Engineering Commons^™

Modeling Chemical Degradation And Proton Transport In Perfluorosulfonic Acid Ionomers, Milan Kumar

Doctoral Dissertations

The ionomer-membrane interface in a membrane electrode assembly connects the catalyst and membrane and allows hydrated protons to move between the catalyst and membrane. The continuous operation of the polymer membrane electrolyte fuel cell at high temperature and/or in frequent freeze/thaw cycles leads to membrane degradation and delamination of the interface, which lower the proton conductivity. In this dissertation, we modeled the chemical degradation and proton conductivity of perfluorosulfonic acid (PFSA) ionomers by ab initio calculations and macroscopic modeling. All ab initio calculations were performed using Gaussian 03 suites of program by employing B3LYP/6-311++G** method/basis set. The macroscopic modeling involves …

Computational Studies Of Ion Transport In Polymer Electrolytes, Hui Wu

Doctoral Dissertations

Improving ionic conductivity and lithium mobility in polymer electrolytes is important for their practical use for battery electrolytes. In this study, a combination of molecular dynamics and Monte Carlo simulations was used to bring insight into lithium ion transport in poly(ethylene oxide) (PEO) with plasticizers and also next to alumina solid surface doped with lithium salt. The simulations were performed using a moderately high molecular weight polymer (Mn = 10,000 g/mol) at an EO:Li ratio of 15. For the plasticized system, the PEO with LiN(CF3SO 2)2 (LiTFSI) was mixed with 10 wt% plasticizers that included either cyclic ethylene carbonate …

Role Of Ammonia In The Activiation Of Methanol Dehydrogenase/Cytochrome C(L) Enzyme, Ancy Kunjumon

Doctoral Dissertations

Recent advancement in enzyme catalysis has opened ways to design efficient biocatalysts, bio-sensors and bio-fuel cells. An in-depth knowledge about the mechanism of the reaction taking place within the enzymes is of great importance to achieve these goals. In this dissertation, various computation methods are applied to investigate the mechanism behind enzyme catalysis in the presence of compounds called activators.

Methanol dehydrogenase (MDH) is a well-known bio-catalyst that can oxidize excess of methanol from the environment to formaldehyde. The enzyme works well within the bacterial environment, but under in vitro, it loses activity. Ammonia is used as an activator …

Bioreactor System Designs For Lipase-Catalyzed Synthesis Of Saccharide- Fatty Acid Esters In Solvent-Free Media, Ran Ye

Doctoral Dissertations

As nontoxic biobased surfactants derived from plant oils and cellulose or starch, saccharide-fatty acid esters are widely used in cosmetics, food, and pharmaceutical industries due to their biocompatibility, biodegradability as well as antimicrobial activity. Generally, saccharide-fatty acid esters are synthesized chemically under high pressure, temperature and the presence of alkaline or acid catalysts leading to low-quality products (chemo-degradation of double bonds and oxygenated moieties) and large amounts of byproducts. In contrast, biocatalytic synthesis enhances sustainability: near-ambient pressure and temperature, the absence of toxic, acids and bases catalysts, and improved selectivity of products. For lipase-catalyzed synthesis under nearly anhydrous conditions, the …

Dynamics Of Polymeric Solutions In Complex Kinematics Bulk And Free Surface Flows: Multiscale/Continuum Simulations And Experimental Studies, Arash Abedijaberi

Doctoral Dissertations

While rheological and microstructural complexities have posed tremendous challenges to researchers in developing first principles models and simulation techniques that can accurately and robustly predict the dynamical behaviour of polymeric flows, the past two decades have offered several significant advances towards accomplishing this goal. These accomplishments include: (1). Stable and accurate formulation of continuum-level viscoelastic constitutive models and their efficient implementation using operator splitting methods to explore steady and transient flows in complex geometries, (2). Prediction of rheology of polymer solutions and melts based on micromechanical models as well as highly parallel self-consistent multiscale simulations of non-homogeneous flows. The main …

Multi-Scale Modeling Of Polymeric Materials: An Atomistic And Coarse-Grained Molecular Dynamics Study, Qifei Wang

Doctoral Dissertations

Computational study of the structural, thermodynamic and transport properties of polymeric materials at equilibrium requires multi-scale modeling techniques due to processes occurring across a broad spectrum of time and length scales. Classical molecular-level simulation, such as Molecular Dynamics (MD), has proved very useful in the study of polymeric oligomers or short chains. However, there is a strong, nonlinear dependence of relaxation time with respect to chain length that requires the use of less computationally demanding techniques to describe the behavior of longer chains. As one of the mesoscale modeling techniques, Coarse-grained (CG) procedure has been developed recently to extend the …

Investigation Of Hydrodynamic Scaling Relationships In Shallow Spouted Beds, Irma Deytia Lima Rojas

Doctoral Dissertations

Important global hydrodynamic relationships for shallow spouted beds of high-density particles were characterized in terms of three features: minimum spouting velocity, overall bed pressure drop at minimum spouting velocity; and fountain height. Spouted bed literature is sparse for shallow beds (static particle depth to bed diameter ≤ 1) and beds with heavy particles (density > 3000 kg/m³). Correlations for such beds were developed here by varying column diameter, static bed height, particle diameter, particle density, gas density and gas flow in an ambient temperature and pressure bed.

The degree of correlation between each of the observed hydrodynamic features and …

Protein Engineering For The Enhanced Photo-Production Of Hydrogen By Cyanobacterial Photosystem I, Ifeyinwa Jane Iwuchukwu

Doctoral Dissertations

Photosystem I (PSI) from plants, algae, and cyanobacteria can mediate H2 evolution in vivo and in vitro. A simple, self-platinization procedure that permits stable PSI-mediated H2 evolution in vitro has been developed. The H2 evolution capabilities of PSI from Thermosynechococcus elongatus have been characterized. This organism utilizes cytochrome c6 (cyt c6) as the e- donor to P700. Using a solution-based, self-organized platinization of the PSI nanoparticles, this study demonstrates a sodium ascorbate-cyt-PSI-Pt-H2 electron transport and proton reduction system that yields light-dependent H2. The system was thermostable with H2 evolution increasing up to 55°C. In addition, stability studies have shown the …

Roles Of Non-Thermal Plasma In Gas-Phase Glycerol Dehydration Catalyzed By Supported Silicotungstic Acid, Lu Liu

Doctoral Dissertations

Acrolein is an indispensable chemical intermediate with a rising demand in recent years. The concern of the increase of propylene prices due to the shrinking supply of nonrenewable crude oil makes the acid-catalyzed gas-phase glycerol dehydration to acrolein a prime candidate for research. Our analysis showed that the sustainable acrolein production from glycerol was both technically and economically viable. Alumina2700^® (Al) and Silica1252^® (Si) loaded with silicotungstic acid (HSiW) possessed distinct features while provided equally good acrolein yield (73.86mol% and 74.05mol%, respectively) optimally.

Due to the unique non-equilibrium characteristics, non-thermal plasma (NTP) could promote a variety of chemical …

Investigation Of Microbubble/Droplet Formation In Cross-Flow And Co-Flow Micro Devices, Tom J. John

Doctoral Dissertations

The primary goal of the work presented in this dissertation is to generate microbubbles of a diameter of less than 15μm inside micro channels. In order to achieve this detailed understanding, the facts and limitations behind the generation of microbubbles inside a micro channel are determined from existing literature. The major limitations of the current bubble/droplet generators are found to be the bubble confinement effect, the merging of bubbles, the difficulty in determining bubble diameter and the need for smaller channels to generate smaller bubbles. A device eliminating these drawbacks is conceptualized, and its feasibility is studied using COMSOL® and …

Surface Modification Of Micro-Fluidic Devices, Zhan Gao

Doctoral Dissertations

"The surface modification, fabrication and characterization of microfluidic sensor systems for oxygen and glucose measurements with the use of polymeric materials were investigated in this dissertation. This dissertation is prepared in publication format. The first manuscript focuses on the surface modification of SU -8 layer to enhance the wettability. The improvement of wettability is critical since biofouling can be minimized during bioanalysis. A novel in situ photopattemable grafting technology was used to attach biocompatible polymer layers on SU-8 surface, changing its property from hydrophobicity to hydrophilicity. The results were confirmed by contact angle measurement and Fourier Transform Infrared (FTIR) spectra. …

Enhanced Heavy Oil Recovery By Alkali-Surfactant In The Pennsylvania Warner Sandstone, Rabia Mohamed Hunky

Doctoral Dissertations

"In this research, a study of the non-thermal method of alkaline-surfactant (AS) flooding to enhance heavy oil recovery from the Pennsylvanian Warner sandstone reservoir in Western Missouri was conducted. This work includ [sic] testing approximately 30 commercial surfactants and using a heavy oil sample with an API of 17. It was found that a number of surfactants could create stable emulsions. The viscosity of heavy oil could be reduced from 18,518 cp to 2.5 cp at 25⁰C through emulsification of certain surfactants. One of the major findings was that the emulsion created by the commercial surfactant, Igepalʼ CO-530 was stable …

Strength Adjustable Preformed Particle Gels For Conformance Control, Jia Zhou

Doctoral Dissertations

"Reservoir heterogeneity and early water breakthrough (also known as fingering) represent two of the greatest challenges to recover crude oil efficiently. Gel treatments have been implemented as a cost-effective method to plug high permeability zones and thus improve sweep efficiency in reservoirs. However, when extensive cross-flows exist between formation layers, gel treatments become less efficient. Polymer was used in polymer flooding to increase the viscosity of the injected fluids and to correct the fingering problem. However, such treatment may be uneconomical since dramatic viscosity loss (80-90%) is caused by shearing degradation during the injection process near the wellbore.

This research …

Biodegradable Polymer/Clay Nanocomposites Based On Poly(Butylene Adipate-Co-Terephthalate) And Polylactide, Mahin Shahlari

Doctoral Dissertations

"In offering a scientifically succinct methodology which leads to property-enhanced biodegradable polymer products for broader application, as well as in promoting the use of bio-sourced renewable polymers such as Polylactide (PLA) in biodegradable polymers with desirable properties from petroleum based polymers such as PBAT, this study and its results both directly and indirectly contribute to the technological solutions that address growing environmental and energy problems caused by the increased use of and reliance upon nondegradable, nonrenewable, petroleum-based plastics. This work studied blends of PBAT and PLA compounded with organoclay through direct melt mixing in a twin-screw extruder and a batch …

Effect Of Hydrophobicity And Surface Roughness On Two-Phase Flow In Rectangular Microchannels, Gautham C. Unni

Doctoral Dissertations

"Two-phase flows in microchannels have received significant attention recently, and have become the cornerstone of numerous microfluidic devices. Microscale devices used for bioengineering applications, oil recovery, and chemical and catalytic microreactor applications involve the transport of bubbles in confined fluidic networks in channels of micrometer length scale. These types of two-phase flows result in pressure variations, leading to an overall increase in pressure drop. Among various flow parameters, pressure drop is extensively used in design of microfluidic devices. There are several parameters that affect the pressure drop across two-phase flow in microchannels. In the present study, the goal is to …