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University of Massachusetts Amherst

Chemical Engineering

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Full-Text Articles in Engineering Science and Materials

Frontiers In The Self-Assembly Of Charged Macromolecules, Khatcher O. Margossian Oct 2022

Frontiers In The Self-Assembly Of Charged Macromolecules, Khatcher O. Margossian

Doctoral Dissertations

The self-assembly of charged macromolecules forms the basis of all life on earth. From the synthesis and replication of nucleic acids, to the association of DNA to chromatin, to the targeting of RNA to various cellular compartments, to the astonishingly consistent folding of proteins, all life depends on the physics of the organization and dynamics of charged polymers. In this dissertation, I address several of the newest challenges in the assembly of these types of materials. First, I describe the exciting new physics of the complexation between polyzwitterions and polyelectrolytes. These materials open new questions and possibilities within the context …

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Experimental Study Of Viscoelastic Fluid-Structure Interactions, Anita Anup Dey Dec 2020

Experimental Study Of Viscoelastic Fluid-Structure Interactions, Anita Anup Dey

Doctoral Dissertations

It is well known that when a flexible or flexibly-mounted structure is placed perpendicular to a Newtonian fluid flow, it can oscillate due to the shedding of vortices at high Reynolds numbers. Unlike Newtonian fluids, viscoelastic fluid flow can become unstable even at infinitesimal Reynolds numbers due to a purely elastic flow instability occurring at large Weissenberg numbers. This thesis focuses on exploring the mechanisms of viscoelastic fluid-structure interactions (VFSI) through experimental investigations on several different combinations of flexible and flexibly-mounted circular cylinders, micro and macro-scale cantilevered beams and viscoelastic fluids such as wormlike micelle solutions and polymer solutions. VFSI …

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The Effect Of Oxygen On Properties Of Zirconium Metal, Jie Zhao Mar 2020

The Effect Of Oxygen On Properties Of Zirconium Metal, Jie Zhao

Doctoral Dissertations

The influence of oxygen on the thermophysical properties of zirconium has been investigated using MSL-EML (Material Science Laboratory Electromagnetic Levitator) on ISS (International Space Station) in collaboration with NASA (National Aeronautics and Space Administration), ESA (European Space Agency), and DLR (German Aerospace Center). Zirconium samples with different oxygen concentrations was subjected to multiple melt cycles during which the thermophysical properties, such as density, viscosity and surface tension, have been measured at various undercooled and superheated temperatures. Also, there are melt cycles for verifying the solidification mechanism. Similar samples were found to show anomalous nucleation of the solid for certain ranges …

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Modeling And Simulation Of Driven Nanopatterning Of Bulk-Material And Thin-Film Surfaces, Ashish Kumar Oct 2019

Modeling And Simulation Of Driven Nanopatterning Of Bulk-Material And Thin-Film Surfaces, Ashish Kumar

Doctoral Dissertations

Material nanostructures such as nanowires, quantum dots, and nanorings have a wide variety of applications in electronic and photonic devices among numerous others. Assembling uniformly arranged and consistently sized nanostructure patterns on solid material surfaces is a major challenge for nanotechnology. This dissertation focuses on developing predictive models capable of simulation and analysis of such nanopattern formation on bulk material and strained thin film surfaces. Single-layer atomic clusters (islands) of sizes larger than a critical size on crystalline conducting substrates undergo morphological instabilities when driven by an externally applied electric field or thermal gradient. We have conducted a systematic and …

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Polymeric Impulsive Actuation Mechanisms: Development, Characterization, And Modeling, Yongjin Kim Oct 2019

Polymeric Impulsive Actuation Mechanisms: Development, Characterization, And Modeling, Yongjin Kim

Doctoral Dissertations

Recent advances in the field of biomedical and life-sciences are increasingly demanding more life-like actuation with higher degrees of freedom in motion at small scales. Many researchers have developed various solutions to satisfy these emerging requirements. In many cases, new solutions are made possible with the development of novel polymeric actuators. Advances in polymeric actuation not only addressed problems concerning low degree of freedom in motion, large system size, and bio-incompatibility associated with conventional actuators, but also led to the discovery of novel applications, which were previously unattainable with conventional engineered systems. This dissertation focuses on developing novel actuation mechanisms …

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Computational Studies Of Structure–Function Relationships Of Supported And Unsupported Metal Nanoclusters, Hongbo Shi Nov 2017

Computational Studies Of Structure–Function Relationships Of Supported And Unsupported Metal Nanoclusters, Hongbo Shi

Doctoral Dissertations

Fuel cells have been demonstrated to be promising power generation devices to address the current global energy and environmental challenges. One of the many barriers to commercialization is the cost of precious catalysts needed to achieve sufficient power output. Platinum-based materials play an important role as electrocatalysts in energy conversion technologies. In order to improve catalytic efficiency and facilitate rational design and development of new catalysts, structure–function relationships that underpin catalytic activity must be understood at a fundamental level. First, we present a systematic analysis of CO adsorption on Pt nanoclusters in the 0.2-1.5 nm size range with the aim …

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Analyses Of Densely Crosslinked Phenolic Systems Using Low Field Nmr, Jigneshkumar Patel Nov 2017

Analyses Of Densely Crosslinked Phenolic Systems Using Low Field Nmr, Jigneshkumar Patel

Doctoral Dissertations

A uniform dispersion of reactants is necessary to achieve a complete reaction involving multi-components, especially for the crosslinking of rigid high-performance materials. In these reactions, miscibility is crucial for curing efficiency. This miscibility is typically enhanced by adding a third component, a plasticizer. For the reaction of the highly crystalline crosslinking agent hexamethylenetetramine (HMTA) with a strongly hydrogen-bonded phenol formaldehyde resin, furfural has been traditionally used as the plasticizer. However, the reason for its effectiveness is not clear. In this doctoral thesis work, miscibility and crosslinking efficiency of plasticizers in phenolic curing reactions are studied by thermal analysis and spectroscopic …

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Deformation And Adhesion Of Soft Composite Systems For Bio-Inspired Adhesives And Wrinkled Surface Fabrication, Michael Imburgia Mar 2017

Deformation And Adhesion Of Soft Composite Systems For Bio-Inspired Adhesives And Wrinkled Surface Fabrication, Michael Imburgia

Doctoral Dissertations

The study of soft material deformation and adhesion has broad applicability to industries ranging from automobile tires to medical prosthetics and implants. When a mechanical load is imposed on a soft material system, a variety of issues can arise, including non-linear deformations at interfaces between soft and rigid components. The work presented in this dissertation embraces the occurrence of these non-linear deformations, leading to the design of functional systems that incorporate a soft elastomer layer with application to bio-inspired adhesives and wrinkled surface fabrication. Understanding the deformation of a soft elastomer layer and how the system loading and geometry influence …

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Integrated Solar Technologies With Outdoor Pedestrian Bridge Superstructure Decking, Richard K. Racz Mar 2016

Integrated Solar Technologies With Outdoor Pedestrian Bridge Superstructure Decking, Richard K. Racz

Masters Theses

Solar technology has been a major topic in sustainable design for many years. In the last five years, however, the solar technology industry has seen a rapid growth in installations and technological advances in cell design. Combined with a rapidly declining overall system cost, the idea of introducing solar technology into a wider range of applications is becoming a focus for engineers and scientists around the world. So many variables which alter solar energy production, such as the sun and surrounding environment, determine whether a solar design is beneficial. This thesis presents a bridge deck surface integrated with solar cells …

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Mimicking The Arterial Microenvironment With Peg-Pc To Investigate The Roles Of Physicochemical Stimuli In Smc Phenotype And Behavior, William G. Herrick Aug 2015

Mimicking The Arterial Microenvironment With Peg-Pc To Investigate The Roles Of Physicochemical Stimuli In Smc Phenotype And Behavior, William G. Herrick

Doctoral Dissertations

The goal of this dissertation was to parse the roles of physical, mechanical and chemical cues in the phenotype plasticity of smooth muscle cells (SMCs) in atherosclerosis. We first developed and characterized a novel synthetic hydrogel with desirable traits for studying mechanotransduction in vitro. This hydrogel, PEG-PC, is a co-polymer of poly(ethylene glycol) and phosphorylcholine with an incredible range of Young’s moduli (~1 kPa - 9 MPa) that enables reproduction of nearly any tissue stiffness, exceptional optical and anti-fouling properties, and support for covalent attachment of extracellular matrix (ECM) proteins. To our knowledge, this combination of mechanical range, low …

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