Browsing by Author "Biswal, Sibani L"
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Item A Systematic Study of Short and Long Range Interactions in Associating Fluids Using Molecular Theory(2015-12-17) Ahmed, Wael; Chapman, Walter G; Cox, Kenneth R; Tomson, Mason B; Biswal, Sibani LParameters needed for the Statistical Associating Fluid Theory (SAFT) equation of state are usually fit to pure component saturated liquid density and vapor pressure. In this thesis, other sources of information such as quantum mechanics, infinite dilution properties, Fourier transform infrared (FT-IR) spectroscopy and molecular dynamic (MD) simulation are used to obtain a unique set of parameters for complex fluids such as water and alcohols. Consequently, the equation of state can be more predictive and the parameters are not anymore system dependent. Moreover, the four vertices of the molecular thermodynamic tetrahedron (phase equilibrium experiments, spectroscopy, MD simulation and molecular theory) are used to study the distribution of hydrogen bonds in water and alcohol containing mixtures. The new sets of physical parameters and the knowledge gained in studying hydrogen bonding are then applied to model water content of sour natural gas mixtures as well as the phase behavior of alcohol + n-alkane and alcohol + water binary systems. Accurate determination of the water content in hydrocarbons is critical for the petroleum industry due to corrosion and hydrate formation problems. Experimental data available in the literature on the water content of n-alkanes (C5 and higher) is widely scattered. The perturbed chain form of the SAFT equation of state (PC-SAFT) was used to accurately correlate water mole fraction in n-alkanes, C1 to C16, which are in equilibrium with liquid water or ice. In addition, a list of experimental data is recommended to the reader based on its agreement with the fundamental equation of state used in this dissertation. The proposed molecular model was then applied to predict water content of pure carbon dioxide (CO2), hydrogen sulfide (H2S), nitrous oxide (N2O), nitrogen (N2) and argon (Ar) systems. The theory application was also extended to model water content of acid gas containing mixtures in equilibrium with an aqueous or a hydrate phase. To model accurately the liquid-liquid equilibrium (LLE) at subcritical conditions, cross association between CO2, H2S and water was included. The hydrate phase was modeled using a modified van der Waals and Platteeuw (vdWP) theory. The agreement between the model predictions and experimental data measured in our lab was found to be good across a wide range of temperatures and pressures. Modeling the phase behavior of liquid water can be quite challenging due to the formation of complex hydrogen bonding network structures at low temperatures. However, alcohols share some similarities with water in terms of structure and physical interactions. As a result, studying alcohol + n-alkane binary systems can provide us with a better understanding of water-alkane interactions. Besides, the application of alcohols in the petroleum and the biodiesel industry is of great importance. As a result, Polar PC-SAFT was used to model short chain 1- alcohol + n-alkane mixtures. The ability of the equation of state to predict accurate activity coefficients at infinite dilution was demonstrated as a function of temperature. Investigations show that the association term in SAFT plays an important role in capturing the right composition dependence of the activity coefficients in comparison to excess Gibbs free energy models (UNIQUAC in this case). Results also show that considering long range polar interactions can significantly improve the fractions of free monomers predicted by PC-SAFT in comparison to spectroscopic data and molecular dynamic (MD) simulations. Additionally, evidence of hydrogen bonding cooperativity in 1-alcohol + n-alkane systems is discussed using spectroscopy, simulation and theory. In general, results demonstrate the theory’s predictive power, limitations of Wertheim’s first order thermodynamic perturbation theory (TPT1) as well as the importance of considering long range polar interactions for better hydrogen bonding thermodynamics. Furthermore, the thermodynamics of hydrogen bonding in 1-alcohol + water binary mixtures is studied using MD simulation and Polar PC-SAFT. The distribution of hydrogen bonds in pure saturated liquid water is computed using TIP4P/2005 and iAMOEBA simulation water models. Results are compared to spectroscopic data available in the literature and to predictions using Polar PC-SAFT. The distribution of hydrogen bonds in pure alcohols is also computed using the OPLS-AA force field. Results are compared to Monte Carlo (MC) simulations available in the literature and to predictions using Polar PC-SAFT. The analysis show that hydrogen bonding in pure alcohols is best predicted using a two-site model within the SAFT framework. On the other hand, simulations show that increasing the concentration of water in the mixture increases the average number of hydrogen bonds formed by an alcohol molecule. As a result, a transition in association scheme occurs at high water concentrations where hydrogen bonding is now better captured using a three site alcohol model within the SAFT framework. The knowledge gained in understanding hydrogen bonding is applied to model the vapor-liquid equilibrium (VLE) and LLE of 1-alcohol + water mixture using Polar PC-SAFT. Predictions are in good agreement with experimental data, thus exhibiting the equation of state predictive power.Item Characterization of Atmospheric Nitrogen Chemistry and the Formation/ Evolution of Particulate Matter in Houston, TX(2015-12-04) Leong, Yu Jun; Griffin, Robert; Cohan, Daniel; Biswal, Sibani LThis thesis covers laboratory experiments to study the homogeneous reduction of nitric acid (HNO₃) to nitrous acid (HONO) in the presence of volatile organic compounds that are surrogates for those emitted by motor vehicles. The results presented in this study focus on the impact of environmental variables on the rate of formation of HONO in this process. The homogeneous conversion of HNO₃ to HONO has significant atmospheric implications due to the “renoxification” of less reactive HNO₃ into more reactive HONO. Consecutively, this thesis describes particulate matter (PM) data collected from a month-long (September 2013) field project in Houston, TX. A mobile laboratory containing state-of-the-art PM instrumentation and auxiliary measurements was deployed. The main focus for the thesis work was to utilize this dataset to better characterize PM pollution in the city of Houston. This was achieved by several analysis approaches including cluster analysis, back-trajectory analysis, and principal component analysis to describe spatial and temporal variations in submicron PM in the Houston region. Finally, this work describes the use of a statistical source apportionment technique, positive matrix factorization, on the field dataset to apportion important constituents of atmospheric aerosols in Houston. This technique allowed the apportionment of four organic aerosol factors, two of which were associated with organic nitrates from biogenic sources. Submicron PM plume events from on-road, industrial, and biomass burning sources in Houston also were chemically characterized. Because sources of PM pollution are still poorly understood, particularly in the highly industrial and urban city of Houston, the results from this thesis will advance PM modeling capabilities and allow improved PM control strategies in polluted urban areas similar to Houston.Item Engineered Nanomaterials for Energy Harvesting and Storage Applications(2014-11-03) Gullapalli, Hemtej; Ajayan, Pulickel M; Vajtai, Robert; Biswal, Sibani L; Arava, Leela Mohana ReddyEnergy harvesting and storage are independent mechanisms, each having their own significance in the energy cycle. Energy is generally harvested from temperature variations, mechanical vibrations and other phenomena which are inherently sporadic in nature, harvested energy stands a better chance of efficient utilization if it can be stored and used later, depending on the demand. In essence a comprehensive device that can harness power from surrounding environment and provide a steady and reliable source of energy would be ideal. Towards realizing such a system, for the harvesting component, a piezoelectric nano-composite material consisting of ZnO nanostructures embedded into the matrix of ‘Paper’ has been developed. Providing a flexible backbone to a brittle material makes it a robust architecture. Energy harvesting by scavenging both mechanical and thermal fluctuations using this flexible nano-composite is discussed in this thesis. On the energy storage front, Graphene based materials developed with a focus towards realizing ultra-thin lithium ion batteries and supercapacitors are introduced. Efforts for enhancing the energy storage performance of such graphitic carbon are detailed. Increasing the rate capability by direct CVD synthesis of graphene on current collectors, enhancing its electrochemical capacity through doping and engineering 3D metallic structures to increase the areal energy density have been studied.Item Engineering Surfaces for Sensitive Detection of Analytes(2023-08-11) Niu, Sunny; Biswal, Sibani LEngineering functional surfaces and tuning their properties has significant implications that allow us to harness their potential in addressing relevant scientific challenges. The work presented in this thesis investigates the intelligent design of micro- and nanoscale surfaces and their interactions with biomolecular and SERS-active analytes in sensing applications. In the first part of this thesis, the numerous surface interactions involved in a biosensor are investigated and optimized to produce a device for detection of blood-based biomarkers of traumatic brain injury. The next body of work presents an alternate sensing platform that also takes advantage of the surface properties of plasmonic, nanoscale materials and their interaction with light. Finally, a novel methodology for surface-sensitive investigation of proteins using ToF-SIMS is presented. Collectively, this work aims to harness interactions at surfaces and interfaces to create novel, functional solutions to sensing challenges.Item Experimental study of the effect of commercial dispersants on the precipitation, aggregation and deposition of asphaltenes(2015-11-30) Melendez Alvarez, Ariana A; Vargas, Francisco M.; Biswal, Sibani L; Verduzco, Rafael; Wellington, ScottAsphaltene precipitation and subsequent deposition is a potential flow assurance problem for the oil industry nowadays. Moreover, because oil production is moving to more difficult production environments – e.g. deeper waters – or is focusing on extracting residual oil using enhanced oil recovery techniques, the significant changes of pressure, temperature and/or composition can aggravate asphaltene deposition problems. One of the most common strategies to prevent or at least reduce asphaltene deposition is the utilization of chemical additives. However, there are still several unresolved challenges associated with the utilization of these chemicals: First, the experimental conditions and results obtained in the lab are not always consistent with field observations. Also, in some cases these chemical additives seem to worsen the deposition problem in the field. Therefore, there is a clear need to revisit the commercial techniques used to test the performance of asphaltene inhibitors and to provide a better interpretation of the results obtained. In this work, a technique based on NIR spectroscopy is presented to evaluate the performance of three commercial asphaltene dispersants. The results are also validated using a digital optical microscope. This technique is faster and more reproducible compared to available methods such as Asphaltene Dispersion Test (ADT) and Solid Detection System (SDS). Also, unlike the ADT test, the proposed method can evaluate the performance of the dispersants in a wide range of temperatures and compositions. The chemical additive dosage, aging time and temperature effect on asphaltene aggregation process are also discussed in this manuscript. A new system to study asphaltene deposition on metal surfaces that offers advantages over capillary systems was developed. This new apparatus is based on a column packed with carbon steel spheres. The current version of this device operates at ambient pressure and has potential for the fabrication of a high-pressure system in the near future. The work presented in this dissertation will contribute to a better understanding of the variables that affect the performance of asphaltene dispersants, and the true effect these chemicals have on the complex multi-step mechanism of asphaltene precipitation, aggregation and deposition.Item Hydrogen doping and the metal-insulator phase transition in vanadium dioxide(2015-04-22) Ji, Heng; Natelson, Douglas; Du, Rui-rui; Biswal, Sibani LStrongly correlated systems represent a major topic of study in condensed matter physics. Vanadium dioxide, a strongly correlated material, has a sharp metal-to-insulator phase transition at around 340 K (67 °C), a moderate temperature which can be easily achieved. Its potential as a functional material in optical switches and semiconductor applications has attracted a great deal of attention in recent years. In this thesis, after a detailed introduction of this material and the methods we used to grow VO2 in our lab (Chapter 1), I will discuss our attempts to modulate the electronic properties and phase transition of single-crystal VO2 samples. It started with a plan to use ionic liquid to apply an electrostatic gate to this material. Although modulation of the resistance was observed, we also discovered an unexpected electrochemical reaction, leading to a suspicion that hydrogen doping is the reason for the change of properties of VO2 (Chapter 2). Next, a series of experiments were performed to systematically study the mechanism of this hydrogen doping process and to characterize the hydrogenated VO2. Our collaborators also provided supporting simulation results to interpret these phenomena from a theoretical point of view, as well as results from synchrotron x-ray diffraction and neutron diffraction experiments. From all these studies, we confirmed the existence of the hydrogen intercalation in VO2 (Chapter 3), and further, plotted the phase diagram as a function of temperature and hydrogen concentration (Chapter 5). We also found that this diffusion process prefers the rutile crystal structure of VO2 (i.e. metallic phase) and specifically, its c-axis (Chapter 4). Finally, the low-temperature electric transport properties of the hydrogenated VO2 material have been studied for the first time, and interesting magneto-resistance responses will be discussed (chapter 6).Item Investigating the use of directed magnetic assembly to create tunable colloidal fractal aggregates and DNA-linked bead-spring chains(2014-09-12) Byrom, Julie Elizabeth; Biswal, Sibani L; Pasquali, Matteo; Morosan, EmiliaThe purpose of this work is to develop techniques for building complex colloidal assemblies using an applied magnetic field. The greatest challenge in this field is creating sophisticated, dynamic structures from relatively simple building blocks and interactions. Particles with magnetic properties assemble via dipolar interactions into chains along the direction of the field. Additionally, it is possible to assemble nonmagnetic particles in a magnetic field if they are immersed in a magnetic fluid. This effect is known as negative magnetophoresis (the nonmagnetic particles develop a dipole in the direction antiparallel to the external field)—and the particles are effectively diamagnetic. However, the anisotropic dipolar interaction can be a limiting factor in producing complex structures, as many magnetic assemblies are one-dimensional. In this proposal, we combine paramagnetic and diamagnetic particles to create assemblies in two-dimensions (both parallel and perpendicular to the field) and demonstrate the ability to change the morphology of these assemblies simply by changing the magnetic susceptibility of the ferrofluid as well as the overall concentration and ratio of colloids in solution. These ramified aggregates may be used in the future to build gel-like networks, which can be used as novel magnetorheological fluids and will offer valuable insight into the process of gelation via dipolar interactions. Although they may lack the complexity of the fractal aggregates just described, chains of colloids are still an important analogue for studying polymer and biofilament behavior. One characteristic which can greatly affect the properties of these filaments is their flexibility. Previous attempts to create linked particle chains have been limited to persistence lengths in the rigid and semiflexible regimes, but here we describe the method we have devised to create chains that fall in the rigid, semiflexible, and flexible regimes. This involves linking the beads of the chain with long strands of DNA, of sizes varying up to the same order of the beads themselves. This creates a physical analogy of the “bead-spring” system proposed by Rouse and Zimm. We show that we can control the flexibility of the chains by either altering the length of the DNA to tune its spring constant, or alternatively we can also tune the magnetic field strength used to assemble the chains. The field strength controls the strength of the dipolar interactions between particles and regulates the interparticle spacing between beads. This can lead to greater or fewer numbers of DNA strands which are able to form bridges, and this changes the effective spring constant holding the beads together. We demonstrate that the flexibility changes predictably within a certain range of DNA sizes, and that when the DNA becomes of similar size to the particles the DNA becomes excluded from the chain and the chains subsequently become more rigid. Unlike chains linked with smaller molecules, these chains are very resilient to shear and torque, which will allow them to be used to study filament buckling and the development of bending instabilities in complex magnetic fields or flow patterns. Finally, we explore the use of shorter DNA linkers to create batches of chains which can exhibit different flexibilities at different temperatures. This is done by exploiting the melting behavior of DNA, because micron sized particles do not exhibit the sharp melting transitions of DNA-linked nanoparticles due to the lower density of DNA on the surface and their inability to melt cooperatively. Thus, as portions of the DNA linkers are melted we see a gradual increase in flexibility of the chains with a minimal amount of breakage along the chain. This process should be reversible and would allow us to create more versatile solutions of chains. Additionally, since the DNA on larger particles has a broader melting curve, we can use them to study the effects of the initial unbinding events, which would not be possible in a system where cooperative melting cascades create sharp melting transitions. Overall, this thesis provides novel insights into the use of directed magnetic assembly to create complex colloidal structures.Item Investigation of a system with a tunable anharmonic interaction potential using paramagnetic colloids(2019-04-19) Hilou, Elaa; Biswal, Sibani LColloidal physics dictates properties of many small-scale and large-scale systems with applications ranging from drug delivery to catalysis. Colloidal systems can also be used as emulsion stabilizers or used in liquid crystal displays. Scientists and engineers have studied colloids to model the behavior of macroscopic systems at the atomic level. Colloids are uniquely suited for this application because the associated length scales are large enough to observe under an optical microscope, yet small enough so that their dynamics are driven by thermal motion. In this work, we manipulate magnetically induced and negatively charged colloidal particles in which we can control their interactions by applying a tunable magnetic field. Magnetically tunable particles provide us the ability to control the structure and phase behavior of the colloidal dispersions. Tunability allows for precise manipulation of particle interactions and thus, particle assembly into colloidal agglomerates that exhibit both fluid-like and crystal-like properties. These collections of particles nucleate, coalesce, and grow over time, which are properties of a model system for non-equilibrium and quasi-equilibrium behaviors. At quasi-equilibrium, these systems do not exhibit great changes in morphology, but can still coarsen over time. A non-equilibrium state is characterized by dynamics such as nucleation, decomposition, and coalescence. The system changes at a scale large enough to affect the energetics and morphological properties of the system. This dissertation is divided into two parts, one that focuses on the characterization of what we call colloidal clusters which are finite-sized aggregates that form in a sample with low particle concentration. These aggregates are individual islands of particles with adequate spacing such that we are able to examine them individually. The second half of this thesis describes the kinetics that take place when a colloidal dispersion undergoes quenching, causing behavior analogous to that of phase separating systems. We quantify the stability and kinetics of the system by measuring thermodynamic properties and morphological features as a function of three main parameters: time, t , field strength, B, and particle concentration. We characterize the phase behavior by considering both the bulk and interfacial properties of colloidal aggregates. We also find a scaling relationship between the three parameters to predict the aggregation kinetics governing systems that undergo quenching caused by long-range interactions.Item Isothermal Nucleic Acid Assays Based on Nucleic Acid Sequence Based Amplification (NASBA) and Recombinase Polymerase Amplification (RPA) for HIV-1 Diagnosis and Management in Low Resource Settings(2015-04-01) Rohrman, Brittany Ann; Richards-Kortum, Rebecca Rae; Biswal, Sibani L; McDevitt, JohnOver two-thirds of the estimated 35 million people worldwide infected with HIV live in the developing world. Nucleic acid tests (NATs) are necessary for early infant diagnosis and for monitoring patients receiving therapy. However, NATs cost $50-100 USD per test and require expensive thermal cycling equipment that may be unavailable in the developing world. This thesis presents two low-cost NATs for HIV-1 diagnosis and management that are based on isothermal amplification, which eliminates the need for expensive thermal cycling equipment. In one assay, HIV-1 viral RNA is detected using nucleic acid sequence based amplification (NASBA) and a custom lateral flow test. This assay costs about \$16 USD and only requires a heat block. When coupled with NASBA, the lateral flow test detected concentrations of synthetic RNA spanning the entire clinical range. When the assay was evaluated using pediatric plasma samples, the sensitivity (61%) and limit-of-detection (10,000 HIV-1 copies/mL plasma) were lower because of the genetic diversity of the samples, and the specificity was lower (88%) due to amplicon contamination. In the other assay, HIV-1 proviral DNA is amplified using recombinase polymerase amplification (RPA). This assay, which costs about \$5 per test, was integrated into a paper and plastic microfluidic device. The device was capable of amplifying 10 copies of plasmid HIV-1 DNA to detectable levels in 15 minutes. The assay was then adapted for real-time quantification. On average, the assay predicted sample concentrations within one order of magnitude of the correct concentration. In addition, a method for incubating RPA reactions without external equipment was developed. Using human body heat for incubation, all RPA reactions with 10 copies of plasmid HIV-1 DNA and 95% of reactions with 100 copies of plasmid HIV-1 DNA tested positive. Finally, concentrations of background DNA found in whole blood were shown to prevent the amplification of target DNA by RPA. To address this problem, three sequence-specific capture methods were developed to enrich target DNA concentration relative to background DNA concentration. These methods may be enable detection of high proviral loads in 0.1 mL infant blood samples but require improvement to detect lower proviral loads.Item Microstructure and Interfacial Properties of Aqueous Mixtures(2014-11-07) Ballal, Deepti; Chapman, Walter G; Biswal, Sibani L; Kolomeisky, Anatoly BUnderstanding the properties of aqueous mixtures has important implications in applications ranging from enhanced oil recovery to biochemical processes. While there has been considerable effort invested in understanding the bulk properties of aqueous mixtures, very few studies have concentrated on their behavior in interfacial systems. Interfacial properties, which are important for applications like coatings and chemical separations, are defined by the molecular structuring of the fluid at the interface. The goal of this thesis is to understand and alter the wetting of solid surfaces by aqueous mixtures. In particular, we study the partitioning of aqueous mixtures of polar and non-polar molecules to different surfaces. What makes aqueous mixtures interesting is the hydrogen bonding nature of water that plays very different roles in the partitioning of polar and non-polar components of the aqueous mixtures. In this thesis, hydrogen bonding is modeled using a thermodynamic perturbation theory due to Wertheim. The theory, included in a classical Density Functional Theory framework, is used to study the molecular structure and interfacial properties of the system. We extend and apply the theory to study a number of aqueous mixtures. Key contributions of this thesis include 1. Predicting the interfacial properties of aqueous mixtures of short alcohols close to a hydrophobic surface 2. Extension of the first order perturbation theory to study the competition between intra and intermolecular hydrogen bonding of molecules in the presence of an explicit water-like solvent 3. Studying the effect of physical conditions and surface chemistry on the wetting of different surfaces by water-oil mixtures 4. Analyzing molecular simulation models for water-alkane interactions through a solubility studyItem Rotational dynamics of superparamagnetic colloidal systems in complex fields(2023-11-29) Spatafora Salazar, Aldo Stefano; Biswal, Sibani LComposite superparamagnetic colloidal suspensions assemble into a variety of higher-order structures when exposed to complex magnetic fields. These magnetic fields vary their direction, strength, or both as a function of time and can have additional dynamical aspects. As a result of the time-varying nature of the complex fields, the assembled structures undergo rotational dynamics. This thesis studies how complex fields modify the morphology of the assemblies and tune the dipolar interactions during rotational actuation. After an extensive review, the first part of the thesis elucidates the deformation of semiflexible DNA-linked superparamagnetic chains undergoing rotational motion under low-frequency circular and eccentric rotating fields. The chain deforms via transient coiling dynamics or steady-state periodic buckling that depend on the evolution of the dipolar interactions over time. In the second part, clusters and dimers of these colloids are studied under a high-frequency alternating rotating field. The inhibited rotation of the clusters coincides with the acquisition of anisotropic shapes. Novel dipolar interactions are uncovered upon analyzing the dynamics of dimers under this field, arising from a delay in the rotational dynamics of the colloids’ magnetization. Overall, this thesis describes how complex fields can be used to externally control the configurations of actuated superparamagnetic colloidal systems.Item Surfactant Enhanced Oil Recovery(2015-02-03) Sagi, Aparna Raju; Hirasaki, George J.; Miller, Clarence A.; Biswal, Sibani L; Li, QilinThe application of surfactants in Enhanced Oil Recovery (EOR) is the central theme of this thesis. The use of different EOR methods, thermal, gas flooding, surfactant flooding, etc. to improve the recovery of oil has become more relevant in recent years with the world’s demand for energy increasing, decreasing oil production from mature fields, and a lower than required rate of addition of new fields to make up for these two trends. Surfactants can be employed in EOR processes in three main ways: (1) to lower the Interfacial tension (IFT) between oil and brine to ultra-low values (lesser than 10-3 mN/m) which will reduce the capillary forces that trap the oil in the pores, and enable the oil to be produced by viscous of gravitational force, (2) by altering the wettability of the reservoir rock from being oil-wet to water-wet thereby resulting in the spontaneous imbibition of brine into the pores and the displacement of oil out of the pores, (3) as foam as to improve the reservoir sweep efficiency of other oil recovery methods like gas floods, surfactant floods, steam floods, etc. This thesis discusses the application of surfactants for a low IFT EOR process tailored to a low temperature (25 °C - 30 °C), low salinity (~11,000 ppm total dissolved solids (TDS) carbonate reservoir, and as a foam based mobility control agent for a miscible enriched hydrocarbon gas flood in a sandstone reservoir at high temperature (68 °C) and moderate salinity (~24,000 ppm TDS). Alcohol Propoxy (PO) Sulfates (APSs) and their blends with Internal Olefin Sulfonates (IOSs) were assessed by surfactant-brine-oil phase behavior studies to identify which of them formed stable aqueous solutions, and were capable of reducing IFT at the given conditions of temperature, salinity and crude oil. The selected surfactant was also evaluated in terms of viscosity of phases, to ensure that no high viscosity phases were formed, and in terms of adsorption on reservoir rock, which needs to be low for the process to be economical. Due to ease of handling initial phase behavior evaluation in this study and in a majority of such studies by others is done with dead crude oil (oil devoid of the light components which come out of the oil when depressurized to atmospheric pressure). But is known that surfactant phase behavior is highly dependent of the composition of the oil. To this end, experiments with live oil were carried out to determine the effect of different gases, methane, ethane, carbon dioxide, and separator gas, on surfactant phase behavior. Some surfactants that were evaluated exhibited non-classical phase behavior, i.e., they did not exhibit the classical Winsor phase transition of Type IType IIIType II, which is accompanied by an increasing oil solubilization parameter (σo) and decreasing water solubilization parameter (σw). These systems did not form a Type III system, and instead showed a Type IType II transition. Moreover, the σo (high σ is an indicator of low IFT) appeared to reach a peak and then decrease in the Type I region. The reasons behind these non-classical aspects of phase behavior were deciphered and are discussed in terms of surfactant partitioning and emulsion stability. In the last part of the thesis, Alpha Olefin Sulfonate (AOS) foam was studied for application in a miscible gas flood, on the principle that foam would form more preferentially in a high permeability low residual oil zone (swept zone), thereby reducing the gas mobility in this zone, resulting in the diversion of the gas to low permeability zones, and reduced bypassing of gas to the production well. AOS foam with nitrogen and enriched hydrocarbon gas at reservoir temperature (68 °C), and pressure (~3,300 psi) was evaluated in consolidated porous media (Berea cores), in terms of foam generation and propagation ability, and foam strength measured as gas apparent viscosity. The effect of miscible flood residual oil saturation on foam strength was evaluated to assess if strong foam could be generated in the presence of oil (which in some cases in known to destabilize foam).Item Synthesis of black silicon anti-reflection layers for silicon solar cells(2015-04-23) Lu, Yen-Tien; Barron, Andrew R; Biswal, Sibani L; Verduzco, RafaelSolar energy is one of the most important renewable energy resources in the world. Among all kinds of solar cells, the fabrication technology of silicon solar cells is relatively mature which makes them more popular in the solar cell market. However, in order to compete with the traditional energy sources, decreasing cost of per watt output seems necessary. Hence, increasing the energy conversion efficiency with an economical approach is an unavoidable issue. One solution is applying anti-reflection layers onto the silicon solar cells to maximize energy conversion efficiency. Recently, black silicon anti-reflection layers have attracted attention because their anti-reflection ability is less confined by the incident light angle and wavelength. In this thesis, two methods, the metal-assisted chemical etching and the contact-assisted chemical etching method, which have potential to economically fabricate large-scale black silicon on silicon solar cells are systematically studied. The complete etching mechanisms of these two methods are also proposed to clearly describe the fabrication process of black silicon.Item The characterization and visualization of multi-phase systems using microfluidic devices(2015-03-10) Conn, Charles Andrew; Biswal, Sibani L; Hirasaki, George J; Wong, Michael S; Riviere, Beatrice MThe stability and dynamics of multi-phase systems are still not fully understood, especially in systems of confinement such as microchannel networks and porous media. In particular, systems of liquids and gases that form foam are important in a number of applications including enhanced oil recovery (EOR). This research seeks to better understand the mechanisms of multi-phase fluid interaction responsible for the displacement of oil. The answers to these questions give insight into the design of efficient EOR recovery strategies, and provides a platform on which researchers can perform studies on pore-level phenomena. Our experiments use poly(dimethylsiloxane) (PDMS) devices which can be made using inexpensive materials without hazardous chemicals and can be designed and fabricated in just a few hours to save time, money, and effort. The unique contribution of this thesis is the development of a general “reservoir-on-a-chip” research platform that facilitates study of multi-phase systems relevant to energy-industry applications. Experiments with a fractured porous media micromodel quantified pressure drop and remaining oil saturation for different recovery strategies. It demonstrated foam flooding’s superior performance compared to waterflooding, gas flooding, and water-alternating-gas flooding by increasing flow resistance in the fracture and high-permeability zones and directing fluids into the low-permeability zone. Mechanisms of phase-separation were observed which suggest it is inappropriate to treat foam as a homogeneous phase. Experiments with foam in a 2-D porous matrix investigated mechanisms of foam generation, destruction, and transport and related foam texture (bubble size) to pressure drop and apparent viscosity. MATLAB code written for this thesis automated quantification of over 120,000 bubbles to generate plots of bubble size distributions for alpha olefin sulfonate (AOS 14-16) at different foam quality (gas fraction) conditions. The experimental devices and analytical software tools developed in this work open the door for future experiments to screen and compare surfactant formulations. One may readily envision developing libraries of surfactant data from micromodel experiments which can then be data-mined to discover relationships between surfactant structure, performance, and environmental conditions.