Graphene Nanopowder Research Articles

Nonenzymatic glucose‐reactive electrodes fabricated from facilely‐precipitated cobalt hydroxide, commercial graphene nanopowder and ionic liquid binder

Fine Co(OH)2 powder was prepared by simple precipitation from aqueous solutions of cobalt sulfate and sodium hydroxide without using sophisticated reagents and/or approaches. The fine powder was homogeneously mixed with protonated betaine bis((trifluoromethyl)sulfonyl)amide ionic liquid ([Hbet][TFSA] IL), an amide-type hydrophobic protic IL, and then dispersed in ethanol with graphene nanopowder for being spin-coated upon screen-printed carbon electrode (SPCE) to prepare the glucose-reactive electrode. Activation of the electrode was essential to expose the glucose-oxidation activity, and the experimental evidences indicated that Co3O4 converted from Co(OH)2 during the activation process was the active species in charge of glucose oxidation. The electrode showed a wide linear dynamic range for glucose from 1 to 1757 µM with a high sensitivity of 632 µA cm− 2 mM− 1 and a detection limit of 1 µM in the electrolyte containing 0.5 M NaOH and 0.1 M NaCl. The electrode showed no response to common interferants, including alcohols, in the concentration the same as to glucose. However, ascorbic acid in the same concentration level showed severe interference but negligible in the physiological level. This study shows that Co(OH)2 prepared by facile precipitation is qualified of being an efficient electrocatalyst precursor for glucose oxidation, and IL is a good binder for immobilizing the electrocatalyst.

Selectively distributed graphene in 1,6-hexanediol diacrylate/epoxy composites via digital light processing 3D printing for enhanced thermal conductivity

A 3D-printer based on digital-light-processing (DLP) was used to build a 3D foam containing graphene nanopowder (GNP) as a thermally conductive filler. 1,6-hexanediol diacrylate (HDDA) was used as a UV-curable resin because of its low viscosity and high fidelity during printing. Foam-shaped GNP-containing HDDA was placed in a disc-shaped Teflon mold, followed by infiltration of epoxy and thermal curing. The construction of a 3D heat path was achieved by selective GNP particle distribution on the HDDA matrix. According to the GNP filler fraction of the foam-shaped composite, epoxy composite with random GNP filler distribution was also fabricated, to investigate the effect of selective to random GNP distribution and the presence of a 3D heat path on thermal conductivity enhancement. When 1.93 wt% GNP was selectively distributed, the composite exhibited about 14.6% higher thermal conductivity compared to samples with random GNP distribution. The enhanced thermal conductivity could be attributed to efficient heat transfer through the heat path constructed inside the polymer matrix.

Process intensified microwave absorption nanocomposite for stealth application

Microwave absorption materials of GHz play a substantial role in High-frequency electronic devices which have always been in high demand for their wide range of applications. In this study, Silicon Carbide - Graphene Nano Powder (SiC-GNP) hybrid nanocomposite was firstly synthesized using process intensified hydrothermal reaction to investigate its microwave absorption performance. The morphology of the hybrid nanocomposite study by Scanning Electron Microscope (SEM) showed that the silicon carbide and Graphene Nano Powder presence in the composites which indicates very much uniform over the surface. The prepared samples were characterized by X-Ray Diffraction (XRD) and Raman spectra. The relative permittivity, permeability and microwave absorption property of the SiC-GNP hybrid composite were calculated over the frequency range 8−12 GHz. The prepared sample of 25 wt.% SiC-GNP hybrid nanocomposite exhibited high microwave absorption property with a maximum reflection value of -35.2 dB with the corresponding absorption bandwidth of 4 GHz with the thickness of 1.5 mm. The result shows that the complex permeability and permittivity spectra of the microwave absorption material increase directly with the graphene volume fraction. The results recommended that the SiC-GNP hybrid nanocomposite has a high absorption at X-band which can be applied for stealth application owing to its light weight and least thickness.

Enhanced Thermo-Mechanical Properties of Poly(vinyl alcohol)/Poly(vinyl pyrrolidone) Polymer Blended with Nanographene

Background: The addition of nanofillers to polymers for enhanced performance is delivering more interesting applications for aerospace, aeronautic industries, and other numerous nanotechnical applications. Objective: The aim was, therefore, to examine the role of graphene nanopowder on the thermal stability and conductivity of the poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) polymer nanocomposites. Methods: In this work, graphene nanofillers were incorporated into the PVA/PVP polymer blended by solution mixing for the preparation of nanocomposite films. Results: Results showed that increasing graphene ratio improved thermal conductivity up to 330%, moreover enhancing hardness shore A up to 16.3% compared to pure PVA/PVP blend polymer. TGA analysis confirmed that the PVA/PVP and graphene network showed good thermal stability. Conclusion: From the present findings, it is proved that PVA/PVP blends have profound effects on thermal stability that cannot be attained by using individual counterparts. The property of the nanocomposite depends on the host blend, morphology, and interfacial characteristics.

Effect of graphene on friction and wear behavior of friction composite tested against grey cast iron disc alloyed with copper

The tribological properties of tribo-pair of friction composite and counter disc are very important for identifying the braking performance in automobiles. Among the various factors influencing the friction and wear of the tribo-pair, the ingredients of the friction composite and material of the disc are significant. In the present study, a new tribo-pair was formed between the friction composite with graphene nanopowder (GNP) and grey cast iron disc alloyed with copper (CuGCI). The tribo pair thus formed was tested in a pin-on-disc machine under dry sliding condition and its performances were compared with the other tribo-pairs formed between friction composites with graphite (Gr), Molybdenum di sulphide (MoS2) and disc. Five composites - 20 wt% MoS2, 20 wt % Gr, 20 wt % GNP, 15 wt % GNP, 10 wt % GNP - were tested against GCI and CuGCI disc thus forming ten different tribo-pair. Results showed that the tribo pair of 10 wt % GNP - CuGCI and 15 wt % GNP - CuGCI proved to have good friction and wear performances compared to the other tribo pairs and also at par with the performance of the commercial pad tested under the same conditions.

An Investigation on the Thermal and Solar Properties of Graphene-Coated Polyester Fabrics

In this study, coatings were made with graphene nanopowder in two different thicknesses (0.1 and 0.5 mm) at three different concentrations (50, 100 and 150 g/kg) on polyester woven fabrics. The effects of the coating thickness and graphene concentration were examined with optical and scanning electron microscopy (SEM) images. The thermal stability properties of the samples were also evaluated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Thermal conductivity was evaluated with two different principles: contact and radiant heat transfer, according to JIS R 2618 and EN ISO 6942, respectively. Solar measurements were performed with a Shimadzu UV-3600 Plus spectrophotometer. The graphene coating improved the thermal stability of the polyester fabrics. The solar absorbance value increased by 80% compared to reference fabrics, and reached approximately 90%. One of the important results was that the thermal conductivity coefficient increased by 87% and 262% for the two coating thicknesses, respectively.

Preparation of hollow PCL microspheres by o/w single emulsion-solvent evaporation method in the presence of graphene nanopowders

Preparation of hollow PCL microspheres by o/w single emulsion-solvent evaporation method in the presence of graphene nanopowders

Flexible Piezoelectric Transducers for Energy Harvesting and Sensing from Human Kinematics

This study reports flexible nanocomposite-based piezoelectric nanogenerators (PENGs) fabricated by dispersing various piezoelectric nanoparticles (BaTiO3, ZnO, and PZT) and graphene nanopowder in a silicone matrix. The results indicated that the PZT-based composites showed superior performance in comparison to other ceramics. Subsequently, practical application of PENGs was demonstrated by developing a fully functioning shoe-insole nanogenerator (SING). The SING generated high open-circuit voltage (∼27 V), short-circuit current (429.23 μA), and power density (402 mW/m2) under real-time human walking. Moreover, a facile and inexpensive fabrication method for efficient, skin-friendly, and highly stretchable biomechanical piezoelectric sensors is also proposed. In this regard, multiwall carbon nanotubes/silicone composite stretchable electrodes were prepared to be compatible with the sensors. The electrodes displayed stability even under high uniaxial elongation (100%), and the fabricated sensors responded effectively to almost every joint movement. The results suggested that the fabricated PENGs can be potentially used as self-powered biomechanical energy harvesters/sensors in wearable electronics, haptic sensing, or internet of human-related applications.

Bio Phantoms Mimicking the Dielectric and Mechanical Properties of Human Skin Tissue at Low-Frequency Ranges

Tissue phantoms are widely used as substitute materials for real tissue validation of various newly emerging biomedical technologies such as ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI). However, there is no specific recipe for fabricating skin-mimicking phantoms which can mimic both the mechanical and dielectric properties of human skin at lower frequency ranges. 
 
 The objective of this paper is to present a variety of tissue-mimicking materials for filling this research gap in the lower frequency range from 20 Hz to 300 kHz. The starting point of our experiments is based on the oil-in-gelatin based tissue-mimicking materials (TMMs) that have shown to mimic the dielectric properties of human skin in higher frequency ranges. This paper examines the mechanical and dielectric performance of five major classes of tissue-mimicking materials (1) Oil-in-gelatin, (2) lignin and graphene nanopowder in gelatin, (3) gelatin and distilled water, (4) mixed oil in gelatin and distilled water, and (5) lignin in gelatin and distilled water. 
 
 Mechanical and electrical testing was performed using compression testing and parallel plate method respectively. The effect of electrode polarization was considered in the measured data and the intrinsic impedance values were found to be following the Cole-Cole equation. The Young's modulus range of all tissue-mimicking materials was within the range of skin.

A novel comparative experimental study on rheological behavior of mono & hybrid nanofluids concerned graphene and silica nano-powders: Characterization, stability and viscosity measurements

ABSTRACT This paper explores a hybrid- and two mono-nanofluids and, to be more specific, it deals with the effect of adding Silica (SiO2) and Graphene (G) nanoparticles and their hybrid (G (30%) + SiO2 (70%)) on viscosity of water. For all designed hybrid- and mono-nanofluids at various concentrations of 0.05–1%, viscosity was measured under the influence of temperature (25–50 °C). Meanwhile, for measuring the viscosity, different shear rates (12.23–122.3 s−1) have been applied to evaluate rheological behavior of nanofluids. The viscosity of hybrid nanofluids lies between the viscosity of mono nanofluids, while G/Water mono-nanofluid samples have the highest value. Experimental results revealed non-Newtonian pseudoplastic behavior for all three types of nanofluids, this behavior is more evident in the G/Water mono-nanofluid. Moreover, G-SiO2(30–70%)/Water hybrid nanofluid has a higher tendency to the behavior of SiO2/Water mono-nanofluid. Finally, via curve fitting method, two-variable correlations were proposed to estimate rheological behavior of G-SiO2(30–70%)/Water hybrid nanofluid.

Flow Behavior and Drug Release Study of Injectable Pluronic F-127 Hydrogels containing Bioactive Glass and Carbon-Based Nanopowders

Injectable biomaterials have gained significant attention in recent years since they can be delivered to the defect sites through minimally-invasive approaches. In this work, thermo-responsive injectable hydrogels containing borate-based bioactive glass particles and carbon-based nanopowders were designed for bone tissue engineering applications. For this purpose, mixtures of Pluronic F127 block-copolymer and 13-93B3 bioactive glass particles with different sizes (2.3 µm, 14 µm, 150 µm) were prepared in aqueous medium and their in situ gelation were investigated through rheological measurements as a function of temperature. Effects of graphene nanopowders and multi-walled carbon nanotubes on the flow behavior of the designed hydrogel system were also investigated. Results revealed that viscosity of the prepared hydrogel system was strongly dependent on the temperature and the bioactive glass particle size. Inclusion of graphene and multi-walled carbon nanotubes in this system caused a further increase in viscosity. All of the hydrogel compositions designed in the study showed shear thinning flow behavior which is a crucial parameter for injectability. Drug release studies showed that the addition of bioactive glass and carbon-based nanoparticles improved the drug release behavior of the prepared hydrogels.

Improved wear resistance and mechanical properties of multifunctional polymer nanocomposites for advanced engineering applications

Improvement of wear behaviour and mechanical properties of polymers as bulk and surface coating materials for advanced engineering applications have been research interest. Improved wear resistance and mechanical properties were achieved in this study by incorporation of surface modified graphene and titanium dioxide nano-powder in poly (vinylidene fluoride) matrix via solution blending and melt compounding. The morphology of the nanocomposites was studied using scanning electron microscope (SEM). The nanocomposites showed significant reduction in wear volume and enhanced mechanical properties due to the presence of surface modified nanofillers. About 76.5% reduction in wear volume, 52% and 186.5% increase in tensile strength and Young modulus respectively were achieved in this study. The surface modification of the nanofillers was essential in dispersion of the nanofillers in the polymer matrix and the improved properties recorded. Such nanocomposites can find applications as protective surface coating materials for high frictional condition and bulk materials for automobile and aerospace components.

Investigation of Ballistic Behavior of Agricultural Waste Doped Hybrid Composite Plates in Vacuum Infusion Method

The vacuum infusion method is used in the production of ballistic composite materials, in the repair of aircraft parts and in the production of layered hybrid composite materials. In this study, production of hybrid composite materials including apricot kernel shell powder, hazelnut shell powder, walnut shell powder and graphene nanopowder added layer were made by vacuum infusion method. Layered hybrid composite samples with pure graphene nanopowder added and different shell powder added were produced. Then the produced hybrid composite samples were subjected to ballistic experiments. Due to the security, only the photographs of the ballistic test results were allowed to be shared.

Ecofriendly high-performance ionic soft actuators based on graphene-mediated cellulose acetate

Ionic-type artificial muscles with eco-friendly, biodegradable, and biocompatible functionalities have attracted attention for a wide range of potential applications in wearable electronics, soft haptic-feedback systems, and active biomedical devices. Here, we report on the development of an ecofriendly high-performance ionic soft actuator based on biofriendly cellulose acetate (CA), graphene nanopowders (GN), ionic liquid (IL) as a plasticizer, and biofriendly-flexible-nonmetallic conducting polymer poly(3,4-ethylene-dioxythiopene)-polystyrenesulfonate (PEDOT: PSS) as an electrode, thereby realizing a novel ecofriendly CA-IL-GN actuator with a large bending mechanical deformation and a fast response time. The proposed CA-IL-GN (0.2 wt%) nanocomposite membrane exhibited dramatic increments in specific capacitance (2.92 times) and Young’s modulus (2.38 times), thus leading to a 2.9 times larger bending deformation and a 4.8 times faster response than those of pure CA-IL actuator. Therefore, the developed ecofriendly high-performance CA-IL-GN actuator can be considered to be a promising candidate for human-friendly electronics, including artificial muscles, flexible haptic devices, soft wearable devices, and bio-medical devices, due to its cost-effectiveness, large bending mechanical actuation, fast response, and bio-friendly functionalities.

Effect of pore architecture on the mesenchymal stem cell responses to graphene/polycaprolactone scaffolds prepared by solvent casting and robocasting

In the study graphene-containing porous, three dimensional polycaprolactone (PCL) scaffolds were prepared by solvent casting-salt leaching and robocasting methods for tissue engineering applications. Graphene nanopowders in the form of nanoflakes were incorporated into the polymer matrix at different concentrations namely 1, 3, 5 and 10 wt%. The dichloromethane was used as the solvent and sodium chloride crystals were utilized as the water-soluble porogen for the formation of an interconnected porous network (with non-oriented pores) inside the composite scaffolds in solvent casting-salt leaching method. On the other hand, acetone was utilized as solvent and PCL solutions were prepared at 20 wt% in robocasting method to construct scaffolds (with oriented pores) having a grid-like structure. The biological response of bone marrow mesenchymal stem cells seeded on these composite constructs having different architecture were tested using MTT method, live-dead cell viability assay and Alcian blue stanining. Cytotoxicity experiments revealed that mesenchymal stem cells did not show toxic response to composite robocast scaffolds. Cells proliferate and differentiate well on the surface of the robocast scaffolds compared to solvent-cast scaffolds under the same conditions. Results showed that scaffolds prepared in the study have potential to be used in cartilage tissue engineering in the presence of electric stimulation.

Characterizing PDMS/MWCNTs and PDMS/GNP composites for biopotential sensing

This article focusses on preparation and mechanical testing of thin-polymer electrodes to efficiently measure the biomedical signals while providing a conformal skin-contact. The method to prepare thin electrode films using Polydimethylsiloxane (PDMS) with different Young’s moduli has been described. The Young’s modulus was evaluated for each film by conducting tension-relaxation tests. The PDMS electrodes were made conductive by mixing them with Multi-Walled Carbon Nano Tubes (MWCNTs) and Graphene Nano Powder (GNP) using an ultrasonic mixer. The current study addresses a novel approach of preparing PDMS based sensors by doping them with CNTs and GNPs and wetting them in N-N Dimethylformamide (DMF) prior to their dispersion in PDMS. This was done to avoid their clumping in PDMS and to ensure more uniform dispersion. The conductance of the PDMS/MWCNT and PDMS/GNP electrodes were measured using an impedance spectrometer and were compared with that of standard silver-silver chloride (Ag/AgCl) and dry silver (Ag) electrodes.

Direct Write Assembly of Graphene/Poly(ε-Caprolactone) Composite Scaffolds and Evaluation of Their Biological Performance Using Mouse Bone Marrow Mesenchymal Stem Cells.

Scaffold and mesenchymal stem cell-based cartilage tissue engineering offers a favorable way for the repair and regeneration of injured cartilage. In this study, poly (ε-caprolactone) PCL scaffolds with grid-like structure having periodic lattice was manufactured by robocasting method in the presence of graphene nanoplatelets for cartilage tissue engineering applications. For this purpose, a PCL solution (20wt%) containing pristine graphene nanopowders in the form of platelets was prepared as printing ink and it was dispensed through a nozzle at room temperature to an ethanol bath at 4°C. The construction of porous scaffolds was made by a layer-by-layer assembly. Results revealed that graphene additions were not detrimental to deposition process and the structure of the resultant scaffolds. In vitro cell tests indicated that the prepared grid-like graphene/PCL composite scaffolds have good cytocompatibility and non-toxicity for mouse bone marrow mesenchymal stem cells. The stem cells attached and proliferated well on the scaffolds and they also demonstrated a chondrogenic differentiation in the absence of transforming growth factors.

Prechondrogenic ATDC5 cell response to graphene/multi-walled carbon nanotube-containing porous polycaprolactone biocomposite scaffolds

In the study graphene and multi- walled carbon nanotube (MWCNT) - containing polycaprolactone (PCL) scaffolds were prepared by solvent casting-particulate leaching method for cartilage tissue engineering applications. Graphene nanopowders or MWCNTs were added to the system at different concentrations namely 1, 3, 5 and 10 wt%. Mechanical, thermal and electrical properties of the scaffolds were measured as a function of additive concentration. Response of prechondrogenic ATDC5 cells seeded on the composite constructs were tested using XTT method and live-dead cell viability assay. Alkaline phosphatase activity of the cells was also tested to investigate differentiation behaviour. Results showed that electrically conductive composite scaffolds prepared in the study have potential to be used in tissue engineering.

Elucidation of an intrinsic parameter for evaluating the electrical quality of graphene flakes

A test method for evaluating the quality of graphene flakes, such as reduced graphene oxide (rGO) and graphene nanopowder (GNP), was developed in this study. The pelletizer was selected for a sampling tool, which enables us to formulate the flake sample as a measurable sample. Various parameters were measured from the pelletized sample in order to elucidate the best parameter for representing the quality of the graphene flakes in terms of their electrical properties. Based on the analysis of 4-probe measurement data on the pelletized sample, the best intrinsic parameter is volume resistivity (or volume conductivity) rather than resistivity (or conductivity). Additionally, the possible modification of a sample before and after the pressurization was investigated by electron microscopy and Raman spectroscopy. No significant modification was observed. The volume conductivity in the two types of the graphene was different from their individual conductivities by one order of magnitude. Based on the results of X-ray photoelectron spectroscopy and Raman spectroscopy measurements, the volume conductivity of the graphene flake samples was governed by the oxygen content in the sample. Our achievements will promote the effective use of powder-type graphene products for further applications.

Tailoring chemical and physical properties of graphene-added DNA hybrid thin films

While the characteristics of DNA and graphene are well studied, the chemical and physical properties of graphene-embedded DNA and cetyltrimethyl-ammonium chloride-modified DNA (CT-DNA) hybrid thin films (HTFs) have been rarely discussed due to the limited development of fabrication methodologies. Herein, we developed a simple drop-casting method for constructing DNA and CT-DNA HTFs added with graphene nanopowder (GNP). Additionally, we demonstrated their distinct characteristics, such as their structure, elemental composition, spin states and chemical functional groups, binding interactions, vibration/stretching modes by UV–Vis absorption, PL, and electrical measurements. The EDS spectra of GNP-added DNA HTFs showed C, N, O, Na, and P peaks at characteristic energies. Because of the physical adsorption of GNP on DNA, the peak shifts and suppression of the core spectra of O 1s and P 2p were observed by XPS. The intensity variation of Raman and FTIR bands indicated hybrid formation of GNP in DNA and CT-DNA through adsorption, electrostatic interaction, and π–π stacking. UV–Vis absorption and PL spectra showed the considerable influence of GNP in DNA and CT-DNA HTFs. DNA and CT-DNA HTFs with relatively higher [GNP] showed significant increases of current due to the formation of interconnected networks of GNP in the DNA and CT-DNA HTFs.