<p> The goal of this research project was the development of a protocol for preparation of optically clear organic/inorganic hybrid materials that was amenable to entrapment of lipophilic biomolecules. The protocol involved the acid-catalyzed hydrolysis of mixtures of tetraethylorthosilicate (TEOS) with organosilane precursors, including methyltriethoxysilane (MTES), dimethyldimethoxysilane (DMDMS) and propyltrimethoxysilane (PTMS) in the presence and absence of the polymer additives poly(ethylene glycol) or poly(vinyl alcohol).</p> <p> The effect of organosilane precursors and polymer additives on the optical clarity, hardness and hydration stability of the resulting materials was characterized. It was determined that there was a limit to the amount of organosilane that could be added before the materials exhibited unacceptable characteristics. These limits were 20.0% (v/v) for MTES, 10.0% (v/v) for PTMS, and 5.0% (v/v) for DMDMS. Addition of PEG to these materials at levels up to 10.0% (w/v) resulted in good material characteristics. However, addition of PVA produced opaque materials with poor material properties. The internal environment of the materials was also probed using the environmentally sensitive fluorescent probes 7-azaindole (7AI) and prodan. These studies showed that the method of hydrolysis of the silane precursors and the aging conditions had a dramatic effect on the resulting material.</p> <p> The hybrid materials were used to entrap human serum albumin (HSA) and lipase to determine the effect of organic content on the biological function of these biomolecules. Both biomolecules retained a portion of their native function when entrapped in sol-gel-derived materials, and it was found that both proteins showed enhanced function in the presence of MTES. In the case of lipase, it was also determined that addition of PEG 600 at 10.0% (w/v in the gelation buffer) provided a dramatic increase in activity compared to materials without this additive, likely owing to a direct effect of the PEG on the stability of the entrapped protein.</p> <p> Following studies using bulk glasses, a protocol was developed for the preparation of optically clear sol-gel-derived thin films that was amenable to entrapment of biomolecules. The optimal method involved dipcasting of co-hydrolyzed materials containing 1.0 to 3.0% PEG. By careful control of the viscosity of the casting solution and the rate of film deposition, it was possible to form very stable thin films with excellent physical characteristics. These films were used to entrap the pH-sensitive, ratiometric fluorescent probe dextran-SNARF-1, resulting in a prototype of a fluorimetric pH sensor. Co-entrapment of the probe and lipase into sol-gel-derived thin films resulted in a rapid, reagentless biosensor prototype that could monitor changes in pH due to the enzyme-catalyzed hydrolysis of triglycerides. These results demonstrate that species entrapped in sol-gel derived thin films are suitable for biosensor development.</p> / Thesis / Master of Science (MSc)

<p> The models derived from classical light scattering theory for predicting Rayleigh light scattering contain useful parameters such as polymer weight average molecular weight, z-average radius of gyration and virial coefficients. The methods used to estimate these model parameters have not been based on sound statistical principles. It is with improved statistical estimation methods for these parameters that this thesis is concerned with. The methods of linear least squares, non-linear least squares and error propagation were applied to the analysis of wide angle and low angle laser light scattering data and the results compared.</p> <p> From the theory of dynamic light scattering, methods have been developed to reconstruct particle size distributions of unimodal, bimodal and polydisperse polymer solutions from the data accumulated in a single experiment. Some of these methods of reconstruction are based upon the estimation of the coefficients in a sum of exponentials. Estimating sums of exponentials is a highly ill-conditioned problem and the problems encountered thereof are examined in this thesis. Linear least squares, non-linear least squares and exponential sampling techniques were applied to experimental data from a number of simulated polymer distributions and the final results compared.</p> / Thesis / Master of Engineering (MEngr)

<p> Fluorescence spectroscopy has been proven to be a useful technique for the investigation of the structural, physical and solution properties of polymers. A polymer system containing a photo physical probe can be investigated using fluorescence quenching and polarization. We have randomly labeled sodium hyaluronate (HA) chains with fluorescent dyes such as 1-(1-pyrenyl)methyl amine and N-ε-dansyl-L-lysine, and studied their physical, structural and solution properties, including interactions with surfactants using the above fluorescence techniques.</p> / Thesis / Master of Science (MSc)

<p> Cationic polyelectrolytes have attracted growing attention in the field of non-viral oligonucleotides (ONs) deliveries because of their ability to bind ONs by electrostatic interactions for efficient cellular uptake. However the formation of electrostatic polymer/ONs complexes and their biological effects are still poorly understood. The relationships between polymer structure and complexation performance have not been well established. The objectives of this research are to synthesize and characterize well-defined and well-controlled cationic polyelectrolytes and to evaluate the effects of polyelectrolyte chain properties on ONs complexation. Poly(2-(dimethylamino) ethyl methacrylate) (polyDMAEMA) and its derivatives are used as the polymer candidate. A fluorescein-labeled oligonucleotide, 5 '-FGCGGAGCGTGGCAGG-3' (F: fluorescein), is used as the oligonucleotide candidate.</p> <p> Low-molecular-weight cationic polyDMAEMA samples having narrow molecular weight distribution were synthesized by living anionic polymerization (LAP) and atom transfer radical polymerization (ATRP) methods. Fully charged polyDMAEMA quats were prepared by sequential quaternization of polyDMAEMA samples, as well as by direct ATRP of the quaternized DMAEMA monomer. An aqueous GPC calibration method was first developed for the characterization of these cationic polyelectrolytes. It was found that the type of counter-ion has little effect on the hydrodynamic volume of polyDMAEMA quat. Therefore the dimethyl sulfate salt of polyDMAEMA provided a reliable calibration standard for other types of quaternized DMAEMA homopolymers.</p> <p> Cationic block copolymers of polyDMAEMA with 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol (PEG) were also prepared by ATRP. It was found that the order of monomer addition, solvent type, temperature, and molecular weight of macroinitiator have significant effects on the living feature of the polymerization. Well-controlled block copolymers were obtained when polyHEMA was used as the macro initiator.</p> <p> The complexation capability of the prepared polyelectrolytes with oligonucleotides (15 mer) was evaluated by a fluorescence technique. It was found that the complexation performance depends on polymer molecular weight, charge density, and counter-ion type, as well as polymer concentration and block composition. The polymer sample that has double molecular weight of the ONs gave the optimal complexation performance.</p> / Thesis / Master of Applied Science (MASc)

<p> Two methods for preparing semiconductor grade copper sulfide films, to be used in low cost thin film solar cells,have been investigated. The sulfurization method involves the controlled chemical conversion of copper films into the desired copper sulfide phase. The other method of evaporating Cu2S pellets is more adaptable for an all evaporated thin film solar cell. The copper sulfide films obtained by these methods were characterized using x-rays, cathodoluminescence, electrical and optical methods. The use of optical method in monitoring the stoichiometry of thin copper sulfide films has been illustrated. The photovoltaic properties of thin copper sulfide films obtained by these methods, were also investigated using Cu2S - Si heterojunctions. The behaviour of these junctions indicates that 900 Ȧ thick copper sulfide film is required for optimum photovoltaic conversion. This result may be of some importance in Cu2S - CdS solar cells in further reducing their thickness. Cu2S - Si heterojunctions can also be used to monitor the properties of copper sulfide, as silicon is a well characterized substrate.</p> / Thesis / Master of Science (MSc)

<p> Gel filtration chromatography on Sephadex gels G15 and G50, was used to characterize the residual organic materials found in effluents from biological treatment. Molecular weight distributions were determined as the equivalent molecular weight distribution of a homologous series of sugars and alcohols. The homologous series was also used to determine equivalent molecular radii, based on Corey-Pauling-Koltun space filling models of the homolgous series.</p> <p> To determine the distributions of residual organics from mixed cultures grown on simple, pure substrates, laboratory batch studies were performed. For this purpose, media containing glucose or glutamic acid substrates and a bicarbonate-phosphate buffer system were innoculated with activated sludge. Both high and low substrate and microorganism concentrations were used at constant temperature and pH. As a comparison for the mixed cultures, a representative strain of Flavobacterium sp. isolated from activated sludge was grown in pure culture on glucose.</p> <p> Both the laboratory mixed culture effluents and treatment plant effluents contained material of equivalent molecular weight less than 1500. However, little similarity appeared to exist between the low molecular weight (<1500) distributions of treatment plant effluents and those from the mixed cultures. A significant fraction of the treatment plant and batch effluents had equivalent molecular weights of greater than 10,000. The pure culture studies showed that a single strain of bacteria can produce material of equivalent molecular weight both greater and less than 1500.</p> / Thesis / Master of Engineering (MEngr)

The invention of Li-ion batteries (LIBs) marks a new era of energy storage and allows for the large-scale industrialization of electric vehicles. However, the flammable organic electrolyte in LIBs raises significant safety concerns and has resulted in numerous fires and explosion accidents. In the pursuit of more reliable and stable battery solutions, interests in aqueous batteries composed of high-energy cathodes and water-based electrolytes are surging. Limited by the narrow electrochemical stability window (ESW) of water, conventional aqueous batteries only achieve inferior energy densities. Current development mainly focuses on manipulating the properties of aqueous electrolytes through introducing excessive salts or secondary solvents, which enables an unprecedentedly broad ESW and more selections of electrode materials while also resulting in some compromises. On the other hand, the interaction between electrodes and aqueous electrolytes and associated electrode failure mechanism, as the key factors that govern cell performance, are of vital importance yet not fully understood. Owing to the high-temperature calcination synthesis, most electrode materials are intrinsically moisture-free and sensitive to the water-rich environment. Therefore, compared to the degradation behaviors in conventional LIBs, such as cracking and structure collapse, the electrode may suffer more severe damage during cycling and lead to rapid capacity decay. Herein, we adopted multi-scale characterization techniques to identify the failure modes at cathode–electrolyte interface and provide strategies for improving the cell capacity and life during prolonged cycling. In Chapter 1, we first provide a background introduction of conventional non-aqueous and aqueous batteries. We then show the current development of modern aqueous batteries through electrolyte modification and their merits and drawbacks. Finally, we present typical electrode failure mechanism in non-aqueous electrolytes and discuss how water can further impact the degradation behaviors. In Chapter 2, we prepare three types of aqueous electrolytes and systematically evaluate the electrochemical performance of LiNixMnyCo1-x-yO2, LiMn2O4 and LiFePO4 in the aqueous electrolytes. Combing surface- and bulk-sensitive techniques, we identify the roles played by surface exfoliation, structure degradation, transition metal dissolution and interface formation in terms of the capacity decay in different cathode materials. We also provide fundamental insights into the materials selection and electrolyte design in the aqueous batteries. In Chapter 3, we select LiMn2O4 as the material platform to study the transition metal dissolution behavior. Relying on the spatially resolved X-ray fluorescence microscopy, we discover a voltage-dependent Mn dissolution/redeposition (D/R) process during electrochemical cycling, which is confirmed to be related to the Jahn–Teller distortion and surface reconstruction at different voltages. Inspired by the findings, we propose an approach to stabilize the material performance through coating sulfonated tetrafluoroethylene (i.e., Nafion) on the particle, which can regulate the proton diffusion and Mn dissolution behavior. Our study discovers the dynamic Mn D/R process and highlights the impact of coating strategy in the performance of aqueous batteries. In Chapter 4, we investigate the diffusion layer formed by transition metals at the electrode–electrolyte interface. With the help of customized cells and XFM technique, we successfully track the spatiotemporal evolution of the diffusion layer during soaking and electrochemical cycling. The thickness of diffusion layer is determined to be at micron level, which can be readily diminished when gas is generated on the electrode surface. Our approach can be further expanded to study the phase transformation and particle agglomeration at the interfacial region and provide insights into the reactive complexes. In Chapter 5, we reveal the correlation between the electrolytic water decomposition and ion intercalation behaviors in aqueous batteries. In the Na-deficient system, we discover that overcharging in the formation process can introduce more cyclable Na ions into the full cell and allows for a boosted performance from 58 mAh/g to 124 mAh/g. The mechanism can be attributed to the water oxidation on the cathode and Na-ion intercalation on the anode when the charging voltage exceeds the normal oxidation potential of cathode. We emphasize the importance of unique formation process in terms of the cell performance and cycle life of aqueous batteries. In Chapter 6, we summarize the results of our work and propose perspectives of future research directions. / Doctor of Philosophy / Li-ion batteries (LIBs) have dominated the market for portable devices and electric vehicles owing to their high energy density and good cycle life. However, frequent battery explosion accidents have raised significant safety concerns for all customers. The root cause can be attributed to the flammable organic electrolytes in conventional LIBs. To address this issue, aqueous batteries based on water-rich electrolytes attract intensive attention recently. Recent research progress has dramatically improved the energy density of aqueous batteries dramatically by modifying the properties of electrolytes. However, most electrode materials are incompatible with water, leading to severe side reactions and an unstable cycle life. Therefore, understanding the failure mechanism of electrode materials in the presence of water is crucial while not fully studied yet. Our projects systematically evaluate the degradation behavior of various electrodes in aqueous electrolytes and uncover the root cause of transition metal dissolution in the electrodes. Our studies shed light on improving battery capacity and cycle life through a specialized formation cycle and polymer coating process. Furthermore, we also provide new approaches to investigate the dynamic process occurring at electrode–electrolyte interface, which is applicable to other solid–liquid systems. In summary, our research reveals the correlation between the failure mechanism and the capacity decay in various electrode materials, proposing effective approaches to enhance the battery performance.

Carbon dioxide electroreduction (CO2R) is a promising and sustainable route to generate valuable feedstocks through the electrochemical conversion from CO2 with electricity generated by renewable energy resources, to reduce greenhouse gas emissions, thereby protecting the global environment. One of the critical challenges for developing practical CO2R developments is understanding the structures and chemistry of CO2R electrocatalysts, and then generating fundamental insights to guide the design and optimization of high-performance electrocatalysts. During my Ph.D. studies, synchrotron-based X-ray spectro-microscopy techniques, scanning transmission X-ray microscopy (STXM) and X-ray spectro-ptychography, were used to study nickel-nitrogen-carbon (Ni-N-C) and electrodeposited Cu-based CO2R electrocatalysts. STXM and ptychography were upgraded to in situ characterizations to provide spectroscopic characterization and quantitative, chemically selective imaging of these catalytic materials under CO2R conditions. To achieve in situ STXM and spectro-ptychography, a micro-fluidic based, liquid-flow electrochemical in situ device was developed, fabricated, and implemented. The in situ device is optimized from previous versions developed by Vinod Prabu, past graduate student of Hitchcock group, and the initial concept was provided by Pablo Ingino and Dr. Martin Obst, collaborators at the University of Bayreuth. In situ STXM and spectro-ptychography provided a detailed chemical and morphological evaluation of catalyst materials at different applied potentials during electrochemical processes. The in situ STXM studies of Cu-based catalysts showed that electrodeposited Cu2O particles are converted to metallic Cu with different reaction rates at applied potentials less negative than that for initiation of CO2R. The in situ STXM results show a degree of heterogeneity in the electrochemical response of discrete nanoparticles and metallic Cu as the active catalyst for CO2 reduction which is structurally relatively stable at CO2R-relevant potentials within the spatial resolution of STXM. In situ spectra-ptychography was used to follow morphological changes of a single Cu-based catalytic particle in the electrochemical regime of CO2R. Our results show that the Cu particle lost the initial cubic structure and formed irregular dendritic-like structures during the CO2R process. To the best of my knowledge, this is the first time in situ STXM has been applied to CO2R electrocatalysts under flow liquid and electrochemical conditions and the first report of in situ spectro-ptychography studies. In summary, my research has successfully achieved the in situ STXM and spectro-ptychography experiments and contributed to an improved understanding of Cu nanoparticle CO2R electrocatalysts. / Dissertation / Doctor of Philosophy (PhD)

Microbiota-released extracellular vesicles (MEVs) have emerged as key players in intercellular signaling in host-microbiome communications. However, their role in gut-brain axis signaling has been poorly investigated. Here, we performed deep multi-omics profiling of MEVs generated ex-vivo and from stool samples to gain insight into their role in gut-brain-axis signaling. Metabolomics unveiled a wide array of metabolites embedded in MEVs, including many neurotransmitter-related compounds such as arachidonyl-dopamine (NADA), gabapentin, glutamate, and N-acylethanolamines. To test the biodistribution of MEVs from the gut to other parts of the body, Caco-2, RIN-14B, and hCMEC/D3 cells showed the capacity to internalize labeled MEVs through an endocytic mechanism. Additionally, MEVs exhibited dose-dependent paracellular transport through Caco-2 intestinal cells and hCMEC/D3 brain endothelial cells. Overall, our results revealed the capabilities of MEVs to cross the intestinal and blood-brain barriers to delivering their cargo to distant parts of the body.

Membrane gas separation became an industrial reality in the late 1970s with Monsanto's first commercial asymmetric hollow fiber membrane modules. Innovations in membrane separations result from new materials that exhibit an improved permeability and are more selective than their predecessors, with materials commonly compared to the "upper bound line." Accurate determination of the three transport properties which characterize a membrane, permeability (P), diffusivity (D), and solubility (S), is thus of great interest to exceed the current upper bound line. Also, proper characterization of membrane materials enables enhancing current commercial membrane processes or allows for new applications. All three transport properties, P, S, and D, can be determined using a single dynamic gas permeation experiment in a constant volume (CV) system, commonly called the time-lag method. This work presents the next-generation CV system that utilizes the two-tank volume concept, namely a reference volume and a working volume. Compared to the previous iteration, the pressure in the reference volume can be reduced to the anticipated pressure in the working volume after initiating the gas permeation experiment. This allows monitoring of the pressure decay in the working volume (i.e., gas permeation into the membranes) using a high-resolution differential pressure transducer (DPT) right after initiating the experiment. The new system's operation is demonstrated by simultaneous monitoring of the upstream pressure decay and the downstream pressure rise during the time-lag experiments using a polyphenylene oxide (PPO) membrane. The values determined using the pressure decay method are compared to those determined using the downstream method to identify any limitations still present in the current iteration of the CV system. To set a reliable benchmark value to compare against, the downstream receiver was redesigned, and an optimal configuration was identified, which was associated with negligible resistance to gas accumulation and, thus, a minor error in the experimental time lag downstream from the membrane. Furthermore, a temperature enclosure was built to minimize errors caused by the constant temperature assumption during the time lag analysis. Additionally, the temperature-controlled enclosure allows for transport properties temperature dependence to be quantified by determining the activation energy of permeability, diffusion, and the enthalpy of solution for a given gas/polymer system.