Doctor of Philosophy, University of Toledo, 2019, Physics

Two topics are explored in this dissertation: metal whiskers (MW) and resistive random access memory (RRAM). Since conductive filament lies at the heart of these distinct topics, they are combinedly presented here as two parts. The first part is dedicated to understanding MW growth and statistics. MW are hair-like conductive filaments that spontaneously grows on technologically significant metals such as Sn, Zn, Cd, and Ag. They can range from tens of nanometers to microns in diameter and hundreds of nanometers to millimeters in length. Longer whiskers can cause shorting in electrical devices posing a serious reliability concerns for virtually every industry. The electrostatic theory of MW explains the physics of whisker growth in terms of field induced nucleation. Imperfections on metals such as impurities, defects, grains, grain-boundaries etc. creates topographically inhomogeneous work function on metal surface. As a result, electrons redistribute themselves to minimize free energy creating superficial charged patches which produce strong near-surface electric field. When a local neighborhood of charged patches all possess like charge, the near-surface electric field amplifies providing necessary driving force for nucleation of metallic embryo protruding from the metal surface. The polarization energy is maximum along the vertical direction, thus embryo takes a needle shape and simultaneously grows. This dissertation includes a brief introduction to the electrostatic theory, whisker length distribution based on the uncorrelated random charge patches and central limit theorem, description of intermittent whisker growth that naturally follows the electrostatic theory, and data on field accelerated whisker growth testing on Zn samples where we found that applying electric field on metal supported whisker growth. The second part is dedicated to the RRAM device operation and various related observation. RRAM is a next-generation non volatile memory (open full item for complete abstract)

Committee: Victor Karpov (Committee Chair); Jacques Amar (Committee Member); Jon Bjorkman (Committee Member); Daniel Georgiev (Committee Member); Nikolas Podraza (Committee Member) Subjects: Electrical Engineering; Experiments; Materials Science; Nanoscience; Physics; Quantum Physics; Solid State Physics; Theoretical Physics

Doctor of Philosophy, University of Toledo, 2016, Physics

Spectroscopic ellipsometry (SE) is a non-invasive optical probe that is capable of accurately and precisely measuring the structure of thin films, such as their thicknesses and void volume fractions, and in addition their optical properties, typically defined by the index of refraction and extinction coefficient spectra. Because multichannel detection systems integrated into SE instrumentation have been available for some time now, the data acquisition time possible for complete SE spectra has been reduced significantly. As a result, real time spectroscopic ellipsometry (RTSE) has become feasible for monitoring thin film nucleation and growth during the deposition of thin films as well as during their removal in processes of thin film etching. Also because of the reduced acquisition time, mapping SE is possible by mounting an SE instrument with a multichannel detector onto a mechanical translation stage. Such an SE system is capable of mapping the thin film structure and its optical properties over the substrate area, and thereby evaluating the spatial uniformity of the component layers. In thin film photovoltaics, such structural and optical property measurements mapped over the substrate area can be applied to guide device optimization by correlating small area device performance with the associated local properties. In this thesis, a detailed ex-situ SE study of hydrogenated amorphous silicon (a Si:H) thin films and solar cells prepared by plasma enhanced chemical vapor deposition (PECVD) has been presented. An SE analysis procedure with step-by-step error minimization has been applied to obtain accurate measures of the structural and optical properties of the component layers of the solar cells. Growth evolution diagrams were developed as functions of the deposition parameters in PECVD for both p-type and n-type layers to characterize the regimes of accumulated thickness over which a-Si:H, hydrogenated nanocrystalline silicon (nc-Si:H) and mixed phase (a+n (open full item for complete abstract)

Committee: Robert Collins (Advisor) Subjects: Materials Science; Physics

Doctor of Philosophy, The Ohio State University, 2023, Welding Engineering

Duplex stainless steels (DSS) are extensively used in heavy industry, such as Oil and gas, pulp and paper, and chemical, due to their remarkable corrosion resistance, yield strength, and toughness. The most corrosion-resistant DSS subgroups, super duplex stainless steels (SDSS) with Pitting Resistance Equivalent numbers (PREn) of 40-48, and the hyper duplex stainless steels (HDSS) with a PREn over 48, are highly alloyed. Additions of Cr and Mo provide better PREn but also promote intermetallic phases such as the chi and sigma phases. These intermetallics form when the material is exposed to temperatures between 600oC – 1100oC. It is known that even small volumetric fractions of the sigma phase severely reduce the material's corrosion resistance and mechanical performance. A dedicated study on sigma phase formation kinetics was developed to control sigma phase presence in these specific alloys. A field studied but not yet completely connected between scientific research and industrial applications. Fundamental aspects of sigma phase kinetics were analyzed, computationally modeled, and experimentally validated. As a result of these efforts, the interface area per unit of volume was revealed as a critical microstructure factor for the sigma phase kinetics. The resultant model's efficacy was further evaluated by building GTAW cladded mockups, and investigation into this material's mechanical and corrosion performance further expanded on the impacts of the sigma phase. A Gleeble® system was used to develop experimental time temperature transformation (TTT) maps on SDSS and HDSS filler metals for sigma phase precipitation kinetics. Classical nucleation theory was then implemented on the CALPHAD-based kinetics model. In this model, the interfacial energy and nucleation sites were identified as the kinetics parameters to adjust the model based on experimental data. The sigma phase kinetics continuous cooling transformation CCT curves were calculated using the additiv (open full item for complete abstract)

Committee: Antonio Ramirez (Advisor); Stephen Niezgoda (Committee Member); Carolin Fink (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

Master of Science (MS), Wright State University, 2021, Chemistry

There have been limited studies on the analysis of the nucleation and precipitation behind calcium fluoride. Earlier studies support a nucleation mechanism in agreement to classical nucleation theory (CNT) in which a surface nucleation mechanism is required for calcium fluoride. This experiment devised using the ISE method to calcium fluoride to find evidence of a nucleation mechanism like that of calcium carbonate (prenucleation cluster pathway). The potential and pH were recorded versus time and the potential data was converted to nCa2+ data of free calcium ions. It was determined that there was evidence of a similar nucleation mechanism for calcium fluoride due to a similar nCa2+ curve being produced. It was also proven that ion pairing of the reaction cell was not a major factor to our experiments by calculations and analysis. The formation constants, Kip, for CaF+ were found to be 3800% higher than the literature value. This experiment indicates that a similar mechanism can occur for calcium fluoride, but further analysis is needed to confirm this.

Committee: Steven Higgins Ph.D. (Advisor); David Dolson Ph.D. (Committee Member); Ioana Pavel Ph.D. (Committee Member) Subjects: Analytical Chemistry; Chemistry; Environmental Science; Geochemistry

Doctor of Philosophy, The Ohio State University, 2019, Chemical Engineering

Particle formation from a supersaturated vapor involves both nucleation and growth processes. The present study investigates the growth of nanoparticles and heterogeneous nucleation onto nanoparticles, processes that play important roles in atmospheric science as well as in industrial applications. To investigate nanoparticle growth in the free molecular regime, the size and temperature of rapidly growing n-propanol droplets produced in a supersonic nozzle are determined and compared to the predictions of the non-isothermal Hertz-Knudsen (HK) growth law. The results of these studies confirm the earlier work of Pathak et al. [Aerosol Sci. Technol., 2013, 47:1310–1324] and Young [PhyscioChem. Hydrodyn., 1982, 3:57–82], who suggested that matching the enhanced experimental growth rates measured under highly non-equilibrium conditions requires retarding the evaporation rate in the HK growth law. For n-propanol droplets in this work also find that good agreement between experimental and theoretical growth rates and droplet temperatures requires condensation (qc) or evaporation (qe) coefficients that differ from 1. In particular, very good agreement was found for both (qc, qe) = (1, 0.6) and (qc, qe) = (1.3, 1), demonstrating that these values are not unique. While the retarded evaporation rate is difficult to justify from a theoretical standpoint, an enhanced condensation rate can be rationalized by invoking long-range interaction between the particle and vapor molecules. To study heterogeneous nucleation of CO2 on n-alkane particles in a supersonic nozzle, we performed pressure trace measurements (PTM), small angle X-ray scattering (SAXS), and Fourier transform infrared spectroscopy (FTIR) experiments. Integrative analysis shows that, under the present experimental conditions and time scales, pure n-hexane particles freeze whereas pure n-pentane particles do not. CO2 condensation takes place on all three sizes of n-hexane particles, but does not take place on th (open full item for complete abstract)

Committee: Barbara Wyslouzil (Advisor); Isamu Kusaka (Committee Member); Sherwin Singer (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, University of Toledo, 2017, Physics

Thin film solar cells based on hybrid organic-inorganic perovskites (HOIPs) have become highly attractive over the past several years due to a high solar to electric power conversion efficiencies (PCEs). Perovskite materials based on methylammonium lead iodide (CH3NH3PbI3, MAPbI3) possess high optical absorption coefficients, long minority carrier lifetimes and diffusion lengths, and desirable optical band gaps, and carrier collection in these materials can be highly efficient when they are paired with appropriate electron and hole transport materials (ETMs and HTMs), respectively. Additionally, perovskite solar cells (PSCs) can be fabricated via a variety of solution-based routes, which are suitable for low-cost, large area manufacturing. The combination of these attributes gives PSCs an advantage over currently available commercial photovoltaic (PV) technologies. Understanding the nucleation and growth mechanisms, and controlling the grain size and crystallinity in the solution-processed fabrication of perovskite thin films are important to prepare electronic-quality materials for PV applications. We investigated the nucleation and growth mechanisms of MAPbI3 formed in a two-step solution process. To prepare the MAPbI3 films, PbI2 films were spin-coated and then were reacted with methylammonium iodide (MAI) in the isopropanol (IPA) solution at various concentrations. We showed that the conversion rate, grain size, and morphology of MAPbI3 perovskite films depend on the concentration of the MAI solution. Three distinct perovskite formation behaviors were observed at various MAI concentrations, and a tentative model was proposed to explain the reaction mechanisms. The nucleation and growth process of MAPbI3 can be significantly changed by adding divalent metal salts into the MAI solution. We showed that the incorporation of Cd2+ ions significantly improved the grain size, crystallinity, and photoexcited carrier lifetime of MAPbI3. Formation of ( (open full item for complete abstract)

Committee: Michael J. Heben Ph.D. (Committee Chair); Randy J. Ellingson Ph.D. (Committee Member); Yanfa Yan Ph.D. (Committee Member); Song Cheng Ph.D. (Committee Member); Terry P. Bigioni Ph.D. (Committee Member) Subjects: Materials Science; Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Materials Engineering

The unique properties resulting from strongly anisotropic chemical bonds found in the whole family of transition metal dichalcogenide materials (TMDs) have been researched for over 50 years for various applications, with MoS2 being the most heavily researched. The pace of research has surged with the recent isolation and analysis of 2D materials exfoliated from Van der Waals solids, first reported by Novoselov and Geim. MoS2 was first identified to have interesting electrical properties in 2D form by Mak et al. in 2010, where it was discovered that at a monolayer, the band structure had shifted to a direct bandgap semiconductor and the band gap shifts from ~1.3 eV to ~1.9 eV. Coupled with mechanical flexibility, optical transparency, and many other unique properties, 2D MoS2 an ideal semiconductor candidate for nanoelectronic applications. The defect engineering that makes silicon-based technology so flexible has yet to be explored in 2D TMD materials. Grain boundaries are currently a structural defect that cannot be eliminated in wafer scale synthesis of these materials, therefore, a better understanding of how to control grain boundary density and understand the effects on properties is an urgent need. Each grain boundary acts as a scatter defect thought to adversely affect carrier mobility and density, negatively affecting device performance. This grain boundary problem is the driving force behind this study to discover the underlying basic principles and impact of sputter plasma deposition parameters, substrate processing conditions, and the nucleation and growth kinetics of 2D MoS2 films. This dissertation consists of three studies designed to tailor grain boundary density in 2D MoS2: 1) a study on the impact of intrinsic plasma parameters and characteristics of the pulsed DC magnetron sputtering discharge on the resulting 2D MoS2 films and their structure/properties, 2) a study on the impact of the partial pressure of the diatomic (S2) species in sulfur vap (open full item for complete abstract)

Committee: Christopher Muratore PhD (Advisor); Andrey Voevodin PhD (Committee Member); Paul T. Murray PhD (Committee Member); Antonio Crespo PhD (Committee Member) Subjects: Engineering; Materials Science; Nanoscience

Doctor of Philosophy, The Ohio State University, 2013, Chemical and Biomolecular Engineering

Raw natural gas consists mainly of methane and has impurities like water vapor, higher alkanes, H2S etc. Dehydration of natural gas is important to prevent hydrate formation in pipelines carrying natural gas over long distances. Traditionally, dehydration is done using chemical methods like pressure swing absorption and glycol dehydration. An alternate method of dehydration is by using a mechanical process of supersonic separation. In this method, raw natural gas is cooled down by adiabatic expansion resulting in condensation of water vapor and higher alkanes. The goal of this work is to understand the nucleation and droplet growth when droplet sizes are of the order of nm and timescales are of the order of microseconds when water and alkanes, two substances which are immiscible, condense together. We use supersonic nozzles in this work where cooling rates are of the order of 105-106 K/s. The supersonic velocities of the flow enable measurements on a resolution of the order of microseconds. Pressure trace measurement (PTM) is our basic experimental technique and it characterizes the flow by measuring the pressure profile inside the supersonic nozzle as the vapor-gas mixture expands and vapor condenses inside the nozzle. These experiments give the initial estimate of temperature, density, velocity and mass fraction of the condensate. We use Fourier transform infrared spectroscopy (FTIR) to get the composition of the condensed liquid/vapor. To determine the amount of nonane condensed, we fit the measured spectrum of nonane to a linear combination of a well-characterized vapor and liquid spectrum. For D2O analysis, we calculate D2O vapor concentration by analyzing the vibrational-rotational spectrum of O-D stretch region. The size and number of droplets is characterized using small angle x-ray scattering (SAXS) that are performed in Argonne National Laboratory. The nucleation rates for pure D2O and nonane agree with previous measurements done by other rese (open full item for complete abstract)

Committee: Barbara Wyslouzil (Advisor); Isamu Kusaka (Committee Member); Bhavik Bakshi (Committee Member) Subjects: Chemical Engineering; Chemistry; Energy; Engineering; Experiments; Physics

MS, University of Cincinnati, 2000, Engineering : Chemical Engineering

In the present work, we have explored numerous ways to reduce the mean particle size of zeolite A, keeping the economic imperatives in mind. In addition to this, efforts were directed towards reducing the crystallization time and having a more narrow particle size distribution. Besides the study of more conventional parameters such as temperature, alkalinity, water content etc., the effect of using microwaves, centrifuge and ultrasonication was also explored. It was expected that the highly localized temperatures of thousands of degree Kelvin and pressures of hundreds of atmospheres produced by ultrasonication might disrupt the nucleation process in a manner so as to lead to smaller crystals. Surprisingly, it was found that the application of ultrasonication does not lead to any decrease in the particle size. Both ultrasonication and stirring being different forms of agitation, one expected to find crystals with similar morphology in the aforementioned two cases. However, the crystal morphologies obtained in the two cases are completely different which was rather unexpected. Subjecting the zeolite batch to short periods of microwave radiation leads to a narrow particle size distribution with small crystal size. A direct correlation between the nominal SiO2/Al2O3 ratio and the particle size was observed. Decreasing SiO2/Al2O3 ratios lead to a narrower particle size distribution. Agitation was noticed to have an adverse effect as regards the final objective of obtaining a small particle size. The use of some of these parameters have a synergistic effect and can be coupled to finally obtain a mean crystal size of about 0.5 mm within a very reasonable time frame of 5-6 hours which we believe can be easily tailored for commercial synthesis of zeolite A. Another method to get small zeolite crystals has been the addition of nano-particles of various materials to act as substrates for zeolite A nucleation and growth. Synthesis using Titania Hombikat and Titania Hombifine ha (open full item for complete abstract)

Committee: Panagiotis Smimiotis (Advisor) Subjects:

PhD, University of Cincinnati, 2008, Engineering : Materials Science

Diamond has exceptional semiconducting and optical properties that can be used for a wide variety of new applications such as high temperature, high power devices, and optical windows. Exploitation of these properties of diamond needs the development of heteroepitaxial diamond growth process on traditional substrates such as Silicon and Silicon Carbide. Bias enhanced nucleation (BEN) followed by Plasma Enhanced Chemical vapor Deposition (PECVD) has been recognized as a promising route to achieve this goal. However, the BEN process for heteroepitaxy and its mechanism is not well understood. In this study, a system is designed and fabricated to enable the application of bias during diamond deposition in an ASTEX PECVD system, and heteroepitaxial diamond films are grown. The evolution of the oriented diamond film and its microstructure is studied by SEM, TEM, and XRD techniques revealing the formation of misoriented grains, extensive twinning and low angle grain boundaries. The effect of the BEN process conditions on the degree of orientation is investigated. It is observed that the orientation of the films improved at lower bias durations, methane flow rates and bias voltages. TEM images of the nucleation layer are analyzed, and the changes in the nucleation layer grain structure with process parameters are studied. Significant variation in the microstructure and grain size from an average of about 560 nm to about 10 nm is observed with change in process conditions. The BEN process is investigated and the nature of the deposit forming during this step is revealed using SEM, TEM and Raman spectroscopy to be predominantly a nanocrystalline diamond film along with rhombohedral and amorphous carbon. A simple model based on the formation of a nanocrystalline diamond particles during BEN, followed by their growth and coalescence under the plasma is proposed to describe the oriented film formation. The variations in microstructures and orientation are correlated with the pro (open full item for complete abstract)

Committee: Dr. Raj Singh (Advisor) Subjects:

PhD, University of Cincinnati, 2004, Engineering : Materials Science

Flame technology is an extremely effective method to synthesize nano-particles of ceramic oxides. The single-step chemistry, the ability to control shape and size and to produce millions of tons of nano-powders per annum with relative ease have made it popular with industry. Although this process primarily focused on oxides of silicon and titanium, it has now been adopted for manufacture of several other oxides of bismuth, vanadium, aluminum, iron, germanium and zirconium. There has been extraordinary progress in the application of flame burner to synthesize newer oxides having a wide range of particle size, polydispersity, composition and aggregation. But the fundamentals behind the mechanisms for particle formation and growth are still not well understood. Due to the extremely fast reaction rates, high temperatures and low concentrations associated with this process, it is difficult to accurately observe the formation of nuclei and their growth to aggregated nano-particles. Entire particle growth from inception to aggregation takes place in a few milliseconds! Light scattering and thermophoretic sampling have been used extensively to study such flames. But light scattering suffers from the brightness of the flame and the limitation on the size-range it can probe. It can only detect aggregates, and information about primary particles needs to be obtained by thermophoretic sampling. However thermophoretic sampling is an intrusive technique and sample collection in the flame involves disturbance of flow of the gases and the particles in the flame. It is necessary to find a single non-intrusive technique that can yield complete information for the flame and detect the rapid growth. In-situ small angle x-ray scattering (iSAXS), which utilizes high energy x-rays from synchrotron sources fits such a role perfectly. iSAXS of particles in the flame provides full information from nano-scale to micron-scale and about the evolution of particles and their morphology. Experimen (open full item for complete abstract)

Committee: Dr. Gregory Beaucage (Advisor) Subjects: Engineering, Materials Science

MS, University of Cincinnati, 2003, Engineering : Chemical Engineering

The most widely used technique for the manufacture of commercial polymeric membranes, the Phase Inversion process, is often associated with formation of macrovoid pores. These are large open cavities interspersed among the smaller pores. They are extremely undesirable in most membrane processes but useful in some specialized applications. The fundamental mechanism(s) for macrovoid formation are poorly understood, leading to formulation of adhoc recipes to remove them in an extremely limited and invasive way. The current research aimed at employing a noninvasive technology to universally control macrovoid formation in polymeric membranes. The technology is based upon the applicability of external noninvasive forces, such as electric fields, in affecting pore structure in several phase separation processes by influencing nucleation and coalescence. Phase inversion in polymeric solutions involves a two-step process of nucleation and coalescence which makes it suitable for the application of an external electric field. Thus, the current research aims at the pioneering concept of the use of electric fields to manipulate nucleation and coalescence in a phase separating polymeric system, thereby affecting the characteristics of macrovoid formation in polymeric membranes. Uniform and nonuniform electric fields were individually used to influence dry and wetcast membranes. The morphology of the resulting membranes was studied via Environmental Scanning Electron Microscopy (ESEM). The latter permits studying the microstructure of the membranes in the uncoated asformed state. After a comparative analysis of the ESEM micrographs, it was concluded that macrovoid pores are not unique structural features and are of several types based on the phaseseparation technique and the membrane formation rate. Furthermore, electric fields have an appreciable effect on macrovoid formation in polymeric membranes. It was found to be most prominent in case of uniform fields, for both wet and dry (open full item for complete abstract)

Committee: Dr. William B. Krantz (Advisor) Subjects: Engineering, Chemical

Doctor of Philosophy, University of Toledo, 2011, Physics

The goal of this dissertation is to improve our understanding of two of the key stages in thin-film growth: (a) submonolayer island nucleation and growth and (b) multilayer growth. To explore these phenomena we have used a variety of different methods including the numerical integration of stochastic differential equations, self-consistent rate-equation calculations, and kinetic Monte Carlo simulations, as well as scaling and analytical methods. In the first part of this thesis we study the roughening process of amorphous silicon thin film grown via low-temperature PECVD (plasma-enhanced chemical vapor deposition). By studying a continuum model which takes into account the effects of shadowing as well as the smoothing effects of surface diffusion, excellent agreement is obtained with experiments. One of our key findings is that surface diffusion plays an important role at short to medium time scales and high H2 dilution ratio, while shadowing effects are dominant at low H2 dilution ratio and large time scales. We also find that the initial submonolayer morphology plays a key role in determining the evolution of the surface roughness in the later stages of growth. Motivated by these results, we have also carried out kinetic Monte Carlo simulations as well as a scaling analysis of the submonolayer growth of 3D islands. In this work we demonstrate that the scaling behavior of the island and monomer densities for 3D islands is significantly different from that for 2D islands and is also different from previous theoretical predictions. However, despite these differences we find very little or no difference in the scaling behavior of the island-size distribution between 3D and 2D islands. Self-consistent rate-equation calculations for the average island and monomer densities as a function of coverage and deposition flux are also presented and excellent agreement with simulations is obtained. Finally, the effects of cluster-diffusion on the scaling of the island-de (open full item for complete abstract)

Committee: Jacques Amar PhD (Advisor); Bo Gao PhD (Committee Member); Rupali Chandar PhD (Committee Member); Robert Collins PhD (Committee Member); Terry Bigioni PhD (Committee Member) Subjects: Physics

Doctor of Philosophy, University of Toledo, 2008, Physics

A variety of nanocrystals, nanoparticles or quantum dots are fabricated using nucleation and growth processes. Therefore, a fundamental understanding of nucleation and growth is crucial to materials science and engineering on the nanoscale. In this dissertation, we explore the fundamental characteristics of nucleation and growth in multiple dimensional systems using several different methods. One method which has been found to be particularly useful is the Monte Carlo (MC) method. In particular, the kinetic Monte Carlo (KMC) method has made MC simulations of complicated many body systems very efficient. In this dissertation, we use KMC simulations to study nucleation, growth, and coarsening in a variety of different systems. In addition, we have carried out a theoretical analysis using rate equations. We have also carried out investigations of the fundamental characteristics of the coarsening process using parallel methods based on a newly developed parallel KMC algorithm. This dissertation is organized in two parts, the first part is about fundamental characteristics of multiple dimensional systems, the second part is about parallel KMC calculation of coarsening process. In Part I, we first study the fundamental characteristics of nucleation and growth in 3 dimensional (3D) systems using a simplified model of nucleation and growth. One of the main goals of this work is to compare with previous work on 2D nucleation and growth in order to understand the effects of dimensionality. The scaling of the average island-size, island density, monomer density, island-size distribution (ISD), capture number distribution (CND), and capture zone distribution (CZD) are studied as a function of the fraction of occupied sites (coverage) and the ratio D/F of the monomer hopping rate D to the (per site) monomer creation rate F. Our model may be viewed as a simple model of the early-stages of vacancy cluster nucleation and growth under irradiation. Good agreement is found between (open full item for complete abstract)

Committee: Jacques Amar Dr. (Committee Chair); Robert Collins Dr. (Committee Member); Robert Deck Dr. (Committee Member); Bo Gao Dr. (Committee Member); Terry Bigioni Dr. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2008, Chemical Engineering

In this research, environmentally benign carbon dioxide (CO2) was used as a physical blowing agent in the foaming of PS and PS nanocomposites due to the phase-out of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). CNFs (carbon nanofibers) and AC (activated carbon) were used as additive/nucleation agents in PS extrusion foaming. Both fillers showed promising application in insulation foams. The typical foaming process includes cell nucleation, cell growth, and cell stabilization. In this study, primary attention was given to the effects of the material related properties, solubility, diffusivity, and shear viscosity, on cell nucleation and cell growth. Two equations of state (EOS), Sanchez-Lacombe (S-L) EOS and perturbed chain statistical associating fluid theory (PC-SAFT), were used to model the solubility and also phase boundaries (binodal and spinodal curves). Nucleation is a very complex phenomenon in physical foam processing. Proposed scaling functions provide a possible way to calculate the energy barrier in the nucleus formation. Cell nucleation rate data were extracted from the literature and also by our experiments. The initial slope of the possible scaling function was calculated by the diffuse interface theory. A scaling function was correlated based on the calculation from experimental data. Shear viscosity of polymers and nanocomposites under high pressure CO2 were studied via unique modified high pressure Couette rheometry. The effects of nanoparticles on shear viscosity of polymer w/ and w/o CO2 were compared. The permeability coefficient, defined as the product of the solubility coefficient and diffusivity, of CO2 and water vapor in polymer nanocomposites and foams were measured near ambient temperature and pressure. The effects of nanoparticle and foam morphology on permeation were studied. To gain more insight on the early stages of the foaming process, in-situ observation of batch foaming and a quenching method were used to study f (open full item for complete abstract)

Committee: David Tomasko PhD (Committee Chair); Ly Lee PhD (Advisor); Kurt Koelling PhD (Committee Member); Isamu Kusaka PhD (Committee Member); Meow Hui Goh PhD (Committee Member) Subjects: Chemical Engineering; Polymers