Dissertations / Theses on the topic 'Graphene dispersion'

Epoxy is one of the most adaptable and widely sold high performance material in the world because of its excellent mechanical properties, thermal stability, chemical and corrosion resistance, low shrinkage, low cost, and ease of processing, etc. Graphene shows good potential for the fabrication of high performance polymer nanocomposites because of its unique planar structure and its superlative mechanical properties, thermal conductivity and excellent electrical conductivity. The layered structure allows a large surface contact area with the matrix and thus leads to improvements in the properties. This work aims at exploiting the potential use of graphene as a filler to reinforce epoxy matrix and the preparation of homogeneously dispersed epoxy/graphene nanocomposites. To explore the maximum property enhancement of graphene in epoxy, dispersion is the key factor. However, in the preparation of epoxy/graphene nanocomposites, there still exist some challenges. One of the largest obstacles it that graphene tends to reagglomerate in liquid epoxy, which is due to the strong van der Waals force on the graphene surface. If not properly dispersed, the agglomerated graphene will act as a defect within the matrix and consequently lower the properties of the nanocomposites. Therefore, the dispersion of graphene and the processing techniques should be studied. In this work, epoxy/graphene nanocomposites had been made by different processing techniques. Different characterization methods had been applied to evaluate the reinforcement effect. By end of this work, graphene dispersion techniques and sample preparation methods have been optimized. Epoxy/graphene nanocomposites have been prepared with enhanced properties.

We have developed a flexible approach to the synthesis of surfactants with an ‘Anchor Linker-Head’ (ALH) architecture. These ALH surfactants are designed for the dispersion of multi-walled carbon nanotubes (MWNTs) and exfoliation of graphite in water. Four series of surfactants have been synthesised, all with a pyrene anchor group, which binds strongly to graphitic surfaces through π-π interactions, and hydrophilic head groups based on a carboxylate moiety, carboxylate dendron, crown ether or podand. These are joined by oligoethylene glycol (OEG) linker groups. The anionic surfactants PyrB-PEGn-CH2COONa (n = 2, 4, 6, 12) PyrB-PEGn-CH2COG1(ONa)3 (n = 2, 4, 6) all disperse MWNTs at least as well as commercial surfactants in Millipore water and achieve higher dispersion levels than comparable amide linker surfactants. Non-ionic surfactants are more effective, dispersing up to 61% of the MWNT feedstock. Exfoliation of graphite has been achieved using anionic and non-ionic surfactants. We examined the effect of salts, including NaCl, KCl and CaCl2, on the ability of surfactants to disperse MWNTs and found the choice of linker and head group to be significant. MWNT dispersing ability in 0.6 M NaCl increases with OEG linker length. Structural variation gives surfactants which show improved, reduced, or comparable dispersion levels in 0.6 M NaCl vs. Millipore water, due to the effects of ionic screening and cation coordination. MWNTs dispersed using anionic surfactants can be precipitated by addition of acid, and re-dispersed by addition of base. Eleven non-ionic surfactants have a lower critical solution temperature (LCST), which is tuned by structural changes. We demonstrate using PyrB-PEG4-CH2CO(15-c-5) that LCST surfactants with a pyrene anchor can be used to repeatedly and reversibly precipitate dispersed MWNTs without harsh re-processing. We believe this to be the first report of such behaviour using a small molecule dispersant.

The dispersion of graphene in 1,2-dichloroethane (DCE), its subsequent attachment at the water-DCE interface and the reduction of oxygen at the water-DCE interface proceeding via interfacial graphene have been investigated. Using addition of an electrolyte which screens surface charge, it was found that electrostatic repulsions play a significant role in determining the kinetic stability of lyophobic non-aqueous graphene dispersions. The onset of aggregation was determined and it was found that dispersions prepared from higher-oxygen content graphite were more stable than those prepared from lower-oxygen content graphite, indicating that oxygen content is important in determining the surface charge on graphene in non-aqueous dispersion. The presence of organic electrolyte was also found to promote assembly of graphene into a coherent film at the liquid-liquid interface. Measurement of the liquid-liquid interfacial tension and three-phase contact angle revealed that the energetics of particle attachment did not change in the presence of organic electrolyte, thus indicating a mechanism of inter-particle electrostatic repulsion minimisation through surface charge screening. Interfacial graphene was found to display a catalytic effect toward the oxygen reduction reaction at the water-DCE interface. A bipolar cell was developed which showed that this reaction occurs heterogeneously, with graphene acting as a conduit for electrons across the water-DCE interface.

Scientific development requires profound understandings of micromechanical and nanomechanical systems (MEMS/NEMS) due to their applications not only in the technological world, but also for scientific understanding. At the micro- or nano-scale, when two objects are brought close together, the existence of stiction or adhesion is inevitable and plays an important role in the behavior operation of these systems. Such effects are due to surface dispersion forces, such as the van der Waals or Casimir interactions. The scientific understanding of these forces is particularly important for low-dimensional materials. In addition, the discovery of materials, such as graphitic systems has provided opportunities for new classes of devices and challenging fundermental problems. Therefore, invesigations of the van der Waals or Caismir forces in graphene-based systems, in particular, and the solution generating non-touching systems are needed. In this study, the Casimir force involving 2D graphene is investigated under various conditions. The Casimir interaction is usually studied in the framework of the Lifshitz theory. According to this theory, it is essential to know the frequency-dependent reflection coefficients of materials. Here, it is found that the graphene reflection coefficients strongly depend on the optical conductivity of graphene, which is described by the Kubo formalism. When objects are placed in vacuum, the Casimir force is attractive and leads to adhesion on the surface. We find that the Casimir repulsion can be obtained by replacing vacuum with a suitable liquid. Our studies show that bromobenzene is the liquid providing this effect. We also find that this long-range force is temperature dependent and graphene/bromobenzene/metal substrate configuration can be used to demonstrate merely thermal Casimir interaction at room temperature and micrometer distances. These findings would provide good guidance and predictions for practical studies.

Orientador: Ricardo Paupitz Barbosa dos Santos
Resumo: Neste trabalho, tivemos como objetivo obter a dispersão de fônons de materiais bidimensionais, por meio de simulações de dinâmica molecular clássica, a fim de examinar propriedades mecânicas e elásticas, como a velocidade do som, módulo volumétrico, módulo de cisalhamento, coeficiente de Poisson e módulo de Young. Apresentamos as principais características da ferramenta utilizada na investigação, o método de dinâmica molecular clássica. Abordamos o Algoritmo Velocity Verlet, empregado para a integração das equações de movimento; o Ensemble estatístico, utilizado para realizar as simulações; o termostato de Nosé-Hoover, responsável por regular a temperatura do sistema; e os potenciais que descrevem as interações atômicas. Utilizamos potenciais reativos, sendo eles Tersoff, Tersoff-2010, AIREBO e ReaxFF. As simulações computacionais foram realizadas através do software LAMMPS. Além disso, discorreremos sobre a dinâmica de rede, a obtenção das curvas de dispersão a partir da construção da matriz dinâmica, por meio da matriz dos coeficientes de rigidez baseado nos deslocamentos dos átomos. Os materiais de baixa dimensionalidade investigados nesta dissertação são derivados do carbono como o grafeno, grafeno bifenileno – BPC e nanotubos. As propriedades vibracionais e elásticas calculadas, para o grafeno foram comparadas com resultados experimentais para o grafite no plano e resultados de simulações de dinâmica molecular. O grafeno bifenileno e os nanotubos de carbono foram compara... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: In this work, we aimed to obtain the phonon dispersion of two-dimensional materials by classical molecular dynamics simulations, in order to explore mechanical and elastical properties, such as velocity of sound, volumetric modulus, shear modulus, Poisson's ratio, and Young's modulus. We present the main features of the tool used in the research, the classical molecular dynamics method. We approach the Velocity Verlet Algorithm, used for the integration of the equations of motion; the statistical Ensemble, used to perform the simulations; Nosé-Hoover’s thermostat, responsible for regulate the system temperature; and the potentials that describe the atomic interactions. We used reactive potentials, being Tersoff, Tersoff-2010, AIREBO and ReaxFF. The computational simulations were performed through LAMMPS software. In addition, we will discuss lattice dynamics, the obtaining the dispersion curves from the dynamic matrix construction, through the matrix of stiffness coefficients based on the displacements of the atoms. The low-dimensional materials investigated in this dissertation are derived from carbon such as graphene, graphene biphenylene - BPC and nanotubes. The calculated vibrational and elastical properties for graphene were compared with experimental results for graphite in-plane and results of molecular dynamics simulations. Graphene biphenylene and carbon nanotubes were compared with graphene values. The other materials, biphenylene nanotubes, were compared with carbo... (Complete abstract click electronic access below)
Mestre

L'écotoxicité de différentes nanoparticules de carbone (NPC) a été évaluée chez des organismes aquatiques, en particulier chez Xenopus laevis. Il a été montré que la surface des NPC est le paramètre le plus pertinent pour décrire l'inhibition de croissance chez le xénope, indépendamment de leur forme allotropique et de leur état de dispersion. L'induction des micronoyaux a aussi été étudiée chez le xénope, et l'oxyde de graphène (GO) s'est révélé génotoxique à faible dose, résultat corroboré par l'étude de l'expression des gènes. Les mécanismes de toxicité impliqués seraient notamment liés aux fonctions oxygénées de la particule. De plus, le GO a aussi entrainé de la génotoxicité chez Pleurodeles waltl. et de la tératogénicité, des retards de développement et de l'inhibition de croissance chez Chironomus riparius. La mise en interaction de ces organismes au sein d'un mésocosme a également conduit à l'observation de génotoxicité chez le pleurodèle en présence de GO
The ecotoxicity of different carbon-based nanoparticles (CNPs) was assessed in freshwater organisms, especially in Xenopus laevis. The surface of the CNPs was shown to be the more relevant parameter to describe the growth inhibition in Xenopus, regardless of their allotropic form and their state of dispersion. Micronucleus induction was also studied in Xenopus and graphene oxide (GO) was found genotoxic at low dose. This result was in compliance with the study of genes expression. The involved toxicity mechanisms would be related to the oxidized functions of the CNP. Moreover, GO was also found responsible for genotoxicity in Pleurodeles waltl. and for teratogenicity, development delay and growth inhibition in Chironomus riparius. These organisms have finally been put together in a mesocosm, which has also led to genotoxicity in Pleurodeles in the presence of GO

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The dispersion of carbon nanoparticles in polymer matrices has been studied by many researchers. This paper used nanoparticles of carbon nanotubes and graphene, in high density polyethylene matrix, making use of solution dispersion and melt dispersion. The solution dispersion used as solvent 1,2 dichlorobenzene and the melt dispersion was performed with torque rheometer. Analysis of Differential Scanning Calorimetry, Thermogravimetry, Size Exclusion Chromatography, Raman Spectroscopy, Infrared Spectroscopy Fourier Transform , analyzes of torque in the melt dispersion, nanoindentation to determine nanohardness and elastic modulus, Vickers hardness, Transmission Electron Microscopy, and Scanning Electron Microscopy with Field Emission. It was found that there was no significant change in melting temperature and crystallization of the nanocomposites. No significant change was identified in thermogravimetric analysis. The results of the elastic modulus demonstrate 22.8% increase in the use of carbon nanotubes for both methods of dispersion. The results obtained in graphene nanocomposites show that the dispersion method directly affects the properties of the nanocomposites. There was a 14% increase in tensile modulus for composites with 1% solution by graphene dispersed and scattered compositions with 5 % in melt dispersion. Analysis of Transmission Electron Microscopy and Scanning Electron Microscopy with Field Emission confirm dispersion states of carbon nanotubes dispersed by fusion , and agglomerated states of graphene in both dispersion processes, with smaller nanoplateletes of the solution dispersion compared to the melt dispersion. Crystallinity index showed similar levels in nanocomposites with carbon nanotubes and differentiated for nanocomposites with graphene, which reduces the degree of crystallinity compared to pure polymer matrix values.
A dispersão de nanopartículas de carbono em matrizes poliméricas tem sido objeto de estudo de diversos pesquisadores. Este trabalho utilizou nanopartículas de nanotubos de carbono e grafenos, em matriz de polietileno de alta densidade, fazendo-se uso de dispersão por solução e dispersão por fusão. A dispersão por solução utilizou como solvente 1,2 diclorobenzeno e a dispersão por fusão foi realizada com reômetro de torque. Foram realizadas análises de Calorimetria Diferencial Exploratória, Termogravimetria, Cromatografia de Exclusão por Tamanho, Espectroscopia RAMAN, Espectroscopia no Infravermelho com Transformada de Fourier, análises de torque na dispersão por fusão, nanoindentação para determinação de módulo de elasticidade e nanodureza, microdureza Vickers, Microscopia Eletrônica de Transmissão e Microscopia Eletrônica de Varredura com Emissão de Campo. Verificou-se que não há alteração significativa da temperatura de fusão e de cristalização dos nanocompósitos obtidos. Não foi identificado alteração significativa do comportamento térmico no ensaio de termogravimetria. Os resultados do módulo de elasticidade demonstram aumento de 22,8% na utilização de nanotubos de carbono, para os dois métodos de dispersão. Os resultados obtidos nos nanocompósitos com grafenos demonstram que o método de dispersão interfere diretamente nas propriedades dos nanocompósitos. Houve aumento de 14% no módulo de elasticidade para composições com 1% de grafeno dispersados por solução e para composições com 5% dispersados por fusão. As análises de Microscopia Eletrônica de Transmissão e Microscopia Eletrônica de Varredura com Emissão de Campo confirmam estados de dispersão de nanotubos de carbono dispersados por fusão, e estados aglomerados de grafenos em ambos os processos de dispersão, havendo dimensões menores dos nanoplateletes na dispersão por solução, em comparação à dispersão por fusão. Os índices de cristalinidade apresentaram teores semelhantes nos nanocompósitos com nanotubos de carbono e valores diferenciados para os nanocompósitos com grafenos, com redução do grau de cristalinidade em relação à matriz polimérica pura.

The diploma thesis deals with the possibility of using the addition of nanoparticles to improve the properties of cement composites. The theoretical part summarizes the findings of research in this area with a focus on methods of dispersion of nanoparticles and their treatment for use in cement composites. The experimental part focuses on the comparison of methods of dispersion and plasma treatment of reduced graphene oxide (rGO) nanoparticle solutions from the point of view of the agglomeration process. During this work, a method of systematic optical/visual monitoring of sedimentation/agglomeration was developed to complement sophisticated methods such as spectrophotometry (UV/Vis) and electron microscopy (SEM). Furthermore, the effect of the addition of rGO on the properties of cement mortar, in the form of aqueous solutions prepared by the dispersion methods determined in the previous section, was investigated.

This diploma thesis deals with the influence of addition of carbon nanoparticles on cement composites. The theoretical part of the diploma thesis is focused on the research of information about carbon nanoparticles, more precisely about carbon nanotubes and graphene oxide. There are summarized methods of dispersing carbon nanotubes and their effects on cement composites. The practical part follows the theoretical part of the research. In the first phase, the correct technique of graphene oxide dispersion was verified. Subsequently, the effects of graphene oxide on the mechanical properties of cement mortars were verified. In the final phase of the diploma thesis, the knowledge gained from the previous part was verified on concrete samples.

Graphene's combination of properties makes it a material with great potential in a wide range of applications. High thermal conductivity and good tribological properties mean graphene has been proposed as an additive for both lubricants and thermal fluids; being used to form nanofluids with improved properties. However, the use of graphene in these applications requires the significant challenge of dispersing graphene in applied fluids to be overcome. In this work graphene, and its functionalised derivatives were dispersed in both polar and non-polar fluids using a range of techniques, following which the properties of these fluids were analysed. Initially, the dispersibility of reduced graphene oxide (rGO) in water was investigated and a novel method of using N-methyl-2-pyrrolidone (NMP)to act as a dispersant for rGO in polar fluids was developed. Using this method dispersions of rGO in water were produced at over six times the concentration possible by standard dispersion. Working in more applied fluids efforts were made to improve the dispersibility of graphene materials in applied polar fluids such as oils. Stable dispersions of graphene materials in commercial oils were produced through functionalisation of graphene, with a range of reagents, to improve its compatibility with non-polar solvents. These functionalised graphenes were then dispersed in commercial lubricants to form stable dispersions and the tribological properties of these dispersions were tested showing that it was possible for functionalised graphenes to improve the performance of commercial lubricants. To assess the impact of graphene on the thermal properties of applied fluids dispersions of graphene materials were prepared in a commercial coolant. The thermal properties of this nanofluid were then determined and it was shown that the addition of graphene materials can improve the thermal properties of applied fluids.

We employ the empirical potential function Airebo to computationally model free-standing Carbon-12 graphene in a classical setting. Our objective is to measure the mean square displacement (MSD) of atoms in the system for different average temperatures and Carbon-13 isotope concentrations. From results of the MSD we aim to develop a technique that employs Transmission Electron Microscopy (TEM), using high-angle annular dark filed (HAADF) detection, to obtain atomic-resolution images. From the thermally diffusive images, produced by the vibrations of atoms, we intent to resolve isotopes types in graphene. For this, we establish a relationship between the full width half maximum (FWHM) of real-space intensity images and MSD for temperature and isotope concentration changes. For the case of changes in the temperature of the system, simulation results show a linear relationship between the MSD as a function of increased temperature in the system, with a slope of 7.858×10-6 Å2/K. We also note a power dependency for the MSD in units of [Å2] with respect to the FWHM in units of [Å] given by FWHM(MSD)=0.20MSD0.53+0.67. For the case of increasing isotope concentration, no statistically significant changes to the MSD of 12C and 13C are noted for graphene systems with 2,000 atoms or more. We note that for the experimental replication of results, noticeable differences in the MSD for systems with approximately 320,000 atoms must be observable. For this, we conclude that isotopes in free-standing graphene cannot be distinguished using TEM.

L'objectif de ce travail est de développer et d’étudier une nouvelle classe de fluidesintelligents à base de dispersions colloïdales de carbone, sensibles à un stimulus externe pour desapplications de conversion et stockage d’énergie. Ces stimuli sont de différentes natures : vibrationmécanique, mouvement humain, variation de pression ou écoulement d'un solvant, et peuventaltérer les structures de tels systèmes. Ceci induit une modification de la structure locale desparticules et par conséquent des propriétés diélectriques et électriques. Habituellement, lessuspensions de matériaux carbonés sont étudiées au repos ou séchées. Toutefois, comprendre leurcomportement en flux est essentiel pour de nouvelles applications où ces matériaux sont exploitésdans des conditions dynamiques telle que le stockage d'énergie électrochimique assisté par flux(FAES). Par exemple, les matériaux à base de graphène jouent désormais un rôle important dans lesnouvelles technologies énergétiques. Ils sont utilisés comme additifs conducteurs dans lesassemblages d'électrodes, mais en raison de leur forme anisotrope spécifique, ils permettentégalement d’obtenir des fluides diélectriques sous écoulement.Les cristaux liquides d'oxyde de graphène, en tant que matériau souple électrostrictif, sont étudiéspour la récupération d'énergie mécanique, ainsi que des dispersions de noir de carbone pour lestockage d'énergie.Les propriétés diélectriques et électriques de ces dispersions fluides dans des conditions statiques etdynamiques sont mesurées et analysées. Enfin, l’effet de l’écoulement sur l’orientation et laréorganisation locale des particules et leur comportement diélectrique et électrique sont examinés
The aim of this work is to develop and study a new class of smart fluids made of colloidalcarbon-based dispersions, which are sensitive to an external stimulus for energy storage orconversion applications. The effect of an external input, such as mechanical vibration, humanmotion, variable pressure, flowing of a solvent, can alter the structures of such systems.Consequently these changes induce modifications of the dielectric and electrical properties. Usually,the suspensions of carbon materials are investigated at rest or dried. However, their flow behavior iscritical when new technologies, which exploit these materials in dynamic conditions such as FAES(Flow-Assisted Electrochemical Energy Storage) are considered. For example, graphene-basedmaterials are now playing a significant role in energy materials. They act as conductive additives inelectrode assemblies, but due to their specific anisotropic shape they also provide a new route toachieve dielectric liquid media.In details, Graphene Oxide liquid crystals as electrostrictive soft material for mechanical energyharvesting and Carbon black dispersions as percolated flowable electrodes for capacitive energystorage are investigated.In particular, the dielectric and electrical properties of these flowable dispersions are studied understatic and dynamic conditions. The effect of the flow-rate on the local orientation and reorganizationof the particles and their related dielectric and electrical behavior are examined

Polarized Raman Spectroscopy (PRS) is one of the experimental methods which can be employed to deduce orientational order parameters, e.g. 〈P_200 〉, 〈P_400 〉, in liquid crystals from the experimental depolarization ratio graph via fitting. However, it has long been known that the order parameters deduced from the different vibrational modes are found to be different within the same sample. As a result, only certain vibrational modes can be reliably selected for analysis, limiting the application of PRS. The possible explanations are discussed in this thesis. The first explanation is given by considering a dipole tilt β_0 which is defined as the tilt angle of the dipole vibrational direction and the molecular long axis. A second explanation comes from assuming different vibrational symmetries, i.e. cylindrical or elliptic cylindrical. Molecular biaxial order parameters are introduced in both explanations. A systematic check via calculation shows that a common set of order parameters (including molecular biaxial order parameters) can be obtained with different depolarization ratio graphs when the explanations are considered. Both depolarization ratio graphs can also agree well with that obtained from phenyl and cyano stretching modes experimentally. A supplementary discussion shows that by using the first explanation, 〈P_400 〉 which, in previous fitting, shown an excessive value by using cyano stretching mode is reduced (15% reduced at β_0=15°, 〈P_402 〉=0.0536). PRS is also employed to analyse the order parameters in a bent-core system using a molecular model with the bend angle Ω and tilt angle B_0. The effects of each of the uniaxial and phase biaxial order parameters are considered. With a total Raman tensor generated by the sum of Raman tensor from each arm, reasonable uniaxial order parameters fitting values can be obtained from PRS without considering biaxial order parameters. These results agree well with those deduced from the refractive index measurements, which shows a new approach to the investigation of bent-core systems. However, it is also shown that introducing phase biaxial order parameters can’t provide robust fitting, leading inaccurate fitting values in the end. Several different liquid crystals (5CB, E7, HAT-6 and SSY) have been examined on seeking graphene/graphene oxide dispersions in liquid crystal systems. Unfortunately, no stable dispersion was obtained by applying simple experimental techniques. However, a highlight comes from the test of a lyotropic liquid crystal formed by a discotic molecule in NMP suggesting a possible dispersion medium for graphene. Meanwhile, by using Raman spectroscopy, the interaction between liquid crystal molecules and graphene can be obtained from the peak shift of vibrational modes. The experimental results suggest a stronger interaction in E7 compared to 5CB. No shift in ZLI-1695 indicates the different effects from the rigid core. Further, the discotic liquid crystal (HAT-6) shows a strong interaction with graphene. These facts lead to a conclusion that the interaction still exists in the graphene/liquid crystal dispersion providing a guide on controlling and optimizing the dispersion quality for the future research.

It has previous been shown that multiwall carbon nanotubes (MWCNT5) and carbon nanofibers can be effectively dispersed in phenylethynyl terminated imide (PETI) resins by high torque melt mixing, and processed into polymer matrix composites with improved electrical, thermal and mechanical properties and improved resistance to moisture adsorption. PETI resins are candidates in a vast array of potential applications that include aerospace vehicles. We found that high torque melt mixing with the combination of energy transferred during melt mixing, and formation of charge transfer complexes between graphene and the PETI resin successfully delaminated graphite, which is considerably less expensive than MWCNTs or graphene, to give dispersed short stacks and possibly individual graphene sheets. Melt rheology was utilized to examine the dispersion of graphene in the PETI resin and the resulting modification of viscoelastic properties including complex viscosity, r, storage modulus, G’, and loss modulus, G’. Raman spectroscopy with 785 nm excitation, X-ray powder diffraction, and scanning electron microscope (SEM) were also used to verify the delamination of graphite to graphene and short graphene stacks. The examination PETI 298 rheological behavior, mirroring resin transfer molding processing conditions, established that PETI 298 can be readily shear thinned, behaving as a non-Newtonian fluid. PETI 298 and dispersed graphite/graphene composites also exhibited non-Newtonian behavior under these conditions, which indicated that these new materials could be processable by Resin Transfer Molding (RTM). Differential scanning calorimetry (DSC) studies on the melt mixed PETI 298 graphite composites indicate that these nanocomposites can be fully cured at 371 °C, to five full cured loaded polyimides with high glass transition temperatures (Tg).

La synthèse du graphène reste une étape problématique mais la technique par dépôt de vapeur chimique sur les métaux a beaucoup progressé ces trois dernières années, c'est-à-dire depuis que l'on sait qu'il est possible de retirer sans le dénaturer le graphène de son support métallique. Cette étape de transfert appelle à l'étude de la force d'interaction qui a lieu entre graphène et métal. L'influence de cette liaison graphène-métal sur la structure électronique a déjà été largement étudiée et nous proposons plutôt ici de nous pencher sur la dispersion des phonons. Celle du graphène isolé est d'ailleurs remarquable pour les deux grandes anomalies de Kohn (KA) qu'elle présente sur sa branche de plus haute fréquence aux points de haute symétrie Gamma et K. La pente de la dispersion autour de ces KA est une mesure directe du couplage électron-phonon (EPC) entre ces modes de phonons et les électrons des points de Dirac. Nous avons montré que cet EPC, qui a par exemple beaucoup d'influence sur la mobilité électronique ou sur le processus de résonnance Raman, est fortement altéré suite à l'interaction avec certains substrats métalliques. Lors de notre étude ab initio du graphène sur nickel(111), nous avons en effet observé une disaparition complète des anomalies de Kohn. Ceci est dû à la forte hybridation entre les bandes pi du graphène et les bandes d du nickel. La spéctroscopie Raman et la diffraction électronique à basse énergie sont des moyens efficaces et courants pour caractériser le graphène sur les substrats métalliques. Nos résultats montrent comment tirer de ces mesures davantage d'informations concernant le caractère physisorbé ou chimisorbé du graphène sur le métal
The fabrication of high quality large-area graphene films is one of the biggest problem. Recently, the synthesis by chemical vapor deposition of hydrocarbons over a metallic substrate have shown promising results. To manage as well as possible the transfer process of the graphene layer in an insulator, it is important to know the interaction strength between the graphene layer and the metallic substrate. We propose in this paper to calculate the phonon dispersion of an adsorbed graphene. The phonon dispersion of graphene is known to display two strong Kohn Anomalies (kinks) in the highest optical branch (HOB) at the high-symmetry points Gamma and K. The phonon slope around the Kohn anomalies is related to the electron-phonon-coupling (EPC) with the graphene pi bands. We show that this EPC, which has strong impact, for example, on Raman scattering and electron transport, can be strongly modified due to interaction with a metallic substrate. For graphene grown on a Ni(111) surface, our ab initio calculations show a total suppression of the Kohn anomaly ; the HOB around Gamma and K becomes completely flat. This is due to the strong hybridization of the graphene pi-bands with the nickel d-bands that lifts the linear crossing of the pi bands at K. Raman spectroscopy and low-energy electron diffraction are quick and reliable methods to characterize graphene on metallic substrates. Our results show how to obtain additional information, by means of vibrational and photoemission spectroscopy, on the chemisorption or physisorption of graphene layers on metal surfaces

This work is focused on segregation processes in the matrix of spheroidal graphite cast iron with different silicon and nickel content during heat treatment. The aim of this work is to trace the redistribution of the elements of interest during homogenization annealing with different dwell time by comparison of the effective distribution coefficients. Comparison of some specific properties and description of structure development of spheroidal graphite cast iron matrix from initial state to the state after ferritization and homogenization annealing is included in this work.

This doctoral thesis deals with the comparison of different methods of alloying elements’ concentration measurement based on energy dispersive spectroscopy and also with the suitability of particular methods of quantitative assessment of heterogeneity of the spheroidal graphite cast iron matrix. The segregation curves construction, distribution coefficient and heterogeneity index formulation is also discussed. The notion “normalized distribution coefficient” is introduced newly. The goal of the thesis, which is to be achieved by means of evaluation of large experimental data sets, is the evaluation of applicability of homogenization annealing of spheroidal graphite cast iron with the aim to eliminate segregation of silicon, and mainly nickel, as pearlite- and carbide-forming agent at the border of an eutectic cell. The result is an optimized homogenization annealing schedule maximizing the suppression of silicon and nickel segregation while taking into account the minimization of financial expenses and risk of grain coarsening.

碩士
國立臺灣大學
高分子科學與工程學研究所
105
The interaction between the platelet-like materials of graphene and nano silicate platelet (NSP) was studied for antistatic applications. Two different source of graphite, electronic graphite and CPC graphite-like materials were compared for illustrating the dispersion mechanism involving the effect of the silicate platelet (NSP) presence. It was discovered that CPC graphite-like with the properties of oleophilic could be well dispersed in aqueous medium. Furthermore, the amphiphilic property and irreversibly dispersion behaviour either in water or in toluene, depending on the exposing order, were achieved for the graphene/NSP nanohybrid. The mechanism involved micelle-like microstructure of oil-in-water and water-in-oil forms. Low molecular weight of POEM (s-POEM), compared with home-made dispersant poly(oxyethylene)-segmented imide (POEM), was synthesized for affecting the dispersibility and long term stability of graphene. As prepared graphene/NSP nanohybrid was solution blending with WPU to form graphene/NSP/WPU nanocomposites film. The comparison among graphene/WPU, NSP/WPU and graphene/NSP/WPU was made. In the absence of NSP, graphene showed sedimentation in the bottom of composite film and resulted in the uneven performance of sheet resistance. The presence of NSP prevented graphene from sedimentation, leading to the Graphene/NSP/WPU nanocomposites, shown the sheet resistance from larger than 1012 of pristine WPU, to 107 ohm/sq with uniform electrical property in both side of film. These graphene/NSP/WPU composites can well meet the requirement of antistatic uses.

碩士
中華科技大學
飛機系統工程研究所
106
Nanomaterials were dispersed in epoxy resin by using ultrasonicationor mechanical stirring is the main method of nanocomposite prepared.However, the above process often takes hours or even longer, which is notcost-effective for future production in the industry. Therefore, this studyhopes to prepare nanocarbon material/epoxy nanocomposites via a rapidly and simple dispersing process. In this study, the preparation method and mechanical properties of graphene nanoplatelets/epoxy nanocomposites were investigated by planetary dispersion method. The graphene nanoplatelet(GNPs) containing different proportions(0.1, 0.25, 0.50, and 1.0 wt%)were used to reinforce epoxy resin to enhance their mechanical properties of nanocomposites.The experimental results showed that the mechanical properties of the nanocomposies steadily improved with 0.1~0.25 wt% GNPs added.Furthermore, the solution of epoxy resin containing the GNPs on the three different proportion(i.e. 0, 0.25, and 1.0 wt%)permeate through a unidirectional(UD)carbon fiber was used to prepare the GNPs/UD CFRP laminates in order to investigate whether different ratios of GNPs have the same reinforcing behavior for GNPs/UD CFRP laminates and GNPs/epoxy nanocomposites. Experimental results showed that when the GNPs added in an amount of 0.25 %, the tensile strength, flexural strength, and interlaminar shear strength of the GNPs/UD CFRP laminate compared to that of neat CFRP were increased by 6%, 4%, and 10%, respectively. However, the Young’s modulus and flexural modulus of the 0.25 wt% GNPs/CFRP laminate show negligible improvements compared to that of the neat composite laminate.

The work presented in this dissertation attempts to form an understanding of the importance of polymer connectivity and nanoparticle shape and curvature on the formation of non-covalent interactions between polymer and nanoparticles by monitoring the dispersion of nanoparticles in copolymers containing functionalities that can form non-covalent interactions with carbon nanoparticles. The first portion of this study is to gain a fundamental understanding of the role of electron donating/withdrawing moieties on the dispersion of the fullerenes in copolymers. UV- Vis spectroscopy and x-ray diffraction were used to quantify the miscibility limit of C60 fullerene with the incorporation of electron donor-acceptor interactions (EDA) between the polymer and fullerene. The miscibility and dispersion of the nanoparticles in a polymer matrix are interpreted to indicate the extent of intermolecular interactions, in this case non-covalent EDA interactions. Experimental data indicate that the presence of a minority of interacting functional groups within the polymer chains leads to an optimum interaction between polymer and fullerene. This is further affirmed by density functional theory (DFT) calculations that specify the binding energy between interacting monomers and fullerenes. The second portion focuses on the impact of sample preparation on the dispersion of graphene nanocomposites. Visualization and transparency are used to quantify the dispersion of graphene in the polymer matrix. In addition, differential scanning Calorimetry (DSC) also provides insight into the efficiency of the preparation process in forming a homogeneous sample, where rapid precipitation and solvent evaporation are studied. Examining the change in glass transition temperature, Tg, with nanoparticle addition also provides insight into the level of interaction and dispersion in the graphene nanocomposites. The approach of utilizing non-covalent interactions to enhance the dispersion of polymer nanocomposites is realized by varying the functional group in the copolymer chains, while the impact of nanoparticle shape is also examined. The optimum enhancement of dispersion is interpreted in terms of the improvement of interaction between polymer and nanocomposites. This interpretation leads to the conclusion that chain connectivity and the ability of the polymer to conform to the nanoparticle shape are two important factors that govern the formation of non-covalent interactions in polymer nanocomposites.

碩士
輔仁大學
化學系
102
Three polyhydroxystyrene-co-polystyrene coploymers (PHS-co-PS) have been synthesized and blend with graphene oxide (GO) to study the anticorrosion properties through H-bond formatiom. Experimental results show that dispersion of GO in the PHS-co-PS is improved as the content of hydroxystyrene increases. The enhanced dispersion morphology leads to a better anticorrosion performance for the PHS-co-PS film. Transmission Electron Microscopy (TEM) and X-ray Diffraction spectroscopy (XRD) are used to characterize the dispersion of GO in PHS-co-PS films. Cyclic Voltammetry is used to study the anticorrosion properties of PHS-co-PS/GO composites. TEM images indicate a phase- separated polystyrene/GO composite is gradually intercalated by copolymerized hydroxystyrene into the polystyrene. H-bonding occurs between GO and PHS-co-PS forces GO to separated. XRD results indicates the separation of GO in the composites. Corrosion Protection Efficiency (P.E.%) measurement from CV experiments show the anticorrosion behavior is enhanced in the higher hydroxystyrene content PHS-co-PS/GO composites. The P.E.% increases from 85.57% for the PS/2 wt% GO film to 99.98% for the PHS-co-PS (PHS 20%)/2 wt% GO film. Evidently, the H-Bond formation between GO and PHS-co-PS dose separate the GO into the PHS-co-PS film and significantly improves the anticorrosion properties of PS/GO film.

Graphene sheets, one atom thick, two dimensional layers of carbon atoms, have gained enormous importance over the past few years due to their unique attributes - high electronic, thermal conductivities and exceptional mechanical strength. Chemical reduction of graphene oxide (GO) has been considered as a viable route for large scale production of graphene sheets. The reduced graphene oxide (r -GO) sheets although their conductivities are comparatively lower than that of graphene are nevertheless versatile material for applications in thin films and composites. An important consideration in the design of solution processing techniques for the preparation of processable graphene sheets is the dispersibility of GO and r -GO in different solvents, especially aqueous dispersibility. While GO is dispersible in water over a wide range of pH values, r -GO shows poor dispersibility and over a limited range of pH values. Graphene oxide, the oxidized form of graphene, are single atomic layers with lateral dimension that can extend to hundreds of nanometers. The sheets contain a sizable fraction of carbons that are sp3 hybridized and covalently bonded to oxygen in the form of epoxy, carbonyls as well as ionizable hydroxyl and carboxylic functional groups located on the rim of the sheets. The remaining carbons form isolated sp2 graphene like networks. On reduction the oxygen functionalities are removed and the sp2 network partially restored. This thesis focuses on the aqueous dispersibility of GO and r -GO, and describes a strategy to enhance the dispersibility of r -GO by cyclodextrin functionalization. Chapter 1 of the thesis provides a brief review of the synthetic procedures and structure of GO and r -GO while Chapter 2 describes the experimental methods and characterization techniques used in the thesis. The chemistry underlying the aqueous dispersibility of GO and r -GO at different values of pH have been investigated by zeta potential measurements, pH titrations and infrared spectroscopy (Chapter 3). These measurements show that r -GO sheets have ionizable groups with a single pKa value (8.0) while GO sheets have groups that are more acidic (pKa = 4.3), in addition to groups with pKa values of 6.6 and 9.0. Infrared spectroscopy has been used to follow the sequence of ionization events. In both GO and r -GO sheets, it is ionization of the carboxylic groups that is primarily responsible for the build up of charge, but on GO sheets, the presence of phenolic and hydroxyl groups in close proximity to the carboxylic groups lowers the pKa value by stabilizing the carboxylate anion, resulting in superior water dispersibility. Till recently GO was primarily considered only as an easily available precursor for chemical routes to r -GO but it has now been recognized as an interesting material in its own right. Two such attributes that have attracted wide spread attention are the in- trinsic and tunable fluorescence of GO as well as formation of liquid crystalline phases. Aqueous dispersions of GO exhibit strong pH dependent fluorescence in the visible region that originates, in part, from the oxygenated functionalities present. In Chapter 4, the spectral migration on nanosecond timescales of the pH dependent features in the fluores- cence spectra of GO is described. The changes in the steady state fluorescence spectra with pH have been correlated with the sequence of dissociation events that occur in GO dispersions at different values of pH described in Chapter 3, from time resolved emission spectra (TRES) constructed from the wavelength dependent fluorescence decay curves, it is shown that the migration is associated with excited state proton transfer. Both ‘intramolecular’ and ‘intermolecular’ transfers involving the quasimolecular oxygenated aromatic fragments are observed. Aqueous dispersions of GO constitute a distinctive class of 2D-anisotropic colloids with competing interactions - long range electrostatic repulsion, originating from ionized carboxylic groups located on the rim of the sheets and weak dispersive attractive interactions originating from the un-oxidized sp2 graphitic domains. In Chapter 5, it is shown that, colloidal dispersions of GO are intrinsically frustrated, exhibiting a range of arrested or metastable states, encompassing fluid, glass and gels that coexist with liquid crystalline order. These states can be accessed by varying the relative magnitudes of the repulsive and attractive forces by changing the ionic strength of the medium, by addition of salt and/or the concentration of the dispersion. At low salt concentrations, where long range electrostatic repulsions dominates, the formation of a repulsive Wigner glass is observed while at high salt concentrations, when attractive forces dominate, the formation of gels that exhibits a nematic to columnar liquid crystalline transition. These studies highlights how the chemical structure of GO - hydrophilic ionizable groups and hydrophobic graphitic domains coexisting on a single sheet - gives rise to a rich and complex phase diagram. The poor dispersibility of r -GO in aqueous media limits its use in practical applica- tions. To enhance the dispersibility, r -GO sheets have been functionalized by covalently linking -cyclodextrin ( -CD) cavities to the sheets via an amide linkage (Chapter 6). The functionalized -CD: rGO sheets, in contrast to r -GO, are dispersible over a wide range of pH values (2 - 13). Zeta potential measurements indicate that there is more than one factor responsible for the dispersibility. It is shown that planar aromatic molecules adsorbed on the r -GO sheet as well as nonplanar molecules included in the tethered -CD cavities have their fluorescence effectively quenched by the -CD: rGO sheets. The -CD: rGO sheets combine the hydrophobicity associated with r -GO along with the hydrophobicity of the cyclodextrin cavities in a single water dispersible material. Resonance Raman spectroscopy is a powerful analytical tool for detecting and identi- fying analytes, but the associated strong fluorescence background severely limits the use of the technique. In Chapter 7, it is shown that the cyclodextrin functionalized -CD: rGO sheets, described in Chapter 6, provides a versatile platform for resonance Raman detection. Planar aromatic and dye molecules that adsorb on the r -GO graphitic domains and non-planar molecules included within the tethered -CD cavities have their fluorescence effectively quenched. Using the water dispersible -CD: rGO sheets, it is possible to record the resonance Raman spectra of adsorbed and included organic chromophores directly in aqueous media without having to extract or deposit on a substrate. The Raman signal intensities show a linear dependence with the concentration of analyte present in water. This is significant, as it allows for the identification and estimation of organic analytes present in water by resonance Raman spectroscopy.

This dissertation explores the microstructural properties, flow, and phase behavior of aqueous suspensions of single-walled carbon nanotube (SWNT) and graphene. Liquid phase processing with scalable and industrially viable methods is used for fabrication of basic engineering materials like thin films, coatings and 1-D fibrillar structures. The electro-optical transport properties of these novel materials are characterized. A recipe for formulation of an aqueous colloidal suspension with high SWNT concentration is presented. A combination of two surfactants provides optimal rheological behavior for "rod coating" uniform transparent conductive SWNT thin films, with minimal dewetting, rupture and defects. "Doping" with acids and metallic nanoparticles yield SWNT films with electrical sheet resistance of 100 and 300 OJ sq for respective optical transparency of 70% and 90%. SWNT thin films with local nematic ordering and alignment are fabricated using a "slow vacuum filtration" process. The technique is successfully demonstrated on several aqueous SWNT suspensions, employing different ionic and non-ionic surfactants, as well as on dispersions enriched in metallic SWNTs, produced by density gradient ultracentrifugation. Scanning electron microscopy and image analysis revealed a local nematic order parameter of 8 "" 0.7-0.8 for the SWNT films. Aligned SWNT films and fibers are employed as templates, in a simple drop drying process, for large scale ordered (8 "" 0.7-0.9) assembly of plasmonic nanoparticles, like gold nanorods, micro-triangles and platelets. Colloidal self-assembly of surfactant stabilized SWNTs and AC dielectrophoresis (DEP) are combined in a novel two-step technique for fabrication of 1-D SWNT fibrils. The self-assembled SWNT-surfactant colloidal structures are 103 - 104 fold more responsive to external AC electrical fields. The DEP SWNT fibrils show significant Raman alignment ratio ("" 3-5) and good electrical conductivity. iii A detailed study on the phase behavior of giant graphene oxide flakes (aspect ratio > 104) suspended in water is presented. The lyotropic suspensions transition from an isotropic to a biphasic system and to a discotic nematic liquid crystal with increasing flake concentration. Polarizing optical microscopy and colloidal particle inclusions reveal the alignment and orientation flakes in the nematic phase, the nematic order parameter (8 f"V 0.43), low optical birefringence (~n = -0.0018), and an average Frank elastic constant (K f"V 100 pN) which is about 100 fold higher than previously studied discotic liquid crystals.

碩士
國立中興大學
化學工程學系所
106
Graphite, one of carbon material, has a layered planar structure that are held together by van der Waals forces. When the number of layers is less than a certain number, it can be called graphene. Due to graphene possesses extraordinary electronic, thermal and optical properties, it holds great promise in a wide range of applications including cooling, composite, medical materials and energy storage, etc. However, surface of graphite has strong van der Waals forces and makes it easy to aggregate to limit its application. Therefore, how to enhance the stability of the dispersion solution and reducing the secondary particle size is a very important issue. In this study, the dispersion and exfoliation of graphite in the solution is carried out by batch or cyclic ultrasonic probe processes. In the experimental design, graphite plays role of the dispersion phase, and the mixture of acetone and deionized water are used as continue phase. Using UV-Visible Spectrometers (UV-Vis) with Taguchi method to find the optimal parameters, indicating the dispersion conditions that allows the dispersion to have the lowest light transmittance, including graphite amount, ratio of acetone to water, dispersion temperature, dispersion time, wetting time, ultrosonic frequency, ultrosonic power, and the flow rate of dispersion solution, in batch and cyclic processes. In the characterization, we used polarized optical microscope (POM) to evaluate the lateral dimensions of the dispersed graphite, atomic force microscopy (AFM) to observe the morphology and thickness of the exfoliated graphene, Raman spectroscopy (Raman) was used to identify the surface properties of graphite and exfoliated graphene. As shown in the results, we summarized the following remarks: (1) According to the results from Taguchi experiment, the optimal condition for the dispersion of graphite in the batch process was A1B4C4D4E4, meaning 1 wt% of graphite, 1/4 ratio of water to acetone, 25 ̊C of dispersion solution, 10 minutes for dispersion, and 7 days for wetting, which the most effect of parameter is graphite amount that contribution reach 73%, as well as that through the cyclic process, the optimal condition was A1B3C3D3E3F2G3H3, expressing 1 wt% of graphite, 1/4 ratio of water to acetone, 25 ̊C of dispersion solution, 25 minutes for dispersion, 5 days for wetting , 0.75: 0.25 of ultrasonic frequency, 175 W of ultrasonic power, and 300 ml/min of dispersion solution flow, which the most influential parameter is also graphite amount contributed by about 65%. (2) As analyzed by POM, smaller average particle sizes of dispersed graphite in mixture of acetone and water by means of batch and cyclic processes were 7.9 μm and 10.2 μm respectively. This discrepancy is because that the optimal conditions of dispersion time and wetting time in batch process are both longer than that in continue ones. If the dispersion time and wetting time of the cyclic process are regulated to be the same as those of the batch ones, the average particle size of dispersed graphite in solution can be reduced to 7.1 μm. This suggests that the wetting and dispersion time are significant factors for the dispersion of graphite in solution through ultrasonic probe. (3) From the Raman spectra, with the optimal conditions of batch and cyclic processes, the ratios of ID/IG and I2D/IG were 1.02 and 0.76, as well as 0.33 and 0.80 respectively. This infers that the disorder of exfoliated graphene by batch process is more than that by cyclic process, but the layer number of exfoliated graphene are almost same for the batch and cyclic process. (4) With the UV-Vis spectra and AFM image under same wetting and dispersion time, the obtained concentration and thickness of exfoliated graphene were 0.0451 mg/ml and 2.29 nm, as well as 0.0360 mg/ml and 1.74 nm, through batch and cyclic processes respectively. (5) As measured by zeta potential and natural sedimentation, with optimal conditions of batch process, the zeta potential of as-prepared dispersion solution of graphite was -31 mV, having well stability, which life time was more than three weeks at least for storage without sedimentation. (6) The yield of graphene can be known by dividing the concentration of graphene after exfoliation from the concentration of graphite before dispersion. As a result, under same wetting and dispersion time, the yield of graphene were 0.37% and 0.31%, for the batch and cyclic process, respectively, meaning that the production rate of graphene is almost same for two different processes in this study.

An experimental activity was performed to observe and study the effects of graphite dispersion and deposition on thermal hydraulic phenomena in a Reactor Cavity Cooling System (RCCS). The small scale RCCS experimental facility (16.5cm x 16.5cm x 30.4cm) used for this activity represents half of the reactor cavity with an electrically heated vessel. Water flowing through five vertical pipes removes the heat produced in the vessel and releases it in the environment by mixing with cold water in a large tank. PIV technique was used to study the velocity field of the air inside the cavity. A set of 52 thermocouples was installed in the facility to monitor the temperature profiles of the vessel and pipes walls and air. 10g of a fine graphite powder (particle size average 2 [mu]m) were injected into the cavity through a spraying nozzle placed at the bottom of the vessel. Temperatures and air velocity field were recorded and compared with the measurements obtained before the graphite dispersion, showing a decrease of the temperature surfaces which was related to an increase in their emissivity. The results contribute to the understanding of the RCCS capability in case of an accident scenario.

碩士
國立臺灣大學
地質科學研究所
94
Graphite encapsulated metal (GEM) nanoparticles is a relatively new material. With an inner ferromagnetic metal core and several layers of outer graphitic shells, GEM (1-100 nm in diameter) can survive in severe environments and still preserve its nanocrystalline properties. GEM has many potential applications, and some of which require dispersive particles, e.g. as a dispersive catalyst on a substrate when making carbon nanotubes; yet before this type of applications could ever become reality one major problem must be solved. The problem is the severe agglomeration of the GEM nanoparticles, which is due to both the van der Waal’s forces among the particles and the strong magnetic forces of their ferromagnetic cores. Because the sizes of agglomerated particles are much larger than nanometer scale, the characteristic properties of nanoparticles, such as high surface to volume ratio and better absorption, will be lost. To effectively disperse the GEM nanoparticles, many organic solvents such as methanol, oleic acid and acetone had been used but with little success. The best results came when a non-ionic surfactant – nonylphenol ethoxylate (NP-9) – was used, combined with an improved synthesis technique to control the average particle sizes by adjusting total pressure, that GEM nanoparticles uniformly suspended in NP9 solution and formed a colloid. Colloids are distinguished from true solutions by the presence of particles that are too small to be observed under a microscope yet are much larger than common molecules. The viscosity of GEM colloids of various weight percentage of NP-9, with fixed temperature and pH, were analyzed by a rheometer. The viscosity apparently decreases with the particle size of GEM. In addition, the solution becomes saturated jelly-like substance as the weight percentage of NP-9 is equal to 40%-50%. Preliminary results show that the key of success is to reduce the average particle sizes of GEM, e.g. from 25 nm to 14 nm such as in this work, thus minimize the magnetic interaction between GEM and increase the effective reaction surface area with surfactant NP-9. Other factors such as temperature and pH value will be included in future experiments.

碩士
靜宜大學
應用化學研究所
98
Because of the worldwide concern about energy source and environment, the development of energy storage products and technologies has been paid highly attention to. Lithium ion battery is one of the most potential energy storage products now. Mesophase graphite powder(MGP) is spherical material with lamellar microstructure and with good performance as an anode material of lithium ion battery. However, the thermal expansion of the electrode will easily spoil the connection between each Mesophase graphite sphere. By adding fibrous conductive additive, Vapor Growth Carbon Fiber (VGCF), the linkage of condcutive channel of graphite spheres will be effectively improved. Nevertheless, the dispersing method of VGCF is the key process of this technology. In this research, the nonionic surfactant, Hypermer KD-1(KD-1) and Polyvinylpyrrolidone K30 (PVP K30) were chosen to improve the dispersity of Mesophase graphite powder and VGCF. The rheometer was applied to analyze rheological properties of anode slurries with different recipes. And the micro-image of electrodes by SEM and uniformity of resistance on electrodes by resistance analyzer were used to understand the relationship between concentration and types of surfactant and dispersity of VGCF. The electrode expansion ratio was tested to prove the influence of VGCF on electrode structure. Then the discharge capacity and the first cycle irreversible loss of the coin-type cells made of the electrodes respectively were tested. The discharge rate test and cycle life test of LiCoO2+ LiNi0.33Co0.33Mn0.33O2/MGP+VGCF cell were tested to check the effectiveness of surfactants and dispersity of VGCF on the performance of cell.

碩士
國立中興大學
化學系所
106
In this study, using magnetic particles as a substrate, modifying graphene oxide can increase the surface area of molecularly imprinted polymers, enhance adsorption capacity, also reduce the adsorbent materials used. After modification of the magnetic particles with graphene oxide, secondary modification of Tetramethylsilane (TMOS) and 3-(trimethoxysilyl) propyl mthacrylate (MPS) with this composite material (MGO) can effectively bond the MIP on the MGO surface. In addition, a certain thickness of cross-linking agent can be used between MIP and MGO to reduce the adsorption capacity of graphene and improve the selectivity to analytes. Hexestrol is used as a template molecule, methacrylic acid (MAA) as functional monomer, Ethylene glycol dimethacrylate (EDGMA) as cross linker, and Azobisisobutyronitrile (AIBN) as initiator in the preparation of MIP. In order to achieve the best extraction efficiency, graphene oxide addition amount, extraction time, desorption time, desorption solvent, pH value, and salting-out effect. The experimental results show that under the condition of pH = 7 only for 5 minutes, the MGO-MIP particles were adsorbed by strong magnets and the matrix solution was removed. After washing with ultrapure water, desorption was performed with 1 ml of acetone. After the extraction solution was dried with nitrogen, it was re-dissolved with 100 μL of acetonitrile and injected into the HPLC-UV analysis. Adsorption of different concentrations of sample under optimized conditions, the linear range of the concentration is 1.5-150 ng∙mL^(-1) with the correlation coefficient of 0.9994. Limit of detection was 0.1 ng∙mL^(-1), limits of quantitative 0.5 ng∙mL^(-1), precision RSD was 1.1 %. The MGO-MIP/SPE was applied in real sample analysis such as river and lake. The relative recoveries were ranged between 93.5 %-101.8 % hexestrol in real samples. Result showed that the MGO-MIP/SPE sorbent for the determination of hexestrol in aqueous samples with HPLC-UV method demonstrated the advantages of simple, rapid, and good recovery sampling pretreatment methods.

Tese de mestrado, Química (Química) Universidade de Lisboa, Faculdade de Ciências, 2019
The use of low-temperature fuel cells as power supplies of energy conversion devices is attracting considerable interest because of the direct electrochemical conversion of a fuel, e.g. hydrogen and glucose, and an oxidant, such as oxygen, producing electrical current. The sluggish kinetic of the oxygen reduction reaction (ORR) on the cathode half-reaction is particularly investigated since its acceleration relies on the development of efficient electrocatalysts. Unfortunately, the most promising catalysts for ORR are platinum-based materials that exhibit poor durability, limited resource and high cost. Under such circumstances, the development of non-noble, efficient and low-cost electrocatalysts has attracted a great deal of attention. The present dissertation focuses on the synthesis and physicochemical characterization of graphene-based materials doped with nitrogen and 2 and 10 wt % transition metals (Fe, Co, Mn, Cu, Ni and Rh), denoted as rGO/M 2 and 10 %, capable of reducing molecular oxygen. Firstly, nitrogen-doped reduced graphene oxide with atomically dispersed transition metal materials were synthesized using commercial graphene as precursor. A sequential extra-exfoliation and oxidation of the graphene increased the d-spacing between carbon layers and created porosity on the structure, which is essential for the diffusion of reactants on the material. Further simultaneous N doping and reduction of graphene oxide using thermal and low-temperature plasma treatment allowed the formation of M-Nx active sites that contribute greatly on the ORR activity. The obtained carbon structure exhibited a large specific surface area (c.a. 800 m2 g-1) doped with c.a. 1.98 wt % of nitrogen. The incorporation of atomically dispersed metal reached 21 % of 2 wt %, 3 % and 0.46 % of 10 wt % using different reduction methods. The engagement of aromatic macrocycle molecules, particularly iron and cobalt metalloporphyrins, in the graphene oxide structure was also studied. The synthesis of these hybrid materials was based on a procedure described previously, relying on the addition of the metalloporphyrin to the graphene structure, followed by its pyrolysis under N2 atmosphere. The ORR electrochemical characterization of the materials was performed using hydrodynamic convective systems: the rotating disk electrode (RDE) and the rotating ring-disk electrode (RRDE), in acidic, alkaline and neutral media. Among all the synthesized materials, iron- and cobalt-based materials showed the highest performance towards ORR. In particular rGO/Fe 2 % exhibited a remarkable activity in acidic (Eonset 0.76 V vs. RHE), alkaline (Eonset 0.91 V vs. RHE) and neutral (Eonset 0.78 V vs. RHE) media, comparable to Pt/C catalysts. A mixed 2- and 4-electron pathway was observed for rGO/Fe 2 % in acidic and alkaline media due to the contributions of several functional groups in the structure. The remaining materials displayed lower onset potential in acidic (0.44 to 0.71 V vs. RHE), alkaline (0.80 to 0.87 V vs. RHE) and neutral (0.64 to 0.74 V vs. RHE) media. The outstanding ORR performance of these materials is attributed to the presence of M-Nx actives sites dispersed in the carbon structure and intrinsic ORR activity of metalloporphyrins.

Dissertação de mestrado integrado em Engenharia de Materiais
No presente trabalho foram estudados os mecanismos de dispersão e reaglomeração de nanocompósitos de polipropileno (PP) /grafite exfoliada na composição e no processamento por extrusão. A composição foi realizada numa mini-extrusora de duplo-fuso com três zonas de mistura intensiva constituídas por elementos de mistura (kneading blocks) separadas por zonas de transporte. Procedeu-se à composição de nanocompósitos de PP com 2% ou 10% (p/p) de grafite GnP C ou grafite GnP H, e o seu posterior processamento numa mini-extrusora de mono-fuso, utilizando duas velocidades de rotação do parafuso. A evolução da dispersão ao longo das duas extrusoras foi analisada por microscopia ótica de campo claro. Também foram estudados o efeito da funcionalização via cicloadição dipolar 1,3 das grafites ligadas covalentemente ao PP enxertado com anidrido maleico (PP-g-AM), bem como as propriedades elétricas dos nanocompósitos. Na etapa de composição, observou-se o decréscimo significativo no tamanho e na quantidade dos aglomerados de grafite na passagem pela primeira zona de mistura intensiva, demonstrando a sua ação eficaz. A dispersão ao longo da mini-extrusora revelou-se constante após a primeira zona. No entanto, a funcionalização da grafite GnP C revelou um aumento da dispersão contínuo até à cabeça de extrusão. Os níveis de dispersão da grafite GnP H funcionalizada foram muito similares às da não-funcionalizada. No processamento, observou-se uma tendência geral de aumento da quantidade de aglomerados visíveis, indicando reaglomeração, independentemente da velocidade de processamento. Esta reaglomeração foi menos expressiva para os nanocompósitos com grafite funcionalizada. A dispersão foi aumentando ao longo da mini-extrusora, sendo o aumento maior para a velocidade mais elevada. A morfologia final dos nanocompósitos processados apresenta um nível de dispersão menor do que a resultante da composição. Simultaneamente, verificou-se um aumento da condutividade elétrica após o processamento. Nos nanocompósitos de PP com grafite GnP C, a funcionalização resultou numa menor condutividade, uma vez que induziu níveis de dispersão maiores.
The present work reports the study on the mechanisms of dispersion of exfoliated graphite/ polypropylene nanocomposites upon melt compounding and extrusion. Compounding was performed in a mini twinscrew extruder containing three intensive mixing zones consisting of kneading blocks. PP with 2wt. % or 10wt. % of GnP C or GnP H were compounded and subsequently processed by a mini single-screw extruder using two different screw speeds. The evolution of dispersion throughout compounding and processing was analysed by optical microscopy. The effect of graphite functionalization via 1,3 dipolar cycloaddition grafted with PP-g-MA (PP grafted with maleic anhydride) was also studied, as well as the electrical properties of the nanocomposites. The first set of kneading blocks were effective in decreasing the number and size of the graphite agglomerates. The dispersion along the mini-extruder proved to be constant after the first zone. However, functionalization of graphite GnP C revealed an increase in dispersion. The dispersing levels of as received and functionalized graphite GnP H were very similar, indicating that this kind of functionalization had no significant impact on dispersion. Along extrusion, the amount of agglomerates increased, indicating re-agglomeration of graphite agglomerates, regardless of processing speed. This re-agglomeration was less pronounced for nanocomposites with functionalized graphite. The final morphology of processed nanocomposites is coarser in comparison with composition. Concerning the electrical properties, there was an increase in conductivity of several orders of magnitude after processing. In the case of nanocomposites with GnP C graphite, functionalization induced lower conductivity, since it resulted in higher levels of dispersion.

碩士
國立臺南大學
綠色能源科技研究所碩士班
99
Lithium ion battery has been requested for further property improvement to meet the need of 3C products, portable equipments and electric vehicles (EVs). Recently, the concept of green-tech has been an important topic for many scientists in all different kinds of fields. In this study, we choose LiFePO4 and natural graphite as the electrode materials, which are cost efficient and environmental friendly. We add conductive addictive into LiFePO4 under different conditions and modified natural graphite with different Tin compounds. By combining two modified methods, we expect to obtain a better electrochemical property. In addition, the improved positive electrode and the modified negative electrode were investigated by half-cell tests to obtain the efficiency of electronic capacity and some electrochemical properties. The results suggest that when using HSC-03 dispersion to LiFePO4 as a conductive additive in positive electrode, the high-rate test and the performance of cycle life are greatly improved (capacity is raised by 40% after 100 cycles at rate of 1C). On the other hand, we modified Tin sulfide or Tin oxide compounds on the surface of natural graphite and surveyed the structural changes of SEI film by CV and ESCA analysis. The Tin compounds are likely to reduce the thermal stability but enhance the capacity and the stability of cycle life. In conclusion, we have proved that the combination of the improved electrodes in this study for full cell test can enhance the capacity and cycling performance for lithium ion battery.

碩士
國立中興大學
化學系所
101
In this work, a new rapid dispersive micro-solid phase extraction (DMSPE) technique coupled electrostatic-assisted collection of sulfonated graphene nanosheets (sGNS) followed by gas chromatography-mass spectrometry (GC-MS) for the determination of polycyclic aromatic hydrocarbons (PAH) in aqueous samples was developed. In this method, water soluble sulfonated graphene nanosheets was synthesized and utilized as nano-sorbent for the extraction of PAH and a newly designed home-made glass extraction device was adopted to collect the negatively charged sGNS based on the electrostatic migration by applying positive high voltage. Parameters affecting the proposed extraction method was thoroughly examined and optimized. The maximum extraction efficiency was obtained under the selected condition as follows; 8 mL of aqueous sample (pH 6) with 1 mg of sGNS were taken in the extraction device and 30 kV was applied to collect sGNS and followed by desorption using 10μL of toluene under ultrasonication for 15 min. Under the optimal conditions, the liner ranges were 1-1000 μg/L for naphthalene, acenaphthylene and acenaphthene, 2-2000 μg/L for fluorine, phenanthrene, anthracene, fluoranthene, pyrene and 3-3000 μg/L for benzo(a)anthracene and chrysene. Detection limits were achieved at level of 0.3-0.9 μg/L and the limit of quantitation were 1.0-3.2 μg/L. The relative recoveries of river samples were between 82.3-117.7 % and RSD were below 8.1%. The results demonstrated that the proposed method was a simple, rapid, sensitive, low cost and eco-friendly approach for the determination of PAH in aqueous samples.