Browsing by Subject "Chemical Engineering"

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Analysis of tensioned-web-over-slot die coating.
(2009-12) Nam, Jaewook
In tensioned-web-over-slot die (TWOSD) coating, web is sustained only by the ten- sion of the web wrapped around the coating die. The distance between the die and web is set by the interaction between the hydrodynamic force of coating liquid and the normal stress resultant from the curved tensioned web, in what is called elaso- hydrodynamic interaction. In order to analyze this particular the coating flow, several tools are developed and tested on other coating flows relatively simpler than TWOSD flow. The theoretical conditions for the onset of vortex that degrades product qualities are proposed and the critical vortex birth trajectories inside the parameter space are tracked automatically by a direct tracking method. To detect a defect-causing flow feature in multi-layer coating, mid-gap invasion, the position of an interlayer separation point was tracked by theoretical model. The results are verified by flow visualization experiment for two- layer fixed-gap slot coating. Also linear stability analysis was performed, in order to detect unstable interlayer that signals coating defects in the two-layer slot coating. The purpose of the research is to understand the complicated flow characteristic inside the coating bead by solving the two-dimensional Navier-Stokes theory using finite element method and visualizing the coating bead flow on a lab-scale TWOSD coater. Using the tools described above, the flow features that leads to coating defects, such as, bead breakup, weeping, mid-gap invasion and feed slot vortex, are identified and mathematical forms of the onset condition for the features are presented. The onset conditions are combined into the direct tracking method that was used to construct the vortex-free operating window for the given die lip configurations. Furthermore, the tracking method can be used to shows the effect of die lip design on the critical parameters for the onset of the flow features.
Application of deep eutectic solvents and ionic liquids to hydrolase-catalyzed reactions.
(2010-01) Gorke, Johnathan Thomas
Hydrolases are important enzymes for stereoselective and environmentally benign synthesis. In nature, hydrolases cleave bonds with water. When used in organic solvents, these enzymes can make synthetically useful bonds through condensation and the release of a small molecule, usually water or an alcohol. Many organic solvents that preserve enzyme activity, such as toluene, can be environmentally damaging or toxic. Room temperature ionic liquids, poorly coordinating salts that are liquid at temperatures below 100 degrees C, are a potential alternative to organic solvents for hydrolase-catalyzed reactions because of their low volatility, moderate polarity, and recyclability. However, many commonly used ionic liquids are orders of magnitude more expensive than conventional organic solvents and may also cause adverse environmental effects if released into aquatic environments. We demonstrate that ionic liquids are effective solvents for the lipase-catalyzed polymerization of epsilon-caprolactone and other poly(hydroxyalkanoates) and are effective in enhancing the electrical conductivity of carotenoid-containing polymers produced enzymatically. However, we found that they were not as effective as toluene for enzyme catalysis, and strove to find better alternative solvents for biotransformations. We discovered that deep eutectic solvents, mixtures of ammonium or metal salts such as choline chloride and hydrogen bond donors such as urea or glycerol, were exceptional low-cost, biodegradable alternatives to organic solvents for hydrolase-catalyzed reactions. These physical mixtures may be thought of as ionic liquids, because they share similar physical properties to those solvents. Though they are composed of potential denaturants such as urea or halide anions, deep eutectic solvents stabilize enzymes. This stabilization is likely due to a preference for intra-solvent hydrogen bonding compared to enzyme-solvent hydrogen bonding. Deep eutectic solvents enhanced enzyme activity for a number of lipases either as pure solvents for reactions such as transesterification or polyesterification; or as additives in aqueous reactions such as epoxide ring opening or ester hydrolysis. We have preliminary evidence that deep eutectic solvents may induce a conformational change in enzymes that can alter reaction rates. These changes appear to be distinct from those caused by denaturing.
Atmospheric nucleation: measurements, mechanisms, and dynamics.
(2009-09) Kuang, Chongai
New particle formation by nucleation of gas-phase species significantly influences the size distributions and number concentrations of atmospheric aerosols. These nucleated particles are formed at rates that are orders of magnitude higher than were predicted by early models and grow at rates that are typically ten times faster than can be explained by the condensation of sulfuric acid alone. The resultant aerosols exert a significant impact on global climate by affecting the earth's radiation balance directly through the scattering and absorption of incident solar radiation, and indirectly through their role as cloud condensation nuclei (CCN). High formation rates and fast growth to CCN sizes ensure that NPF contributes significantly to the global CCN population. It is the primary goal of the research described in this thesis to develop robust models, constrained by measurement, for the sequential formation of CCN from the nucleation of gas-phase precursors. To this end, my thesis focuses on four topics: the development of nucleation rate parameterizations from correlations between formation rates of 1 nm particles and gas-phase sulfuric acid concentrations in diverse environments; the development of a cluster formation mechanism incorporating energetic barriers at the smallest clusters; the derivation of a simple, dimensionless criterion determining whether or not NPF would occur on a particular day; and the determination of the survival probability of newly formed particles (3 nm) as they grow to a CCN-active size (100 nm).
Atomic Layer Deposition and Annealing of Co3O4 for Electrocatalytic Oxygen Evolution
(2022) Nivarty, Tejas;
In the fight against climate change, renewable energy must be employed to reduce fossil fuel dependence. However, intermittent renewable energy sources like wind and solar require grid energy storage to be feasible at a large scale. Hydrogen shows promise as an energy storage medium, and is also an important chemical feedstock. However, current production of hydrogen is carbon-intensive, and green hydrogen produced by water electrolysis is expensive due to a lack of highly effective, non-precious metal oxygen evolution (OER) electrocatalysts. Co3O4 is one of the most effective metal oxide OER electrocatalysts, but thin films of Co3O4 produced via atomic layer deposition (ALD) have never been explored for OER. Uniform thin films of Co3O4 were successfully produced via ALD using CoCp2 and O3 precursors, and the crystallinity and stoichiometry of these thin films were studied before and after annealing using X-ray photoelectron spectroscopy and X-ray diffraction. The catalytic decomposition of O3 by Co3O4 during ALD was mitigated by using a 200 °C deposition temperature and a 10 s long O3 pulse at 10 torr. 7 nm and 27 nm thick films showed no difference in surface stoichiometry after being deposited by ALD. Annealing under H2 reduced Co3O4 films to CoO, as did annealing under N2 at a high temperature. 27 nm Co3O4 films were found to be much more crystalline than 7 nm Co3O4 films before annealing, and 27 nm films showed improvements in crystallinity after annealing while 7 nm films did not.
An Attempt to Make Low-Sulphur Coke from High-Sulphur Coal
(1922-06) Lee, Melville R.
Autothermal oxidative pyrolysis of biomass feedstocks over noble metal catalysts to liquid products.
(2011-07) Balonek, Christine Marie
Two thermal processing technologies have emerged for processing biomass into renewable liquid products: pyrolysis and gasification/Fischer-Tropsch processing. The work presented here will demonstrate oxidative pyrolysis of biomass as an alternative process to avoid the intrinsic disadvantages of traditional pyrolysis. Additionally, work has been conducted to examine the processing of biomass derived synthesis gas to condensable products, which involves mitigating new challenges when compared with the processing of conventional coal-based feedstocks during gasification/Fischer- Tropsch. The research group of Professor Lanny D. Schmidt has pioneered autothermal partial oxidation of a variety of gas and liquid feedstocks on noble metal catalysts to synthesis gas with high selectivity, char-free operation, and on millisecond timescales at temperatures of 600 - 1000 ◦C. More recently, cellulose has been shown to decompose on the catalyst surface to also produce high selectivities to synthesis gas. Chapter 2 discusses the discovery of an intermediate liquid phase during the autothermal processing of cellulose particles over rhodium-based catalysts. Volatilization of 300 μm cellulose particles on a 700 ◦C catalytic surface were filmed using a high speed camera capable of 1000 frames per second. The cellulose particles decomposed through an intermediate liquid, which boiled to gaseous species that convected into the catalyst bed. The high heat transfer rates made possible by the intimate contact of the boiling liquid and the hot surface allowed rapid reactions without leaving char residues. This unique insight allows new processes to be designed that exploit this type of cellulose thermal decomposition. Experiments were conducted to investigate the extension of catalytic partial oxidation over noble metal catalysts to convert biomass to liquid pyrolysis products, termed ‘oxidative pyrolysis’. Model compounds were chosen to represent the lignin fraction of lignocellulosic biomass to more easily and accurately study the proposed system. Chapter 3 discusses the autothermal oxidative pyrolysis of monoaromatics over noble metal catalysts. Benzene, toluene, ethylbenzene, cumene, and styrene were independently studied over five noble metal-based catalysts (Pt, Rh, Rh/ -Al2O3, Rh-Ce, and Rh-Ce/ -Al2O3) while varying the carbon-to-oxygen feed ratio. Aromatic rings were observed to be very stable in the reactor system, while homogeneous reactions of the alkyl groups of ethylbenzene and cumene were prevalent. Chapter 4 addresses the oxidative pyrolysis of microcrystalline cellulose particles as a model for lignocellulosic biomass to yield liquid products. Cellulose was demonstrated to autothermally convert to combustion, partial oxidation, and pyrolysis products without char formation. The effects of support geometry, catalyst metal, and hydrogen addition on product selectivities were studied. Platinum-coated alumina spheres maximized the yield of pyrolysis products by favoring combustion chemistry and minimizing reforming activities, as compared with rhodium-based catalysts. Up to 60 % carbon selectivity to pyrolysis products could be achieved on a Pt catalyst with hydrogen addition. As mentioned, previous research in the Schmidt group has shown high selectivities to synthesis gas by autothermal reforming of cellulose particles. However, utilizing this biomass-derived syngas, as opposed to traditional coal-based syngas, is not well studied. Biomass-derived synthesis gas presents a new set of inorganic impurities that may affect catalyst performance during Fischer-Tropsch processing. Small quantities (ppm) of typical biomass inorganics (Na, K, Li, and Ca) were loaded onto -Al2O3- supported Co-Re powder catalysts to study the effect on product selectivities (Chapter 5). The inorganic impurities were found to affect the reduction of Co and increase CO2 and C5+ selectivities, which were largely attributed to electronic effects. Chapter 6 proposes future research utilizing gas chromatography and mass spectrometry to identify and quantify specific components within liquid pyrolysis products, generally termed ‘pyrolysis oil’. This work will build on the research presented in Chapter 4: the demonstration of oxidative pyrolysis of cellulose to produce up to 50 % carbon selectivity to pyrolysis products. Further characterization of the pyrolysis oil will involve pH and water fraction measurements. Preliminary work shows the presence of several acids, alcohols, phenols, pyrans, among other small oxygenated species in the pyrolysis oil. Levoglucosan was identified as being the largest carbon-based fraction of the oil, up to 11 wt% under certain conditions. Additional experiments extending oxidative pyrolysis to process polymer feedstocks are also proposed
A bistable genetic switch controls antibiotic resistance transfer in Enterococcus faecalis.
(2011-08) Chatterjee, Anushree
The recent rise in microbial drug resistance is a growing challenge for future therapy of bacterial infections. Increased prevalence of antibiotic resistance in bacteria is an outcome of evolution via natural selection. However, the built-in design feature of bacteria to transfer DNA containing antibiotic resistance both within the same species and across species is the main culprit for the spread of drug resistance. One of the main factors driving the rise of drug resistant microbes is the transfer of antibiotic resistance genes present on mobile plasmids between donor and recipient cells via the mechanism of conjugation. In order to combat microbial drug resistance, novel strategies need to be developed to block such transmission of antibiotic resistance. In this work, the gene regulatory components involved in transfer of tetracycline resistance confers plasmid pCF10 between plasmid-carrying donor cells and plasmid-deficient recipient cells in bacterium Enterococcus faecalis is investigated. In the native state the donor cell exists in an OFF or conjugation-incompetent state. A pheromone released by the recipient cells serves as the chemical trigger for switching the donor cell from OFF to an ON or conjugation-competent state. The onset of conjugation is tightly regulated via multi-layered regulation offered by two-key genes prgQ and prgX present on pCF10 in response to the pheromone secreted by recipient cells. Using mathematical modeling and experimentation, we describe a novel mechanism of gene-regulation due to transcriptional interference and sense-antisense RNA interaction as a result of convergent transcription in the prgX/prgQ operon. We demonstrate that such a multi-layered gene-regulatory mechanism confers the system a bistable genetic switch controlling conjugative gene transfer between donor and recipient cells. A similar regulatory advantage offered by convergent transcription in attributing a bistable switch-like behavior in the scbA-scbR operon controlling antibiotic production in S.coelicolor is also investigated. Both mathematical model and experiments demonstrate that donor cells also control response to pheromone by changing the number of copies of pCF10 plasmid inside the cell. Cells with higher copies show increased robustness of the bistable switch and lower sensitivity to pheromone. Once bistable genetic-switch is ON, expression of genes encoding various proteins involved in the transfer of the plasmid are induced, however, this also causes production of an inhibitor of conjugation, thus giving rise to negative feedback loop which causes the donor to return to OFF state. Modeling and experimental analysis of dynamic response to induction indicate that this negative feed-back loop causes a brief surge of expression of the entire operon. We show that the inhibitor signaling peptide for pCF10 based system, acts as quorum-sensing signal with the role of turning-OFF conjugation at a population-wide scale. An interplay of positive and negative feedback loops allows the donor cell to quickly transition between ON and OFF states and is critical both for the transfer of plasmid and survival of the cell. Studying both the turning-ON and turning-OFF mechanisms of the switch allows identification of potential drug targets for blocking transmission of antibiotic resistance for use in future therapy.
Block copolymer modified epoxy: role of epoxy crosslink density.
(2010-03) Thompson, Zachary John
Epoxies of systematically varying crosslink density containing 5% by weight of a poly(ethylene oxide)-b-poly(ethylene-alt-propylene) (OP) block copolymer were prepared and characterized. The block copolymer self-assembled to form particles with diameters ranging from 15 to 100 nm. Transmission electron microscopy of the modified epoxies revealed that the block copolymer nanostructure can be altered by changing the epoxy crosslink density. The block copolymer structures displayed a decrease in surface curvature as the crosslink density was reduced. The strain energy release rate, Gc, of the block copolymer-modified epoxies, which can be related to fracture resistance, increased dramatically with a decrease in the epoxy network crosslink density and plateau at a value 13 times greater than the unmodified material. This trend was observed with both high and low molecular weight OP additives. The toughening behavior is dependent on the block copolymer nanostructure in highly crosslinked system while lightly crosslinked block copolymer-modified epoxies display similar fracture resistances for each block copolymer additive. Scanning electron microscopy of fracture surfaces revealed extensive voiding and plastic deformation near the crack tip of the modified epoxies. Addition of the block copolymer did not appreciably decrease the Young's modulus or glass transition temperature compared to the unmodified material. Epoxies with varying concentrations of block copolymer additive were prepared and further demonstrated the role of crosslink density on improving fracture resistance. Lightly crosslinked epoxies were able to maintain extraordinary toughness at block copolymer concentrations as low as 1 wt%. Increasing crosslink density decreases the toughening ability of the block copolymer and a higher concentration is required to provide adequate fracture resistance.
Block copolymer self-assembly in solution: structure and dynamics.
(2010-08) Choi, Soo-Hyung
Block copolymers can self-assemble into micelles or vesicles when dispersed in a selective solvent. In this study, spherical micelles were formed by poly(styrene-bethylene- alt-propylene) (PS-PEP) in squalane, highly selective to PEP blocks, leading to PS cores and swollen PEP coronas. The micelle structure was characterized by dynamic light scattering (DLS) and small-angle x-ray scattering (SAXS). The experimental results provide a detailed picture of micelle structure and intermicelle interaction as a function of block copolymer molecular weight and composition, concentration, and temperature. Based on this structural information, the single molecular exchange kinetics between the spherical micelles in dilute solution was examined by time-resolved small-angle neutron scattering (TR-SANS). Two pairs of structurally matched partially protonated and deuterated micelles were prepared and each pair was blended to provide an initially isotopically segregated state in solution. The SANS intensity is directly related to the concentration of protonated chains in the micelle cores. Therefore, a reduction in the measured scattering intensity can be quantitatively correlated with the exchange of chains. This measurement was aimed at probing the dependence of molecular exchange kinetics on temperature, molecular weight, and concentration. The temperature dependence of the chain exchange rate R(t) can be explained based on the core block dynamics, while the documented quasi-logarithmic decay of R(t) is shown to be consistent with single chain exchange that is hypersensitive to the core degree of polymerization and therefore polydispersity. Complementary measurements were also conducted with concentrated solutions where the micelles pack onto a body-centered cubic lattice. Based on a first-principles model, the exchange kinetics are expected to be independent of micelle concentration. However, slower dynamics in ordered micelles were observed. These results suggest that contributions from factors other than core block dynamics can come into play in the exchange kinetics for ordered micelles.
Block polymer membranes for selective separations.
(2009-06) Phillip, William A.
Polymeric membranes are used for many separations. Some act as selective filters, separating viruses and other undesirable solutes from drinking water. Others perform chemical separations, separating air to make an atmosphere which extends fruit shelf-life. The ability of a membrane to perform a separation is determined by its chemistry and microstructure. Block polymers are macromolecules composed of two or more chemically incompatible polymers (blocks) covalently bonded together. Depending upon the relative amounts of each block, the polymer forms different ordered structures 5-50 nm in scale. This control over the constituent polymers and microstructure will be used to produce membranes with different transport properties. Ammonia selective membranes which retain selectivity in mixed gas systems are made from poly(cycloocetene-b-styrene sulfonate). Using poly(styrene-b-lactide) as a template, ultrafiltration membranes with a monodisperse pore size distribution are formed.
Bridging the gap between theory, experiments and simulations of nanochannel confined DNA
(2020-08) Bhandari, Aditya Bikram
The study of nanochannel confined DNA has garnered substantial attention since the early 2000's owing to its application in genome mapping, the coarse-grained counterpart to DNA sequencing, which is an indispensable tool in biological research. However, our understanding of the physics behind confined DNA is rather simplified and incomplete. Thus, theory, simulation and experiment have by and large been at odds with one another. The results of this dissertation are aimed at understanding and attempting to resolve the source of these discrepancies. Our strategy for this dissertation is three-pronged. First, we revisit a historically cited explanation for the discrepancies - the lack of understanding behind the wall depletion length denoting the wall-DNA electrostatic interactions. Second, we considered the intersection of theory and simulation, which recent developments have managed to bring sufficiently into accord. We found that the deviations between the fractional extension distributions predicted by an asymptotic theory and those observed experimentally, are not due to a breakdown of the theory, even for experimental conditions which typically do not strictly satisfy the asymptotic limits of the theory. This motivated a closer inspection of the theories to determine a missing link between theory and experiment. Finally, by studying a recently generated dataset of fractional extensions spanning a wide range of the experimental parameter space, we were able to isolate this missing link as the effect of long-range electrostatics in the system which are typically ignored in the simplified theories, wherein the DNA is assumed as a neutral polymer confined in a channel of a reduced effective channel size. We believe that our findings within this dissertation will provide a better understanding of confined polymers and, in particular, the nanochannel confined DNA system used in genome mapping, as well as provide new directions of study in the future.
Catalytic autothermal reforming of biomass to synthesis gas.
(2010-07) Colby, Joshua Leigh
Please see PDF abstract!
Catalytic partial oxidation of renewable feedstocks.
(2012-07) Chakrabarti, Reetam
The current world energy and economic infrastructure is heavily reliant on fossil fuels such as coal, oil, and natural gas. The limited availability of fossil fuels along with environmental effects and economic uncertainties associated with their use has motivated the need to explore and develop other alternative sources of energy. Lignocellulosic biomass like fossil fuels is carbon-based and has the potential to partly supplant the energy supplied by fossil fuels. Lignocellulosic biomass is a complex mixture of polymers such as cellulose, hemicellulose, lignin along with small concentrations of inorganics and extractives. Recent research has shown that lignocellulosic biomass and biomass model compounds can be processed autothermally by catalytic partial oxidation in millisecond residence times over noble metal catalysts at high temperatures (600-1000 °C) to syngas (a mixture of carbon monoxide and hydrogen) [1-3]. The syngas stream can then be upgraded to fuels and chemicals. In Chapter 2, spatially resolved concentration and temperature profiles of methane and dimethyl ether, a model compound for biomass, are compared. Dimethyl ether can be produced renewably through syngas upgrading. Maximum temperature and concentration gradients were found within the oxidation zone. Most of the oxygen (∼ 95 %) was converted within the first 2.2 mm and syngas formation was observed despite the presence of oxygen. The catalytic partial oxidation process has been demonstrated using compounds which, unlike most biomass sources, contain negligible quantities of inorganics. Some of these inorganics have catalytic properties themselves and some may act as poisons for the Rh-based catalyst. The effects of common biomass-inorganics (silicon, calcium, magnesium, sodium, potassium, phosphorus, sulfur) on rhodium-based catalysts in autothermal reactors have been studied. To understand the effects of biomass inorganics on Rh catalysts, two sets of experiments surveying common inorganics were performed - in the first set, inorganics were directly deposited on the rhodium catalyst and tested using steam methane reforming as a model reaction (Chapter 3); whereas in the second set, inorganics were introduced to a clean catalyst in an ethanol feed to simulate actual inorganic-containing biomass (Chapter 4). In both sets of experiments, performance testing, catalyst characterization and regeneration were carried out to probe the mechanism of inorganic interaction with the rhodium-based catalyst. Large decreases in reforming activity were observed on phosphorus- and sulfur-doped catalysts. Deactivation due to calcium and magnesium was primarily due to blocking of active sites. Potassium and silicon were volatile at the high temperatures within the reactor. Potassium introduced alkaline chemistry promoting acetaldehyde formation from ethanol while phosphorus introduced acid chemistry promoting formation of ethylene from ethanol. The effects of potassium and phosphorus on catalytic partial oxidation of methane and ethanol at different concentrations and temperatures have been studied in Chapter 5. The synergistic effects of potassium and phosphorus were studied by distributing the inorganics together on the catalyst as monobasic potassium phosphate. The effects of both potassium and phosphorus were observed in the catalytic partial oxidation of methane on a potassium phosphate-doped catalyst at low temperatures. At high temperatures, only effects due to phosphorus were observed because of potassium volatilization. The results show that biomass-sources containing low concentrations of inorganics can be processed autothermally to a high selectivity syngas stream. The distribution and interactions of the inorganics within the catalyst can be used to design better pretreatment, processing, and regeneration strategies to minimize catalyst deactivation during biomass processing. Alcohols represent an important intermediate in different biomass upgrading routes. Chapter 6 discusses the behavior of butanol isomers, 1-butanol, isobutanol, 2-butanol, and tert-butanol over four different catalysts; Rh, Pt, RhCe, and PtCe at different fuel to oxygen (C/O) ratios. At low C/O ratios, equilibrium species such as CO, CO₂, H₂ and H₂O were obtained while non-equilibrium species such as carbonyls and olefins were dominant at high C/O ratios. Low reforming activity was observed on Pt and PtCe catalysts. All isomers decompose primarily by dehydrogenation through a carbonyl intermediate except tert-butanol which decomposes by dehydration to isobutene; however, the reactivity of tert-butanol was unaffected. In Chapter 7, isobutanol autothermal reforming is integrated with a water gas shift stage downstream to produce hydrogen containing low concentrations of carbon monoxide for portable fuel cell applications. A RhCe-based catalyst was selected to carry out autothermal reforming of isobutanol while a PtCe catalyst was selected for the water gas shift stage. This staged reactor produced high yields of hydrogen (> 120 % selectivity) containing low concentrations of CO (< 2 mol %) in less than 100 ms making the effluent ideal for portable high temperature PEM fuel cell applications. The water gas shift stage also reduced the concentration of non-equilibrium products formed in the autothermal reforming stage by over 50 %. Thermodynamic analysis of the system showed that staged autothermal reforming of isobutanol integrated with a fuel cell can potentially lead to 2.5 times more efficient energy usage when compared to burning isobutanol in a conventional combustion engine. The results in this thesis give an insight into the mechanisms and processing challenges involved in converting renewable feedstocks to syngas by catalytic partial oxidation. Further experiments based on the conclusions of this thesis are discussed in Chapter 8. Spatial profile experiments to determine roles of mass transfer, steam reforming, and dry reforming during catalytic partial oxidation of oxygenates are proposed. Spatial profile studies for catalytic partial oxidation over inorganic-doped catalysts and feed are proposed to determine their concentrations and nature on the catalyst surface during reactor operation.
Cesium dodecyl sulphate phase behavior in aqueous solutions and comparison with the sodium dodecyl sulphate/water phase diagram
(2010-02) Vagias, Apostolos Nikolaou
The goal of this Master’s Thesis has been to interpret the phase behavior of the cesium dodecyl sulphate/water system and compare the findings with the analogous findings of the SDS/water system. The synthesis of CsDS has been examined through 2 different methods: recrystallization and ion exchange. The phase behavior of the CsDS/water system has been examined, using several characterization methods. Macroscopic observation with cross-polarized light was used to interpret the solubility curve in the concentration region 1 wt % - 30 wt % CsDS. X-ray Diffraction was used in order to identify the unit cell crystal structure of CsDS and deduce conclusions about similarities and differences among different CsDS samples, unheated and heated. Cryo-TEM was used in order to observe the CsDS micellar nanostructures in an aqueous CsDS solution at a concentration higher than the CMC of CsDS for the given temperature. Optical microscopy with cross-polarized light was used in order to check for presence of liquid crystals, as well as to verify the solubility curve observed by the macroscopic observation. Small Angle X-ray Scattering was used in order to identify the phase of the liquid crystal structure (hexagonal or lamellar) in the intermediate concentration region (30-50 wt %).This study also includes the examination of possible organic and/or inorganic impunities in the CsDS/water phase behavior in the low concentration region (5-40 wt%) using macroscopic observation with cross-polarized light. The studies have indicated certain differences between the Cs+ and the Na+ system. The solubility curve of the CsDS/water system in the concentration region 1 wt % - 40 wt % CsDS is relatively flat, characterized by higher Krafft temperatures than the SDS/water system, for the same concentration region. This can be explained by the differences in the hydrated radii between the alkali metals, Cs+ and Na+ .The larger ionic radius of Cs+ attracts weaker the electrons of the water molecules. This corresponds to a smaller hydrated radius for Cs+ compared to Na+ and therefore to less hydrophilicity and lower solubility (higher Krafft temperature) for a given concentration, for the CsDS/water system compared to the SDS/water system. Another difference is the width in terms of concentration of the two-phase region of liquid crystals and micelles. This is larger for the Cs+ system and it indicates stronger van der Waals forces between the less ordered micellar phase and the more ordered liquid crystal phase. Both ellipsoidal micelles and threadlike structures were observed on the same grid in a CsDS/water solution, using Cryo-TEM. The ellipsoidal micelles that were observed for the CsDS/water system are twice as large as the ones observed for the SDS/water system, while it is very likely that the threadlike structures are related to some birefringent, intermediate liquid crystals that were observed by the macroscopic observation with cross–polarized light, when the heating rate was larger than 0.2[°C/min]. Therefore, it is concluded that heating rates larger than that value can affect the structures observed macroscopically, as well as microscopically. The X–ray Diffractograms of all CsDS samples had similar 2·θ diffraction angles which may indicate similar unit cell crystal structures. The diffractograms of the unheated CsDS and SDS crystals also exhibit similarities in their diffraction angles in the diffraction angle examined.
Component terminal dynamics in weakly and strongly interacting blends.
(2009-12) Ozair, Sehban N.
Miscible blend dynamics have been long been a subject of interest and are not as well understood as dynamics of homopolymer melts. Their anomalous behavior, such as time-temperature superposition failure, broadening of calorimetric glass transition, etc., makes these systems very intriguing and challenges our understanding of miscible blend dynamics. In this work we investigated temperature and composition dependence of two different, dynamically heterogeneous blend systems using rheology and forced Rayleigh scattering (FRS). The first blend investigated was a weakly interacting one comprising poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA). Monomeric friction factors of PEO and PMMA were reported for a wide range of temperature and composition. PEO terminal dynamics were found to have strong composition dependence unlike that of PEO segmental dynamics previously reported. Also, PEO maintained its rapid relaxation mechanisms even in stiffer surroundings. The PEO hydroxyl end groups were found to have no significant impact on component chain dynamics. The FRS and rheology results agreed remarkably well for this system. The Lodge-McLeish model failed to describe the experimental results. In order to understand the role of hydrogen bonding on chain dynamics, a strongly interacting system of PEO/poly(vinyl phenol) (PVPh) was investigated using rheology. The blends consisted of a high molecular polymer tracer dispersed in low molecular weight matrix to extract relevant dynamic information from tracer contribution to material properties. Monomeric friction factors were reported for a wide temperature and composition range. Time-temperature superposition failure was observed in PEO tracer blends at high PVPh concentration. The shape of tracer relaxation spectra for PVPh tracer blends had a strong composition dependence while those for PEO tracer blends were independent of composition. The tracer contribution to blend viscosity had a strong temperature dependence at high PVPh composition. Across the composition range, single and narrow glass transitions were observed for these blends. PVPh chain conformations were investigated using SANS and contradictory conclusions were reached. Therefore, no conclusive remarks can be made regarding PVPh chain conformations in dilute solution.
Composition of Corncob Tar
(1922-06) Schermer, Oscar Cornelius
Confined synthesis of Silicalite-1 in nanoporous polymer templates.
(2011-03) Ramkrishnan, Aruna
The project goal is to achieve confined synthesis of zeolites in nanoporous polymers. Different research directions have been explored towards this goal in terms of both choice of a suitable polymer template and choice of a suitable zeolite synthesis method, until the correct conditions for confined synthesis of zeolite in nanoporous polymers were found. The main contributions of this body of work are: (i) The stability of polymer thin films has been studied under zeolite synthesis conditions and the formation of sub-monolayers of a,b oriented Silicalite-1 crystals on a polymer thin film has been reported. (ii) Confined synthesis of disordered, mesoporous Silicalite-1 has been demonstrated in a nanoporous linear polyethylene template. (iii) Solvothermal synthesis methods have been explored using ethanol as a medium to synthesize Silicalite-1 for potential application to confined synthesis.
Confined Synthesis of zeolite particles: micro meso porous materials.
(2010-12) Wydra, James W.
Summary abstract not available.
Convective assembly of nanoparticles into thin structured films.
(2010-05) Lee, Jun Alexander
Convective nanoparticle film assembly is a process whereby particles from dilute liquid suspension assemble onto a substrate. Assembly occurs at the suspension-substrate-air contact line, where particles are carried toward it by convective currents set up in the meniscus region due to liquid evaporation. In the past, convectively assembled nanosphere films have been shown to be highly ordered. Convective assembly is initially explored as a potential method for the fabrication of ``tiled'' (uniformly oriented) nanocrystal films for application in zeolite membrane technology. It is found that films are generally assembled into jumbled multilayers, and that they are often nonuniform in coverage, sometimes leaving large areas of bare substrate in a banded pattern. Nevertheless, particles are shown quantitatively to be preferentially oriented, and some regions of the films do exhibit the desired ``tiled'' arrangement. A convective assembly apparatus is introduced as an experimental platform for further investigation of the method as a practicable one for large-scale production of thin particle films in general, and zeolite membrane precursor films in particular. The apparatus performance and final film characteristics are explored using a model silica nanosphere system. Monolayer film assembly turns out to be possible but difficult, with discrete banded film patterns being common in both sub-monolayer and super-monolayer films. The regularity and repeatability of these banded films are, however, very high. The wavelength of the banded film patterns (specifically, inter-band spacing) are shown to be strongly dependent on particle size in sub-monolayer films. The relationship is investigated by experiment, and modeled using a simple geometric exclusion argument based on the liquid meniscus profile described by the Young-Laplace equation. The model implies that band wavelength should also be dependent on the thickness of the films in super-monolayer films. The above model makes unrealistic assumptions about the liquid meniscus during convective assembly, namely that the system is static. Thus, the final topic is to attempt an extension of the model by including liquid flow. This quantitatively refines the meniscus geometry and allows a wider range of predictions of band spacing, although it seems to be far from the last word on modeling the banding phenomenon.
Cure induced stress generation and viscoelasticity in polymer coatings.
(2010-01) O’Neal, Daniel Jeffrey
Coatings solidified by free-radical polymerization and crosslinking (curing) reactions initiated with ultraviolet (UV) light do so quickly and at room temperature. Low viscosity monomer or oligiomer makes the use of volatile solvent unnecessary, decreasing energy use and making the process more environmentally friendly but photoinitiators can be toxic, limiting certain applications. Stress may be generated by a changing specific volume during cure, and stress-induced defects are undesirable. The goal of this research is to understand stress generation in UV irradiated coatings and to model stress generation and viscoelasticity seen during curing. Two new mathematical models were created to accomplish viscoelastic stress modeling. The first, a network model, uses a two-dimensional network of one-dimensional elements to replicate deformation in the coating. The second uses continuum momentum conservation and linear viscoelastic equations. Inertial forces can be neglected and a substitution performed, making the solution more rapid and simple with standard finite element methods. Stress generation in uniformly cured coatings depends on how quickly the specific volume and physical properties change. Reaction kinetics, volume, and stress are calculated simultaneously. Rapid initiation from high initiator concentration or UV light intensity delays volume change, generating more stress because the volume changes with a higher modulus. An optimum curing schedule would insure the actual specific volume and its equilibrium value remain the same. Inhomogeneities in the substrate or the presence of defects change the stress field. Knowing forces on the coating boundaries suggests defect locations and types. Probing the types of geometries and surface roughnesses seen in different types of coatings shows that restricted deformation increases stress concentrations and surface forces seen. Also, avenues for reducing stress via relaxation are discussed. The two-dimensional stress profiles used in these analyses are not possible to measure experimentally, making computational modeling essential. The models developed and methodology presented may be extended to other UV cured coatings or to other methods of coating solidification. Process windows of allowable final conversion-stress-energy-time states suggest what tradeoffs must be made to meet constraints.

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