The development of efficient, high-performance materials for electrical energy storage and conversion applications has become a must to meet an ever-increasing need for electrical energy. Among devices developed for this purpose, capacitors have been used for pulsed power applications that require large power density with millisecond-scale charge and discharge. However, conventional polymeric films, which possess high breakdown strength, are limited due to low permittivity and hence compromise the energy storage capability of capacitors. In order to develop high energy density dielectric materials for pulsed power applications, two hurdles must be overcome: 1) the appropriate selection of materials that possess not only large permittivity but also high breakdown strength, 2) the optimization of material processing to improve morphology of dielectric films to minimize loss during energy extraction process. This thesis will present the development of novel dielectric material, with emphasis on the optimization of material and thin film processing toward improved morphology as ways to achieve high energy density at the material level. After first two chapters of introduction and experimental details, Chapter 3 will demonstrate the improvement of nanocomposite morphology via processing optimization and study its effect on the energy storage characteristics of nanocomposites thereof. Chapter 4 will investigate dielectric sol-gel materials containing dipolar cyano side groups, which are relatively a new class of material for pulsed power applications. Finally, Chapter 5 will discuss the effect of tunneling barrier layer on sol-gel films to mitigate charge carrier injection and associated conduction and breakdown phenomena, which would be significantly detrimental to the energy storage performance of dielectric sol-gel films.

Ph.D. (Chemistry) / This study addressed the incorporation of nanotechnology-based materials, either through incorporating nanomaterials or by introducing nanostructures onto the membrane matrix, to form nano-enabled polymeric membranes with high specific flux and better anti-fouling profile. The aim of the study was to integrate nanotechnology and membrane science in order to improve the performance of water filtration membranes by alleviating some of the specific shortcomings of water treatment membranes......

Flexible fillers has recently been implemented as corrosion protection for post-tensioning tendons used in bridge structures in Florida. There are two different explanations why corrosion could take place: 1. water is able to reach the steel 2. Microbiologica l ly Influenced Corrosion. The aim of this research is to evaluate corrosion protection effectiveness of five differe nt microcrystalline waxes under different environmental conditions. Specimens tested ranged from 7-wire steel strands to single wires (12-16 cm). Another aim is the appraisal of wax degradation by fungi species. Single wires coated with each of the investigated protection materials, were sprayed with suspensions of three different fungi species and a mix of them. For single wires, independent of the environmental condition the specimen with more corrosion was Nontribos, as well as the filler coated wires contaminated with Fungi. Fungi species investigated were able to utilize the waxes as carbon source and caused differe nt extents of MIC. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

With the goal of improving chemical detection methods for buried improvised explosive devices (IED’s), the intention of this study is to show that functionalized nano-particles improve the sensing properties of a polymer applied to gas sensors. The approach was reinforcing the polymer, Nafion, with acid-functionalized carbon nanotubes (CNT’s). Ammonia was chosen as the analyte for its similarity to IED byproducts without the dangers of toxicity or explosion. Two sensor platforms were investigated: Quartz crystal microbalances (QCM’s) and microcantilevers (MC’s). Preliminary evaluation of treated QCM’s, via frequency analyzer, showed improvements in sensitivity and fast reversal of adsorption; and suggested increased stability. Tests with coated MC’s also supported the findings of QCM tests. Amplitude response of MC’s was on average 4 times greater when the Nafion coating contained CNT’s. Quantitative QCM testing with gas-flow meters showed that with CNT inclusion: the average number of moles adsorbed increased by 35% (>1.2 times frequency response); sensitivity improved by 0.63 Hz/ppt on average; although the detection threshold decreased marginally; but reusability was much better after extended exposures to concentrated ammonia. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

This thesis focuses on the study of nanotechnology and its applications in immunology and mechanosensing using micro- and nano-scale topographies, such as gratings, grids, and pillar substrates. In the past five years, we have developed three types of platforms and explored the influence of nano-patterned substrates on cell morphology, proliferation, protein secretion, and mechanosensing. I will introduce the three generations of Integrated Mechanobiology Platform (IMP) for T cell study, including the fabrication process of each generation of IMP, their advantages and disadvantages, and the comparison with existing High Throughput Screening System (HTSS). For the applications of IMP, I will focus on grating and grid topographies with IMP generation 3 format, and study how these nano-patterned substrates affect T cell morphology, expansion, cytokine secretion, drug-topography combination effects on T cells and long-term expansion for adoptive immunotherapy. I will demonstrate how IMP enables such studies in a high throughput manner. I also will discuss how Multiple Stiffness Pillar Platform (MSPP) facilitates the study of mechanosensing in cells spanning across different rigidities. First, I will talk about how MSPP is different from existing dual stiffness platforms. Differences include flexibility in distribution of different rigidities, consistency in pillar dimensions and ease of controlling the stiffness fold increase. In the sections of MSPP fabrication and characterization, I will focus on measurements of stiffness change and surface chemistry uniformity. I will then discuss the Mouse Embryonic Fibroblast (MEF) mechanosensing study on dual stiffness pillar substrates, including the preferential localization of rigidity sensing associated proteins (myosin IIA, phosph-myosin, paxillin, and p130CAS), MEFs actomyosin network building, and adhesion formation. These studies revealed previously undiscovered results in MEF mechanosensing, and demonstrate the great potential of MSPP in this research discipline. In the last part of this thesis, I will present on the mass production of thermoplastic nanopatterned molds. The demonstrated technology can produce large batches of nanostructured molds with decreased fabrication time and expense. In this chapter, I will discuss the necessity of developing such a technology and platform, as well as the design, fabrication, and characterization of the thermoplastic nano-patterned molds.

Polymer nanocomposites (PNCs), mixtures of nanometer-sized particles and polymeric matrices, have attracted continuing interest over the past few decades, primarily because they offer the promise of significant property improvements relative to the pure polymer. It is now commonly accepted in the community that the spatial organization of nanoparticles (NPs) in the polymer host plays a critical role in determining the macroscopic properties of the resulting PNCs. However, till date there is still dearth of cost-effective methods for controlling the dispersion of NPs in polymeric hosts. In this dissertation, we are dedicated to developing practically simple and thus commercially relevant strategies to controllably disperse NPs into synthetic polymer matrices (both amorphous and semicrystalline). We first investigate the influence of casting solvent on the NP spatial organization and the thermomechanical properties in a strongly attractive PNC consisting of bare silica NPs and poly(2-vinylpyridine) (P2VP) hosts cast from two different solvents - methylethylketone (MEK) or pyridine. In MEK, we show that P2VP strongly adsorbs onto the silica surface, creating a stable bound polymer layer and thus helping sterically stabilize the NPs against agglomeration. On the contrary, in pyridine, P2VP does not adsorb on the silica NPs, and the phase behavior in such case is a subtle balance among electrostatic repulsion, polymer-induced depletion attraction, and the kinetic slowdown of diffusion-limited NP aggregation. Using Brillouin light scattering, we further show that in pyridine-cast films, there is a single acoustic phonon, implying a homogeneous mixture of silica and P2VP on the mesoscopic scales. However, in MEK-cast samples, two longitudinal and two transverse acoustic phonons are probed at high particle content, reminiscent of two metastable microscopic phases. These solvent-induced differences in the elastic mechanical behavior disappear upon thermal annealing, suggesting that these nanocomposite interfacial structures in the as-cast state locally approach equilibrium upon annealing. Next, to disperse silica NPs into an energetically unfavorable polystyrene (PS) matrix in a controllable fashion, we have proposed a simple and robust strategy of adsorbing a monolayer of PS-b-P2VP block copolymer onto the silica surface, where the short P2VP block is densely coated around the silica particles and thus helps to reduce the inter-core attraction while the long PS block provides a miscible interface with the matrix chains. As a result, we have found that the silica particles can be uniformly dispersed in the PS matrices at a low grafting density of 0.01 chains/nm2. Even more interestingly, we have shown that the BCP coated NPs are remarkably better dispersed than the ones tethered with bimodal PS-P2VP brushes at comparable PS grafting characteristics. This finding can be reconciled by the fact that in the case of BCP adsorption, each NP is more uniformly coated by a P2VP monolayer driven by the strongly favorable silica-P2VP interactions. Since each P2VP block is connected to a PS chain we conjecture that these adsorbed systems are closer to the limit of spatially uniform sparse brush coverage than the chemically grafted case. Finally, we have examined the interplay between NP organization and polymer crystallization in a melt-miscible model semicrystalline nanocomposite comprised of poly(methyl methacrylate) or poly(methyl acrylate) grafted silica NPs in poly(ethyleneoxide) matrices. Here we have achieved active NP organization at a length scale of 10-100 nm by isothermal polymer crystallization. We have shown that the melt-miscible spherical NPs are engulfed by the polymer crystals and remain spatially well-dispersed for crystallization faster than a critical growth rate (G > Gc ~ 0.1 um/s). However, anisotropic sheet-like NP ordering results for slower G - the NPs are preferentially segregated into the interlamellar zone of the multiscale, hierarchical polymer crystal structure spanning lamellae (10-50 nm), fibrils (um) and spherulites (mm). This NP ordering is found to favorably impact the elastic modulus while leaving fracture toughness unaffected. We thus conclude that polymer crystal growth kinetics coupled to the unusual morphology of semicrystalline polymers represent a novel handle for in-situ fabricating hierarchical, anisotropic NP structures in a synthetic semicrystalline polymer, which could inspire significant applications.

In recent years, the United States Departments of Homeland Security (DHS) and Customs and Border Protection (CBP) have been charged with the task of scanning every cargo container crossing domestic borders for illicit radioactive material. This is accomplished by using gamma-ray detection systems capable of discriminating between non-threatening radioisotopes, such as Cs-137, which is often used in nuclear medicine, and fissile material, such as U-238, that can be used to make nuclear weapons or "dirty" bombs. Scintillation detector systems, specifically thallium-doped sodium iodide (NaI(Tl)) single crystals, are by far the most popular choice for this purpose because they are inexpensive relative to other types of detectors, but are still able to identify isotopes with reasonable accuracy. However, increased demand for these systems has served as a catalyst for the research and development of new scintillator materials with potential to surpass NaI(Tl). The focus of a majority of recent scintillator materials research has centered on sintered transparent ceramics, phosphor-doped organic matrices, and the development of novel single crystal compositions. Some of the most promising new materials are glass-ceramic nanocomposites. By precipitating a dense array of nano-scale scintillating crystals rather than growing a single monolith, novel compositions such as LaBr₃(Ce) may be fabricated to useful sizes, and their potential to supersede the energy resolution of NaI(Tl) can be fully explored. Also, because glass-ceramic synthesis begins by casting a homogeneous glass melt, a broad range of geometries beyond the ubiquitous cylinder can be fabricated and characterized. Finally, the glass matrix ensures environmental isolation of the hygroscopic scintillating crystals, and so glass-ceramic scintillators show potential to serve as viable detectors in alpha- and neutron-spectroscopy in addition to gamma-rays. However, for the improvements promised by glass-ceramics to become reality, several material properties must be considered. These include the degree of control over precipitated crystallite size, the solubility limit of the glass matrix with respect to the scintillating compounds, the variation in maximum achievable light yield with composition, and the peak wavelength of emitted photons. Studies will focus on three base glass systems, sodium-aluminosilicate (NAS), sodium-borosilicate (NBS), and alumino-borosilicate (ABS), into which a cerium-doped gadolinium bromide (GdBr₃(Ce)) scintillating phase will be incorporated. Scintillator volumes of 50 cubic centimeters or greater will be fabricated to facilitate comparison with NaI(Tl) crystals currently available.

Because the gel-spinning process has the potential to yield fibers of high strength and high modulus, this technique was employed to process continuous filaments of PVA/CNT, having CNTs at ¡Ü1 weight percent of polymer. A gel aging technique was employed with the goal of increasing the draw ratio for composite fibers and for promoting the development of crystalline PVA. Since residual solvent can lower the mechanical properties of drawn fibers, solvent phases of water and dimethyl sulfoxide (DMSO) within the drawn fibers were also characterized. As embedded SWNTs were uniaxially aligned along the drawn fiber axis, they were found to induce preferential alignment in the PVA side groups as well as for the residual solvent. This was attributed to charge transfer between SWNT and the respective functional groups. This orientation behavior has been characterized using Raman spectroscopy and infra-red dichroism. The behaviors of gel crystallization and solvent freezing within PVA/CNT dispersions were studied using thermal analysis and rheology. Carbon nanotubes were found to nucleate PVA crystallization in the gel state. PVA/CNT gel aging behavior was characterized by structural, thermal, and mechanical, and dynamic mechanical means. Gel aging was shown to increase the draw ratio of PVA/CNT fibers, and the development of the higher temperature melting peak was attributed to the draw induced ordering of PVA along CNTs. The scanning electron micrographs of fractured PVA/CNT fibers showed fibrils having an average diameter of about 22 nm. The storage modulus of aged gel was a function of solvent diffusion, which changed with aging time. CNTs were shown to have stabilized the gel network, as characterized by the dynamic mechanical properties, and to provide nucleation sites for the ordering of PVA chains, as characterized by WAXD.

The performances of current electrical energy storage systems (both batteries and electrochemical capacitors) are not capable of meeting the ever-increasing demands of emerging technologies. This is because batteries often suffer from slow power delivery, limited life-time, and long charging time whereas electrochemical capacitors suffer from low energy density. While extensive efforts have been made to the development of novel electrode materials, progress has been hindered by the lack of a profound understanding on the complex charge storage mechanism. Therefore, the main objective of this research is to develop novel electrode materials which can exhibit both high energy and power density with prolonged life-time and to gain a fundamental understanding of their charge storage mechanism. First, nanostructured, thin, and conformal coatings of transition metal oxides have been deposited onto three-dimensional porous substrates of current collectors to form composite electrodes. The structures and compositions of the oxide coatings are further altered by a controlled annealing process and characterized by electron microscopy and spectroscopy, laboratory X-ray diffraction, gas adsorption analysis, and in-situ and ex-situ synchrotron-enabled X-ray diffraction and absorption spectroscopy. The structural features have also been correlated with the electrochemical behavior of the transition metal oxides as an electrode in an electrochemical capacitor. It is found that the electrochemical performance of the composite electrodes depends sensitively on the composition, nanostructure, and morphology of the oxide coatings. When optimized, the electrodes displayed the highest energy and power density with excellent cycling life among all materials reported for electrochemical capacitors. Finally, new charge storage mechanisms have also been proposed for the novel electrode materials based on insights gained from in-situ synchrotron-based X-ray absorption spectroscopy.

The main goal of this research is to construct hierarchical microstructures from polymer nanocomposites. Specifically, the research focused on constructing tensegrity-inspired microstructure where the nanoparticles are the compression members and the polymer matrix is tensile web. In order to achieve the tensegrity-inpired microstruture, the research was conducted with the following objectives. 1. Synthesis of Hydroxyapatite (HAp) nanoparticles of controlled shapes using block copolymer templates. 2. Investigation of the effects of particle loadings and shapes on isotropic nanocomposite properties. 3. Construction of HAp building blocks into the tensegrity-inspired microstructures First, in order to use the nanoparticles for this structure, needle-shaped HAp nanoparticles were synthesized using block copolymer templates. The results indicated that significant amount of polymer remained on particle surface. Since these particles were coated with polymer blocks, the decorated polymer blocks were considered as the interphase material which would be used to prestress the HAp nanoparticles, and the particles would be acted as the building blocks for constructing tensegrity-inspired microstructure. For nanocomposites, polymer coating on HAp nanoparticles promoted particle dispersion. The effect of particle shapes on thermomechanical properties did not show significant differences between the two particle systems due to their low aspect ratios and chemical similarity. However, the polymer crystallinity and crystallization showed different trend as a function of particle loadings in two particle systems, and the behavior was unified through a common particle spacing of approximately 120 nm. In order to investigate the effect of particle arrangement in the polymer matrix, needle-shaped HAp nanoparticles synthesized with two different block copolymers were mixed with different morphology of polymer matrices and manipulated particle arrangement using the drawing process. Nanocomposites prepared with different matrix morphologies showed the similar dispersion characteristics and reinforcement behavior. The experimental results showed the drawing process influenced the particle arrangement in the polymer matrix, and the particle arrangement and reinforcement behavior were influenced by polymer matrix morphology. The thermomechanical properties of both matrix systems enhanced through the drawing process in the glassy region, but the effect of degree of particle orientation was difficult to distinguish due to low aspect ratios of HAp particles which was not enough to impact on overall microstructure.