Engineering Science and Materials Commons^™

Encapsulation And Culture Of Plant Protoplasts In Hydrogel Microspheres Using Droplet Microfluidics, Matthew Grasso

Graduate College Dissertations and Theses

Plant morphogenesis requires the coordinated growth between cells and their neighbors. This coordination is regulated by internal and external signals that are both physical and chemical. It is understood that both mechanical and molecular signals are involved in the regulation of plant morphogenesis however, how mechanical signals induce molecular signals and vice versa is not. This is due to a lack of research tools for manipulating and measuring the mechanical environment of growing plant cells. Such tools would ideally provide individual plant cells with mechanically tunable physical microenvironments. This may allow changes in the cells physical environment to be linked …

Atomic-Scale Analysis Of Solute Segregation Energy Into Grain Boundaries And Polycrystals, Tara Nenninger

Graduate College Dissertations and Theses

Solute segregation in grain boundaries (GBs) is used in design to stabilize nanocrystalline alloys. While analyzing GB segregation energy as a spectrum allows for a more in-depth analysis of the effects of GB atomic structure on solute segregation, this method inherently ignores solute-solute interaction by nature of considering one solute at a time. Here we develop an efficient molecular statics (MS) algorithm for determining the local effect of solute-solute interaction on GB segregation. We apply this algorithm to a Σ9 (221) symmetric tilt grain boundary in a bicrystal as well as a randomly oriented polycrystal for Ni and Cu solutes …

Strain-Enhanced Coherent Exciton-Polaron States In 1d Phthalocyanine Crystalline Thin Films, Libin Liang

Graduate College Dissertations and Theses

Organic semiconductors are at the forefront of materials research, due to their desired electric and mechanical properties. They offer the unique opportunity to modify material properties during synthesis process, opening an avenue to the development of novel flexible and wearable electronic and photonic devices.Molecular excitons are of importance in organic semiconductor properties. While majority of research studies are centered on achieving good control of amorphous or polycrystalline thin film properties, the static disorder effect leads to poor device performance when compared to inorganic semiconductors with superior crystalline ordering. On the other hand, the macroscopic molecular long-range ordering can enhance device …

Tuning Electroluminescence From Resonators Based On Fabry-Pérot Microcavity Oleds, Ekraj Dahal

Graduate College Dissertations and Theses

This thesis comprises a series of methods for controlling the electroluminescence from Fabry-Pérot microcavity OLEDs by varying the resonator geometry and the location of the organic emitter within the resonator. In pursuit of this thesis, I conducted three experimental projects backed by theoretical modeling. First the thickness of the microcavity was varied to observe changes in resonant state wavelength, linewidth of the states, angular dispersion, and polarization splitting. The resulting electroluminescence can be tuned to span the entire color gamut using a single green chromophore. Electroluminescence of this green chromophore was used to pump the optical states of nominally identical …

Atomistic Simulation Study Of Nickel Solute Segregation And Mechanical Behavior In Nanocrystalline Fcc, Bcc And Hcp Binary Alloys, Eve-Audrey Picard

Graduate College Dissertations and Theses

Nanocrystalline metals and alloys have been proven to possess unprecedentedly higher tensile strength than coarse-grained conventional metals. The extreme grain refinement in nanocrystalline metals, however, negatively affects these materials by reducing their ductility through grain-boundary embrittlement and shear localization mechanisms that are promoted by segregation of solute atoms to the interfaces. Different segregation behaviors described in the literature can be divided into either heterogeneous or homogeneous types. Yet current understanding of the impact of solute atom arrangements within grain boundary networks on mechanical properties of cubic and hexagonal nanocrystals remains limited. In this thesis, hybrid Monte-Carlo and molecular dynamics simulations …

Quantum Simulations Of Low Dimensional Systems And Analytic Continuation Of Imaginary Time Correlation Functions, Nathan Scott Nichols

Graduate College Dissertations and Theses

For over thirty years, a long standing problem in quantum many-body physics has been to reliably extract dynamical information from imaginary time quantum Monte Carlo data. I report on a new method developed using modern evolutionary computation routines to approach this notoriously ill-posed problem. Motivation towards a solution will be presented as a brief summary of work on quantum simulations of low dimensional systems including helium on strained graphene and helium confined within rare gas plated mesoporous silica. The Differential Evolution for Analytic Continuation (DEAC) algorithm reconstructs the dynamic structure factor from imaginary time density-density correlations at zero and finite …

Nonlinear Impedance Spectroscopy To Characterize Hole Transport And Recombination Dynamics In Organic Semiconductor Devices, Robin Rice

Graduate College Dissertations and Theses

Impedance Spectroscopy (IS) is an increasingly common technique to characterize both solid state and electrochemical systems including solar cells and light emitting diodes (LEDs). However, IS relies on a system response being linear with its input such that a time invariant impedance can be defined. This is usually achieved by a small amplitude input. However, doing so suppresses responses of the nonlinear processes which are of considerable interest to those designing and optimizing these devices, such as charge carrier recombination and space charge effects. This investigation employs the recently developed nonlinear extension to IS (NLIS) based in Fourier analysis of …

Strengthening Mechanisms In Nanocrystalline Silver-Nickel Nanolayered Materials, Malcolm Ryan Pringle

Graduate College Dissertations and Theses

Among all metals, silver has the highest electrical conductivity but also is one of the softest materials under mechanical deformation. Therefore, developing means and methods for strengthening silver without reducing conductivity is critically important for its use as a conductive electrode material in various engineering applications such as solar cells and touchscreen displays. This thesis presents a molecular-dynamics simulation study of strengthening mechanisms by intercalating nanocrystalline silver films with amorphous nickel layers, characterizing the structure of nanolayered material prototypes obtained by sputtering deposition technique. The objectives of the thesis are three-fold: To study the effects of Ni layer thickness and …

Transient Effects In Solution-Processed Organic Thin Films, Jing Wan

Graduate College Dissertations and Theses

Due to the weak van der Waals forces between organic semiconductor molecules, the molecular packing depends sensitively on the processing methods and conditions. Thus, understanding the crystallization mechanisms during solution deposition are essential for fundamental studies and reproducible fabrication of electronic devices.The performance of Organic field effect transistors (OFETs) also depends heavily on extrinsic factors such as contact resistance and interfacial defects, which can produce a different kind of transient effect at the metal-semiconductor contact. We have observed structural transient effects during the crystallization process of two small molecule organic semiconductors made from solution. We report in situ X-ray scattering …

Enhancement Of Charge Transfer In Thermally-Expanded And Strain-Stabilized Tips-Pentacene Thin Films, Yang Li

Graduate College Dissertations and Theses

Two of the most critical experimentally accessible properties of small-molecule organic semiconductor materials are the charge carrier mobility, which probes charge transport, and the optical absorption spectrum which probes the energy levels of excited states. The impact of molecular packing on the optical and charge transport properties are often treated separately. However, these effects are actually linked at a fundamental level, and it is of interest to understand the interrelationship between them, as well as how they respond to strain and thermal expansion. In this thesis, we highlight the fundamental relationship between these two phenomena in 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene).

We present …

Exciton Coherence In 1d Phthalocyanine Based Organic Crystalline Thin Films, Kimngan Burrill

Graduate College Dissertations and Theses

Quantum coherence plays a vital role in the excitonic properties of organic semiconductors. Several theoretical and experimental studies have shown an unprecedented role of coherence in charge transfer and transport processes, which in turn can improve the performance of electronic devices. Specifically, an enhancement of exciton coherence size can result in fast energy transport and efficient charge separation. The ability to tailor the design and performance of organic electronics based on exciton coherence effects represents the possibility of ultrafast electronic applications in communication and information technology.

The objective of this thesis is the excitonic coherence studies of 1D crystalline thin …

Using Dielectric Characterization To Study Transport And Thermal Properties Of Gas/Supercritical Fluid Embedded Polymer Solution, Xiangxiao Yao

Graduate College Dissertations and Theses

Gas/supercritical fluid (SCF) and polymer mixtures are applied broadly in industry, such as rigid and light foam products for aircraft use, foamed cushion in chairs or shoes, and gas separation membranes for capturing methane from landfill gas. To understand the gas transport properties and polymer thermal properties of the mixture, we detected the dielectric properties of the mixture at two conditions and developed a novel self-designed system for high temperature and high pressure measurement.

The transport properties of physical blowing agents in polymers is viewed as a critical parameter controlling the final foam product’s foam density, cell density, and cell …

Experimental And Computational Studies Of Heat Transfer In Flexible Two-Dimensional Woven Fiber Ceramic Materials, Rodrigo Penide Fernandez

Graduate College Dissertations and Theses

Flexible thermal protection materials made from two-dimensional woven ceramics fibers are of significant interest for hypersonic inflatable aerodynamic decelerators being developed by NASA for future missions on Mars and other planets. A key component of the thermal shield is a heat-resistant outer ceramic fabric that must withstand harsh aero-thermal atmospheric entry conditions. However, a predictive understanding of heat conduction processes in complex woven-fiber ceramic materials under deformation is currently lacking. This dissertation presents a combined experimental and computational study of thermal conductivity in alumina-based Nextel-440 and silicon carbide Hi-Nicalon 5-harness-satin woven fabrics, using the hot-disk transient plane source method and …

Understanding Grain Boundary And Stress Concentration Effects On Strengthening Mechanisms In Nanotwinned Metals, Qiongjiali Fang

Graduate College Dissertations and Theses

The superior strength and large tensile plasticity of nanotwinned (nt) face-centered-cubic metals have been explained by different twin size-dependent dislocation mechanisms and their inherent strengthening/softening effects. Grain boundary (GB) plasticity generally induces softening in nanocrystalline metals; however, our current understanding of the role of GBs in plasticity of nt metals remains limited. Contradicting reports exist in literature on how twin size influences stress concentration at GB – twin boundary (TB) intersections, which facilitates dislocation nucleation. In this thesis, molecular dynamics (MD) simulations and finite element analysis (FEA) were used to study the effects of GB plasticity and stress concentrations, on …

Atomistic Simulation Studies Of Grain-Boundary Segregation And Strengthening Mechanisms In Nanocrystalline Nanotwinned Silver-Copper Alloys, Xing Ke

Graduate College Dissertations and Theses

Silver (Ag) is a precious metal with a low stacking fault energy that is known to form copious nanoscale coherent twin boundaries during magnetron sputtering synthesis. Nanotwinned Ag metals are potentially attractive for creating new interface-dominated nanomaterials with unprecedented mechanical and physical properties. Grain-boundary segregation of solute elements has been found to increase the stability of interfaces and hardness of nanocrystalline metals. However, heavily alloying inevitably complicates the underlying deformation mechanisms due to the hardening effects of solutes, or a change of stacking fault energies in Ag caused by alloying. For the above reasons, we developed a microalloying (or doping) …

Development And Characterization Of Multi-Crosslinking Injectable Hydrogels For Use In Cell And Drug Delivery, Jennifer Etter

Graduate College Dissertations and Theses

Injectable hydrogels are important for use in tissue engineering due to their permeability and biocompatibility. Those that have shear thinning properties allow for minimally-invasive surgical procedures and a way to administer bioactive agents, and therapeutic cells by injection. Currently available injectable hydrogels have a single or dual input/stimulus for crosslinking which limits the range of mechanical properties and often utilize potentially toxic ultraviolet radiation that reduces viability of injected cells. To overcome these shortcomings, a tri-stimuli-responsive alginate-based injectable hydrogel was developed based on: 1) supramolecular complex formation between β-cyclodextrin (β-CD) conjugated alginate and thermo-responsive tri-block Pluronic® copolymers, 2) visible light …

Design, Prototyping And Fabrication Of Powder Spray Device For Dehydrated Biological Particulates, James Reilly

Graduate College Dissertations and Theses

Tissue sealants of a liquid based formulation are widely studied in biomedical research with many starting to gain FDA approval. To date, little investigation has been put toward methods of application for tissue sealant materials, more specifically a powder based formulation. The focus of this research was to develop and prototype a powder spray device capable of administering powder based formulations with a long-term goal of integrating the device within the clinical setting. Powders can be administered in a variety of dry forms. These forms can range from non-homogenous nanoscale particles to homogeneous micro and nano-scale spheres. Incorporation of therapeutics …

Quantum Many - Body Interaction Effects In Two - Dimensional Materials, Sanghita Sengupta

Graduate College Dissertations and Theses

In this talk, I will discuss three problems related to the novel physics of two-dimensional quantum materials such as graphene, group-VI dichalcogenides family (TMDCs viz. MoS2 , WS2, MoSe2 , etc) and Silicene-Germanene class of materials.

The first problem poses a simple question - how do the quantum excitations in a graphene membrane affect adsorption? Using the tools of diagrammatic perturbation theory, I will derive the scattering rates of a neutral atom on a graphene membrane. I will show how this seemingly naive model can serve as a non-relativistic condensed matter analogue of the infamous infrared problem in Quantum Electrodynamics. …

Fabrication And Thermoelectric Characterization Of Stretchable Conductive Latex-Based Composites, Cory Michael Arcovitch

Graduate College Dissertations and Theses

Miniaturized stretchable electronic devices that can be bent and strained elastically without breaking, have drawn considerable research interest in recent years for wearable computers and integrated bio-sensor applications. Portable electrical power harvesting remains a critical challenge in flexible electronics materials. One proposed solution has been to convert waste heat from the human body into electricity using thermoelectric materials. Traditionally, however, these materials are brittle ceramic semiconductors with limited fracture resistance under deformation. The primary objective of this thesis is to address this challenge by fabricating and studying the mechanical, thermal and electrical performance of stretchable composites combining natural latex polymer …

Seaweed To Sealant : Multifunctional Polysaccharides For Regenerative Medicine And Drug Delivery Applications, Spencer Lincoln Fenn

Graduate College Dissertations and Theses

Pneumothorax, or a collapsed lung, is a serious medical condition resulting when air or fluid escapes the lung into the chest cavity and prevents the lung from inflating. Few viable means of sealing the damaged and leaking tissues are currently available, leading to longer hospital stays, multiple interventions, and increasing costs of care. The motivation of this dissertation is to engineer a novel polysaccharide-based therapeutic surgical sealant, which can be utilized to seal trauma-induced damage to the outer lining of the lung, i.e. pleura, preventing or reversing lung collapse to restore normal breathing function.

The use of polysaccharides, such as …

A Study Of The Physicochemical Properties Of Dense And Mesoporous Silica Nanoparticles That Impact Protein Adsorption From Biological Fluids, Alden Michael Clemments

Graduate College Dissertations and Theses

At the intersection of materials chemistry and biology, biomaterials have been successfully employed in an array of medical applications. From diagnostic tools to targeted drug delivery, the modular physical and chemical properties of these materials provide numerous applications. For example, porous nanoparticles have been widely integrated as vehicles to carry chemotherapeutics to localized tumor sites. By encapsulating these cytotoxic compounds within a porous framework, the commonly associated adverse side effects of conventional chemotherapeutics, such as Doxorubicin, have been greatly reduced. One such material, mesoporous silica, has received widespread attention due to its excellent biocompatibility, high surface area to mass ratio, …

Investigating The Influence Of Gold Nanoparticles On The Photocatalytic And Catalytic Reactivity Of Porous Tungsten Oxide Microparticles, Daniel P. Depuccio

Graduate College Dissertations and Theses

Tungsten oxide (WO3) is a semiconducting transition metal oxide with interesting electronic, structural, and chemical properties that have been exploited in applications including catalysis, gas sensing, electrochromic displays, and solar energy conversion. Nanocrystalline WO3 can absorb visible light to catalyze heterogeneous photooxidation reactions. Also, the acidity of the WO3 surface makes this oxide a good thermal catalyst in the dehydration of alcohols to various industrially relevant chemicals. This dissertation explores the photocatalytic and thermal catalytic reactivity of nanocrystalline porous WO3 microparticles. Furthermore, investigations into the changes in WO3 reactivity are carried out after modifying the porous WO3 particles with gold …

Excitonic States In Crystalline Organic Semiconductors: A Condensed Matter Approach, Lane Wright Manning

Graduate College Dissertations and Theses

In this work, a new condensed matter approach to the study of excitons based on crystalline thin films of the organic molecule phthalocyanine is introduced. The premise is inspired by a wealth of studies in inorganic semiconductor ternary alloys (such as AlGaN, InGaN, SiGe) where tuning compositional disorder can result in exciton localization by alloy potential fluctuations. Comprehensive absorption, luminescence, linear dichroism and electron radiative lifetime studies were performed on both pure and alloy samples of metal-free octabutoxy-phthalocyanine and transition metal octabutoxy-phthalocyanines, where the metal is Mn, Co, Ni, and Cu. Varying the ratios of the metal to metal-free phthalocyanines …

Exchange Mechanisms In Macroscopic Ordered Organic Magnetic Semiconductors, Naveen Rawat

Graduate College Dissertations and Theses

Small molecule organic semiconductors such as phthalocyanines and their derivatives represent a very interesting alternative to inorganic semiconductor materials for the development of flexible electronic devices such as organic thin field effect transistors, organic Light Emitting Diodes and photo-voltaic cells. Phthalocyanine molecules can easily accommodate a variety of metal atoms as well in the central core of the molecule, resulting in wide range of magnetic properties. Exploration of optical properties of organic crystalline semiconductors thin films is challenging due to sub-micron grain sizes and the presence of numerous structural defects, disorder and grain boundaries. However, this can be overcome by …

Ruo2 Nanorods As An Electrocatalyst For Proton Exchange Membrane Water Electrolysis, Richard Smith

Graduate College Dissertations and Theses

The desire for pure diatomic hydrogen gas, H2(g), has been on the rise since the concept of the hydrogen economy system was proposed back in 1970. The production of hydrogen has been extensively examined over 40 + years as the need to replace current fuel sources, hydrocarbons, has become more prevalent. Currently there are only two practical and renewable production methods of hydrogen; landfill gas and power to gas. This study focuses on the later method; using various renewable energy sources, such as photovoltaics, to provide off-peak energy to perform water electrolysis. Efficient electrolysis takes place in electrochemical cells which …

The Interaction Mechanisms Of A Screw Dislocation With A Defective Coherent Twin Boundary In Copper, Qiongjiali Fang

Graduate College Dissertations and Theses

Σ3{111} coherent twin boundary (CTB) in face-centered-cubic (FCC) metals and alloys have been regarded as an efficient way to simultaneously increase strength and ductility at the nanoscale. Extensive study of dislocation-CTB interaction has been carried out by a combination of computer simulations, experiments and continuum theory. Most of them, however, are based on the perfect CTB assumption. A recent study [Wang YM, Sansoz F, LaGrange T, et al. Defective twin boundaries in nanotwinned metals. Nat Mater. 2013;12(8):697-702.] has revealed the existence of intrinsic kink-like defects in CTBs of nanotwinned copper through nanodiffraction mapping technique, and has confirmed the effect of …

Aero-Thermal Characterization Of Silicon Carbide Flexible Tps Using A 30kw Icp Torch, Walten Owens

Graduate College Dissertations and Theses

Flexible thermal protection systems are of interest due to their necessity for the success of future atmospheric entry vehicles. Current non-ablative flexible designs incorporate a two-dimensional woven fabric on the leading surface of the vehicle. The focus of this research investigation was to characterize the aerothermal performance of silicon carbide fabric using the 30 kW Inductively Coupled Plasma Torch located at the University of Vermont. Experimental results have shown that SiC fabric test coupons achieving surface temperatures between 1000°C and 1500°C formed an amorphous silicon dioxide layer within seconds after insertion into air plasmas. The transient morphological changes that occurred …

Path Integral Quantum Monte Carlo Study Of Coupling And Proximity Effects In Superfluid Helium-4, Max Graves

Graduate College Dissertations and Theses

When bulk helium-4 is cooled below T = 2.18 K, it undergoes a phase transition to a superfluid, characterized by a complex wave function with a macroscopic phase and exhibits inviscid, quantized flow. The macroscopic phase coherence can be probed in a container filled with helium-4, by reducing one or more of its dimensions until they are smaller than the coherence length, the spatial distance over which order propagates. As this dimensional reduction occurs, enhanced thermal and quantum fluctuations push the transition to the superfluid state to lower temperatures. However, this trend can be countered via the proximity effect, where …

Electron Correlation Effects In Strained Dual-Layer Graphene Systems, Peter Karl Harnish

Graduate College Dissertations and Theses

In low dimensional systems, electron correlation effects can often be enhanced. This can be vital since these effects not only play an important role in the study of many-electron physics, but are also useful in designing new materials for various applications. Since its isolation from graphite in 2004, graphene, a two dimensional sheet of carbon atoms, has drawn considerable interest due to its remarkable properties. In the past few years, research has moved on from single to bi-, dual- and multi-layer graphene systems, each displaying their own multitudes of intriguing properties. In particular, multi-layer systems that are electronically decoupled, but …

Surface Gas Permeability Of Porous Building Materials: Measurement, Analysis And Applications, David Klein Weibust Grover

Graduate College Dissertations and Theses

In many events affecting our civil infrastructure, such as contamination or weathering, it is likely that only the surfaces of the affected building materials will be available for non-destructive measurements. In this work, we describe and analyze surface gas permeability measurements on a variety of natural and engineered building materials using two types of relatively new, non-destructive surface permeameters. It is shown that the surface gas permeability measurements correlate well with each other and could provide rapid estimates of macroscopic gas permeability and degradation of materials due to weathering. It is hypothesized that surface permeability can be used to predict …