Engineering Commons^™

Synthesis And Study Of Hybrid Organic – Inorganic Polyhedral Oligomeric Silsesquioxanes (Poss) Based Polymers, Gunjan A, Gadodia

Open Access Dissertations

Hybrid organic-inorganic materials represent a new class of materials having scientific and technological potential. In this thesis, Polyhedral Oligomeric Silsesquioxanes (POSS) are used as an inorganic building block which has been tethered to an organic polymer. POSS are silica precusors, having a well defined silsesquioxane cental core surrounded by an organic periphery which makes them compatible with monomers and possibly polymers. The objectives of this study are to (1) study the basic structures of POSS homopolymers, (2) to incorporate POSS building blocks by a bottomup approach into polymer chains and study the resulting morphologies, and (3) to study the thin …

Understanding Adsorption And Desorption Processes In Mesoporous Materials With Independent Disordered Channels, Peter A. Monson, Sergej Naumov, Rustem Valiullin, Jörg Kärger

Peter A. Monson

Using a lattice-gas model in mean-field theory, we discuss the problem of how adsorption and desorption of fluids in independent cylinderlike pores is influenced by variations in the pore diameter along the length of the pore, surface roughness of the pore walls, and chemical heterogeneity. We also consider the impact of contact with the bulk phase via the pore opening and the possibility of interactions between neighboring pores via a liquid film on the external surface of the material. We find that a combination of pore size variation along the length of the pore and surface roughness yields sorption hysteresis …

Small-World Network Models Of Intercellular Coupling Predict Enhanced Synchronization In The Suprachiasmatic Nucleus, Christina Vasalou, Erik D. Herzog, Michael A. Henson

Michael A Henson

The suprachiasmatic nucleus (SCN) of the hypothalamus is a multioscillator system that drives daily rhythms in mammalian behavior and physiology. Based on recent data implicating vasoactive intestinal polypeptide (VIP) as the key intercellular synchronizing agent, we developed a multicellular SCN model to investigate the effects of cellular heterogeneity and intercellular connectivity on circadian behavior. A 2-dimensional grid was populated with 400 model cells that were heterogeneous with respect to their uncoupled rhythmic behavior (intrinsic and damped pacemakers with a range of oscillation periods) and VIP release characteristics (VIP producers and nonproducers). We constructed small-world network architectures in which local connections …

Atomic-Scale Analysis Of Plastic Deformation In Thin-Film Forms Of Electronic Materials, Kedarnath Kolluri

Open Access Dissertations

Nanometer-scale-thick films of metals and semiconductor heterostructures are used increasingly in modern technologies, from microelectronics to various areas of nanofabrication. Processing of such ultrathin-film materials generates structural defects, including voids and cracks, and may induce structural transformations. Furthermore, the mechanical behavior of these small-volume structures is very different from that of bulk materials. Improvement of the reliability, functionality, and performance of nano-scale devices requires a fundamental understanding of the atomistic mechanisms that govern the thin-film response to mechanical loading in order to establish links between the films' structural evolution and their mechanical behavior. Toward this end, a significant part of …

Developing Reactive Molecular Dynamics For Understanding Polymer Chemical Kinetics, Kenneth D. Smith

Open Access Dissertations

One of the challenges in understanding polymer flammability is the lack of information about microscopic events that lead to macroscopically observed species, and Reactive Molecular Dynamics is a promising approach to obtain this crucially needed information. The development of a predictive method for condensed-phase reaction kinetics can provide significant insight into polymer ammability, thus helping guide future synthesis of fire-resistant polymers. Through this dissertation, a new reactive forcefield, RMDff, and Reactive Molecular Dynamics program, RxnMD, have been developed and used to simulate such material chemistry. It is necessary to have accurate description of chemical kinetics to describe quantitative chemical kinetics. …

A Multipurpose Microfluidic Device Designed To Mimic Microenvironment Gradients And Develop Targeted Cancer Therapeutics, Neil S. Forbes, Colin L. Walsh, Brett M. Babin, Rachel W. Kasinskas, Jean A. Foster, Marissa J. Mcgarry

Neil S. Forbes

The heterogeneity of cellular microenvironments in tumors severely limits the efficacy of most cancer therapies. We have designed a microfluidic device that mimics the microenvironment gradients present in tumors that will enable the development of more effective cancer therapies. Tumor cell masses were formed within micron-scale chambers exposed to medium perfusion on one side to create linear nutrient gradients. The optical accessibility of the PDMS and glass device enables quantitative transmitted and fluorescence microscopy of all regions of the cell masses. Time-lapse microscopy was used to measure the growth rate and show that the device can be used for long-term …

Supercritical Fluid Deposition Of Thin Metal Films: Kinetics, Mechanics And Applications, Christos Fotios Karanikas

Doctoral Dissertations 1896 - February 2014

In order to meet the demands of the continuous scaling of electronic devices, new technologies have been developed over the years. As we approach the newest levels of miniaturization, current technologies, such as physical vapor deposition and chemical vapor deposition, are reaching a limitation in their ability to successfully fabricate nano sized electronic devices.

Supercritical fluid deposition (SFD) is a demonstrated technology that provides excellent step coverage for the deposition of metals and metal oxides within narrow, high aspect ratio features. This technique shows the potential to satisfy the demands of integrated circuit miniaturization while maintaining a cost effective process …

Understanding Adsorption In Mesoporous Materials Through Lattice-Based Density Functional Theory And Monte Carlo Simulation, Bradd E Libby

Doctoral Dissertations 1896 - February 2014

Confining walls induce qualitative changes in adsorbed fluids. Among the most intriguing phenomena is hysteresis, where a pore fills with fluid at a greater pressure than it empties. The causes and mechanisms by which this occurs are intensely investigated yet still poorly understood. Ordered mesoporous silicas, recently discovered materials with well-defined pore size distributions, provide an opportunity to deepen our understanding of the fundamental physics of the interaction of fluids with complex solids.

In part of this computational investigation we examine idealized pores. In agreement with other recent studies, we find that in 'inkbottle'-shaped pores, where a large cavity is …

Microwave Reactor Engineering Of Zeolites Synthesis, Murad Gharibeh

Doctoral Dissertations 1896 - February 2014

Microwave chemistry has expanded over the last two decades due to the enhanced reaction rates achieved for many processes, including organic synthesis, inorganic synthesis and polymerization. Significant time and energy saving can be realized using microwave chemistry, which is important both commercially and for the environment.

One of the most exciting and commercially/technologically significant areas where microwave energy has been demonstrated to influence the kinetics and selectivity is in the synthesis of nanoporous materials, such as zeolites. New nanoporous materials can be created, and the times for their syntheses can be significantly reduced, involving using less energy. By reducing the …

Index To The Selected Works Of Otto Vogl, Otto Vogl

Emeritus Faculty Author Gallery

No abstract provided.

Drag Reduction In Turbulent Flows Over Micropatterned Superhydrophobic Surfaces, Robert J. Daniello

Masters Theses 1911 - February 2014

Periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide drag reduction in the laminar flow regime, have been demonstrated capable of reducing drag in the turbulent flow regime as well. Superhydrophobic surfaces contain micro or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to skin friction drag reductions approaching 50%. At a given Reynolds number, drag reduction was found to increase with increasing feature size and spacing, as in …

Patterned Well-Ordered Mesoporous Silica Films For Device Fabrication, Todd A. Crosby

Masters Theses 1911 - February 2014

Developing effective methods of generating thin metal oxide films are important for sensing and separations applications. An obstacle to device fabrication is controlling the size and spatial orientation of domain level pores while retaining the ability to generate arbitrary device level patterns. Well-ordered hexagonally packed cylindrical pores were created by taking advantage of block copolymer self-assembly followed by selective condensation of silica precursors using supercritical carbon dioxide as the solvent. It was possible to control the pore size by choosing PEO-PPO-PEO (Pluronic® series) triblock copolymers of differing molecular weights.

These processes were then incorporated with conventional lithographic techniques to generate …

More On Powers Of Ten, Morton Sternheim

Nanotechnology Teacher Summer Institutes

A powers of ten personation and activity adapted from the Nanosense project:

http://nanosense.sri.com/activities/sizematters/index.html

Kinetics And Mechanism Of Cellulose Pyrolysis, George W. Huber, Y. C. Lin, J Cho, P. R. Westmoreland

George W. Huber

In this paper we report the kinetics and chemistry of cellulose pyrolysis using both a Pyroprobe reactor and a thermogravimetric analyzer mass spectrometer (TGA-MS). We have identified more than 90% of the products from cellulose pyrolysis in a Pyroprobe reactor with a liquid nitrogen trap. The first step in the cellulose pyrolysis is the depolymerization of solid cellulose to form levoglucosan (LGA; 6,8-dioxabicyclo[3.2.1]octane-2,3,4-triol). LGA can undergo dehydration and isomerization reactions to form other anhydrosugars including levoglucosenone (LGO; 6,8-dioxabicyclo[3.2.1]oct-2-en-4-one), 1,4:3,6-dianhydro-β-d-glucopyranose (DGP) and 1,6-anhydro-β-d-glucofuranose (AGF; 2,8-dioxabicyclo[3.2.1]octane-4,6,7-triol). The anhydrosugars can react further to form furans, such as furfural (furan-2-carbaldehyde) and hydroxymethylfurfural (HMF; 5-(hydroxymethyl)furan-2-carbaldehyde) …

Rippling Instability On Surfaces Of Stressed Crystalline Conductors, Dimitrios Maroudas, M. R. Gungor, V. Tomar

Dimitrios Maroudas

We report a surface morphological stability analysis for stressed, conducting crystalline solids without and with the simultaneous application of an electric field based on self-consistent dynamical simulations according to a fully nonlinear model. The analysis reveals that in addition to a cracklike surface instability, a very-long-wavelength instability may be triggered that leads to the formation of secondary ripples on the surface morphology. We demonstrate that the number of ripples formed scales linearly with the wavelength of the initial perturbation from the planar surface morphology and that a sufficiently strong electric field inhibits both the cracklike and the rippling instability.

Aromatic Production From Catalytic Fast Pyrolysis Of Biomass-Derived Feedstocks, George W. Huber, T. R. Carlson, G. A. Tompsett

George W. Huber

The conversion of biomass compounds to aromatics by thermal decomposition in the presence of catalysts was investigated using a pyroprobe analytical pyrolyzer. The first step in this process is the thermal decomposition of the biomass to smaller oxygenates that then enter the catalysts pores where they are converted to CO, CO2, water, coke and volatile aromatics. The desired reaction is the conversion of biomass into aromatics, CO2 and water with the undesired products being coke and water. Both the reaction conditions and catalyst properties are critical in maximizing the desired product selectivity. High heating rates and high catalyst to feed …

Analysis Of Diamond Nanocrystal Formation From Multiwalled Carbon Nanotubes, Dimitrios Maroudas, E. S. Aydil, T. Singh, A. R. Muniz

Dimitrios Maroudas

A systematic analysis is presented of the nanocrystalline structures generated due to the intershell C-C bonding between adjacent concentric graphene walls of multiwalled carbon nanotubes (MWCNTs). The analysis combines a comprehensive exploration of the entire parameter space determined by the geometrical characteristics of the individual graphene walls comprising the MWCNT with first-principles density-functional theory calculations of intershell C-C bonding and structural relaxation by molecular-dynamics simulation of the resulting nanocrystalline structures. We find that these structures can provide seeds for the nucleation of the cubic-diamond and hexagonal-diamond phase in the form of nanocrystals embedded in the MWCNTs. The resulting lattice structure …

Linear Stability Of A Volatile Liquid Film Flowing Over A Locally Heated Surface, N Tiwari, Jm Davis

Jeffrey M. Davis

The dynamics and linear stability of a volatile liquid film flowing over a locally heated surface are investigated. The temperature gradient at the leading edge of the heater induces a gradient in surface tension that leads to the formation of a pronounced capillary ridge. Lubrication theory is used to develop a model for the film evolution that contains three key dimensionless groups: a Marangoni parameter (M), an evaporation number (E), and a measure of the vapor pressure driving force for evaporation (K), which behaves as an inverse Biot number. The two-dimensional, steady solutions for the local film thickness are computed …

Reactive Boiling Of Cellulose For Integrated Catalysis Through A Liquid Intermediate, Paul J. Dauenhauer, J. L. Colby, C. M. Balonek, W. J. Wieslaw, L. D. Schmidt

Paul J. Dauenhauer

Advanced biomass processing technology integrating fast pyrolysis and inorganic catalysis requires an improved understanding of the thermal decomposition of biopolymers in contact with porous catalytic surfaces. High speed photography (1000 frames per second) reveals that direct impingement of microcrystalline cellulose particles (300 μm) with rhodium-based reforming catalysts at high temperature (700 °C) produces an intermediate liquid phase that reactively boils to vapors. The intermediate liquid maintains contact with the porous surface permitting high heat transfer (MW m−2) generating an internal thermal gradient visible within the particle as a propagating wave of solid to liquid conversion. Complete conversion to liquid yields …

The Critical Role Of Heterogeneous Catalysis In Lignocellulosic Biomass Conversion, George W. Huber, Y. -C Lin

George W. Huber

Lignocellulosic biofuels have a tremendous potential to reduce problems caused by our dependence on fossil fuels. The current roadblock with biofuels is the lack of economical conversion technologies. Heterogeneous catalysis offers immense potential in helping to make lignocellulosic biofuels a commercial reality. In this article we discuss the central role of heterogeneous catalysis in biomass conversion. We review the science of catalysis and the different routes to make biofuels. During the last several decades multiple new spectroscopic, theoretical, and synthesis tools are available that allow us to study catalysis at a molecular level. These new tools will allow us to …

Comparative Study Of The Mechanical Behavior Under Biaxial Strain Of Prestrained Face-Centered Cubic Metallic Ultrathin Films, Dimitrios Maroudas, M. R. Gungor, K. Kolluri

Dimitrios Maroudas

We report a molecular-dynamics study of the mechanical response to dynamic biaxial tensile straining of nanometer-scale-thick Al, Cu, and Ni films. We find that the mechanical behavior of such films of face-centered cubic metals with moderate-to-high propensity for stacking-fault formation (Cu and Ni) is significantly different from those where such propensity is low (Al). The plastic strain rate in Cu and Ni films is greater than that in Al ones, leading to an extended easy-glide stage in Cu and Ni but not in Al films. These differences arise due to the different dislocation annihilation mechanisms in the two film categories.

Molecular-Dynamics Simulations Of Stacking-Fault-Induced Dislocation Annihilation In Prestrained Ultrathin Single-Crystalline Copper Films, Dimitrios Maroudas, K. Kolluri, M. R. Gungor

Dimitrios Maroudas

We report results of large-scale molecular-dynamics simulations of dynamic deformation under biaxial tensile strain of prestrained single-crystalline nanometer-scale-thick face-centered cubic (fcc) copper films. Our results show that stacking faults, which are abundantly present in fcc metals, may play a significant role in the dissociation, cross slip, and eventual annihilation of dislocations in small-volume structures of fcc metals. The underlying mechanisms are mediated by interactions within and between extended dislocations that lead to annihilation of Shockley partial dislocations or formation of perfect dislocations. Our findings demonstrate dislocation starvation in small-volume structures with ultrathin film geometry, governed by a mechanism other than …

Modeling Relaxation Processes For Fluids In Porous Materials Using Dynamic Mean Field Theory: An Application To Partial Wetting, Peter A. Monson, John R. Edison

Peter A. Monson

We review a recently developed dynamic mean field theory for fluids confined in porous materials and apply it to a case where the solid-fluid interactions lead to partial wetting on a planar surface. The theory describes the evolution of the density distribution for a fluid in a pore that has contact with the bulk during a quench in the bulk chemical potential. In this way the dynamics of adsorption and desorption can be studied. By focusing on partial wetting situation we can investigate influence of a weaker surface field on the mechanisms of capillary condensation and desorption. We have studied …

Kinetic Monte Carlo Simulations Of Surface Growth During Plasma Deposition Of Silicon Thin Films, Dimitrios Maroudas, T. Singh, S. Pandey

Dimitrios Maroudas

Based on an atomically detailed surface growth model, we have performed kinetic Monte Carlo (KMC) simulations to determine the surface chemical composition of plasma deposited hydrogenated amorphous silicon (a-Si:H) thin films as a function of substrate temperature. Our surface growth kinetic model consists of a combination of various surface rate processes, including silyl (SiH3) radical chemisorption onto surface dangling bonds or insertion into Si–Si surface bonds, SiH3 physisorption, SiH3 surface diffusion, abstraction of surface H by SiH3 radicals, surface hydride dissociation reactions, as well as desorption of SiH3, SiH4, and Si2H6 species into the gas phase. Transition rates for the …

On The Hydrogen Storage Capacity Of Carbon Nanotube Bundles, Dimitrios Maroudas, A. R. Muniz, M. Meyyappan

Dimitrios Maroudas

An analytical model is presented to describe the effect of carbon nanotube (CNT) swelling upon hydrogenation on the hydrogen storage capacity of single-walled CNT bundles; the model is properly parameterized using atomistic calculations for the relationship between CNT swelling and the degree of hydrogenation as measured by the coverage of the CNTs by chemisorbed atomic H. The model generates experimentally testable hypotheses, which can be used to explain the lower H storage capacities reported for CNT bundles and the experimentally observed nonuniformity of hydrogenation of CNT bundles.

Production Of Hydrogen, Alkanes And Polyols By Aqueous Phase Processing Of Wood-Derived Pyrolysis Oils, George W. Huber, T. P. Vispute

George W. Huber

Pyrolysis oils are the cheapest liquid fuel derived from lignocellulosic biomass. However, pyrolysis oils are a very poor quality liquid fuel that cannot be used in conventional diesel and internal combustion engines. In this paper we show that hydrogen, alkanes (ranging from C1 to C6) and polyols (ethylene glycol, 1,2-propanediol, 1,4-butanediol) can be produced from the aqueous fraction of wood-derived pyrolysis oils (bio-oils). The pyrolysis oil was first phase separated into aqueous and non-aqueous fraction by addition of water. The aqueous phase of bio-oil contained sugars; anhydrosugars; acetic acid; hydroxyacetone; furfural and small amounts of guaiacols. The aqueous fraction was …

Nonmodal And Nonlinear Dynamics Of A Volatile Liquid Film Flowing Over A Locally Heated Surface, N Tiwari, Jm Davis

Jeffrey M. Davis

The stability of a thin, volatile liquid film falling under the influence of gravity over a locally heated, vertical plate is analyzed in the noninertial regime using a model based on long-wave theory. The model is formulated to account for evaporation that is either governed by thermodynamic considerations at the interface in the one-sided limit or limited by the rate of mass transfer of the vapor from the interface. The temperature gradient near the upstream edge of the heater induces a gradient in surface tension that opposes the gravity-driven flow, and a pronounced thermocapillary ridge develops in the streamwise direction. …

Solid−Fluid And Solid−Solid Equilibrium In Hard Sphere United Atom Models Of N-Alkanes: Rotator Phase Stability, Peter A. Monson, M. Cao

Peter A. Monson

We present a study of the phase behavior for models of n-alkanes with chain lengths up to C21 based on hard sphere united atom models of methyl and methylene groups, with fixed bond lengths and C−C−C bond angles. We extend earlier work on such models of shorter alkanes by allowing for gauche conformations in the chains. We focus particularly on the orientational order about the chain axes in the solid phase near the melting point, and our model shows how the loss of this orientational order leads to the formation of rotator phases. We have made extensive calculations of the …

Biopolymerization-Driven Self-Assembly Of Nanofiber Air-Bridges, Santosh Pabba, Mehdi M. Yazdanpanah, Brigitte H. Fasciotto Totten, Vladimir V. Dobrokhotov, Jeremy M. Rathfon, Gregory N. Tew, Robert W. Cohn

Gregory N. Tew

Several proteins, including actin and fibrin, polymerize in vivo to form nanometre diameter fibers. These processes can be duplicated in vitro using only the essential enzyme and protein precursors. These same protein solutions are directed to self-assemble into oriented arrays of air-bridges using only the crude operation of hand brushing them over textured micron-scale surfaces. The creation of these suspended structures could be used as nanomechanical elements in various sensors and actuators, and their fabrication by this rapid directed self-assembly method would be useful, especially during the early phases of prototype device development. The fabrication method extends earlier studies (Harfenist …

Fast Disinfecting Antimicrobial Surfaces, Ahmad E. Madkour, Jeffery M. Dabkowski, Klaus Nüsslein, Gregory N. Tew

Gregory N. Tew

Silicon wafers and glass surfaces were functionalized with facially amphiphilic antimicrobial copolymers using the "grafting from" technique. Surface-initiated atom transfer radical polymerization (ATRP) was used to grow poly(butylmethacrylate)-co-poly(Boc-aminoethyl methacrylate) from the surfaces. Upon Boc-deprotection, these surfaces became highly antimicrobial and killed S. aureus and E. coli 100% in less than 5 min. The molecular weight and grafting density of the polymer were controlled by varying the polymerization time and initiator surface density. Antimicrobial studies showed that the killing efficiency of these surfaces was independent of polymer layer thickness or grafting density within the range of surfaces studied.