Graphite Nanoplatelets Research Articles

Effect of dispersion methods on the performance of novel rigid copolymer polyurethane nanocomposites based on graphene nanofillers

ABSTRACT The Rigid Copolymer Polyurethanes (RCPUs) as nanocomposites were synthesized by in-situ polymerization (ISP), melt compounding (MC), and solution mixing (SM) with wide range of weight ratios of graphite nanoplatelets (GNP). The blending process was utilized to obtain well- dispersed of GNP and thus strong interaction, leading to an effective performance of the RCPU/GNP nanocomposites. The structure of RCPU/GNP nanocomposites was studied using FTIR test. The thermal stability of RCPU nanocomposites was seen by TGA analysis, showing an increase with addition of GNP nanofillers. Rheology analysis revealed network formation with well-dispersed GNP regarding different dispersion approaches. Thermal and electrical tests were also conducted, approving that dispersion and interaction of GNP can play a crucial role for enhancing the thermal and electrical properties. Such a significant improvement in RCPU matrix performance could lead to the use of this material for different application.

Zero valence iron nanocube decoration of graphitic nanoplatelets

Graphitic nanoplatelets (GNPs) have been treated using an ultrasonicated ozonolysis procedure to produce stable aqueous dispersions that facilitate deposition of thin films using electrophoretic deposition. The thin GNP films were then coated with zero valence (ZV) iron nanocubes using a pulsed electrodeposition technique. Characterization of the ZV-iron coating with deposition time revealed that the changing magnetic character of the ferromagnetic-graphitic hybrid material was related to the nucleation density and growth of the ZV-iron nanocubes. Density functional theory calculations show a preference for ZV-iron adsorption at the oxygen sites of the GNPs, with ZV-iron displacement of oxygen groups favored in some configurations. Transmission electron microscopy studies confirm ZV-iron growth nucleates preferentially at the graphite nanoplatelet edges and the hybrid material magnetism is affected by the convergent crystalline grain boundaries formed between adjacent ZV-iron nanocubes.

Poly(Lactic Acid)/Graphite Nanoplatelet Nanocomposite Filaments for Ligament Scaffolds.

The anterior cruciate ligament (ACL) is one of the most prone to injury in the human body. Due to its insufficient vascularization and low regenerative capacity, surgery is often required when it is ruptured. Most of the current tissue engineering (TE) strategies are based on scaffolds produced with fibers due to the natural ligament’s fibrous structure. In the present work, composite filaments based on poly(L-lactic acid) (PLA) reinforced with graphite nanoplatelets (PLA+EG) as received, chemically functionalized (PLA+f-EG), or functionalized and decorated with silver nanoparticles [PLA+((f-EG)+Ag)] were produced by melt mixing, ensuring good filler dispersion. These filaments were produced with diameters of 0.25 mm and 1.75 mm for textile-engineered and 3D-printed ligament scaffolds, respectively. The resulting composite filaments are thermally stable, and the incorporation of graphite increases the stiffness of the composites and decreases the electrical resistivity, as compared to PLA. None of the filaments suffered significant degradation after 27 days. The composite filaments were processed into 3D scaffolds with finely controlled dimensions and porosity by textile-engineered and additive fabrication techniques, demonstrating their potential for ligament TE applications.

Rheological Properties of HDPE based Thermoplastic Polymeric Nanocomposite Reinforced with Multidimensional Carbon-based Nanofillers

The present investigation focused on the evaluation of rheological properties HDPE reinforced with equal weight percentage (i.e., 0.1 wt. %) of Nano-diamond (0D), Carbon nanotubes (1D), and Graphite Nano-platelets (2D) multidimensional nanofillers. The results like storage modulus, loss modulus, Tan delta, and complex viscosity results expounded from the rheological test with a frequency sweep from 10-1 to 102 rad/s. The highest storage modulus was perceived by 0.1 CNT-based composites, i.e., 18408 Pa, which decreased to 19, 52, and 85 % for 0.1 GNP, 0.1 ND, and pure, respectively. A similar trend was observed for loss modulus and damping factor results. The shear-thinning behavior observed in viscosity results and the addition of ND nanofillers improve the viscosity to a large amount. The potential applications of the composites include polymer gears, landing mats, cams, and various functional elements.

Structural, thermal and dielectric behaviour of exfoliated graphite nanoplatelets (xGnP) filled EVA/EOC blend composites

Nano-composites of xGnP filled ethylene vinyl acetate (EVA)/ethylene-octene copolymer (EOC) (80–20) blend with 0, 1, 3, 5, 9, 11 wt % of xGnP were fabricated by solution casting followed by compression moulding. The room temperature X-ray diffraction (XRD) pattern and field emission scanning electron microscope (FESEM) of the investigated samples reflect distribution of exfoliated graphite nanoplatelets (xGnP) in the EVA/EOC matrix. The thermo-physical properties of the composites were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis shows that with increase in xGnP contents, crystallisation temperature increase and act as a nucleating agent. TGA analysis data validates the stability of composites with increase in xGnP wt % in the composites. The dielectric and conducting behaviours of the studied samples were investigated by computer controlled impedance analyser within the frequency range of 100 Hz to 5 MHz. The room temperature relative permittivity (εr) value increases with rise in wt % of xGnP loading and achieved maximum at 9 wt % and then it falls. Similar behaviour also noticed in ac conductivity study. The nature of charge carriers in the composites were investigated by utilising non-destructive impedance spectroscopy technique. The theoretical fitting of experimental data of Nyquist plot reveals all the compounds perform the bulk behaviour. Additionally, ac conductivity study validates Johnsher’s universal power law which confirms motions of the charges are translational one. I ∼ V characteristics of the studied samples were carried out by using Keithly electrometer which confirms that conduction behaviour was non-Ohmic at lower wt % xGnP loading but Ohmic conduction was achieved at higher wt % xGnP loading. From both impedance and I ∼ V study we have also confirmed the increases in conductance with increase in wt % of xGnP loading and shows similar phenomena as observed in dielectric study.

A qualitative understanding of high intensity mechanical shearing and exfoliation of graphite nanoplatelets in a three-body contact using molecular dynamic simulations

Graphite and graphene-based lubricants are increasingly investigated for manufacturing processes such as forming and machining. Their effectiveness depends on trapping graphite particles in between the tribologically interacting surfaces and the consequent shearing and exfoliation of the graphitic layers. The mechanism by which such shearing and exfoliation occurs is however difficult to elucidate through experiments. To address the aforementioned difficulty, we have carried out molecular dynamics studies of graphene exfoliation by simulating a three-body rubbing contact scenario, with graphite nanoplatelet trapped between iron and diamond. The iron is given simultaneous normal and shear velocities towards the stationary diamond surface. High intensity continuous rubbing, simulated via large sliding distances and diminishing gaps between the iron and diamond surfaces, is used to understand the extent of exfoliation and the damage incurred in the exfoliated layers. Simulations show that under certain conditions, layer shearing and exfoliation result in graphene layers being produced. Increasing normal velocity and decreasing the shear velocity increases the number of fragments produced. Several phenomena observed in the simulations, such as locking-in of layer orientations, tearing of edges, amorphization, and iron contamination, agree qualitatively with experimental observations. The insights from this study can be used to optimize and control the process parameters of friction induced mechanical exfoliation processes and also to understand the usable life of graphite-based lubricants.

Excellent Thermally Conducting Ni Plating Graphite Nanoplatelets/Poly(phenylene sulfone) Composites for High-Performance Electromagnetic Interference Shielding Effectiveness.

First, nickel particles were deposited on the surface of graphite nanoplatelets to fabricate highly conductive GnPs@Ni core-shell structure hybrid fillers via electroplating. The modified GnPs were blended with polyphenylene sulfone via the solution blending method, followed by the hot-pressing method to achieve high thermally conducting GnPs@Ni/PPSU composites for high performance electromagnetic interference effectiveness. The results showed that in-plane and through-plane thermal conductivity of the composite at the 40 wt% filler loading could reach 2.6 Wm−1K−1 and 3.7 Wm−1K−1, respectively, which were 9.4 and 20 times higher than that of pure PPSU resin. The orientation degree of fillers was discussed by XRD and SEM. Then, heat conduction data were fitted and analyzed by the Agari model, and the heat conduction mechanism was further explored. The testing results also demonstrated that the material exhibited good conductivity, electromagnetic shielding effectiveness and superior thermal stability. Overall, the GnPs@Ni/PPSU composites had high thermal conductivity and were effective electromagnetic shielding materials at high temperatures.

Graphite nanoplatelets filled silicone composites with novel electrical and dielectric properties

In the design of medium and low voltage equipment such as cable accessories, generator, motor end windings or bushings, issues with electrical field enhancement occur at interfaces between insulators and conductors, resulting in accelerated material ageing. The purpose of this paper is to present a novel dielectric composite material which has the properties to mitigate this local amplification. It is a functional dielectric which resistivity decreases by several orders with electric field from 1014 to 109 Ωm up to 1 kV mm−1 while the dielectric constant decreases from 15 to 12 in the 10–2–106 Hz range. This novel material is made with graphite nanoplatelets. It may be used as a resistive or capacitive field grading material in electrical applications.

Effect of graphite nanoplatelets percentage on the in plane thermal diffusivity of ultra-thin graphene based (nanostructured) composite

The increasing demand for high-performance materials in thermal management has focussed the attention on new materials like graphene/graphite paper. These materials offer a unique combination of properties, such as: high electrical and thermal conductivity, high thermal diffusivity, they are flexible, lightweight, good mechanical properties and, sometimes, cost-effective. However, compared to traditional materials, their thermal characterization is more complex. Consequently, it is important to develop and assess both low-cost techniques for GNP composite paper production, as well as procedures to measure their thermal properties. In the present work, graphite nanoplatelets composite (GNPs composite) with different GNP content (in the range 70–100%) were adopted for the production of thin foils (50–70 µm in thickness) by solvent impregnation techniques, followed by hot plate curing. Spatially Resolved Method (SRM) technique was adopted to measure the in-plane thermal diffusivity of the composites. Tests were carried out adopting a diode laser as a heat generator and an IR camera to acquire the temperature distribution after heating. Two different procedures were adopted: in the first, the samples were coated by a radiation absorbent paint, with a known emissivity. The second one involves the use of the “as-received” samples and their actual emission coefficient. ANalysis Of VAriance was adopted to discriminate the effect of the radiation absorbent coating and the GNP content. From the results, the SRM technique is an effective method for the measurement of in-plane thermal diffusivity of ultra-thin GNP composites. The latter varies in the range 33–87 mm2/s, according to the GNP content.

Magnetoresistance of graphite nanoplatelets with different structure

The magnetoresistance of bulk specimens of graphite nanoplatelets obtained by different methods is studied in magnetic fields up to 2.2 T. It has been established that magnetoresistance is negative for graphite nanoplatelets prepared by chemical treatment of source graphite with a solution of potassium permanganate in sulfuric acid. This negative magnetoresistance can be explained in terms of the model of charge carrier's weak localization in a system with imperfect structure. It has been established that the magnetoresistance is positive and independent of temperature for graphite nanoplatelets produced by sonication method. Moreover, magnetoresistance is linear relative to a magnetic field in fields above ∼0.7 T. It is shown that linear magnetoresistance can be explained in the terms of the Abrikosov's model of quantum linear magnetoresistance.

Semi-quantitative orientation control of graphite nanoplatelets in GNP/PU nanocomposite via balancing the effects of gravity and micro-flow field and application in manufacturing heat spreader substrate with excellent thermal conductivity

As the huge demand for a multifunctional electronic device with high performance, an important technology in next-generation electronics is thermal management and there are numerous uses for it in enhancing the reliability and sustainable utilization. In this work, a high thermal conductivity substrate based on graphite nanoplatelets (GNPs)/ polyurethane (PU) nanocomposite film is fabricated. The GNPs’ orientation can be semi-quantitative controlled by balancing the effect of gravity and micro-flow field, which results in a thermal conductivity varies from 38.1 W (m·K)-1 to 19.8 W (m·K)-1 as the orientation rearrangement. Meanwhile, Interfacial thermal resistance is evaluated by the Effective medium theory (EMT) models, which is about 1.76 × 10-6 K m2/W to 2.0 × 10-6 K m2/W at 30 °C. Additionally, the chip fixed to the GNP/PU substrate (38.1 W (m·K)-1) could work under a lower temperature than the commercial polycarbonate substrate. Our method is a promising strategy for thermal management of next-generation electronics devices.

3D Interconnected Conductive Graphite Nanoplatelet Welded Carbon Nanotube Networks for Stretchable Conductors

AbstractStretchable conductors with stable electrical conductivity under harsh mechanical deformations are essential for developing next generation portable and flexible wearable electronics. To achieve both high stretchability and conductivity with electromechanical stability, highly stretchable conductors based on 3D interconnected conductive graphite nanoplatelet welded carbon nanotube (GNP‐w‐CNT) networks are fabricated by welding the junctions of CNTs using GNPs followed by infiltrating with poly(dimethylsiloxane) (PDMS). It is observed that GNPs can weld the adjacent CNTs to facilitate the formation of continuous conductive pathways and avoid interfacial slippage under repetitive stretching. The enhanced interfacial bonding enables the conductor both high electrical conductivity (>132 S m−1) and high stretchability (>150% strain) while ensuring long‐term stability (1000 stretching‐releasing cycles under 60% tensile strain). To demonstrate the outstanding flexibility and electrical stability, a flexible and stretchable light‐emitting diode circuit with stable performance during stretching, bending, twisting, and pressing conditions is further fabricated. The unique welding mechanism can be easily extended to other material systems to broaden the application of stretchable conductors to a myriad of new applications.

Effect of addition polyethylene glycol on morphology and functional groups of composite films bacterial nanocellulose - graphite nanoplatelets

Polyethylene Glycol (PEG) existence on the composite film bacterial nanocellulose (BNC) reinforced with graphite nanoplatelets (GNP) has been analyzed in this research. Pineapple peel waste extract was used to synthesis the bacterial cellulose (BC) pellicle. A 1% NaOH solution was used to remove impurities from the BC pellicle. Mechanical disintegration and a high-pressure homogenization method were used to synthesize BNC. The high-pressure homogenizer (HPH) runs for five cycles at 150 bar before being filtered with a vacuum filter. The composite films are synthesized using a mixture of BNC, PEG 1%, and GNP 2.5%. Then the mixed slurry was dried using an oven for 14 hours at a temperature of 80 degrees Celsius. The morphology of composite BNC film was observed by using SEM. The addition of PEG causes the BC structure to become more porous. GNP is not well distributed in the BNC matrix but still acts as a dispersed filler. FTIR analysis is conducted to see its functional groups. The addition of GNP caused the hydroxyl group to be significantly reduced.

Effect of graphite nanoplatelets on spark plasma sintered and conventionally sintered aluminum-based nanocomposites developed by powder metallurgy

Abstract In this work, aluminum (Al)-based nanocomposites reinforced with graphite nanoplatelets (GnPs) have been fabricated by conventional sintering as well as spark plasma sintering (SPS) techniques, and their microstructure and mechanical properties have been studied. The powder metallurgy (PM) route has been adopted to fabricate the various Al–GnP nanocomposites. Characterization of the powder mixtures and the nanocomposites has been carried out through different characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. Compressive strength, Young's modulus, density, and Vickers microhardness of the various nanocomposites have also been determined. The HRTEM results show the formation of nonstoichiometric Al4C3 nanoparticles – during both conventional sintering and SPS – at the interface of the Al grains and GnP, which worsen the mechanical properties of the nanocomposites. SPSed nanocomposites show superior mechanical properties due to higher densification, finer grain size, and homogeneous nanofiller dispersion in the Al matrix, compared to the conventionally sintered Al–GnP nanocomposites.

Structure and adhesion properties of waterborne poly(urethane urea)s containing small amounts of different graphene derivatives

Waterborne poly(urethane urea)s (PUDs) containing graphene derivatives with different morphologies and surface polarities were synthesized via in situ polymerization by using the acetone method. Small amounts (0.04–0.30 wt.%) of graphene oxide (GO), graphite nanoplatelets (GP) or milled graphite (MG) were mixed with polyadipate of 1,4-butanediol polyol and added during synthesis of the PUDs. The addition of graphene derivatives changed differently the degree of micro-phase separation of the poly(urethane urea)s (PUs) depending on the balance between the extent of covalent interactions between the surface functional groups on the graphene sheets and the isocyanate groups, and the number of stacked graphene sheets. Whereas MG mainly intercalated between the soft segments showing a typical behavior of nanofiller, GP and, particularly, GO showed different degrees of micro-phase separation due to more net covalent interactions with the poly(urethane urea) chains which caused higher crystallinity. The addition of graphene derivative decreased the glass transition temperature of the hard segments and increased the percentages of associated by hydrogen bond urethane and urea groups, more noticeably by adding GP and MG. Lower temperatures of decomposition and higher amounts of urethane and urea hard domains, and soft domains were found in PU + GO and PU + MG, and they showed an additional structural relaxation at 11–16 °C. PU and PU + GP had higher thermal stabilities than PU + GO and PU + MG and the addition of GP and, more markedly, GO imparted toughening to the poly(urethane urea). The T-peel strength values were higher in the joints made with PUD + GO due to the more net covalent interactions between the surface functional groups on the GO sheets and the poly(urethane urea) chains. On the other hand, the lap-shear strength of the joints made with PUD + MG and, in less extent, with PUD + GP noticeably increased.

Energy performance evaluation of heat storage of calcium sulfate hemihydrate composite with fine aggregate based on paraffinic phase change material

Calcium sulfate hemihydrate has been used as a building material because of its economical and non-combustible characteristics. By applying a heat storage material to a calcium sulfate hemihydrate composite (CSHC), the building energy consumption can be reduced. In this study, a CSHC with a high heat storage capacity was prepared using fine aggregates based on paraffinic shape-stabilized phase change materials (Fa-PSSPCMs) with exfoliated graphite nanoplatelets as stabilizing additives. The heat storage CSHC (Hs-CSHC) was prepared by mixing Fa-PSSPCM and calcium sulfate hemihydrate powder with water and then casting the mixture as boards using molds. For the Hs-CSHC containing 30 wt% Fa-PSSPCM, the latent heat capacities during heating and cooling were 46.39 and 44.28 J/g, respectively; its phase transition occurred at 20–35 °C. Based on analysis results, the Hs-CSHC exhibited acceptable chemical stability and high thermal performance, including a considerable latent heat capacity. The peak temperatures of Hs-CSHCs were approximately 1–2 °C lower than those of the plain CSHC. Moreover, compared with the plain CSHC, the Hs-CSHC with 30 wt% Fa-PSSPCM exhibited a time lag effect exceeding 720 min. In the energy simulation analysis, an 8.18% maximum cooling energy reduction was observed when the Hs-CSHC with 30 wt% Fa-PSSPCM was used. However, the effect of heating load reduction was insignificant due to the low outside temperature. Therefore, when a phase change material is utilized in a building, the phase change temperature and heat storage performance must be considered.

Preparation of Anticorrosive Coating with No Solvent for Repairing

The solvent-free fast-curing coating for repairing is prepared using polyurea as matrix and graphite nanoplatelets (GNPs) as fillers. The effects of GNPs on the coating are studied. The coating is prepared by HDI tripolymer and polyetheramine. The GNPs is functionalized (f-GNPs) by aminopro-pyltriethoxysilane (APTES) in mixture of water and ethanol. The performances of the coatings are tested by salt spray time, polarization curves and electrochemical impedance. The coating presents solvent-free and fast-curing characteristics and is suitable for repairing. The f-GNPs provide both physical barrier and coulomb block for the coating. When the f-GNPs added amount is 0.6 wt%, the salt spray resistance time of the coating is more than 420 h, and the corrosion potential is –0.6428 V. The effects of GNPs on coating are investigated. The results can provide a new idea for preparation of anticorrosive coating used for repairing, and can benefit in-depth understanding of the influence of f-GNPs on the coatings. The coating for repairing is prepared by adding f-GNP as fillers. The anticorrosive mechanism and performance of the coating are discussed in detail.

Copper-Exfoliated Graphite Nanoplatelet 하이브리드 입자를 이용한 PC 복합체의 기계적 성질과 열전도도

본 연구에서는 폴리카보네이트/구리-팽창흑연 나노판(PC/Cu-xGnP) 복합체가 제조되었다. PC 복합체 제조에 앞서 두 종류의 Cu-xGnP 하이브리드 입자가 제조 되었는데 하나는 xGnP가 구리에 완전 삽입된 Cu-xGnP 입자이고 다른 하나는 부분 삽입된 Cu-xGnP 입자이다. 두 종류의 하이브리드 입자의 삽입 정도는 투과 전자 현미경으로 확인되었다. 구리와 xGnP를 이용하여 제조된 PC/Cu 및 PC/xGnP 복합체와 비교하여 Cu-xGnP로 제조된 PC/CuxGnP 복합체의 기계적 성질과 열전도도가 더 우수하였다. 부분 삽입된 PC/Cu-xGnP 복합체의 열전도도는 완전 삽입된 PC/Cu-xGnP 복합체보다 모든 함량에서 높게 관찰되었다. 반면에 기계적인 성질에서는 완전 삽입된 PC/CuxGnP 복합체가 부분 삽입된 PC/Cu-xGnP 복합체보다 우수하였다.

Nano germanium incorporated thin graphite nanoplatelets: A novel germanium based lithium-ion battery anode with enhanced electrochemical performance

First-principles calculations forecast that germanium incorporated graphite has potential to be used as high performance negative electrode for lithium-ion batteries due to large mobility of electrons at the heterointerface. Inspired by this first-principles calculations, a novel functional structure of thin graphite nanoplatelets embedding a finely dispersed germanium component is fabricated through a scalable ball milling technique for the first time. Nitrogen adsorption-desorption isotherms and electron microscopy investigation demonstrate that the obtained electrode materials exhibit mesoporous features where germanium nanoparticles are implanted into the graphitic matrix of thin flakes. Such a novel structure provides several advantages including large surface area, high accessibility of lithium ions and shortened lithium ion diffusion distances, which enable fast ion and electron transfer at the interface of electrolyte and electrode. As results, the obtained electrode demonstrates promising electrochemical performance with a charge capacity of 822 mAh g−1 after 200 cycles at 0.1 C, high rate capacity of 325 mAh g−1 at 10 C and good cyclic stability with a capacity retention of 97%. This work delivers a robust electrode design strategy as well as the most practical route for the improvement of germanium-based anodes for application in lithium-ion batteries.

High-thermal-conductivity phase-change composites prepared by in situ synthesis of graphite Nanoplatelets/Cu networks for effective thermal management

Phase-change materials show considerable potential for the thermal management and thermal energy harvesting of electronics and appliances. However, the utilization of phase change materials (PCMs) for high-performance thermal management is hampered by low thermal conductivity and leakage problems. Herein, we report a novel method for preparing phase change composites (PCCs) with high thermal conductivity and inhibited leakage by constructing a network of graphite nanoplatelets (GNPs) and Cu nanoparticles (100 - 500 nm) with paraffin (PW) as the functional matrix. The study results demonstrated that under loads of 22 wt% EG and 45 wt% Cu, the thermal conductivity of the PCC sample reached 34.26 W m−1 k−1, which is a 258% increase over that of EG/PW (13.29 W m−1 k−1) and a 17000% increase over that of PW (0.2 W m−1 k−1). In addition, at ambient room temperature, the incorporation of PCCs can reduce the working temperature of a heating chip by more than 12-13 K, showing efficient and reliable thermal management performance. Skilfully designed PCCs can serve as an effective device for high energy density heat dissipation and thermal storage. The proposed method is a promising approach for preparing PCCs for use in large-scale heat storage and electronic equipment thermal management.