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<div>For over 20 years, biaxially oriented polypropylene (BOPP) has been used in capacitors as the dielectric material. BOPP has very high breakdown strength, low electric loss, and is relatively inexpensive however, it suffers from low dielectric constant and low usage temperature. The ever growing technology market requires more robust capacitors which can be used in high temperature and pulsed power applications, and the aim of this research is to meet or exceed dielectric properties of BOPP by combining specific polymer materials in layered structures, biaxially orienting the films, and heat setting the films to further improve thermal stability. Post-processing is done on custom built machines which track real-time true stress, true strain and birefringence values, allowing for a more complete picture of mechano-optical properties generated during the stretching process. These data, along with offline characterization techniques such as X-ray scattering and DSC, were coupled with dielectric property testing to help form relationships between polymer processing, morphology, and dielectric properties.</div><div><br></div><div>In Chapter 3, microlayer PET and PVDF (50:50 ratio) films with 32 total layers and thickness around 125 micron were provided by PolymerPlus. Films were first stretched uniaxially at varying temperatures in order to optimize processing conditions. Characterization confirmed PVDF crystal form transformation from alpha to beta form when films were stretched at 95^oC, and presence of - PVDF when stretched in molten state at 185^oC, sandwiched between solid PET layers. Dielectric properties were tested for films stretched at 150^oC, which exhibited low dielectric constant when PVDF spherulites or smaller, broken up fibrils were present, but improved dielectric constant when PVDF morphology consisted of long, highly ordered fibrils. Uniaxial drawing helped lower dielectric loss, and it further signicantly decreased at very high strains. In this case, morphology of uniaxially drawn PET did not have a strong correlation with dielectric constant, but higher PET crystallinity and orientation likely helps to lower dielectric losses.</div><div><br></div><div>Polymer microlayer fims consisting of 32 layers, 50:50 ratio PET to PVDF films were also studied extensively using thermal heat setting technique. Samples with good thickness uniformity after stretching were selected for these experiments, and offline characterization techniques were applied to study morphology. Films were annealed at temperatures around PVDF melting peak, which caused transformation of PVDF polymorphs from primarily alpha to combined gamma and/or gamma' forms. When oriented at 150^oC to 1.5X1, and ' -PVDF were detected in small amounts (via DSC) after annealing at 172^oC, and only ' after higher temperature annealing. Stretching at 150^oC to higher strains produced high amounts of '-PVDF only when annealed at 155^oC for films stretched to 3.5X1, and annealed at 150^oC for films stretched to 2.5X1. Offline characterization led to development of a structural model for PVDF layers alone, by de-laminating film layers. Then, morphology was correlated with dielectric properties by testing lms at room temperature, and at constant frequency, in temperature ramping experiments. Temperature ramping dielectric experiments showed that high percent crystallinity of PET may also help improve loss behavior at high temperatures. Furthermore, samples containing gamma and/or gamma'-PVDF had increasing dielectric constant with increasing temperature, however dielectric loss also greatly increased with increasing temperature. A significant conclusion was that the annealed sample without gamma or gamma'-PVDF present had only a slightly lower dielectric constant at high temperature testing, but also had much lower loss, making it a potential candidate for high temperature capacitor applications.</div><div><br></div><div>Other materials for potential dielectric film applications were studied as well. Two fluoropolymer films consisting of monolayers of ETFE and THV were uniaxially oriented and their morphology was characterized offline to elucidate structure-process-property relationships. Film samples produced were not large enough to be tested for dielectric properties, however morphology development during uniaxial orientation was evaluated. Both films showed nearly affine stretching behavior, and mechano-optical properties were studied during stretching at several temperatures. Combinations of X-ray scattering experiments and AFM led to proposed morphological structure models for each material at varying levels of deformation.</div><div><br></div><div>Finally, in collaboration with A. Schulman, Inc., PET and EVOH compounded blend and three layer PET-EVOH-PET films were oriented uniaxially and the morphology of the two was compared to each other. Potential applications include high barrier food packaging applications, due to the very high oxygen barrier but poor water vapor barrier of EVOH, which can be complimented by PET's high water vapor barrier. Uniaxial orientation of these two film systems showed that mechano-optical behavior was significantly different for blend versus layered films. Crystalline orientation factors were calculated from 1D WAXS data, which showed PET orientation was largely unaffected by increasing EVOH content in blend films, but blending decreased orientation of EVOH. PET's orientation in layered films was also largely unaffected by amount of EVOH in inner layer. EVOH's orientation factor was higher in all layered film compositions compared to neat EVOH film after stretching, suggesting that the coextrusion process is beneficial to increasing orientation of EVOH.</div><div><br></div>

Modern three-dimensional integrated circuit design is rapidly evolving to more complex architecture. With continuous downscaling of devices, there is a pressing need for metrology tool development for rapid but efficient process and material characterization. In this dissertation work, application of a novel multiple internal reflection infrared spectroscopy metrology is discussed in various semiconductor fabrication process development. Firstly, chemical bonding structure of thin fluorocarbon polymer film deposited on patterned nanostructures was elucidated. Different functional groups were identified by specific derivatization reactions and model bonding configuration was proposed for the first time. In a continued effort, wet removal of these fluorocarbon polymer was investigated in presence of UV light. Mechanistic hypothesis for UV-assisted enhanced polymer cleaning efficiency was put forward supported by detailed theoretical consideration and experimental evidence. In another endeavor, plasma-induced damage to porous low-dielectric constant interlayer dielectric material was studied. Both qualitative and quantitative analyses of dielectric degradation in terms of increased silanol content and carbon depletion provided directions towards less aggressive plasma etch and strip process development. Infrared spectroscopy metrology was also utilized in surface functionalization evaluation of very thin organic films deposited by wet and dry chemistries. Palladium binding by surface amine groups was examined in plasma-polymerized amorphous hydrocarbon films and in self-assembled aminosilane thin films. Comparison of amine concentration under different deposition conditions guided effective process optimization. A time- and cost-effective method such as current FTIR metrology that provides in-depth chemical information about thin films, surfaces, interfaces and bulk layers can be increasingly valuable as critical dimensions continue to scale down and subtle process variances begin to have a significant impact on device performance.

Fluorinated polymers are niche macromolecules that play an essential role in modern life. The special properties of fluorine, including among others, a large electronegativity (ca 3.98), low polarisability, small van der Waal’s radius (135 pm) and the strong C-F bond (ca 485 kJ · mol−1), impart unique properties to organofluorine compounds. Flu-oropolymers exhibit a combination of desirable traits, including high thermal stability, low coefficient of friction, chemical inertness, oleo- and hydrophobicity, and low surface tension. Among the fluoropolymers, polyvinylidene fluoride (PVDF), and copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), have found applications in the coatings industry as the binder in exterior coatings. The chemical inertness of poly(VDF-co-HFP) copolymer, however, prevents disper-sion of pigments into the coating and also inhibits adhesion of the coating onto substrates. An acrylic modifier polymer is typically added to the poly(VDF-co-HFP) copolymer to improve the dispersion of pigments and the adhesion of the coating. This acrylic copoly-mer is physically blended with the poly(VDF-co-HFP) copolymer on a macromolecular scale (i.e. it forms a thermodynamically miscible blend). The loading of acrylic copolymer in commercial PVDF coatings is often in the range of 20 to 30 % by weight of polymer solids. Typically, copolymers of methyl methacrylate, ethyl acrylate and methacrylic esters are employed. Alternative strategies to overcome the adhesion problem include, among others, chem-ical modification of the surface of the fluoropolymer film. This can be achieved by graft copolymerisation or core shell emulsion polymerisation. These methods are used to funcionalise the polymer chains, while maintaining the desirable properties of the parent polymer. Due to environmental regulations, industry focus has shifted towards develop-ing coatings with a low volatile organic compound (VOC) content. Aqueous, low VOC, air-drying coatings can be formulated directly from the acrylic modified fluoropolymer (AMF) latex and have superior properties to solvent based, high VOC, air-dry coatings. Their advantages include low viscosities, reduced flammability, reduced odour and easy application using conventional equipment. A large portion of the aqueous coatings are sold into the architectural market with over 70 % of architectural paints used in the United States being classified as aqueous. Arkema Inc. has developed a commercial aqueous fluoropolymer latex using the method of seeded emulsion polymerisation. VDF and HFP monomers are randomly copolymerised via emulsion polymerisation. This poly(VDF-co-HFP) copolymer may be used as the seed material in a core-shell polymerisation using acrylic monomers. Kato et al. [49] discloses the preparation of an AMF formulation for poly(VDF-co-HFP) copoly-mer. Preliminary testing of membrane textiles coated with such formulations showed that the AMF coatings degrade under UV irradiation more rapidly than is is expected for poly(VDF-co-HFP) copolymer. The patent indicates that the nature of the product formed by the emulsion polymerisation is not well understood and the product my be either a graft copolymer of a core-shell system. The aim of this research reported in this dissertation was to shed light on the nature of the final product, and to verify the claims made in the above-mentioned patent. Various acrylic monomers were copolymerised via seeded emulsion polymerisation us-ing commercial poly(VDF-co-HFP) copolymer as the seed material. The concentration and the ratios of the monomers were varied according to the formulation guidelines in Kato et al.[49]. ATR-FTIR spectroscopy and19F NMR spectroscopy was used to de-termine the microstructure of the resultant latexes. ATR-FTIR spectra confirmed the presence of C=C and C=O bonds in latexes. This indicates that unreacted acrylic com-ponents are present. The ATR-FTIR spectra of the films indicated the disappearance of the C=C bonds from the latex, which indicates that the monomers are evaporated easily from the latexes during film formation. The 19F NMR spectra confirmed that no modi-fication of the poly(VDF-co-HFP) copolymer backbone took place during the reactions. The particle size distribution graphs showed an increase particle sizes and this suggested that some self polymerisation of the monomer occurred. The viscosity of the latexes were lower compared to the due to the experiments being conducted under dilution. The flow characteristics of the poly(VDF-co-HFP) copolymer was also influenced with some reactions yielding shear thickening latexes as compared to the shear thinning poly(VDF-co-HFP) copolymerc. The reactions also yielded latexes which displayed lower and higher surface tensions than the poly(VDF-co-HFP) copolymer. Therefore, the conclusion may be drawn from this work that core-shell formation occurred during the emulsion copolymerisation, as opposed to grafting of the monomer onto the poly(VDF-co-HFP) copolymer backbone. The claims made in the literature could not be substantiated; in particluar, the reported improvements in film forming ability were not realised. No commercially useful advantage exists for the emulsion copolymerisation of poly(VDF-co-HFP) copolymer with acrylic monomers over the solution blending of poly(VDF-co-HFP) copolymer with acrylic copolymers. / Dissertation (MEng)--University of Pretoria, 2019. / Chemical Engineering / MEng / Unrestricted

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<p>Throughout the last century, energetic materials have been subject to drop weight impact tests to measure their sensitivity, with which material’s properties are correlated to their impact sensitivity. However, there is little research that focuses on utilizing the piezoelectric effect to control the sensitivity of energetics. Piezoelectricity is the effect of an electric charge accumulating due to an applied mechanical stress. It is demonstrated in previous work that fluoropolymers such as polyvinylidene fluoride (PVDF) contribute to higher sensitivity in nanocomposite energetic materials through their piezoelectric properties. This property can be amplified in fluoropolymers in the beta (β) phase through polling methods and can be quantitatively analyzed by the piezoelectric coefficient (d₃₃). This research is focused on characterizing the effect of piezoelectricity on the impact sensitivity and ignition delay of nAl/PVDF-TrFE composites through the presence of varied d₃₃ coefficients. The composite films were fabricated with the tape casting method with 85 μm thickness. The content of nAl was limited to 10 wt% in order to sustain feasible poling. Poling was achieved without any further manipulation of the composition so that a direct comparison could be observed. The magnitude of effect that the piezoelectric coefficient has on an energetic composite was discovered. The samples that had no d₃₃ value were 8% less sensitive and experienced longer ignition delay times compared to the poled samples. This work proved that impact sensitivity and ignition delay can be manipulated through poling methods. This concept of controlling the sensitivity of energetic materials can be used to develop more customizable composites in the future.</p>

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This study is an investigation of the chemical vapor deposition (CVD) of aluminum and copper on fluoropolymer surfaces and the subsequent interfacial interactions.