<p>Among the existing corrosion control methods, surfactant inhibitors have widely been used for corrosion inhibition of pipelines in water-oil-steel pipe (WOS) environments. This dissertation includes a systemic review of the causes of pipeline corrosion in WOS environments containing carbon dioxide (CO2), general corrosion control using surfactant inhibitors and associated concerns, and commonly used classes of surfactants and their properties, various processes and phenomena that affect overall surfactant performance. This dissertation also provides a review of experimental evaluation techniques and various developed models (semi-empirical model, mechanistic model, and multiphysics model) in evaluation of surfactant inhibition efficiency. An integrated corrosion inhibition (ICI) model is proposed, developed, and validated based on the current understanding of the inhibition of CO2 corrosion in WOS environments using surfactants. The developed ICI model for the modeling and prediction of corrosion inhibition efficiency of mixed surfactant inhibitors is a multiphysics model, based on the fundamentals from many areas of corrosion science, electrochemistry, metallurgical engineering, and chemical and analytical engineering, etc., and the integration of several submodels, including a water-oil surfactant distribution submodel, the aqueous cmc prediction submodel, and the modified Langmuir adsorption (MLA)/ modified quantitative structure activity relation (MQSAR) submodel. Software is developed based on the ICI model and the use of computational and programming resources. The phenomena and processes integrated into the ICI model include surfactant partitioning between oil and water, micellization and precipitation, adsorption/desorption at surfaces and interfaces, surfactant-solvent interactions, surfactant-counterion pairing, lateral interactions between surfactant molecules, and fluid flow. These phenomena are incorporated into three main processes and associated modeling: partitioning between oil and water, micellization/precipitation, and effective adsorption on metal substrate and water/oil interface. The framework of multiphysics ICI model is intended to serve as a basic framework in the understanding of mixed surfactant inhibitor performance with a focus on the application in salt-containing WOS environments. Beyond this, other potential applications may be extended to the design of surfactants, selection of optimal surfactants for specific applications, experimental validation of developed models, simulation of conceivable processes and phenomena, and the integration into more comprehensive lifetime prediction models in which all the surfactant efficiency-affecting factors may be evaluated.

<p> In this study, the performance of a Gold-Copper alloy has been examined in order to explore the possibility of its use as a cathode catalyst in a Proton Exchange Membrane (PEM) Fuel Cell. The performance of Oxygen Reduction Reaction (ORR), which occurs at the cathode, is evaluated using the Density Function Theory (DFT) computational code, SeqQuest. A surface segregation study is performed to identify a low energy surface of the catalyst. A binding site analysis of various intermediate molecules that occur during the ORR process is performed. The intermediate reactions of the ORR are simulated on the surface. Using the binding energies and energy barriers, the pathway that the Gold-Copper alloy prefers to follow is determined. The alloy is found to be a promising catalyst as it prefers to take the four electron pathway. An estimation of the Current Density has been made, and the effect the operating temperature has on it is observed.</p>

<p> The next generation of rechargeable batteries must have significantly improved gravimetric and volumetric energy densities while maintaining a long cycle life and a low risk of catastrophic failure. Replacing the conventional graphite anode in a lithium ion battery with lithium foil increases the theoretical energy density of the battery by more than 40%. Furthermore, there is significant interest within the scientific community on new cathode chemistries, like sulfur and air, that presume the use of a lithium metal anode to achieve theoretical energy densities as high as 5217 W&dot;h/kg. However, lithium metal is highly unstable toward traditional liquid electrolytes like ethylene carbonate and dimethyl carbonate. The solid electrolyte interphase that forms between lithium metal and these liquid electrolytes is brittle which causes a highly irregular current distribution at the anode, resulting in the formation of lithium metal protrusions. Ionic current concentrates at these protrusions leading to the formation of lithium dendrites that propagate through the electrolyte as the battery is charged, causing it to fail by short-circuit. The rapid release of energy during this short-circuit event can result in catastrophic cell failure. </p><p> Polymer electrolytes are promising alternatives to traditional liquid electrolytes because they form a stable, elastomeric interface with lithium metal. Additionally, polymer electrolytes are significantly less flammable than their liquid electrolyte counterparts. The prototypical polymer electrolyte is poly(ethylene oxide). Unfortunately, when lithium anodes are used with a poly(ethylene oxide) electrolyte, lithium dendrites still form and cause premature battery failure. Theoretically, an electrolyte with a shear modulus twice that of lithium metal could eliminate the formation of lithium dendrites entirely. While a shear modulus of this magnitude is difficult to achieve with polymer electrolytes, we can greatly enhance the modulus of our electrolytes by covalently bonding the rubbery poly(ethylene oxide) to a glassy polystyrene chain. The block copolymer phase separates into a lamellar morphology yielding co-continuous nanoscale domains of poly(ethylene oxide), for ionic conduction, and polystyrene, for mechanical rigidity. On the macroscale, the electrolyte membrane is a tough free-standing film, while on the nanoscale, ions are transported through the liquid-like poly(ethylene oxide) domains. </p><p> Little is known about the formation of lithium dendrites from stiff polymer electrolyte membranes given the experimental challenges associated with imaging lithium metal. The objective of this dissertation is to strengthen our understanding of the influence of the electrolyte modulus on the formation and growth of lithium dendrites from lithium metal anodes. This understanding will help us design electrolytes that have the potential to more fully suppress the formation of dendrites yielding high energy density batteries that operate safely and have a long cycle life. </p><p> Synchrotron hard X-ray microtomography was used to non-destructively image the interior of lithium-polymer-lithium symmetric cells cycled to various stages of life. These experiments showed that in the early stages of lithium dendrite development, the bulk of the dendritic structure was inside of the lithium electrode. Furthermore, impurity particles were found at the base of the lithium dendrites. The portion of the lithium dendrite protruding into the electrolyte increased as the cell approached the end of life. This imaging technique allowed for the first glimpse at the portion of lithium dendrites that resides inside of the lithium electrode. </p><p> After finding a robust technique to study the formation and growth of lithium dendrites, a series of experiments were performed to elucidate the influence of the electrolyte&rsquo;s modulus on the formation of lithium dendrites. Typically, electrochemical cells using a polystyrene &ndash; block&not; &ndash; poly(ethylene oxide) copolymer electrolyte are operated at 90 &deg;C which is above the melting point of poly(ethylene oxide) and below the glass transition temperature of polystyrene. In these experiments, the formation of dendrites in cells operated at temperatures ranging from 90 &deg;C to 120 &deg;C were compared. The glass transition temperature of polystyrene (107 &deg;C) is included in this range resulting in a large change in electrolyte modulus over a relatively small temperature window. The X-ray microtomography experiments showed that as the polymer electrolyte shifted from a glassy state to a rubbery state, the portion of the lithium dendrite buried inside of the lithium metal electrode decreased. These images coupled with electrochemical characterization and rheological measurements shed light on the factors that influence dendrite growth through electrolytes with viscoelastic mechanical properties. (Abstract shortened by ProQuest.)</p>

<p> Thermoplastic elastomers are a class of rubbery polymeric materials that exhibit solidlike properties due to physically associating moieties. Block copolymers are often used as the network forming component of thermoplastic elastomers. Additionally, block copolymers can be modified with block selective solvents that contribute a specific functionality to the system; these solvent modified systems will be referred to throughout as thermoplastic elastomer gels. Thermoplastic elastomers and their gels have a long history of applications as specialty materials for passive systems where traditional rubbers cannot meet the required design criteria&mdash;often properties of softness, toughness and low hysteresis are of interest. Herein, we discuss the use of thermoplastic elastomer gels as active materials that respond to external stimuli to change their mechanical and thermal properties.</p><p> First, the text will introduce concepts of phase behavior and resultant physical behavior of block copolymers in the presence of a selective solvent. Included are specific details pertinent to materials used in experimental discussions presented in this work. Following this broad discussion, the introduction of a specific class of smart and responsive materials, known as dielectric elastomer actuators, is detailed in a survey of recent technological developments in the field.</p><p> The main body of the text describes multiple applications of thermoplastic elastomer gels. It begins with an entirely novel use of a semi-crystalline olefin block polymer gel as a dielectric elastomer actuator exhibiting programmable anisotropy and promising actuation behavior. The subsequent study uses specific control over the architecture of a polydimethylsiloxane elastomer to make ultra-soft films for exceptional dielectric elastomers. These so-called bottlebrush elastomers are formed from heavily grafted polymer backbones that reduce entanglements resulting in incredibly soft elastomers. As dielectric elastomers, these materials operate with no mechanical prestrain and achieve strains greater than 300% by area. This is followed by the use of a traditional ABA triblock copolymer (poly[styrene-bethylene- co-butylene-b-styrene]) with a crystallizing selective solvent to impart shape memory behavior. This is the first demonstration of a dielectric elastomer utilizing crystallization for electroactive strain fixation. Finally, we conclude with the discussion of thermoplastic copolyester based gels as form-stable phase change materials. These phase change gels have applications in passive thermal energy management systems and compete with existing commercial technologies.</p><p>

<p>Accessing improved elastomeric composites filled with functionalized graphene sheets (FGSs) requires an understanding of how the FGSs aggregate and how the position of FGSs affects the mechanical properties of the final composite material. In this thesis, I study both effects by devising models for 2-D particles in the 10s of microns scale and comparing my results with experiments. These models enable an understanding of the effect of the particles in a level that is hard to be studied experimentally or by molecular models. In the first part, I present a model for aggregation of 2-D particles and apply it to study the aggregation of FGS in water with varying concentrations of sodium dodecyl sulfate (SDS). The model produces clusters of similar sizes and structures as a function of SDS concentration in agreement with experiments and predicts the existence of a critical surfactant concentration beyond which thermodynamically stable FGS suspensions form. Around the critical surfactant concentration, particles form dense clusters and rapidly sediment. At surfactant concentrations lower than the critical concentration, a contiguous ramified network of FGS gel forms which also densifies, but at a lower rate, and sediments with time. This densification leads to graphite-like structures. In the second part, I present a model for the prediction of the mechanical properties of elastomers filled with 2-D particles. I apply this model to the Poly-dimethylsiloxane (PDMS)-FGS system. For a perfect polymer matrix and when inter-particle forces are ignored the strength of the composite can be increased with the addition of particles but elongation at failure decreases relative to neat PDMS. Maximum load transfer to the particles is achieved when particles are covalently linked to span the whole polymer matrix. Minimum drop in elongation at failure can be achieved by maximizing the distance between the covalently linked particles. When the assumption of a perfect polymer matrix is relaxed, it can be shown that there is a certain particle concentration range for which elongation at failure can be increased as the particles can protect the polymer by redistributing high stresses created by inherent polymer defects that would lead to early failure.

<p>Understanding the curing kinetics of a thermoset resin has a significant importance in developing and optimizing curing cycles in various industrial manufacturing processes. This can assist in improving the quality of final product and minimizing the manufacturing-associated costs. One approach towards developing such an understanding is to formulate kinetic models that can be used to optimize curing time and temperature to reach a full cure state or to determine time to apply pressure in an autoclave process. Various phenomenological reaction models have been used in the literature to successfully predict the kinetic behavior of a thermoset system. The current research work was designed to investigate the cure kinetics of Bisphenol-A based Benzoxazine (BZ-a) and Cycloaliphatic epoxy resin (CER) system under isothermal and nonisothermal conditions by Differential Scanning Calorimetry (DSC). The cure characteristics of BZ-a/CER copolymer systems with 75/25 wt% and 50/50 wt% have been studied and compared to that of pure benzoxazine under nonisothermal conditions. The DSC thermograms exhibited by these BZ-a/CER copolymer systems showed a single exothermic peak, indicating that the reactions between benzoxazine-benzoxazine monomers and benzoxazine-cycloaliphatic epoxy resin were interactive and occurred simultaneously. The Kissinger method and isoconversional methods including Ozawa-Flynn-Wall and Freidman were employed to obtain the activation energy values and determine the nature of the reaction. The cure behavior and the kinetic parameters were determined by adopting a single step autocatalytic model based on Kamal and Sourour phenomenological reaction model. The model was found to suitably describe the cure kinetics of copolymer system prior to the diffusion-control reaction. Analyzing and understanding the thermoset resin system under isothermal conditions is also important since it is the most common practice in the industry. The BZ-a/CER copolymer system with 75/25 wt% ratio which exhibited high glass transition temperature compared to polybenzoxazine was investigated under isothermal conditions. The copolymer system exhibited the maximum reaction rate at an intermediate degree of cure (20 to 40%), indicating that the reaction was autocatalytic. Similar to the nonisothermal cure kinetics, Kamal and Sourour phenomenological reaction model was adopted to determine the kinetic behavior of the system. The theoretical values based on the developed model showed a deviation from the obtained experimental values, which indicated the change in kinetics from a reaction-controlled mechanism to a diffusion-controlled mechanism with increasing reaction conversion. To substantiate the hypothesis, Fournier et al?s diffusion factor was introduced into the model, resulting in an agreement between the theoretical and experimental values. The changes in cross-linking density and the glass transition temperature (Tg) with increasing epoxy concentration were investigated under Dynamic Mechanical Analyzer (DMA). The BZ-a/CER copolymer system with the epoxy content of less than 40 wt% exhibited the greatest Tg and cross-linking density compared to benzoxazine homopolymer and other ratios.

Zeolite NaA films and membranes have been prepared using both in situ and seeded growth preparation processes. Films prepared using in situ preparations have shown this technique to be unsuitable for further development due to its inability to control the film microstructure, poor reproducibility, and dissolution of the substrate resulting in amorphous material incorporated in the film. Seeded growth, however, shows the ability to prepare highly oriented zeolite NaA films, the first zeolite films reported with this high degree of orientation. For the seeded growth preparation, nanometer sized zeolite particles are used in suspension to cast seed films. These films are prepared using dip coating, film casting, and electrostatic deposition. The seed films show a high degree of orientation with the [h00] planes of the seed crystals aligned parallel to the substrate surface. A higher degree of orientation where the particles are deposited in a hexagonal packed array can be achieved using dip coating with extremely slow withdrawal rates (∼1 cm/hr). These seed films are then subjected to a secondary growth process to eliminate the interzeolitic pores and form continuous zeolite layers. This has been achieved with clear solutions or gels resulting in continuous films 0.5 to 7μm thick with a high degree of orientation. The regrowth mechanism was investigated and results indicate that the growth of zeolite A films proceeds by multiple processes including epitaxial growth of the seeds and deposition of particles from solution. The membranes have been used for alcohol/water pervaporation. The membranes are highly selective for water and show selectivities >3,100 for water using (90/10) ethanol/water feed systems. In permeation measurements, these membranes show no selectivities other than Knudsen for permanent gases. Unlike Knudsen diffusion, these membranes show increasing permeation with increasing temperature. This indicates the probability of small defects in the films around 10Å. The defects shown by the gas permeation measurements indicate that cracks have formed in the membranes, possibly upon drying. It is believed that these are caused by the contraction of the zeolite NaA structure upon removal of water, which gives a 0.16% contraction in the dimensions of the unit cell.

Microphase separated block copolymers have been subject of investigation for past two decades. While most of the work is focused on classical phases of lamellae or cylinders, spherical phases have received less attention. The present study deals with the self-assembly in spherical phases of block copolymers that results into formation of a three-dimensional cubic lattice. A model triblock copolymer with several transition temperatures is chosen. Solidification in this model system results from either the arrangement of nanospheres of minor block on a BCC lattice or by formation of physical network where the nanospheres act as crosslinks. The solid-like behavior is characterized by extremely slow relaxation modes. Long time stress relaxation of the model material was examined to distinguish between the solid and liquid behavior. Stress relaxation data from a conventional rheometer was extended to very long times by using a newly built instrument, Relaxometer. The BCC lattice structure of the material behaves as liquid over long time except at low temperatures where an equilibrium modulus is observed. This long time behavior was extended to low shear rate behavior using steady shear rheology. The zero shear viscosity observed at extremely low shear rates has a very high value that is close to the viscosity calculated from stress relaxation experiments. The steady shear viscosity decreases by several orders of magnitude over a small range of shear rates. SAXS experiments on samples sheared even at very low rates indicated loss of the BCC order that was present in the annealed samples before shearing. In the second part, response of the BCC microstructure to large stress was explored. Shearing at constant rate and with LAOS at low frequencies lead to destruction of BCC lattice. The structure recovers upon cessation of the shear with kinetics similar to the one following thermal quench. Under certain conditions, LAOS leads to formation of monodomain textures. At low frequencies, there exists an upper and lower bound on strain amplitude where mono-domain textures can be obtained. Upon alignment, the modulus drops by about 30%. Measurement of rheological properties offers an indirect method to distinguish between polycrystalline structure and monodomain texture.

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 this study is focused on the analysis of atomic-scale mechanisms of plastic deformation in freestanding, ultrathin films of face-centered cubic (fcc) copper (Cu) that are subjected to biaxial tensile strain. The analysis is based on large-scale molecular-dynamics simulations. Elementary mechanisms of dislocation nucleation are studied and several problems involving the structural evolution of the thin films due to the glide of and interactions between dislocations are addressed. These problems include void nucleation, martensitic transformation, and the role of stacking faults in facilitating dislocation depletion in ultrathin films and other small-volume structures of fcc metals. Void nucleation is analyzed as a mechanism of strain relaxation in Cu thin films. The glide of multiple dislocations causes shearing of atomic planes and leads to formation of surface pits, while vacancies are generated due to the glide motion of jogged dislocations. Coalescence of vacancy clusters with surface pits leads to formation of voids. In addition, the phase transformation of fcc Cu films to hexagonal-close packed (hcp) ones is studied. The resulting martensite phase nucleates at the film’s free surface and grows into the bulk of the film due to dislocation glide. The role of surface orientation in the strain relaxation of these strained thin films under biaxial tension is discussed and the stability of the fcc crystalline phase is analyzed. Finally, the mechanical response during dynamic tensile straining of pre-treated fcc metallic thin films with varying propensities for formation of stacking faults is analyzed. Interactions between dislocations and stacking faults play a significant role in the cross-slip and eventual annihilation of dislocations in films of fcc metals with low-to-medium values of the stable-to-unstable stacking-fault energy ratio, γs/γu. Stacking-fault-mediated mechanisms of dislocation depletion in these ultrathin fcc metallic films are identified and analyzed. Additionally, a theoretical analysis for the kinetics of strain relaxation in Si1-xGex (0 ≤ x ≤ 1) thin films grown epitaxially on Si(001) substrates is conducted. The analysis is based on a properly parameterized dislocation mean-field theoretical model that describes plastic-deformation dynamics due to threading dislocation propagation; the analysis addresses strain relaxation kinetics during both epitaxial growth and thermal annealing, including post-implantation annealing. The theoretical predictions for strain relaxation as a function of film thickness in Si0.80Ge0.20 /Si(001) samples annealed after growth, either unimplanted or after He+ implantation, are in excellent agreement with reported experimental measurements.

The separation of hydrogen from other light gases is of particular importance to the chemical process industry. Membrane based processes offer a cost effective alternative to traditional processing while allowing the combination of separation and reaction in a single unit. Dense palladium or palladium alloy films are a natural choice for hydrogen separation due to their potential infinite selectivity for hydrogen. In this dissertation we investigated the construction of palladium-based supported hydrogen separation membranes using Supercritical Fluid Deposition (SFD). Compared to other deposition methods, SFD offers an effective metal deposition approach for porous materials due to its high precursor solubility, rapid mass transfer, and lack of surface tension. Three palladium precursors were evaluated for membrane construction in terms of thermal stability, reactivity and surface selectivity. Pd-X (X = Ag, Ni, or Cu) co-depositions were studied to determine the potential of SFD for direct alloy deposition. Intrinsic to effective membrane construction is the control of membrane location and thickness. Several different reactor and reactants geometries were utilized to control membrane location. An opposed reactants geometry was used to produce sub-surface membranes at controlled depths (80–600 μm) in porous α-alumina. A same-sided reactants geometry was used to produce surface films ranging in thickness from 100 nm to 5 μm on numerous support materials. Membranes were characterized using a variety of techniques including: SEM, XPS, XRD, EPMA, and gas permeation.