In this thesis study, the use of clay-polymer nanocomposites for their applicability in landfill sites as a product of retardation of waste water infiltration was evaluated. For this purpose, organophilic clays from HDTMA+ organic cation and nanocomposites of montmorillonite were prepared. The bentonite samples B1, B2 and B3 dominantly contain 2:1 layer montmorillonite and 1:1 interstratification of illite/smectite mixed layer as clay minerals. B1 is an unmodified yellow bentonite and B2 is a grey bentonite modified from B1, by the addition of Na2CO3 (Soda Ash). They were obtained from Han&ccedil / ili (Kalecik-Ankara) bentonite deposit which belongs to the Hancili Formation of Early Pliocene age. B3 is a standard Wyoming (SWy-1) white bentonite and belongs to the Newcastle formation of Cretaceous age. Their cation exchange and swelling capacity values were determined and the values increase from B1, B2 to B3. In order to produce clay-polymer nanocomposites, firstly organoclays were produced in bentonite samples. Claypolymer nanocomposite production was achieved by in situ intercalative polymerization successfully with intercalation and partly exfoliation of clay minerals with polyacrylamide (PAM). The samples of sand (S1), sand+bentonite (S2) and sand+nanocomposite (S3) mixtures were prepared and their permeability was determined. As a result of these values, the permeability of samples decrease from S1, S2 to S3. The results imply that the permeability of sample decreases as the claypolymer nanocomposite content increases resulting in a retardation of water penetration throughout the sample. The product has a potential to be used as a retardant for waste water infiltration in landfill sites.

This study aims synthesis of metal/polymer one dimensional nanostructures by micelle formation, reduction, and electrospinning route, and to analyze the morphological characteristics of composite nanofibers. The study was carried out in three main steps. First, the reverse micelle structures were established between the anionic surfactant and the metal ion. The surfactant acts as an agent to bind metal ions together so that the arrangements of metal ions can be controlled in the solution. As the surfactant concentration increases, reverse micelles grow and reverse wormlike micelle structures are observed. Wormlike micelles are elongated semi flexible aggregates which form a spherocylinder form repeating units. Metal ions are in the core and surrounded with the surfactant. The polymer attached to the wormlike structure acts as a shield and prevents phase separation in a hydrophilic medium. Different polymer and surfactant concentrations were tried to determine the optimum polymer and surfactant concentrations for reverse micelle formation. The size analyses of the reverse micelle structures were done by dynamic light scattering technique. In the second step, metal ions in the micelles were reduced by using hydrazine hydrate to obtain metal cores in the center of wormlike micelles. Finally, electrospinning was carried at room temperature and in air atmosphere. The characterization of nano composites was done by Scanning Electron Microscopy. It was found that the size of the reverse micelle structures affects the distribution of metal nano partices in polymer nano fibers. In order to distribute the metal nano particles homogeneously, the optimum size of reverse wormlike micelles was found to be between 420 and 450 nm.

Metal coordinated polymer nanocomposites have gained great attention due to their superior characteristics. Polymethylmethacyrlate (PMMA) is the most commonly used polymer since it is easily processed. In this study, modified TiO2 nanoparticles prepared by insitu and exsitu methods were embedded into PMMA in order to improve its thermal stability and the effects of TiO2 nanoparticles on thermal characteristics of PMMA were investigated by direct pyrolysis mass spectrometry. The insitu method which is a sol gel method, TiO2/SiO2 nanoparticles were synthesized by mixing titanium(IV) tetraisopropoxide, TTIP, with silane coupling agent, 3-(3-methoxysilyl)methylmetacrylate, MSMA in absolute ethanol. In exsitu method, TiO2 powder was directly mixed with silane coupling reagent. TiO2/SiO2 nanoparticles were embedded into the PMMA by direct mixing resulting in exsitu and insitu TiO2/SiO2/PMMA nanocomposites. The synthesized TiO2/SiO2/PMMA nanocomposites were characterized by TEM, ATR-FT-IR and analyzed for the investigation of their reaction mechanism and thermal characteristics by pyrolysis mass spectroscopy. iv TEM images confirmed the formation of TiO2/SiO2 nanoparticles and TiO2/SiO2/PMMA nanocomposites and indicated that the average particle size of TiO2/SiO2 nanoparticles was around 6 nm whereas average particle size of SiO2/TiO2/PMMA nanocomposites were around 25 nm. The increase in the size of nanoparticles is associated with incorporation of TiO2/SiO2 nanoparticles into PMMA matrix. ATR-FTIR spectrum of 5% TiO2/SiO2/PMMA nanocomposites showed the formation of TiO2/SiO2 nanopartciles clearly. Pyrolysis mass spectrometry analysis revealed that incorporation of TiO2/SiO2 nano- particles into PMMA resulted in higher thermal stability only for low weight percentage insitu TiO2/SiO2/PMMA. At high weight percentages a decrease in thermal stability was detected. On the other hand, in case of exsitu TiO2/SiO2/PMMA, contrary to our expectations a decrease in thermal stability was detected. The decrease in thermal stability was attributed to evolution of methacrylic acid during thermal degradation of silane groups.

Polymer nanocomposite foams have attracted tremendous interests due to their multifunctional properties in addition to the inherited lightweight benefit of being foamed materials. Polymer nanocomposite foams using high performance polymer and bio-degradable polymer with carbon nanotubes were fabricated, and the effects of foam density and pore size on properties were characterized. Electrical conductivity modeling of polymer nanocomposite foams was conducted to investigate the effects of density and pore size. High performance polymer Polyetherimide (PEI) and multi-walled carbon nanotube (MWCNT) nanocomposites and their foams were fabricated using solvent-casting and solid-state foaming under different foaming conditions. Addition of MWCNTs has little effect on the storage modulus of the nanocomposites. High glass transition temperature of PEI matrix was maintained in the PEI/MWCNT nanocomposites and foams. Volume electrical conductivities of the nanocomposite foams beyond the percolation threshold were within the range of electro-dissipative materials according to the ANSI/ESD standard, which indicates that these lightweight materials could be suitable for electro-static dissipation applications with high temperature requirements. Biodegradable Polylactic acid (PLA) and MWCNT nanocomposites and their foams were fabricated using melt-blending and solid-state foaming under different foaming conditions. Addition of MWCNTs increased the storage modulus of PLA/MWCNT composites. By foaming, the glass transition temperature increased. Volume electrical conductivities of foams with MWCNT contents beyond the percolation threshold were again within the range of electro-dissipative materials according to the ANSI/ESD standard. The foams with a saturation pressure of 2 MPa and foaming temperature of 100 °C showed a weight reduction of 90% without the sacrifice of electrical conductivity. This result is promising in terms of multi-functionality and material saving. At a given CNT loading expressed as volume percent, the electrical conductivity increased significantly as porosity increased. A Monte-Carlo simulation model was developed to understand and predict the electrical conductivity of polymer/MWCNT nanocomposite foams. Two different foam morphologies were considered, designated as Case 1: volume expansion without nanotube rearrangement, and Case 2: nanotube aggregation in cell walls. Simulation results from unfoamed nanocomposites and the Case 1 model were validated with experimental data. The results were in good agreement with those from PEI/MWCNT nanocomposites and their foams, which had a similar microstructure as modeled in Case 1. Porosity effects on electrical conductivity were investigated for both Case 1 and Case 2 models. There was no porosity effect on electrical conductivity at a given volume percent CNT loading for Case 1. However, for Case 2 the electrical conductivity increased as porosity increased. Pore size effect was investigated using the Case 2 model. As pore size increased, the electrical conductivity also increased. Electrical conductivity prediction of foamed polymer nanocomposites using FEM was performed. The results obtained from FEM were compared with those from the Monte-Carlo simulation method. Feasibility of using FEM to predict the electrical conductivity of foamed polymer nanocomposites was discussed. FEM was able to predict the electrical conductivity of polymer nanocomposite foams represented by the Case 2 model with various porosities. However, it could not capture the pore size effect in the electrical conductivity prediction. The FEM simulation can be utilized to predict the electrical conductivity of Case 2 foams when the percolation threshold is determined by Monte-Carlo simulation to save the computational time. This has only been verified when the pore size is small in the range of a few micrometers. / text

Research in local fracture processes and micro-machining of polymers and polymer-based composites has attracted increasing attention, in development of composite materials and miniaturisation of polymer components. In this thesis, sectioning (machining) of a glassy polymer and a carbon nanotube based composite at the nanoscale was performed by an instrumented ultramicrotome. The yield stresses and fracture toughness of these materials were determined by analysing the sectioning forces. Fractographic analysis by atomic force microscopy was conducted to characterise the topographies and elastic properties of the sectioned surfaces to explore the deformation and fracture behaviour of the polymer during nanosectioning. The study reveals that a transition from homogenous to shear localised deformation occurred as the uncut chip thickness (depth of cut) or sectioning speed increased to a critical value. Analytical and finite element methods were used to model the nanosectioning process. The shear localised deformation was caused by thermal softening due to plastic dissipation. Although not considering sectioning, the tensile properties of a polymer nanocomposite were additionally investigated, where the degree of nanofibrillation and polyethylene glycol (PEG) content had significant effects.

Title: Preparation of Nanocomposites of Metal Oxides in Plasma Polymer and Study of Their Properties Author: Oleksandr Polonskyi Department: Department of Macromolecular Physics, MFF UK Supervisor of the doctoral thesis: Prof. RNDr. Hynek Biederman, DrSc. Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University in Prague Abstract: This thesis is devoted to a study of nanocomposite films Al (Al oxide)/plasma polymer prepared by various techniques using magnetron sputtering, plasma polymerization and cluster beam deposition. The formation and deposition of metal/metal oxide nanoclusters using a gas aggregation cluster source (GAS) was also considered. The role of low concentration of oxygen in the aggregation gas on the process of Al and Ti cluster deposition was studied. Properties of the nanoclusters and nanocomposite films were characterized by various techniques. Morphology of the nanocomposites was examined by AFM, TEM or HRTEM and SEM. Elemental analysis and chemical composition of the films were studied by XPS and FTIR. Optical characterization of the prepared films was done by UV-Vis spectroscopy and spectroscopic ellipsometry. It has been shown that using GAS nanocomposite Al(AlxOy)/C:H may be prepared. Keywords: nanocomposite thin film, plasma polymer, metal...

Epoxy resins have been broadly used in the industry for adhesives, laminates, coatings, composites, encapsulation of electronic devices, printed circuit boards, etc. Despite their excellent adhesion to different materials, heat and chemical resistance and good mechanical properties, they also exhibit few drawbacks like brittleness, high thermal expansion coefficient (CTE), poor resistance to crack initiation and growth. Therefore, the thesis is focused on the preparation of epoxy-silica hybrid materials exhibiting improved thermomechanical properties compared to the neat epoxides, without impairing their beneficial features. The main synthetic route of epoxy-silica hybrids' preparation has been the sol-gel process of alkoxysilanes, allowing either in-situ formation of high purity and homogeneity silica particles or creation of various siloxane structures in a form of liquid (sol) silica-based precursors. The sol-gel method, on one hand, helps to omit too high viscosity of nanofiller suspension and energy-intensive nanofiller dispergation problems, but on the other hand, is often associated with necessity to use solvents and to remove formed volatiles. Therefore, in the first part of the thesis, a simple solvent-free sol-gel procedure, enabling to minimize the side-effect of solvent evaporation and...

Medium-voltage silicon carbide power devices, due to their higher operational temperature, higher blocking voltage, and faster switching speed, promise transformative possibilities for power electronics in grid-tied applications, thereby fostering a more sustainable, resilient, and reliable electric grid. The pursuit of increasing power density, however, escalates the blocking voltage and shrinks the module size, consequently posing unique insulation challenges for the medium voltage power module packaging. The state-of-the-art solutions, such as altering the geometry of the insulated-metal-substrates or thickening or stacking them, exhibit limited efficacy, inflate manufacturing costs, raise reliability concerns, and increase thermal resistance. This dissertation explores a material-based approach that utilizes a nonlinear resistive polymer nanocomposite field-grading coating to enhance insulation performance without compromising thermal performance for medium-voltage power modules. The studied polymer nanocomposite is a mutual effort of this research and NBE Technologies. Instead of using field-grading materials as encapsulation, a thin film coating (about 20 μm) can be achieved by painting the polymer nanocomposite solution to the critical regions to grade the electric field and extend the range of the applicability of the bulk encapsulation. A polymer nanocomposite's electrical properties were characterized and found theoretically and experimentally to be effective in improving the insulation performance or increasing the partial discharge inception voltage, of direct-bonded-copper substrates for medium-voltage power modules. By applying the polymer nanocomposite coating on the direct-bonded- copper triple-point edges, the partial discharge inception voltages of a wide range of direct-bonded-coppers increased by 50-100%. To assure its effectiveness for heated power modules during operation, this field-grading effect was then evaluated at elevated temperatures up to 200°C and found almost unchanged. The nanocomposite's long-term efficacy was further corroborated by voltage endurance tests. Building on these promising characterizations, functional power modules were designed, fabricated, and tested, employing the latest packaging techniques, including double-sided cooling and silver-sintering. Prototypes of 10-kV and 20-kV silicon carbide diode modules confirmed the practicality and efficacy of the polymer nanocomposite. The insulation enhancements observed at the module level mirrored those at the substrate level. Moreover, the polymer nanocomposite coating enabled modules to use insulated-metal-substrates with at least 100% thinner ceramic, resulting in a reduction of at least 30% in the junction-to-case thermal resistance of the module. Subsequently, to test the nanocomposite's performance during fast-switching transients (> 300 V/ns), 15-kV silicon carbide MOSFET modules were designed, fabricated, and evaluated. These more complex modules passed blocking tests, partial discharge tests, and double-pulse tests, further validating the feasibility of the nonlinear resistive polymer nanocomposite field-grading for medium-voltage power modules. In summary, this dissertation presents a comprehensive evaluation of a nonlinear resistive polymer nanocomposite field-grading coating for medium-voltage power modules. The insights and demonstrations provided in this work bring the widespread adoption of this packaging concept for medium-voltage power modules significantly closer to realization. / Doctor of Philosophy / This dissertation delves into a novel approach to improving the resilience and reliability of our electric grid by employing medium-voltage silicon carbide power devices. These power devices, due to their superior performance at higher temperatures and faster switching speeds, can revolutionize grid-tied power electronics. However, the challenge lies in safely packaging these devices, given their high blocking voltage and compact size. To address this, the study explores an innovative solution that uses a material called a nonlinear resistive polymer nanocomposite. This nanocomposite can improve insulation and endure high temperatures, promising a significant boost in performance for these power devices. The study reveals that applying this nanocomposite coating to the edges of direct- bonded-copper, a component of the power module, can enhance the insulation performance by 50-100%. Building on these findings, we designed, made, and tested functional power modules, using cutting-edge packaging techniques that we developed. The tests confirmed the practicality and effectiveness of the polymer nanocomposite, leading to insulation improvements on both the substrate and module levels. Importantly, this coating also reduced the thermal resistance of the module by at least 30%, signifying a more efficient operation. Then we evaluated the nanocomposite's performance during fast-switching transients in more complex silicon carbide modules. The modules passed multiple tests, further validating the feasibility of the nanocomposite coating for medium-voltage power modules. In essence, this dissertation uncovers a promising approach to more efficient and resilient power module packaging, paving the way for potential widespread adoption in the power electronics industry.

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The aim of this study is to demonstrate the possibility of production of nanocables as an alternative to the other one dimensional metal/polymer composite structures like nanowires and nanorods. There is no certain definition of nanocables / however they could be considered as assemblies of nanowires. Nanocable structure can be defined as a core-shell structure formed by a polymeric shell and a metal core that runs continuously within this shell. To produce nanocables, two main steps were carried out. Firstly, monodispersed silver metal nanoparticles to be aligned within the cable core were produced. Investigations on reduction reactions in the presence of strong and weak reducing agents and different capping agents revealed the importance of the kinetics of reduction in the production of monodispersed nanoparticles. Use of capping agents to give a positive reduction potential, resulted in the slow reduction rates that was critical for fine tuning of the final particle sizes between 1-10 nm. Hydrazine hydrate and oleylamine/ oleic acid systems were used as strong and weak reducing agents, respectively. By using weak reducing agent, monodisperse spherical silver nanoparticles with the diameter of 2.7 nm were produced. It was shown that particles with controlled diameter and size distribution can be obtained by tuning the system parameters. Secondly, particles produced as such were electrospun within the core of the polymer nanofibers and long continuous nanocables were produced. Polyvinyl pyrrolidone and polycaprolactone were used in shell part of nanocables. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), X-ray diffraction (XRD) and surface plasmon resonance spectroscopy (SPR) analyses were carried out in order to understand the mechanism by which the nanoparticles were reduced and for further characterization of the product.