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Articles 1 - 14 of 14
Full-Text Articles in Engineering
Engineering High Performance Epoxy Thermosets Using Next-Generation Impact Modification, Madhura Pawar
Engineering High Performance Epoxy Thermosets Using Next-Generation Impact Modification, Madhura Pawar
Doctoral Dissertations
Optimization of fracture toughness of high Tg thermosets was done through systematic investigation of different formulations of reactive functional modifiers using soft particle impact modification. Important parameters like particle size, interparticle distance (IPD) were varied by altering cure kinetics and modifying the molecular architecture of the additives. The best performing systems showed an increase in fracture toughness of 70-80% with an optimum Rp of 1.3 μm and IPD of 0.4 μm at 15 vol% impact modifier. In addition, a new platform of using block copolymer blends was studied for its feasibility to achieve non-spherical morphology for effective impact …
Fabrication Of High Refractive Index, Periodic, Composite Nanostructures For Photonic And Sensing Applications, Irene Howell
Fabrication Of High Refractive Index, Periodic, Composite Nanostructures For Photonic And Sensing Applications, Irene Howell
Doctoral Dissertations
This dissertation examines methods of fabricating high refractive index, periodic structures and their applications. Structures with a refractive index periodicity in one-dimensionally are fabricated by stacking layers of (high-refractive index) nanoparticle-filled and unfilled layers. More complex two- and three-dimensional structures are fabricated by direct printing of nanoparticles via solvent-assisted soft nanoimprint lithography. Polymer-nanoparticle composites are an active area of research and development especially for photonic applications. We show use of two composite formulations, first for fabrication of one-dimensional photonic crystals, and second for scalable UV-nanoimprinting. One dimensional photonic crystals, which possess a periodicity in refractive index, result in a constructive …
Probing Local Vacancy-Driven Resistive Switching In Metal Oxide Nanostructures, Jiaying Wang
Probing Local Vacancy-Driven Resistive Switching In Metal Oxide Nanostructures, Jiaying Wang
Doctoral Dissertations
Novel nonvolatile memory technologies garner intense research interest as conventional ash devices approach their physical limit. Memristors, often comprising an insulating thin film between two metal electrodes to constitute a class of two-terminal devices, enable a variety of important large data storage and data-driven computing applications. In addition to nonvolatile behavior, other features such as high scalability, low power consumption, and sub-nanosecond response times make memristors among the most attractive candidate systems. Their strength in electronic storage relies on the unique properties of the tunable variations in resistance induced from the accumulation of charged defects based on the applied bias …
Swelling Induced Deformation Of Thermally Responsive Hydrogels, Ying Zhou
Swelling Induced Deformation Of Thermally Responsive Hydrogels, Ying Zhou
Doctoral Dissertations
Hydrogels are crosslinked polymeric networks imbibed with aqueous solutions. They undertake dramatic volume changes through swelling and deswelling processes, which can be stimulated by factors like temperature, pH or different chemicals. These unique properties render hydrogels particularly interesting for shape morphing related applications. In this thesis, we focus on the swelling induced deformation of thermally responsive hydrogels with lower critical solution temperatures (LCSTs), including poly(N-isopropylacrylamide) (PNIPAm) and poly(N,N-diethylacrylamide) (PDEAm). Particularly, benzophenone containing monomers are copolymerized with NIPAm or DEAm to create photocrosslinkable temperature-responsive polymers, which allows fabrication of hydrogels with controlled shapes and crosslinking …
Extreme Indentation And Fracture Of Soft Polymer Gels, Shruti Rattan
Extreme Indentation And Fracture Of Soft Polymer Gels, Shruti Rattan
Doctoral Dissertations
The mechanical properties of conventional hard materials, such as metals and ceramics, have received widespread attention in the past several decades; however mechanical characterization, failure in particular, of soft materials, such as polymer gels, elastomers, and biological tissues and organs, has largely been ignored. While practical issues such as difficulty in handling, processing, and slippage offer complexities in characterization, the breakdown of the fundamental assumptions of linear elastic fracture mechanics due to large strains prior to failure, significant energy dissipation ahead of a crack tip and rate and time dependent effects makes understanding of failure in soft materials even more …
Parallel Algorithms For Time Dependent Density Functional Theory In Real-Space And Real-Time, James Kestyn
Parallel Algorithms For Time Dependent Density Functional Theory In Real-Space And Real-Time, James Kestyn
Doctoral Dissertations
Density functional theory (DFT) and time dependent density functional theory (TDDFT) have had great success solving for ground state and excited states properties of molecules, solids and nanostructures. However, these problems are particularly hard to scale. Both the size of the discrete system and the number of needed eigenstates increase with the number of electrons. A complete parallel framework for DFT and TDDFT calculations applied to molecules and nanostructures is presented in this dissertation. This includes the development of custom numerical algorithms for eigenvalue problems and linear systems. New functionality in the FEAST eigenvalue solver presents an additional level of …
Increasing Organic Semiconductor Performance Through Chemical And Processing Modifications, Edmund Burnett
Increasing Organic Semiconductor Performance Through Chemical And Processing Modifications, Edmund Burnett
Doctoral Dissertations
This thesis focuses on tuning molecular packing of organic semiconductors through processing or chemical modifications to increase performance and establish structure-property relationships. Chapter 2 utilizes differing processing techniques to alter the molecular packing of bistetracene in the thin film and thorough polymorph characterization to relate the modification of molecular packing to the increase in charge mobility and mechanism. Chapter 3 introduces the oligomer as a model system to resolve issues that would be difficult or impossible using polymeric systems, due to their monodispersity and increased crystallinity allows for more detailed structural characterization. In this chapter we determine a crystal packing …
Phonon Transport At Boundaries And Interfaces In Two-Dimensional Materials, Cameron Foss
Phonon Transport At Boundaries And Interfaces In Two-Dimensional Materials, Cameron Foss
Masters Theses
A typical electronic or photonic device may consist of several materials each one potentially meeting at an interface or terminating with a free-surface boundary. As modern device dimensions reach deeper into the nanoscale regime, interfaces and boundaries become increasingly influential to both electrical and thermal energy transport. While a large majority of the device community focuses on the former, we focus here on the latter issue of thermal transport which is of great importance in implementing nanoscale devices as well as developing solutions for on-chip heat removal and waste heat scavenging. In this document we will discuss how modern performance …
Dynamics And Structure Of Polyelectrolyte Complexes, Hamidreza Shojaei-Mahib
Dynamics And Structure Of Polyelectrolyte Complexes, Hamidreza Shojaei-Mahib
Doctoral Dissertations
Interaction of charged macromolecules among themselves and with charged interfaces in salty aqueous medium is a common phenomenon prevalent in biology and synthetic systems. We have addressed several inter-related issues in this general context. First we present a theory of adsorption of polyelectrolytes on the interior and exterior surfaces of a charged spherical vesicle. We derive the critical adsorption condition and the density profile of the polymer in terms of various characteristics of the polymer, vesicle, and the solution, such as the length and charge density of polymer, the radius and charge of the vesicle, the salt concentration of the …
Self-Assembling Networks In Soft Materials, Ishan Prasad
Self-Assembling Networks In Soft Materials, Ishan Prasad
Doctoral Dissertations
This dissertation presents a study on heterogeneous network structure in two distinct classes of soft material systems: disordered assemblies of jammed binary spheres and ordered morphologies of block copolymer melts. The aim is to investigate the combined role of geometry and entropy in structure formation of soft matter assemblies. First, we investigate the influence of particle size asymmetry on structural properties of jammed binary sphere mixtures. We give evidence of two distinct classes of materials separated by a critical size ratio that marks the onset of a sharp transition due to simultaneous jamming of a sub-component of the packing. We …
Engineering Next Generation Anisotropic Materials And Composites, Nihal Kanbargi
Engineering Next Generation Anisotropic Materials And Composites, Nihal Kanbargi
Doctoral Dissertations
Polymer-based composite systems have been developed for a wide variety of applications ranging from aerospace to electronics. My work has focused on the structure-process-property relationships of anisotropic polymeric materials and composites, aimed primarily for structural applications. Anisotropic materials such as fibers have superior mechanical properties along the axial direction and this property can be exploited to engineer exceptionally strong and light materials. In the first chapter, we discuss the physics of degradation of Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers. PBO, a fiber of extraordinary tensile modulus and strength has been found to degrade rapidly under moderate conditions of humidity and heat. Solid-state NMR …
High Strain Rate Dynamic Response Of Aluminum 6061 Micro Particles At Elevated Temperatures And Varying Oxide Thicknesses Of Substrate Surface, Carmine Taglienti
High Strain Rate Dynamic Response Of Aluminum 6061 Micro Particles At Elevated Temperatures And Varying Oxide Thicknesses Of Substrate Surface, Carmine Taglienti
Masters Theses
Cold spray is a unique additive manufacturing process, where a large number of ductile metal micro particles are deposited to create new surface coatings or free-standing structures. Metallic particles are accelerated through a gas stream, reaching velocities of over 1 km/s. Accelerated particles experience a high-strain-rate microscopic ballistic collisions against a target substrate. Large amounts of kinetic energy results in extreme plastic deformation of the particles and substrate. Though the cold spray process has been in use for decades, the extreme material science behind the deformation of particles has not been well understood due to experimental difficulties arising from the …
Role Of Rigidity And Flexibility Of Functional Groups Within The Interior Of Supramolecular Assemblies And Their Implications, Oyuntuya Munkhbat
Role Of Rigidity And Flexibility Of Functional Groups Within The Interior Of Supramolecular Assemblies And Their Implications, Oyuntuya Munkhbat
Doctoral Dissertations
Engineering of supramolecular assemblies at molecular level renders functional nanomaterials that present explicit response to certain environmental changes. Systematic structure-property correlation studies will unravel the fundamental design constraints of these functional nanomaterials that fulfill the emergent need. This dissertation will primarily focus on understanding the role of rigidity and flexibility of functional groups within amphiphilic assemblies and employing this basic concept in drug delivery and diagnostics applications. Supramolecular assemblies formed by amphiphilic dendrimers and polymers are preferred for this study as they exhibit high thermodynamic stability and structural flexibility. The role of aromatic interaction on the unimer-aggregate dynamic equilibrium was …
Modeling Deformation Behavior And Strength Characteristics Of Sand-Silt Mixtures: A Micromechanical Approach, Mehrashk Meidani
Modeling Deformation Behavior And Strength Characteristics Of Sand-Silt Mixtures: A Micromechanical Approach, Mehrashk Meidani
Doctoral Dissertations
This dissertation is comprised of six chapters. In the first chapter the motivation of this research, which was modeling the deformation behavior and strength characteristics of soils under internal erosion, is briefly explained. In the second chapter a micromechanis-based stress-strain model developed for prediction of sand-silt mixtures behavior is presented. The components of the micromechanics-based model are described and undrained behavior of six different types of sand-silt mixtures is predicted for several samples with different fines contents. The need for a more comprehensive compression model for sand-silt mixtures is identified at the end of this chapter. This desired compression model …