Adding Graphene Nanoplatelets Research Articles

Exploring the Thermal Potential of Shape Stabilized Graphene Nano Platelets Enhanced Phase Change Material for Thermal Energy Storage

Low thermal conductivity and liquid phase leakage impede the widespread adoption of phase change materials (PCMs). To enhance PCM performance and practical viability, addressing these limitations is crucial. Current study addresses low thermal conductivity and leakage issues. Enhanced thermal conductivity in PCMs is achieved by adding graphene nanoplatelets (GnPs), while expanded graphite (EG) acts as a leak‐proof barrier. The composite PCM (ss‐NePCM) composite is developed by ultra‐sonication followed by vacuum impregnation process. The samples underwent comprehensive analysis: thermal conductivity (TEMPOs), chemical composition (FTIR), photo‐transmittance (UV–Vis), and thermal stability (TGA). The results show that the composite with 0.6 wt% GnP (NePCM3) has the highest thermal conductivity enhancement of ≈112% while adding 15 wt% EG (ss‐NePCM3) diminishes leakage problem. According to the optical performance assessment, the composite exhibits a notable increase in absorbance of 116% higher than that of the base PCM. However, due to the introduction of additives, the differential scanning calorimeter (DSC) detected a minor variation from 154 to 144.76 J g−1 in the latent heat. Furthermore, the composite demonstrates chemical stability and thermal reliability following 250 heating and cooling cycles. The ss‐NePCM holds promise for thermal systems, where leakage could jeopardize system integrity.

Role of aloe vera based nanofluids for cool thermal energy storage system: A comparative study

The present experimental investigation incorporates the preparation of aloe vera gel-based phase change nanofluid (NFPCM) for a cool thermal energy storage (CTES) system. Two sets of NFPCMs were produced by adding graphene nanoplatelets (GNP) in deionized water and aloe vera gel (0.20 wt%, 0.40 wt%, and 0.60 wt%). The zeta potential analysis shows that the NFPCM with aloe vera gel is more stable even after 60 days from the preparation (−44 mV). The thermal conductivity of NFPCMs was analyzed through the transient hot wire method and the enhancement of 42 %, and 37.5 % were measured in the ice phase for NFPCMs with aloe vera gel and DI water (0.60 wt%) respectively at the heat transfer fluid temperature of −15 °C. The NFPCMs with aloe vera gel show that the addition of GNP prepended the peak melting temperature from −16 °C to −10.5 °C, which is due to the quick formation of nuclei as compared to NFPCMs with DI water. Additionally, a slight reduction in the latent heat of only 7 % was observed. The charging characteristics of NFPCMs were studied in a single spherical capsule at −8 °C. The maximum reduction in total charging time of 25 % was recorded for the aloe vera gel-based NFPCM with a maximum concentration of GNP (0.60 wt%). The green synthesis of aloe vera gel-based NFPCM exhibited noteworthy enhancements in thermophysical properties. Additionally, it was observed that the long-term stability of the NFPCM was achieved by excluding surfactants during the preparation process. The incorporation of graphene nanoplatelets (GNP) into aloe vera gel as the foundational phase change material (PCM) facilitates the partial charging of the CTES system with a reduced energy input.

Conductive and auxetic composite membranes based on graphene nanoplatelets and polybutylene succinate produced via electrospinning

AbstractThis work presents a method to produce conductive and auxetic composite membranes from a biobased and biodegradable matrix: polybutylene succinate (PBS). The conductivity was improved by the addition of graphene nanoplatelets (GNP) and the samples were produced via solution electrospinning. The membrane properties were shown to increase with increasing GNP concentration and the rotational speed of the collector. In particular, a membrane having 0.2% w/v GNP and fabricated at the highest collector speed (9.96 m/s) showed the highest electrical conductivity (1.56 × 10−4 S/m) while having a negative Poisson's ratio (NPR) of −1.5 in tension. To complete the analysis, mechanical characterizations showed that the presence of GNP led to a substantial increase in Young's modulus (234%) and tensile strength (190%) compared to the neat PBS membrane produced under the same conditions. Differential scanning calorimetry (DSC) revealed a slight crystallinity increase since GNP are acting as heterogeneous nucleating agents, while thermogravimetric analysis (TGA) showed an improved thermal stability for the GNP/PBS membranes. This unique combination of auxetic and conductive properties can be useful for a wide range of innovative applications such as electronic devices, smart textiles, biomaterials, and biomedical devices.Highlights Electrospinning was successful to produce polybutylene succinate (PBS) nanofibers. A careful control of the processing conditions led to auxetic fiber mats. Electrically conductive mats were produced by adding graphene nanoplatelets (GNP) to PBS. The PBS mechanical properties were highly improved (200%) with low GNP content (0.2%).

Performance evaluation of structurally modified wellbore cement with graphene nanoplatelets undergone thermal cyclic loading

Geothermal energy is identified as one of the alternatives to fossil fuels in global climate crisis and the effective efforts for net-zero carbon emissions by 2050. The potential of geothermal heat at high temperatures is yet to be unlatched thus requiring a novel approach in all aspects of wellbore technology including cementing. Understanding the characteristics of the geothermal system is critical as we aim to develop wellbore materials for these thermally and chemically challenged wells. Materials used require stability at high temperatures and chemical resilience in contact with geofluids, where ordinary Portland cement (OPC) is deteriorating due to low pH that leads to loss in overall mechanical strength. Recent studies have shown that adding graphene nanoplatelets (GNP) to OPC based materials can improve properties and reduce risks from mechanical failures. GNP effect on overall cement properties has been studied and experimental results show promising outcomes at very low concentrations (<1% bwoc), significantly impacting strength and stiffness of the cement. The Class-H cement is hydrated with and without, liquid and powdered GNP at 0.008% and 0.1% concentrations each and cured in approximately pH 13 Ca(OH)2 solution to examine the influence of GNP on cement hydration. All the samples were subjected to cyclic temperature loading between 20 °C and 110 °C at 95% RH following an 8-hour cycle for 7 and 28 days in an environmental chamber. These temperature cycles help us evaluate close to the subsurface conditions where enhanced geothermal systems undergo thermal changes over tens of thousands of times during a lifetime of a well. Following API RP-10B specifications, GNP in the powdered form (PG) prepared from environmental waste and a 99.5% carbon purity lab grade liquid dispersion GNP (LG) were used. 0% GNP (neat) control, 0.008%, 0.1% of PG and LG mix design cement samples were prepared. Results show that 0.1%LG samples hydrated for 28 days had greater dispersion of GNP with a notable increase in the ductile behavior out of all the designs tested. There is a 13.21% decrease in permeability, 27.77% decrease in hardness and 50.71% decrease in elastic modulus when compared to neat sample hydrated for 28 days thus proving its effectiveness for wellbore integrity with increase in hydration time.

Improvement in Bond Strength of Steel Bar in Geopolymer Concrete by Adding Graphene Nanoplatelets

Improvement in Bond Strength of Steel Bar in Geopolymer Concrete by Adding Graphene Nanoplatelets

Variation in cooling performance of a bio-based phase change material by adding graphene nanoplatelets with surfactants

In this paper, thermal characteristics of various phase change materials induced with additives and surfactants are studied to enhance cooling properties and chemical stability. In this regard, graphene nanoplatelets at various mass fractions are integrated with surfactant-induced-PureTemp PCM and used as a heat sink for an electric heating source. The surfactants considered in this study are sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium stearoyl lactylate. The thermal characteristics are measured in terms of indices such as thermal conductivity, thermal capacity, and time of reaching the reference temperature. The results indicate that composite samples are superior in cooling when compared to the plain PureTemp PCM. Also, the highest thermal conductivity and phase change enthalpy are recorded in NanoPCM-SDS at 5% GnPs mass fraction and NanoPCM-SSL at 1% GnPs mass fraction amounting to 1.03 W/m.K and 236.5 J/g, respectively. NanoPCM-SSL displayed the longest delay of 1015 s to reach the reference temperature of 43 °C.

Electrochemical degradation of antibiotic enoxacin using a novel PbO2 electrode with a graphene nanoplatelets inter-layer: Characteristics, efficiency and mechanism

A novel PbO2 electrode was fabricated by adding graphene nanoplatelets (GNP) inter-layer into β-PbO2 active layer (called GNP-PbO2) and utilized to degradation of antibiotic enoxacin (ENO). The GNP-PbO2 electrode had a much rougher surface than the typical PbO2 electrode, with smaller crystal size and lower charge-transfer resistance at the electrode/electrolyte interface. Notably, the GNP inter-layer increased the oxygen evolution potential of PbO2 electrode (2.05 V vs. SCE), which was very beneficial to inhibit oxygen evolution and promote ·OH production. The relatively best operating parameters for ENO removal and energy efficiency were current density of 20 mA cm−2, initial pH of 7, initial ENO concentration of 100 mg L−1 and electrode distance of 4 cm. Furthermore, indirect radical oxidation was found to be the main way during electrolysis process. Based on the observed analysis of intermediate products, the main reaction pathways of ENO included hydroxylation, defluorination and piperazine ring-opening. Finally, combinating with the electro-oxidation capability, stability and safety evaluation, we can conclude that GNP-PbO2 is a promising anode for treatment of various organic pollutants in wastewater.

Enhanced mechanical and tribological properties of oscillatory pressure sintered WC–GNPs composites

AbstractIt remains as a challenge to develop binderless WC ceramics that integrate high mechanical properties and low friction wear. Here, we report the preparation of strong and tough WC ceramics with low wear rate by adding graphene nanoplatelets (GNPs) and using oscillatory pressure sintering (OPS) process. The introduced GNPs lead to the formation of nearly fully dense composites with the aid of an oscillatory pressure. The OPS‐prepared WC–0.3‐wt% GNPs composites reached a high flexural strength, hardness, and fracture toughness, being up to 1420 MPa, 24.9 GPa, and 6.89 MPa m1/2, respectively. Moreover, a low friction wear rate of 3.17 × 10−7 mm3 N−1 m−1 is achieved for such composites, which can be ascribed to the formation of a friction lubrication film during dry sliding friction process and their higher mechanical properties.

Enhanced Thermal and Mechanical Properties of 3D Printed Highly Porous Structures Based on γ‐Al2O3 by Adding Graphene Nanoplatelets

AbstractOne of the main challenges to widen the potential applications of 3D printed highly porous ceramic structures in catalysis, energy storage or thermal management resides in the improvement of both their mechanical resistance and thermal conductivity. To achieve these goals, highly hierarchical γ‐alumina (γ‐Al2O3) scaffolds containing up to 18 vol% of graphene nanoplatelets (GNP), including channels of controlled size and shape in the millimeter scale and meso‐porosity within the rods, are developed by robocasting from boehmite‐based aqueous inks without other printing additives. These 3D structures exhibit high porosity (85%) and specific surface area of 100 m2 g−1. The incorporation of 12 vol% GNP leads to an enhanced mechanical response of the scaffolds, increasing the compressive strength and the elastic modulus up to ≈80% as compared with data for plain γ‐Al2O3 scaffolds. The thermal conductivity is measured by the transient plane source method using specifically designed 3D structures with external sidewalls and additional top/bottom covers to assure a good contact at the outer surfaces. The thermal conductivity of 3D porous structures augments with the GNP content, reaching a maximum value four times higher for the scaffolds containing 18 vol% GNP than that attained for the 3D monolithic γ‐Al2O3.

Effect of Graphene Nanoplatelets on Tribological Properties of Bacterial Cellulose/Polyolester Oil Bio-Lubricant

The demand for bio-degradable lubricants is continuously increasing due to environmental concerns. One of the methods to achieve the bio-degradability property of lubricants is by using nanoparticles from bio-resources as additives in bio-degradable oils. Among the nanomaterials are nanofibers, cellulose, and graphene nanoplatelets. They can be mixed in Polyolester (POE) oil to produce lubricants for tribological applications. In a previous study, it has been confirmed that friction and wear of the tribo-pair reduced from 5 to 10% by mixing various volume percentages of bacterial cellulose (BC) into PEO as the base lubricant. The tribological performance BC containing POE base lubricant can further be enhanced by incorporating graphene nanoplatelets. This study shows that the specific wear rate of the material decreased by 20% by adding graphene nanoplatelets in BC containing POE oil. The friction and wear improvement can be related to the formation of tribofilm on the contact interface. EDS analysis indicates that oxygen played an important role in the friction and wear performance of the POE oil-based lubricant with BC and graphene additives. The tribofilm shows significant traces of oxygen elements. The presence of graphene nanoplatelets in POE oil removed the oxygen-rich layer but could not reduce the wear rate. However, incorporating both graphene and BC in POE oil significantly improved friction and wear, although the oxygen element was still traceable on the contact interface.

Improving the tribological performance of a biodegradable lubricant adding graphene nanoplatelets as additives

This research is based on the investigation of the tribological properties of a biodegradable polymeric ester lubricant (BIOE) additivated with two different pristine graphene nanoplatelets (GnPs), named as GnP7 and GnP40. These GnPs have lateral sizes of 7 and 40 μm, and thickness of 3 and 10 nm, respectively. Four different nanoadditive loadings: 0.015, 0.035, 0.055 and 0.075 wt% have been used. Stability of nanolubricants has been investigated using the visual control and the refractive index evolution during time, revealing a slightly better stability for the nanolubricants formulated with the largest lateral size graphene nanoplatelets (GnP40). The influence of the thickness and lateral size of these carbon-based nanoadditives on the antifriction and antiwear capabilities of BIOE is analysed. For this purpose, rotational friction tests were taken with the eight nanolubricants under a 20 N working load and 340 m sliding distance. All nanolubricants showed friction coefficients and worn area lower than those previously reported for the unadditivated BIOE. As regards friction, the ideal loading for both GnPs was 0.055 wt% GnP, being the best anti-friction behaviour obtained using GnP40 as additive (up to 26% reduction), whereas the 0.055 wt% GnP7/BIOE nanolubricant leads to the best anti-wear capability with wear reductions up to 56%. Finally, from Raman microscopy and roughness assessments on the worn surfaces, it can be determined that the good tribological performance of nanolubricants is owing to the protective film formation and surface repairing mechanism.

Effects of SiO2 particles in copper current collector on diffusion induced stresses in layered Li-ion battery electrodes

One of the limiting factors in the life of lithium-ion batteries is the diffusion-induced stresses on their electrodes that cause cracking and consequently, failure. Therefore, improving the structure of these electrodes to be able to withstand these stresses is one of the ways that can extend the life of the batteries as well as improve their safety. In this study, the effects of adding graphene nanoplatelets and microparticles into the active plate and current collectors, respectively, on the diffusion induced stresses in both layered and bilayered electrodes are numerically investigated. The micromechanical models are employed to predict the mechanical properties of both graphene nanoplatelet-reinforced Sn-based nanocomposite active plate and silica microparticle-reinforced copper composite current collector. The effect of particle size and volume fraction in the current collector on diffusion induced stresses has been studied. The results show that in electrodes with a higher volume fraction of particles and smaller particle radii, decreased diffusion induced stresses in both the active plate and the current collector are observed. These additions will also result in a significant decrease in the bending of the electrode.

Mode I Fracture Toughness of Graphene Reinforced Nanocomposite Film on Al Substrate.

Nanocomposites were prepared by adding graphene nanoplatelets (GNP) into epoxy with a variety of loadings. The thickness of GNPs used in this study was in a range of 1 nm to 10 nm. Nanocomposite film was deposited on the aluminum (Al) substrate via a spinning coating process. Tensile tests were carried out to determine the elastic modulus, ultimate strength and fracture strain of the nanocomposites. Theoretical prediction of the fracture toughness of the film/substrate composite structure with an interfacial crack under mode I loading was derived utilizing linear elastic fracture mechanics theory. Four-point bending tests were performed to evaluate the mode I fracture toughness. It was observed that the performance of the nanocomposite, such as elastic modulus, ultimate strength, and fracture toughness, were significantly enhanced by the incorporation of GNPs and increased with the increase in GNP concentration. The elastic modulus and mode I fracture toughness of the epoxy reinforced with 1 wt.% of GNPs were increased by 42.2% and 32.6%, respectively, in comparison with pure epoxy. Dispersion of GNPs in the epoxy matrix was examined by scanning electron microscope (SEM). It can be seen that GNPs were uniformly dispersed in the epoxy matrix, resulting in the considerable improvements of the ultimate strength and fracture toughness of the nanocomposite.

Development of a semi-crystalline hybrid polyurethane nanocomposites for hMSCs cell culture and evaluation of body- temperature shape memory performance and isothermal crystallization kinetics

We report synthesis and characterization of a group of reactive in-situ polyurethane (PU) nanocomposites based on PCL1000-PEG2000-PCL1000 block copolymer- diol and MWCNT/Graphene nanoparticles. The experiments were designed to tune shape fixity (SF) and shape recovery (SR) of the specimens. Hydroxyl-functionalized MWCNTs’ content was set constant at 0.25 wt% (T0.25) and Graphene’s content was varied in the range of 0 to 0.75 wt% (G (0–0.75)) to control the crystallization of the soft segment blocks and elastic modulus of the PU nanocomposites. The pure and T0.25G0.50 showed the highest shape fixity (SF = 100%). The optimum sample was PU nanocomposite of T0.25G0.50 with an SR of 95%. The results of Dynamic Mechanical Thermal Analysis (DMTA) indicated lack of flowage for the nanocomposites and their thermoset nature. The non-isothermal crystallization analysis indicated a sharp decline in crystallization temperature (Tc) of the soft segments of T0.25G0 sample and adding graphene nanoplatelets improved the crystallization extent and increased Tc. The isothermal crystallization kinetics of the PUs indicated an increase in crystallization kinetics by increasing graphene’s content compared to T0.25G0 sample. The results of Human Mesenchymal Stem cells (hMSCs) culture indicated an increase in cell adhesion and proliferation as a function of Graphene’s content.

Granular-slurry rheology and asphalt compaction

Hot mixed asphalt (HMA) is a mixture of particles (coarse and fine aggregates) and interstitial fluid (asphalt binder) designed to compact and harden for long-lasting roads. In this study, we implement a two-scale approach to capture the compaction behaviour of hot asphalt mixtures using both a granular-slurry rheology (GSR) at a smaller scale and a discrete element method (DEM) simulation at the scale of a compactor. We show that this modelling effort captures the compaction of HMA with different binder viscosities modified by adding graphene nano-platelets (GNP). This research has the capacity to shed light on how the properties of mixture components can influence compaction efficiency and effectiveness.

Spark plasma sinterability and thermal diffusivity of TiN ceramics with graphene additive

The effects of adding graphene nano-platelets (6 wt%) on the microstructure and thermal diffusivity and conductivity of TiN-based ceramics were investigated. Two samples, a monolithic TiN, and a graphene-added TiN ceramics were fabricated using spark plasma sintering technique at 1900 °C for 7 min under 40 MPa. The microstructure of the polished and fractured surfaces of both samples was analyzed by scanning electron microscopy. Adding graphene resulted in a 2% reduction in the relative density, but led to obtaining a fine-grained microstructure. The consumption of graphene nano-additive during the sintering, through the reduction of surface oxide layers of TiN matrix (TiO2), and consequently, the formation of titanium carbonitride (TiN0·8C0.2) were disclosed by X-ray diffraction analysis. The measurement of the thermal diffusivity was done using the laser flash technique. The TiN–6 wt% graphene sample obtained lower thermal conductivity compared to the monolithic TiN, which can be attributed to the smaller grain size of the graphene-added sample.

Microstructure and friction properties of GNP/Ni-based superalloy composite coating by laser melting deposition

The GNP/Ni-based superalloy composite coating was prepared by laser melting deposition. Compared with superalloy coating, the state of graphene nanoplatelets, friction and wear performance of composite coating were studied. Microstructural characterization of composite coating is performed by SEM, TEM and Raman spectroscopy, which indicates that graphene nanoplatelets are homogeneously distributed in composite coating. The Ni-Cr-Fe phase is the main component and forms a coral-like eutectic group with carbides in the composite coating. Furthermore, the existence of graphene dramatically improves the wear performance of the composite coating. The wear rate and friction coefficient of the GNP composite coating are only 0.019 and 0.73 of those of the Ni-based superalloy coating, respectively. Graphene nanoplatelets wear debris forms a lubricant layer at the friction interface, which significantly improves the wear resistance of the composite coating. We envisage that adding graphene nanoplatelets could be an effective way to improve the tribological properties of laser-deposited Ni-based superalloy coatings.

Endowing the sustainable antistatic properties to epoxy-based composites through adding graphene nanoplatelets

In order to explore the possibility of reducing the potential hazards caused by the accumulation of static charges in electronic components, graphene nanoplatelets with remarkable conductive property were added as functional fillers into epoxy matrix to enhance the antistatic property of composites used as the encapsulating materials. Optical microscope and scanning electron microscope were used to observe the dispersion of graphene fillers in the polymer to indicate the completeness of the establishment of the conductive network. The surface of the material was charged by corona discharge method, then the decay characteristics of the static charges was continuously measured. The accumulation and decay of the static charges on the surface of the sample were systematically analyzed by combining with water contact angle, resistivity and relevant permittivity parameters. Results showed that the antistatic ability of material had been constantly enhanced with the increase of graphene content. It was worth noting that when only 0.5 wt% graphene fillers were added, the surface and volume resistivity of composite could reach 5.38 × 1012 Ω/square, 2.37 × 1010 Ω.cm respectively, fully meeting the requirement standard of antistatic encapsulating material for electronic devices. It is forecasted that the prepared composites have considerable prospects in the antistatic encapsulation of electronic devices and aerospace fields.

The effect of graphene nanoplatelets on the flexural properties of fiber metal laminates under marine environmental conditions

In this research, the effects of adding graphene nanoplatelets (GNPs) on the flexural properties of fiber metal laminates (FMLs) under marine environmental conditions were investigated. The FMLs were fabricated with alternating layers of Al6061 and glass fiber reinforced epoxy (GFRE) with different concentrations of GNPs (0.25, 0.5, and 1.0 wt%). The samples were immersed in the 3.5 wt% NaCl solution for different immersion times (7, 14, and 28 days) at room temperature. The addition of GNPs led to decreasing the water absorption of samples after immersion in the 3.5 wt% NaCl solution; the lowest absorbed water was for the samples with 0.25 wt% GNPs. Although the flexural properties of samples decreased by increasing the immersion time, the lowest reduction in flexural properties was obtained for the sample with 0.25 wt% GNPs. Results showed that by adding GNPs and immersing the specimens in the 3.5 wt% NaCl solution for 28 days, the flexural strength and modulus, and strain values of specimens containing 0.25 wt% GNPs were respectively about 128%, 63%, and 1.85 times higher than those of samples without GNPs. Also, the reduction of the flexural properties caused by immersion in NaCl solution was lower than that of samples without GNPs. Moreover, the water uptake of samples with 0.25, 0.5, and 1.0 wt% GNPs was about 38%, 31%, and 37% lower than that of samples without GNPs after 28 days of immersion. Microstructural analyses revealed that the improvements in the metal/polymer adhesion and mechanical properties of the polymeric part of FMLs resulting from various mechanisms were the main reasons for the improved performance of samples with GNPs under marine conditions.

Continuous Manufacturing of Graphene-Contact Ion-Selective Electrodes Using Roll-to-Roll Processes: The Case for Nitrate Sensors

Soil contains various species of nitrogen, which is crucial for plant growth. Nitrate ion (NO3 -) is essential for promoting high crop yields and is widely used in fertilizers, however groundwater can be polluted by the overuse of nitrate. “Smart agriculture” can be supported by monitoring NO3 - in ground-soil using a distributed network of disposable potentiometric sensors. We have found the performance of such sensors to be enhanced by adding graphene nanoplatelets (GrNPs) as a conductive yet hydrophobic solid contact between the electrode and ion-selective membrane. Exfoliated GrNPs can be stably dispersed in ethyl acetate by liquid-assisted ball-milling, then deposited using methods compatible with the scalable roll-to-roll (R2R) production of ion-selective electrodes (ISEs). Ultra thin layers of GrNPs were formed by spray-coating onto a moving web of screen-printed Ag electrodes on polyethylene terephthalate (PET), followed by in-line deposition of a NO3 - selective membrane and silicone sealant then oven drying. Multiple electrodes from each production run were conditioned in aqueous KNO3 solutions and potentiometric characterizations of sensitivity, selectivity and stability were completed using an 80-channel analyzer. The GrNP layer serves as a hydrophobic transducer of ion adsorption and provides a high capacitance for stable potentiometric signals while also protecting SC-ISEs from damage caused by water permeation. We find that R2R processes can successfully produce graphene-contact NO3 - ISEs for agricultural applications, with extended operational lifetimes and high levels of quality control.