Supramolecular ionic assemblies not only provide alternatives to conventional polymers, but also introduce unique and interesting functions for the design of "smart" polymeric assemblies for use in a number of fields due to their programmable and reversible properties. Research in the area has led to an understanding of the connection between molecular contributions and macroscopic properties, as well as a range of applications from material processing/manufacuturing to energy transfer and storage. To this end, we have developed a library of charged building blocks based on ionic liquids to create functional supramolecular ionic assemblies. The polymeric ionic assemblies prepared from a di-phosphonium and poly (acrylic acid) were first studied and found to have the potential to be utilized as "smart" materials due to their ability to reversibly respond to stimuli such as temperature and pressure. With the interest of elucidating the molecular contributions to the bulk macroscopic material properties, six supramolecular assemblies were sequentially characterized in terms of thermal, rheological and X-ray studies. The effect of side alkyl chain was found to dramatically change the material properties. A second type of supramolecular assembly was investigated based on a poly-phosphonium ionic liquid, which was complexed with a number of carboxylic acids. The material properties were easily manipulated from a sticky fiber to a brittle solid by changing the composition of the carboxylic acid. A crosslinked supramolecular assembly combining ionic interactions and weak covalent bonds, specifically disulfide bonds, was next designed and characterized. The network properties could be switched between "on and off" using mild conditions. The polymeric ionic networks and their building block ionic liquids are also of interest as safe electrolytes in energy storage devices due to their non-flammability, non-volatility, etc. We have identified one ionic liquid with superior thermal stability, high lithium salt solubility, and good conductivity in a lithium metal battery. The prototype battery performed safely at 100 degree celsius for more than 30 days. Thermally stable Li metal batteries are of interest in the oil industry for downhole applications. These studies were extended to an ionic polymer that exhibits a lamellar structure as a new polymer electrolyte.

By virtue of their non-toxic nature and their attractive photoluminescence (PL) properties, Carbon-dots (or C-dots) represent an emerging class of environmentally benign multifunctional materials. They exhibit excitation-dependent emission and demonstrate colloidal and structural stability. As a result, C-dots are promising candidates for a wide spectrum of applications.

abstract: Collective cell migration in the 3D fibrous extracellular matrix (ECM) is crucial to many physiological and pathological processes such as tissue regeneration, immune response and cancer progression. A migrating cell also generates active pulling forces, which are transmitted to the ECM fibers via focal adhesion complexes. Such active forces consistently remodel the local ECM (e.g., by re-orienting the collagen fibers, forming fiber bundles and increasing the local stiffness of ECM), leading to a dynamically evolving force network in the system that in turn regulates the collective migration of cells. In this work, this novel mechanotaxis mechanism is investigated, i.e., the role of the ECM mediated active cellular force propagation in coordinating collective cell migration via computational modeling and simulations. The work mainly includes two components: (i) microstructure and micromechanics modeling of cellularized ECM (collagen) networks and (ii) modeling collective cell migration and self-organization in 3D ECM. For ECM modeling, a procedure for generating realizations of highly heterogeneous 3D collagen networks with prescribed microstructural statistics via stochastic optimization is devised. Analysis shows that oriented fibers can significantly enhance long-range force transmission in the network. For modeling collective migratory behaviors of the cells, a minimal active-particle-on-network (APN) model is developed, in which reveals a dynamic transition in the system as the particle number density ρ increases beyond a critical value ρc, from an absorbing state in which the particles segregate into small isolated stationary clusters, to a dynamic state in which the majority of the particles join in a single large cluster undergone constant dynamic reorganization. The results, which are consistent with independent experimental results, suggest a robust mechanism based on ECM-mediated mechanical coupling for collective cell behaviors in 3D ECM. For the future plan, further substantiate the minimal cell migration model by incorporating more detailed cell-ECM interactions and relevant sub-cellular mechanisms is needed, as well as further investigation of the effects of fiber alignment, ECM mechanical properties and externally applied mechanical cues on collective migration dynamics. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2019

abstract: Photovoltaics (PV) is one of the promising options for maintaining sustainable energy supply because it is environmentally friendly, a non-polluting and low-maintenance energy source. Despite the many advantages of PV, solar energy currently accounts for only 1% of the global energy portfolio for electricity generation. This is because the cost of electricity from PV remains about a factor of two higher than the fossil fuel (10¢/kWh). Widely-used commercial methods employed to generate PV energy, such as silicon or thin film-based technologies, are still expensive as they are processed through vacuum-based techniques. Therefore, it is desirable to find an alternative method that is open-air and continuous process for the mass production of solar cells. The objective of the research in this thesis is to develop low-cost spray pyrolysis technique to synthesize oxides thin films for applications in solar cells. Chapter 4 and 5 discuss spray-deposited dielectric oxides for their applications in Si solar cells. In Chapter 4, a successful deposition of Al2O3 is demonstrated using water as the solvent which ensures a lower cost and safer process environment. Optical, electrical, and structural properties of spray-deposited Al2O3 are investigated and compared to the industrial standard Atomic Layer Deposition (ALD) Al2O3/Plasma Enhanced Chemical Vapor Deposition (PECVD) SiNx stack, to reveal the suitability of spray-deposited Al2O3 for rear passivation and optical trapping in p-type Si Passivated Emitter and Rear Cell (PERC) solar cells. In Chapter 5, The possibility of using low-cost spray-deposited ZrO2 as the antireflection coating for Si solar cells is investigated. Optical, electrical and structural properties of spray-deposited ZrO2 films are studied and compared to the industrial standard antireflection coating PECVD SiNx. In Chapter 6, spray-deposited hematite Fe2O3 and sol-gel prepared anatase TiO2 thin films are sulfurized by annealing in H2S to investigate the band gap narrowing by sulfur doping and explore the possibility of using ternary semiconductors for their application as solar absorbers. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2019

The main application of superconducting materials is to generate very high magnetic fields in reduced spaces i.e. built strong magnets (16 T – 100 T) for diverse applications such as nuclear magnetic resonance (NMR), magnetic resonance imaging (MRI), and particle accelerators. Since their discovery in 2008, Fe-based superconductors (FBS) have drawn attention from the technological point of view due to the interesting combination of properties that these materials possess for potential high field magnet applications. Also from the scientific community because superconductivity is a property of Fe-As layers in these compounds, yet magnetism in Fe has long been assumed to destroy superconductivity. Although, FBS have been extensively studied, it was not until 2012 that Weiss et al. demonstrated the potential of FBS for practical applications, reporting a surprisingly high critical current density (Jc) of 104 Acm-2 at 10T in untextured polycrystals. This result is considered a breakthrough because previous studies in cobalt-doped (Co-doped) BaFe2As2 bicrystals suggested that, similarly to YBa2Cu3O7-δ (YBCO), high-angle grain boundaries block supercurrent. That fact indicated that FBS would need to be textured like YBCO coated conductors in order to carry significant Jc for practical applications. YBCO coated conductors are state of the art materials for high field magnet applications. However, due to texturing the manufacturing of these materials is still very expensive ($100/Km of flat wire) reducing their usage to a small niche of applications. The unexpected high intergrain Jc was measured in potassium-doped BaFe2As2 (K-doped Ba-122) untextured round wires; the round geometry is preferred by far by magnet builders and eliminates the costs of expensive substrates needed for texturing. The high Jc in K-doped Ba-122 was associated with its having a fine grain size. However, even with the surprisingly high Jc, current transport across grain boundaries is still about a factor of 10 too low for practical applications. The main goals of this research were to understand what blocks current at grain boundaries of Ba-122, and to develop methods to increase current transport across grain boundaries to obtain a polycrystalline conductor that is closer to the application limit 105 Acm-2 at 10 T. This was done: 1) By investigating what type of impurities and other extrinsic factors are blocking Jc of Ba-122 samples; 2) By developing new protocols for cleaner synthesis process to continue raising Jc in Ba-122 compounds; 3) By studying effects of grain size on Jc; 4) By studying how different doping schemes change the electromagnetic properties of Ba-122 polycrystals. The significance of this research was to explore new ways to increase Jc in untextured Ba-122 polycrystals. I studied the impact that careful processing and chemical doping have on the microstructural, nano-structural, and superconducting properties of untextured polycrystals of Ba-122. The aim was to produce materials with clean and well connected grain boundaries that allow effective current flow. One of my contributions was to synthesize samples using the low temperature processing developed in Weiss’s study, but focusing on the elimination of oxygen and moisture absorption during synthesis to avoid oxides and hydroxides formation along the grain boundaries that blocks supercurrent. Also, I optimized the previous processing to produce even finer grain samples to raise Jc at low fields by modifying the milling process and heat treatment of the samples. Another contribution was the study of novel dopant combinations such as double doping different sites to investigate how doping alters Jc within grains and across grain boundaries in Ba-122. K-doped Ba-122 combines a very high upper critical field (> 100 T), a low anisotropy, and high intragranular Jc. And because we have shown that intergranular Jc is high in an untextured polycrystal that can be formed into a round wire, this technology could potentially displace the highly-textured YBCO coated conductors for high-field NMR magnets at 4.2 K. Coated conductors are currently considered the state of the art technology for these applications. / A Dissertation submitted to the Program in Material Science and Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / November 9, 2018. / Ba-122, Bulk superconductors, critical current density, grain boundaries, Superconductivity, TEM / Includes bibliographical references. / Eric Hellstrom, Professor Directing Dissertation; Munir Humayun, University Representative; David Larbalestier, Committee Member; Theo Siegrist, Committee Member; Kenneth G. Hanson, Committee Member.

REBCO coated conductors have recently become viable for high field superconducting magnets, but their use brings new challenges. Knowledge of the transport critical current density over a wide range of magnetic field and temperature, Jc(B, T), is essential to accurately model quench behavior and assure protection in REBCO superconducting magnets. At the National High Magnetic Field Laboratory (NHMFL), 12 km of REBCO tapes were purchased and characterized at 4.2 Kelvin (K) with field orientation B⊥tape and at 18° off-axis to select tapes for the construction of the all-superconducting 32 T user magnet that successfully reached field recently. Of the tapes selected for 32 T, three were chosen for additional Jc(B, T) characterization from 4.2 K to 75 K and fields from 1 T to 15 T in the B⊥tape orientation. A new probe was designed to accommodate these measurements on 4mm wide REBCO tapes up to 700 Amps. We found that the transport Jc(B, T) dependence described using Ginzburg-Landau models of vortex pinning for HTS fit well to a power law for Jc(B) and to an exponential temperature dependence for T < 45 K and 3 T < B < 15 T. A fourth tape from the 32 T magnet was then selected to test the predictability of our modeling. Using this extensive data set, the correlation between Jc(B, 4.2 K) and Jc(B , T) enabled us to predict Jc(B, T) for all tapes procured for the 32 T magnet with an accuracy of 10% or less for T < 40 K. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2019. / April 19, 2019. / Flux Pinning, High Temperature Superconductivity, Magnet Design, REBCO, Superconductivity, Transport Critical Current Measurements / Includes bibliographical references. / David C. Larbalestier, Professor Directing Thesis; Fumitake Kametani, Committee Member; Wei Guo, Committee Member; Dmytro Abraimov, Committee Member.

<p> During heat treatment of polycrystalline materials, grain shape affects the rate of grain growth. In 2-D, the von Neumann-Mullins Law requires grains with fewer than six edges to shrink, greater than six edges to grow, and hexagonal grains to be stable regardless of edge lengths or curvatures. The 3-D analogue, described by the MacPherson-Srolovitz relation, does not explicitly depend on any topological feature (number of faces, edges, or vertices), yet there is bias in the observed grain topologies in 3-D metal polycrystals. In order to investigate this bias and determine its origins, numerical simulations of ideal polycrystalline materials, characterization of topologies, and comparisons to possible polyhedral shapes were performed.</p><p> Normal grain growth in polycrystalline materials is characterized by a self-similar distribution of topological properties: the average grain area increases with heat treatment time, but the average number of faces per grain remains constant. Therefore, distributions of the number of faces per grain are commonly reported characteristics of polycrystals. To investigate bias in grain topologies, the number of edges per face on each grain in the polycrystal was extracted, then the standard deviation of this quantity was computed for each grain. For grains resembling Platonic solids with equal numbers of edges on each face, such as the Platonic tetrahedron, hexahedron, and dodecahedron, this quantity is zero. In typical grains with more diverse faces, the standard deviation increases. The average, upper, and lower bound of standard deviations possible for all polyhedra with a given number of faces were determined by enumerating each using a graph theory-based code, plantri. Several polycrystalline datasets were then obtained and analyzed: two synthetic, two simulated grain growth, and one experimental reconstruction of titanium. The polycrystals all exhibited lower averages of the standard deviation of edges per face than the enumerated polyhedra, demonstrating bias. Specifically, the bias in grain growth favors more "regular" topologies, with a smaller spread in the number of edges per face than would occur at random.</p><p> One dataset, a synthetic microstructure with flat edges and faces, was biased more weakly than the rest. The remaining four datasets involved motion by mean curvature, the fundamental mechanism of grain growth, under which interfaces move toward their center of curvature with velocity proportional to that curvature: sharply curved faces move faster than more gently curved ones, and flat faces move not at all. To satisfy force balance at the vertices, three-edged faces in polycrystals become highly curved and quickly collapse during grain growth, but the laws of topology require that grains with between ten and sixteen faces have five edges per face, on average. This span covers the median and mean number of faces in polycrystalline grain populations. Therefore, as three-edged faces collapse, faces with more than 5 edges must also lose edges to maintain grain boundary network connectivity.</p><p> By changing the physics of grain growth to decrease edge and face curvature, the population of three-edged faces should increase, with the standard deviation in edges per face increasing proportionally. To test this hypothesis, a phase-field model of grain growth was implemented with lower mobility on triple junctions than on other features. This approach, known as a "vertex drag" model in 2-D, tends to straighten grain edges. From large-scale 2-D simulations, vertex mobility 100x lower than the edge mobility was found to increase the relative proportion of 3-edged grains by 25%. While the effect is small in magnitude, this result supports motion by mean curvature as the root cause of bias in polycrystalline grain topology.</p>

<p> Grain boundary (GB) segregation and embrittlement of copper (Cu) by small amounts of bismuth (Bi) has been investigated on 6&deg;, 13&deg;, and 33&deg; Cu twist bicrystals. The results from micro-mechanical double edge notched testing showed no embrittlement effects in the 6&deg; GB. The 33&deg; GB has been shown to be significantly embrittled by the introduction of Bi. Single edge notch testing of the 13&deg; GB also showed a reduction in fracture toughness. These mechanical results have been interpreted through the use of analytical electron microscopy (AEM) studying the GB geometry, the atomic structure, the electronic structure, and the chemical compositions of the GBs. The 6&deg; and 33&deg; GBs were found to be close to pure twist boundaries but with more accurate twist angles of 4.3&deg; and 38.0&deg;, respectively. The electronic structure of the GBs was not found to be a good indication of the presence of Bi, which was confirmed on the 13&deg; and 33&deg; GBs. The Bi GB coverage was confirmed via quantitative XEDS on the 33&deg; GB to correspond to 0.12 &plusmn; 0.03 monolayers of Bi and through 3-dimensional scanning transmission electron microscope (STEM) through focus imaging to be 0.02 &ndash; 0.09 monolayers of Bi. The presence of edge dislocations along the 33&deg; GB was confirmed with Bi segregating to edge dislocation cores. The Bi atoms on the dislocation cores embrittle the GB by increasing the energy required to move a dislocation in response to an applied stress resulting in reduced plasticity at the crack tip which promotes GB cleavage.</p>

Note: / Stream current, electro-osmotic flow, conductance, and permeability measurements were carried out on a cylindrical pads composed of different fibrous materials over a range of solid concentrations. The Z-potentials calculated from stream current and electro-osmotic measurements on the same pad were shown to be identical. Some deficiencies of the bubble flowmeter used to meaure the electro-osmotic flow were investigated and explained theoretically; a new type of flowmeter, free from these defects, was proposed.

During operation of a CANDU reactor, corrosion occurs which results in free hydrogen that can diffuse into the tubes. Once the solid solubility of hydrogen in the zirconium matrix is exceeded, the hydrogen will precipitate as a flake-like brittle hydride phase. The natural orientation of the hydride flakes is in the circumferential direction but under a tensile hoop stress the hydrides are able to reorientate themselves to the radial direction. This makes the pressure tubes susceptible to delayed hydride cracking (DHC) which can cause failure of the tubes. A memory effect has been observed to cause hydrides that would otherwise form in the circumferential direction to form in the radial direction. Studies have been previously performed to examine the memory effect however they have not quantified the hydride orientation distribution. This study examined the memory effect in Zr-2.5Nb micro pressure tubes with three different microstructures and textures. A stepped micro pressure tube sample design was hydrided to 100 ppm(wt%) and pressurized to obtain a nominal hoop stress ranging from 65 MPa to 350 MPa. Each of the samples was heated to 350oC to dissolve all of the hydrogen followed by cooling under stress. Samples were then reheated to 350oC for 1 hour and 24 hours and cooled without stress. Almost complete reorientation was observed in typical pressure tube material which had a very fine microstructure and a large portion of basal plane normals in the transverse direction. After reheating, little memory effect was found in material similar to the commercially used pressure tube material. However a clear memory effect was observed in the other two samples. The memory effect was observed in the range of angles where hydrides are naturally present. A second flanged sample design was used to find the dilational strain associated with hydride reorientation from which the normal strain could be calculated. The strain normal to the hydride, εnormal, was calculated to be 0.11 ± 0.05. This study provides a valuable resource that can be used to improve DHC models which are used to determine the useful life of the pressure tubes. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2010-10-01 01:26:49.608