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DOI

Analysis of the Mechanisms Determining the Thermal and Electrical Properties of Epoxy Nanocomposites for High Voltage Applications

25 Jan 2016-
TL;DR: In this paper, a number of epoxy nanocomposites and mesocomposite were synthesized aiming at the analysis of the parameters which influence their thermal and electrical properties.
Abstract: The addition of microsized fillers to polymers, in order to tailor their properties, has been extensively used in many industrial applications since the 1960s. The same approach applies to the field of electrical insulation. Epoxy resin is a widely used polymer in the electrical power sector, but it is usually loaded with microsized fillers, such as aluminum oxide and silicon dioxide, mainly to increase its thermal conductivity, improve its mechanical properties, and to decrease cost. Polymers with microsized fillers are called microcomposites. In the mid-1990s, a new type of polymeric composites for high voltage applications, the so-called nanocomposites, emerged. The main characteristic of these composites is the small filler size, which is smaller than 100 nm at least in one dimension. Since then, there has been a growing interest in the performance of polymeric nanocomposites for high voltage applications, including epoxy nanocomposites. The performance of nanocomposites is mainly related to the tremendous effective internal surface area of these materials because of the high surface-tovolume ratio of nanofillers. After 20 years of research, a significant amount of data has been generated which reflects the potential of nanodielectrics. It has been shown that nanofillers are capable of contributing to the improvement of both the thermal and electrical properties of polymers. However, the laboratory performance of nanocomposites is inconsistent and unpredictable. These are the main factors which inhibit the applicability of nanodielectrics. Important challenges in the field of epoxy nanocomposites should be overcome before nanodielectrics can be produced on an industrial level. The most important challenge is related to the dubious reproducibility of the nanocomposite performance which is closely related to sample homogeneity. Thus, the effectiveness of separating the nanoparticles from each other and the homogeneous incorporation of them into the polymer matrix are expected to affect the performance of nanocomposites. However, the extent to which the behavior of nanocomposites is influenced by sample homogeneity is not well defined. In this thesis, a number of epoxy nanocomposites and mesocomposites were synthesized aiming at the analysis of the parameters which influence their thermal and electrical properties. The analysis includes the thermal and electrical conductivity, dielectric response, and breakdown strength under both AC and DC electric fields. The experimental results demonstrate the important role of interfaces in the behavior of epoxy nanocomposites. Based on the experimental results, important parameters for determining the performance of nanocomposites are suggested to be the polymer re-organization and water uptake. The former is related to the influence of nanofillers on the polymer structure, i.e., the areas in the vicinity of nanofillers are assumed to exhibita different behavior from the rest of the polymer matrix. The uptake of water is related mainly to the hydrophilic nature of nanofillers and plays a significant role in the electrical performance of nanocomposites. Apart from the aforementioned mechanisms, the presence of structural imperfections should not be neglected as they affect both the thermal and electrical properties of epoxy nanocomposites. Additionally to the experimental part, models were developed for both the relative permittivity and thermal conductivity of nanocomposites. The models are based on the two aforementioned parameters; polymer re-organization in the vicinity of nanofillers and water uptake due to the hydrophilicity of nanofillers. The main characteristic of both models is the use of the same structure which strengthens the validity of the assumptions. The experimental results are in good agreement with the model results. Also, a large part of the thesis is devoted to the evaluation of the influence of sample homogeneity on the performance of nanocomposites. For this purpose, nanocomposites with different synthesis techniques were fabricated. The results suggest that the thermal conductivity, dielectric response, and breakdown strength (AC and DC) of epoxy nanocomposites are not significantly influenced by the nanoparticle distribution. This observation suggests that high levels of reproducibility can be achieved when the particles are similarly dispersed and differently distributed. Finally, hybrid composites which combine both microsized and nanosized fillers were fabricated, tested, and analyzed. This type of composites is more likely to be employed in industry as epoxy resin in its pure form is rarely used for high voltage applications. It is usually reinforced with high loadings of microparticles. Microcomposites reinforced only with a small amount of nanofillers, i.e., less than 1 % by volume, show a significant thermal and electrical improvement.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the dispersion of the organically modified ZnO nanoparticles has been successfully tuned through the maleic anhydride graft and the block copolymer nanostructure.

20 citations

11 Jul 2017
TL;DR: In this paper, different approaches to prepare a new generation of nanostructured insulating materials featuring controlled nanoparticles dispersion, using block copolymers and polymer blends as template matrices were reported.
Abstract: This thesis reports different approaches to prepare a new generation of nanostructured insulating materials featuring controlled nanoparticles dispersion, using block copolymers and polymer blends as template matrices. Two types of nanoparticles, both organically modified, were used: zinc oxide (ZnO) and Montmorillonite clay. In addition, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) triblock copolymer, composed of two polystyrene (PS) endblocks in the form of well-ordered nanodomains and one poly(ethylene-co-butylene) (PEB) elastomer middle block, was selected as a template matrix. SEBS/clay and SEBS/ZnO nanocomposites featuring different configurations of PS domains and clay platelets, namely: isotropic, partially oriented and oriented morphologies were achieved by varying the processing techniques. Besides, the spatial distribution of clay platelets and ZnO nanospheres and their affinities to either PS block or PEB block were tuned by the presence or not of maleic anhydride (MA) graft attached to PEB block. In particular, the dispersion of both types of nanoparticles was considerably improved in the presence of MA. Dielectric, rheological, thermal and mechanical properties of these nanocomposites were characterized in correlation with their morphologies. In SEBS/clay nanocomposites, it was found that the incorporation of clay induced slower dynamics of PEB chains located in the interfacial region. A new interfacial glass transition (Tgi), higher than the glass transition (Tg) of bulk PEB, was attributed to these interfacial chains. Furthermore, the orientation and location of clay affected the interfacial dynamics: the highest Tgi temperatures were related to samples with lower alignment degree and preferential location of clay in PEB phase. Functional properties were also affected by the orientation. To be more specific, SEBS/clay nanocomposites with totally aligned clay platelets and PS domains were simultaneously the most efficient in improving the breakdown strength up to 45% and the less efficient in improving the mechanical strength. However, nanocomposites with partially oriented morphologies provided the best combination of dielectric breakdown strength and mechanical strength. In SEBS/ZnO nanocomposites, the improved dispersion and affinity to PEB block, achieved in the presence of MA, induced the formation of networks between ZnO nanoparticles and SEBS chains. This behavior was accompanied by an increase of thermal conductivity and excellent improvement of the resistance to surface erosion: eroded volume reduced by 90% at only 5wt% ZnO. In the last part of the project, selected SEBS/ZnO nanocomposites were mixed with polyethylene (PE) to prepare blend nanocomposites as new candidates for HV insulation. Although the overall dielectric performance of unfilled PE/SEBS blend was reduced compared to neat PE, PE/SEBS/ZnO blend nanocomposites featured higher resistance to surface erosion and mechanical flexibility compared to conventional PE/ZnO nanocomposites. This improvement was correlated with the improved dispersion of ZnO nanoparticles in PE/SEBS/ZnO compared to PE/ZnO nanocomposites and their selective localization in SEBS phase and potentially at the interfaces between PE and SEBS.

2 citations

References
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Book
01 Jan 1873
TL;DR: The most influential nineteenth-century scientist for twentieth-century physics, James Clerk Maxwell (1831-1879) demonstrated that electricity, magnetism and light are all manifestations of the same phenomenon: the electromagnetic field as discussed by the authors.
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Journal ArticleDOI
TL;DR: In this article, the Berechnung der dielektrizitatatkonstanten and der Leitfahigkeiten fur Elektriatitat and Warme der Mischkorper aus isotropen Bestandteilen behandelt.
Abstract: Es werden verschiedene physikalische Konstanten heterogener Korper aus den Konstanten ihrer homogenen Bestandteile nach einer einheitlichen Methode berechnet. In dieser ersten Arbeit wird die Berechnung der Dielektrizitatskonstanten und der Leitfahigkeiten fur Elektrizitat und Warme der Mischkorper aus isotropen Bestandteilen behandelt. Die Genauigkeit der alteren Formeln wird untersucht und die bis jetzt unbekannten Konstanten dieser Formeln werden berechnet. Sodann wird die Theorie gepruft an Messungen der Leitfahigkeit bei heterogenen Metallegierungen und an den DK. von gepresten Pulvern und Emulsionen; die verschiedenen Formeln werden bestatigt. Bei dieser Anwendung werden einige Widerspruche zwischen fruheren Untersuchungen aufgehoben und es wird versucht, einige ungenau bekannte DK. genauer zu bestimmen.

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Journal ArticleDOI
TL;DR: In this article, a review of polymer nanocomposites with single-wall or multi-wall carbon nanotubes is presented, and the current challenges to and opportunities for efficiently translating the extraordinary properties of carbon-nanotubes to polymer matrices are summarized.
Abstract: We review the present state of polymer nanocomposites research in which the fillers are single-wall or multiwall carbon nanotubes. By way of background we provide a brief synopsis about carbon nanotube materials and their suspensions. We summarize and critique various nanotube/polymer composite fabrication methods including solution mixing, melt mixing, and in situ polymerization with a particular emphasis on evaluating the dispersion state of the nanotubes. We discuss mechanical, electrical, rheological, thermal, and flammability properties separately and how these physical properties depend on the size, aspect ratio, loading, dispersion state, and alignment of nanotubes within polymer nanocomposites. Finally, we summarize the current challenges to and opportunities for efficiently translating the extraordinary properties of carbon nanotubes to polymer matrices in hopes of facilitating progress in this emerging area.

3,239 citations

Journal ArticleDOI
TL;DR: A review of the literature on thermal transport in nanoscale devices can be found in this article, where the authors highlight the recent developments in experiment, theory and computation that have occurred in the past ten years and summarizes the present status of the field.
Abstract: Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.

2,933 citations

Book
01 Jan 1995
TL;DR: In this paper, Free-Radical Chain-Growth Polymerization (FRCG) and Ionic chain-growth polymers (Ionic chain growth polymers) are discussed.
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2,239 citations