Engineering Commons^™

Synthesis Of Zeolites With Controlled Defects By Understanding The Role Of Charge Balance In Zeolite Crystallization, Song Luo

Doctoral Dissertations

Zeolites are well-defined and ordered microporous crystalline materials constructed by the continuous linkage of corner sharing TO4 tetrahedra (taking T atoms (e.g., Si or Al) as the tetrahedral center). Due to the structural and compositional diversities and superior hydrothermal stability, zeolites have been broadly utilized to many industrial fields, including gas separation and catalysis heterogeneous catalysis. However, understanding zeolite crystallization mechanisms remains a tantalizing challenge, which causes challenges in tailoring this material for advanced applications. Raman spectroscopy has emerged as a powerful tool for probing medium-range (0.35 - 1 nm) structures. Since this scale is consistent with the micropore size …

Investigation Of The Thermodynamics Of Iron Phosphate Melts And Stability Of Iron Phosphate Glasses: Effects Of Composition And Iron Redox Ratio, Melodie Linda Schmitt

Doctoral Dissertations

“Iron phosphate glasses with Fe/P = 0.33 - 0.67, O/P = 3.0 - 3.5 and Fe²⁺/ΣFe = 0.16- 0.52 were prepared by altering batch compositions and melt conditions. Thermal analyses indicate polyphosphate glasses with intermediate chain lengths are most stable against devitrification. Heterogeneous crystallization occurs on the glass surface and is dependent on iron valence state, particle size, heating rate, temperature and oxygen availability in the atmosphere. Oxidation of ferrous iron on the glass surface occurs at temperatures as low as Tg, and thus crystallization behavior and stability can be altered via post-melt heat treatments. A novel preparation …

Perovskite Thin Films Annealed In Supercritical Fluids For Efficient Solar Cells, Gilbert Annohene

Theses and Dissertations

In the field of photovoltaics, scientists and researchers are working fervently to produce a combination of efficient, stable, low cost and scalable devices. Methylammonium lead trihalide perovskite has attracted intense interest due to its high photovoltaic performance, low cost, and ease of manufacture. Their high absorption coefficient, tunable bandgap, low-temperature processing, and abundant elemental constituent provide innumerable advantages over other thin film absorber materials. Since the perovskite film is the most important in the device, morphology, crystallization, compositional and interface engineering have been explored to boost its performance and stability. High temperatures necessary for crystallization of organic-inorganic hybrid perovskite films …

Tuning Degradation And Cell Adhesion In Next Generation Resorbable Implants, Ufuomaroghene Ikoba

USF Tampa Graduate Theses and Dissertations

Osteoarthritic and bone degenerative diseases are expected to grow immensely as the aging population, 65 years and older increases. Orthopedic implants are one sub-class of medical devices that are used to treat bone breaks and fractures. Traditionally, internal fixation implants are manufactured using titanium or stainless steel. Magnesium, a bioresorbable and biodegradable material, has been proposed as an alternative to titanium and stainless steel. The goal of this research is to control the degradation behavior of magnesium implants by developing crystallized thin poly(lactic acid) copolymer films as protective coatings. To do this, this work was divided into two aims. Aim …

High-Pressure Studies On The Transition From Red Phosphorus To Black Phosphorus, Heng Xiang

Electronic Thesis and Dissertation Repository

Black phosphorus (BP) is a promising material in many research fields. However, the transition process from amorphous red phosphorus (ARP) is elusive and hence hinders large scale synthesis and applications. This work describes the application of the high-pressure method to study the transition process from ARP to BP.

In this thesis, the following three objectives were achieved: (1) to understand the mechanism of the transition, (2) to facilitate the synthesis of BP by taking the advantage of less pure ARP, (3) to propose new methods of synthesizing BP-based materials, such as the moderately oxidized BP and the black phosphorus/ amorphous …

The Role Of Chain Configuration In Governing The Rational Design Of Polymers For Adhesion, Onyenkachi Wamuo

Doctoral Dissertations

ABSTRACT THE ROLE OF CHAIN CONFIGURATION IN GOVERNING THE RATIONAL DESIGN OF POLYMERS FOR ADHESION SEPTEMBER 2017 ONYENKACHI C. WAMUO, B.Eng., FEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI (FUTO), NIGERIA M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Shaw Ling Hsu The chain configurational control of polymers used in adhesion can be utilized as a means of tuning the cohesive properties of hot melt adhesives (HMAs). The cohesive properties control the solidification, strength, setting speed. Propylene-Ethylene copolymers (PP-co-PE) and thermoplastic polyurethanes (TPUs) were studied. In the first project, the effects of sequence distribution of the two types …

End-Capping Star-Like Polycaprolactone With Different Functional Groups And The Interaction With Smooth Muscle Cells, Qingya Zeng

Masters Theses

Polycaprolactone (PCL) is a PDA-approved biodegradable polymer with excellent biocompatibility and flexibility. My work has been designed to find out how different functional end groups in star-like PCL samples affect the surface properties (such as hydrophilicity, morphology) and bulk properties (such as thermal, mechanical, rheological properties, and crystallization), and consequently the behavior and functions of primary rat aortic smooth muscle cells (SMCs).

I focused on the synthesis of PCL with different functional groups and their characterizations. In chapter 2, PCL samples with four or six hydroxyl end groups were synthesized with different molecular weights ranging from 8,000 to 30,000 g/mol …

Mold Flux Crystallization And Mold Thermal Behavior, Elizabeth Irene Peterson

Masters Theses

"Mold flux plays a small but critical role in the continuous casting of steel. The carbon-coated powder is added at the top of the water-cooled copper mold, over time it melts and infiltrates the gap between the copper mold and the solidifying steel strand. Mold powders serve five primary functions: (1) chemical insulation, (2) thermal insulation, (3)lubrication between the steel strand and mold, (4) absorption of inclusions, and (5)promotion of even heat flux. All five functions are critical to slab casting, but surface defect prevention is primarily controlled through even heat flux. Glassy fluxes have high heat transfer and result …

Solution, Interfacial, And Interlayer Studies Of Electronically Active Polymers, Hsin-Wei Wang

Doctoral Dissertations

This thesis describes the solution behavior and interfacial properties of electronically active polymers. The performance of such polymers in devices is often determined by their chain conformation and morphology in solution and in thin films. For example, the intricate balance between polymer domain size and crystalline packing of electron donor and acceptor components, as well as the properties at the polymer-metal interface, are crucial for achieving optimal performance in devices, such as solar cells. Chapter 1 presents the current progress in polymer-based solar cells, their fundamental principles, and key factors to improve their efficiency. Literature precedents on the development of …

Process-Structure-Property Relationship In Ultra High Molecular Weight Polytetrafluoroethylene And Double Network Epoxies, Ranadip Ganguly

Doctoral Dissertations

The focus of this dissertation is to develop a fundamental understanding of process-structure-property relationship in two different classes of polymers: semi-crystalline Ultra High Molecular Weight Polytetrafluoroethylene (UHMWPTFE) and amorphous glassy double network (DN) epoxies. Conventional melt processing techniques such as extrusion and injection molding cannot be applied to UHMWPTFE due to its very high melt viscosity (10¹⁰-10¹¹ poise). Therefore, UHMWPTFE is industrially processed by a modified metallurgy technology-sintering. However, the fundamental mechanism for UHMWPTFE sintering is unknown. Further, this process is highly time consuming, cost inefficient and hinders the recyclability of the material. The first part of …

On The Morphology Of Polymer-Based Solar Cells To Achieve Higher Device Performance, Yu Gu

Doctoral Dissertations

It has been recognized that the morphology of the active layer of the polymer-based solar cells has a great influence on the device performance. To push the efficiency to a higher level, morphology design and control by varying processing conditions are crucial. The theme of this dissertation is to characterize and understanding of the morphology of the active layer of polymer-based solar cells and the role that the morphology plays on device performance, so as to develop routes by which the morphology can be optimized. The focus of this dissertation is first on a binary system consisting of poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) …

Effects Of Molecular Architecture On Crystallization Behavior Of Pol(Lactic Acid) And Ethylene-Vinyl Acetate, Jeffrey Paul Kalish

Open Access Dissertations

The relationship between polymer chain architecture, crystallization behavior, and morphology formation was investigated. The structures formed are highly dependent on chain configuration and crystallization kinetics. Poly(lactic acid) (PLA) and Poly(ethylene-co-vinyl acetate) (EVA) random copolymers were studied. Sample characterization was performed using a variety of techniques, including spectroscopy, scattering, and calorimetry. In PLA, structural differences between α’ and α crystalline phases were analyzed using cryogenic infrared and Raman spectroscopy. Compared to the  crystal, the ’ crystal has slightly looser packing and weaker intermolecular interactions involving carbonyl and methyl functional groups. Simulations in conjunction with Raman scattering analyzed the …

A Study Of Metallic Eutectics, Robert P. Corbett

Bachelors Theses and Reports, 1928 - 1970

All of the metals have definite melting points. When a metal is heated above the melting point, it exists as a liquid. Now if the melt is allowed to cool, it will solidify when a temperature corresponding to the melting point is reached.

However, if one metal is added to another metal, both of which are mutually soluble in the liquid state, a certain effect can be noted. The melt will not solid­ify when the melting point of the pure metal is reached, but will freeze at a lower temperature.