aspect ratio 40. In composites with pristine GNP particles their aspect ratio is 110, whereas ultrasonic processing reduces it to 40–50. This change of aspect ratio of filler particles and their aggregates results in different properties of composites with pristine and sonicated GNP. Percolation threshold for composites with pristine GNP is 0.25% vol. In composites with sonicated GNP it is 2–3% vol. This is due to reduction in the size of filler particles aggregates and more uniform distribution of particles in polymer matrix after ultrasonic treatment. The presence of nanocarbon filler (GNP or fullerene) makes α‐transition, associated with the glass transition of the amorphous phase of polypropylene, clearly resolved. Its intensity increases with the concentration of nanofiller, which acts as a dielectric probe. POLYM. COMPOS., 36:1006–1011, 2015. © 2015 Society of Plastics Engineers

Wet spun fibers from solutions of cellulose in an ionic liquid with suspended carbon nanoparticles

ABSTRACTWet spun fibers from solutions of dissolving pulp in 1‐ethyl‐3‐methylimidazolium acetate (EmimAc) with up to 50 wt % (based on cellulose) suspended carbon black and graphene nanoplatelets particles were studied. Carbon fillers were dispersed by simple shearing in a Couette type mixer and the resulting spin dope was extruded into a hot water coagulation bath from a single hole spinneret. Microstructure, mechanical properties, and electrical conductivity were assessed as a function of filler loading and discussed in comparison to melt spun fibers with similar fillers. The coagulation process and subsequent drying of wet spun fibers was found to produce a significant microporosity, more so the higher the filler loading. The electrical percolation threshold was quite high in the wet spun fibers and relatively modest values of conductivity were obtained with regard to the high filler loadings. Carbon black was found to be superior to graphene nanoplatelets. This was related to flow‐induced orientation effects. The mechanical properties of the carbon‐filled fibers were found to be similar or lower compared to the pure cellulose fibers because of low interfacial interactions and formation of microporosity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41417.

Effect of graphene nanoplatelets on coefficient of thermal expansion of polyetherimide composite

Thermal expansion is one of the major concerns for polymer composites. In this research, graphene nanoplatelets (GNPs) were added to polyetherimide (PEId) thermoplastic polymer in order to reduce the coefficient of thermal expansion (CTE) of the injection molded composite. First, the coefficient of linear thermal expansion (LTE) was measured in three directions in the anisotropic coupon: 0°, 90° and the out of plane Z direction. It is found that the GNP particles are very effective in terms of reducing the LTE in 0° direction due to high degree of alignment. After annealing above glass transition temperature, significant increase of 0° LTE and decrease of Z° LTE were observed. The bulk CTE was calculated by adding up the LTEs in all three directions and is found to be independent of annealing. Second, several models were applied to predict both CTE and LTE. It is found that Schapery's lower limit model fits the experimental CTE very well. Chow's model was applied for LTEs in three directions. The behavior of GNP-5/PEId composites is explained by the combination of Chow's model and morphology obtained by scanning electron microscope (SEM).

Dielectric and microwave attenuation properties of graphene nanoplatelet–epoxy composites

Graphene nanoplatelet (GNP)–epoxy composites were fabricated for the investigation of the dielectric permittivity and microwave absorption in a frequency range from 8 to 20 GHz. The intrinsically conductive GNP particles and polarized interfacial centers in the composites contribute to the microwave absorption. A minimum reflection loss of −14.5 dB at 18.9 GHz is observed for the GNP–epoxy composites with 15 wt. % GNP loading, which is mainly attributed to electric conductivity and the charge multipoles at the polarized interfaces in the GNP–epoxy composites.

Multifunctional high‐density polyethylene nanocomposites produced by incorporation of exfoliated graphene nanoplatelets 2: Crystallization, thermal and electrical properties

AbstractThis research investigates the effect of exfoliated graphene nanoplatelets (GNP) on the crystallization behavior, thermal conductivity, and electrical conductivity of high‐density polyethylene (HDPE)/GNP nanocomposites. HDPE/GNP nanocomposites were fabricated by melt blending followed with injection molding. Results indicate that GNP is a good nucleating agent at low loading levels and as a result can significantly increase crystallization temperature and crystallinity of HDPE. At high GNP loadings, however, the close proximity of GNP particles retards the crystallization process. The thermal stability and thermal conductivity of HDPE/GNP nanocomposites were found to be significantly enhanced as a function of GNP concentration owing to the excellent thermal properties of GNP. Finally, the high percolation threshold of HDPE/GNP nanocomposites (∼10–15 vol%), prepared by melt blending and injection molding was successfully reduced to around 5 vol% of GNP loading by employing a novel compounding method, solid‐state ball milling. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Electron and Phonon Transport in Au Nanoparticle Decorated Graphene Nanoplatelet Nanostructured Paper

Monodispersed Au nanoparticles are synthesized on the surface of exfoliated graphene nanoplatelets (GNP) in the presence of polyethyleneimine (PEI) with microwave assisted heating. A highly structured layered Au/GNP "paper" with good flexibility and mechanical robustness is prepared by vacuum assisted self-assembly. The thermal and electrical conductivity of the hybrid paper with and without the Au nanoparticles are investigated after different experimental processing conditions including thermal annealing and cold compaction. Annealing effectively decomposes and removes the adsorbed PEI molecules and improves thermal contact between Au/GNP particles, whereas cold compaction reduces porosity and induces stronger alignment of the Au/GNP within the hybrid paper. Both approaches lead to improvement in electrical and thermal conductivity. It is also found that adjacent GNP particles are electrically connected by the Au nanoparticles but thermally disconnected. It is believed that phonons are scattered at the Au/GNP interfaces, whereas electrons can tunnel across this interface, resulting in a separation of electron and phonon transport within this hybrid paper.

Mechanical and electrical property enhancement in exfoliated graphene nanoplatelet/liquid crystalline polymer nanocomposites

A liquid crystalline polymer (LCP) poly(benzoyl-1,4-phenylene)-co-(1,3-phenylene)], nanocomposite was prepared with exfoliated graphene nanoplatelets (GnP) to achieve both high mechanical modulus and electrical conductivity. The fabrication technique and the dispersion of nanoplatelets have been shown to be critical to achieve high mechanical modulus at low filler loading. A loading of only 1vol.% of the GnP particles improved the modulus of the LCP nanocomposite by 25% and 55% at a loading of 5vol.%. The electrical conductivity the non-conductive LCP improved to a very high value of 4.5×10−4S/cm with the addition of 5vol.% of GnP nanoparticles.