Thermal Conductivity Of Graphene Oxide Research Articles

Rheology and thermal conductivity of graphene oxide and coal fly ash hybrid nanofluids for various particle mixture ratios for heat transfer applications: Experimental study

This work presents the synthesis of graphene oxide (GO) and coal fly ash (CFA) nanoparticles (NP) to produce water base mono and hybrid nanofluids (HNF) for different particle mixture ratios of 50:50 and 30:70. X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), dynamic light scattering analysis (DLS), Fourier transform infrared (FTIR), field emission scanning electron microscope (FESEM), Ultraviolet-visible spectroscopy analysis (UV–Vis), and zeta-potential tests were carried out. The non-ionic surfactant polyvinylpyrrolidone (PVP) is added to the nanofluid (NF) to improve stability. The thermal conductivity (TC) and rheology experiments are carried out for the concentration range of 0.1 to 1.0 vol% in the temperature range of 30 to 60 °C. The results show that TC and viscosity (VST) enhancement of GO NF is higher than the studied HNF. The maximum VST enhancement of 177%, 152%, and 113% are observed for GO, and GO/CFA (50:50) and, GO/CFA (30:70), respectively for a concentration of 1 vol% at 30°C relative to water. Based on the obtained data, regression analysis is formed to estimate the TC and VST of the studied HNF. The performance enhancement ratio (PER) results show that GO NF and HNF with a mixture ratio of 30:70 are beneficial for thermal applications at all temperatures, whereas HNF with a mixture ratio of 50:50 is only at 45°C and above.

Effect of nanospray on hydrodynamic cylindrical film flow of Sutterby–Casson nanoliquids: A renewable energy application

Renewable energy is the most prominent energy source due to its industrial and technological needs. A computational examination is performed to explore the result of the nanospray on the film flow of Casson and Sutterby nanofluids over a cylindrical surface. Due to the effective thermal conductivity of graphene oxide, the water–graphene oxide nanofluid is considered in the existence of radiative heat, Catteneo–Christove heat flux, and hydrodynamic effects. A mathematical model is established and resolved numerically by applying appropriate similarities. Simultaneous results are obtained for Sutterby and Casson nano models. The impact of considered physical features on the flow and heat transmission of both liquids is studied with the help of pictorial and mathematical outcomes. The heat transmission rate of the Casson nanoliquid is higher than the Sutterby nanoliquid. Hence, the fluids with Casson rheological nature are helpful in heat transfer applications. Both liquids’ flow and heat transport rate can be regulated by adjusting the film thickness.

Investigation of the thermal and light sensing properties of graphene oxide and reduced graphene oxide films obtained by spin coating method

This paper reported the thermal and light sensing properties of graphene oxide (GO) and reduced graphene oxide (RGO) films obtained by spin coating on soda lime glass. GO showed a higher thermal sensing response of 9.0 compared to RGO which had a maximum thermal sensing response of 2.2 at 623 K. The thermal conductivity of GO and RGO increased with temperature although RGO typified better thermal conductivity. For GO, a negative temperature coefficient of resistance (NTC) of 0.0032153 /K was obtained which is higher than values obtained in literatures while RGO had a NTC value of 0.00201/K. For the photo sensing, the peak photo resistance of GO corresponds to an energy band gap of 3.5 eV while the peak photo resistance of RGO corresponds to a decreased energy band gap of 2.76 eV. It was also confirmed that lower bandgap favored improved photosensing function. RGO film showed intrinsic photoconductivity as the photoconductivity increased at longer wavelengths. The photo sensing of GO and RGO were dominated by inter-band optical transitions in the UV to mid infrared region. The obtained NTC values for GO and RGO and the photoconductivity of the materials can promote further utilization in robotics and optical applications.

Thermal Conductivity of Graphene Oxide: A Molecular Dynamics Study

The thermal properties of graphene oxide containing hydroxyl and epoxy functional groups were studied using non-equilibrium molecular dynamics to understand the thermal transport phenomena involved and the structure factors limiting heat conduction. Estimates were given in terms of phonon mean free paths for the reduction in thermal conductivity by interior defects due to scattering. The mechanism of phonon transport in the graphene oxide was discussed. The results indicated that the degree of oxidation can significantly affect the thermal performance of graphene oxide. A low degree of oxidation is necessary to enhance the phonon transport properties of graphene oxide and reduce the probability of phonon-defect scattering. Phonon transport in graphene oxide with a high degree of oxidation is governed by the mean free path of phonons associated with scattering from interior defects. Oxygen-containing functional groups can adversely affect performance and reduce the efficiency of phonon transport in graphene oxide due to phonon mean free paths limited mainly by interior defects. The calculated intrinsic thermal conductivity of graphene oxide at room temperature is about 72 W/(m K) with an oxidation degree of 0.35 and about 670 W/(m K) with an oxidation degree of 0.05. The phonon mean free path decreases with increasing the degree of oxidation due to enhanced phonon-defect scattering, making the thermal conductivity very sensitive to the concentration of oxygen-containing functional groups.

Dispersive Magnetic Solid-Phase Extraction Coupled to Direct Analysis in Real Time Mass Spectrometry for High-Throughput Analysis of Trace Environmental Contaminants.

Coupling dispersive magnetic solid-phase extraction (DMSPE) to direct analysis in real time mass spectrometry (DART-MS) with a newly developed metal iron probe enables high-throughput, sensitive detection of herbicides such as triazine in environmental waters. Magnetic graphene oxide was used as a dispersive sorbent because it increased adsorption capacity in the DMSPE process. The planar structure and excellent thermal conductivity of graphene oxide facilitated the desorption and ionization of target analytes in DART-MS analysis. The iron probe, which is designed to fit into the moving trail of the DART interface, served as the sorbent collector as well as the support for the magnetic graphene oxide after DMSPE, and was put directly into the DART system. The ratio of magnetic core to graphene oxide in the nanoparticles and other key parameters in DMSPE and DART-MS procedures were systematically investigated and optimized. In addition, the presence of water on the sorbent proves to have a significant effect on DART-MS analysis. No organic solvents are used in this method, and the reusable iron probe is of low cost. Under the optimal conditions, limits of detection were found in the range of 1.6-152.1 ng/L for the triazines. Recovery and reproducibility were found to be in the ranges of 87.5-115.0% and 1.9-10.2%, respectively, for the six herbicides studied. The analytical performance of the DMSPE-DART-MS method indicated that applications for trace analysis of other compounds in liquid samples are also possible.

Thermal Conductivity of Defective Graphene Oxide: A Molecular Dynamic Study.

In this paper, the thermal properties of graphene oxide (GO) with vacancy defects were studied using a non-equilibrium molecular dynamics method. The results showed that the thermal conductivity of GO increases with the model length. A linear relationship of the inverse length and inverse thermal conductivity was observed. The thermal conductivity of GO decreased monotonically with an increase in the degree of oxidation. When the degree of oxidation was 10%, the thermal conductivity of GO decreased by ~90% and this was almost independent of chiral direction. The effect of vacancy defect on the thermal conductivity of GO was also considered. The size effect of thermal conductivity gradually decreases with increasing defect concentration. When the vacancy defect ratio was beyond 2%, the thermal conductivity did not show significant change with the degree of oxidation. The effect of vacancy defect on thermal conductivity is greater than that of oxide group concentration. Our results can provide effective guidance for the designed GO microstructures in thermal management and thermoelectric applications.

Tailoring thermal conductivity of bulk graphene oxide by tuning the oxidation degree

Bulk graphene oxide (GO) shows great potential in a variety of applications, such as sensors, photodetectors, supercapacitors, lithium ion batteries and catalysts. However, its thermal conductivity, one of the most important and fundamental physical properties, is still less known. Herein, we have systematically investigated the thermal conductivity of bulk GOs and find that it can be tailored by tuning their oxidation degree during preparation process. Notably, the cross-plane thermal conductivity of bulk GO, in comparison with its precursor graphite, exhibits more than 100 times decrease at room temperature. The dependence of thermal conductivity of GO on oxidation degree is attributed to the chemical and structural changes by introducing oxygen atoms and oxygen-containing functional groups, which can lead to a significant enhancement in atomic- and nano-scale phonon scattering. Furthermore, we reveal that the thermal conductivity of bulk GOs exhibits evident anisotropic behavior. These results provide fundamental understanding and valuable information on thermal transport properties of bulk GOs for various practical applications.

Experimental evaluation and ANN modeling of thermal conductivity of graphene oxide nanoplatelets/deionized water nanofluid

In this research study, the thermal conductivity of graphene oxide nanoplatelets/deionized water nanofluid is studied in different temperatures and weight fractions using artificial neural network (ANN) and experimental data. For the purpose of training the ANN, the thermal conductivity of nanofluid is measured in temperatures between 25 and 50°C and weight fractions equal to 0.001, 0.005, 0.015 and 0.045. For the purpose of evaluating the accuracy of the proposed model by ANN, root mean square error (RMSE), R2 and also mean absolute percentage error (MAPE) are utilized. The best ANN model has two hidden layers and one output layer and also utilizes tansig, logsig and pureline functions and the number of neurons is 4–8–1 in the mentioned layers respectively. The inputs of the ANN model are weight fraction and nanofluid temperature and the output of the network is the thermal conductivity of the nanofluid. The results indicate that the proposed model by ANN can precisely predict the thermal conductivity of the nanofluid.

Effect of alkyl functionalization on thermal conductivity of graphene oxide nanosheets: a molecular dynamics study

In this study, the influence of alkyl functional groups on thermal conductivity of graphene oxide (GO) nanosheets is studied using a reverse non-equilibrium molecular dynamics simulation. The different types of alkyl-functionalized GO with functional groups containing six, twelve, sixteen and eighteen carbon atoms are investigated while the functional groups were bonded to the GO nanosheets both covalently and non-covalently. The objective is to investigate the effect of functional groups length as well as functionalization mechanisms on thermal conductivity of nanosheets. The results demonstrate that the thermal conductivity of GO reduces after alkylation and decreases with an increase in the chain length of functional groups. The analysis of the phonon spectra demonstrates that the functionalization of GO disrupts its phonon vibrations which results in a reduction of the thermal conductivity. Furthermore, the investigation of the alkylation mechanisms shows that the major portion of the reduction in the thermal conductivity is due to the non-covalent functionalization. This study can provide helpful information for controlling the thermal properties of alkylated GO for diverse applications such as superhydrophobic coatings, polymer composites, and nanocolloids. It also enhances the understanding of the mechanisms which affects the thermal properties after functionalization process.

Tunable thermal conductivities of graphene oxide by functionalization and tensile loading

Thermal conductivities of graphene oxide (GO) sheets with different degrees of functionalization and their responses to uniaxial tensile loads have been studied by molecular dynamics simulations. The thermal conductivity of GO is only 5% that of pristine graphene due to the phonon scattering induced by functionalization. Reduction of GO significantly improves the thermal conductivity by more than 4-folds, but still is unable to recover to the full extent. The thermal conductivity of GO unexpectedly increases in response to an external tensile load, a completely opposite trend to those shown by other nanostructured materials, including pristine graphene. We reveal, for the first time, that phonon softening – the commonly-known mechanism that controls the thermal conductivity of graphene upon stretching – does not prevail in GO. The unique structure of GO suppresses the phonon scattering under tension, effectively ameliorating thermal conduction. The anomaly offers a new avenue to tailor the transport phenomenon in GO sheets for various thermal applications.

Tailoring Thermal Transport Property of Graphene through Oxygen Functionalization

We compute thermal conductivity of graphene oxide at room temperature with molecular dynamics simulation. To validate our simulation model, we have investigated phonon scattering in graphene due to crystal boundary length and isotope defect, both of which are able to diagnose the behavior of long wavelength and short wavelength phonon scattering. Our simulation shows that thermal conductivity of pristine graphene has logarithmic divergence for the boundary length up to 2 μm. As compared with pristine graphene, thermal conductivity of graphene oxide can be reduced by a factor of 25 at low oxygen defect concentration. Moreover, we find that not only the concentration but also the configuration of the oxygen functional groups (e.g., hydroxyl, epoxide, and ether) has significant influence on the thermal conductivity. Through phonon mode analysis, phonon defect scattering as well as phonon localization are mainly responsible for the conspicuous reduced thermal conductivity. The simulation results have provided...

졸-젤 법을 이용한 Al(OH)3처리된 그래핀/에폭시 복합체의 열 및 전기전도 특성 분석

그래핀의 우수한 열적 특성을 이용하여 에폭시 수지의 열전도 특성을 향상시키며 전기 절연성질을 유지하는 기능화된 그래핀/에폭시 복합체를 제작하여 전기 및 열전도도를 측정하였다. 기능화된 그래핀은 Hummers법을 이용하여 산화그래핀(GO)을 얻어낸 후 aluminum isopropoxide를 졸-젤 반응을 통해 <TEX>$Al(OH)_3$</TEX>를 그래핀 표면에 도입하여 제작하였다(Al-GO). GO와 Al-GO의 기능화 여부 확인을 위하여 XPS, FE-SEM, FE-TEM 분석을 시행하였으며 GO 표면에 <TEX>$Al(OH)_3$</TEX> 층이 생성된 것을 확인하였다. 기능화된 그래핀/에폭시 복합체는 bisphenol A(DGEBA) 계열의 에폭시에 1, 3 wt%의 GO와 Al-GO를 첨가하여 전기저항을 측정하였으며 Al-GO가 GO와 비교하여 전기 절연성질이 우수하였다. 또한 DGEBA와 bisphenol F(DGEBF) 계열의 에폭시에 1 wt%의 GO와 Al-GO를 첨가하여 열전도 특성을 비교하였으며 순수 에폭시 레진과 비교하여 Al-GO/DGEBF는 23.3%, Al-GO/DGEBA는 21.8%의 열전도도 증가를 보였다. Functionalized graphene/epoxy composites were prepared to miprove thermal conductivities of epoxy composites and to maintain electrical insulating property. Graphene oxide (GO) was prepared using Hummers method, and then GO was reacted with aluminum isopropoxide to functionalize <TEX>$Al(OH)_3$</TEX> layer onto GO surface by a simple sol-gel method (Al-GO). GO and Al-GO were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The analyses confirm that GO was coated with a large and dense coverage of <TEX>$Al(OH)_3$</TEX>. GO and Al-GO (1 and 3 wt%) were embedded in bisphenol A (DGEBA) to investigate the effects of electrical insulating property. Electrical resistivity showed that Al-GO had better insulating property than GO. Further, the thermal conductivity of GO and Al-GO/epoxy composites was higher than that of neat epoxy resins. In particular, the thermal conductivity of Al-GO/bisphenol F (DGEBF) improved by 23.3% and Al-GO/DGEBA enhanced by 21.8% compared with pure epoxy resins.

Significant thermal conductivity enhancement for nanofluids containing graphene nanosheets

We developed a facile technique to produce ethylene glycol based nanofluids containing graphene nanosheets. The thermal conductivity of the base fluid was increased significantly by the dispersed graphene: up to 86% increase for 5.0 vol % graphene dispersion. The 2D structure and stiffness of graphene and graphene oxide help to increase the thermal conductivity of the nanofluid. The thermal conductivity of graphene oxide and graphene in the fluid were estimated to be ∼4.9 and 6.8 W/m K, respectively.