Browsing by Author "Ardebili, Haleh"
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Item A Simulation Approach to Thermodynamics in Interfacial Phenomena(2013-05) Pandey, Yogendra Narayan 1982-; Doxastakis, Manolis; Krishnamoorti, Ramanan; Stein, Gila E.; Ardebili, Haleh; Kulkarni, YashashreeIndustrial applications such as production of high performance polymer-nanocomposites, semiconductor fabrication, and catalysis involve molecular level phenomena governed by interfacial interactions. Precise control of these interactions will leverage the performance of materials in these applications. However, the ability to tailor the molecular characteristics is hindered by incomplete understanding of the controlling factors. This dissertation is broadly divided in three parts discussing the development and application of modern computational methods to elucidate such characteristics. In the first part, detailed atomistic simulations of polymer-nanoparticle systems are performed by coupling preferential sampling techniques with connectivity-altering Monte Carlo algorithms to address the challenges in modeling polymer melts in proximity to a solid. The results reveal that polymer architecture holds a prominent role in systems with nanoscopic particles. Furthermore, a scheme for developing coarse-grained models of polymers with specific chemistry in contact with the solid surface is presented and quantitatively evaluated. These models are necessary to address the larger length scales required for study of polymer-particle mixtures. Interfaces and substrate interactions play an important role for increasingly thinner polymer films employed in the semiconductor industry. There is a clear need to develop predictive models capable of describing reaction-diffusion phenomena in chemically-amplified resists and analyze their performance as a function of film thickness. In this dissertation, using mesoscopic models it is found that a central aspect governing reactions is the anomalous diffusion of the photogenerated acid. The anomalous diffusion coupled with a simple second-order acid annihilation scheme quantitatively captures experimental data for all practical conditions - with only two adjustable parameters. The need to combine the developed scheme with substrate interactions is demonstrated. Finally, the mechanism of zeolite crystal growth in solutions in the presence of growth modifiers is probed by employing atomistic simulations. It is hypothesized that molecules preferentially bind to specific crystal surfaces, which alters the crystal morphology. Using free energy calculations, the affinity of these molecules to interact with model zeolite surfaces is estimated. Distinct free energy minima and orientations of the inhibitor molecule in these minima are characterized and quantified providing a unique molecular understanding of the phenomena.Item AC Losses and Mechanical Properties of Multifilamentary High Temperature Superconductor Tapes and Wires(2019-05) Ben Yahia, Anis; Selvamanickam, Venkat; Ryou, Jae-Hyun; Wolfe, John C.; Kulkarni, Yashashree; Ardebili, HalehWith the ability to operate at high magnetic fields and high temperatures, and with significant progress in critical current density, RE-Ba-Cu-O (REBCO, RE = rare earth) coated conductors (CC) have an immense potential for use in various coil and cable applications. However, the tape form of these CC creates additional problems. The excessively high AC losses and the limited flexibility are major challenges impeding the development and commercialization of these tapes. Recently, there have been efforts to convert flat REBCO tapes into a round wire. The diameter of these wires has been reduced using thinner substrate tapes and by positioning the copper stabilizer mainly on the REBCO film side. In this dissertation, using a combination of experimental and analytical results, the copper thickness on the REBCO side has been optimized to maximize the critical current retention of tapes with various substrate thicknesses at small bend diameters. The presented analytical method accounts for the neutral axis shift caused by the progressive plastic deformations. Using these results, an optimal design for ultra-small diameter symmetric tape round (STAR) wires is also proposed. In addition, an alternate approach to enhance REBCO CC bending properties by using two tapes joined face-to-face is presented. In this structure, the two REBCO layers are positioned closer to the neutral axis. Two methods to fabricate such structures were implemented and their bending performance characterized. To reduce the AC losses in REBCO tapes, a fully-scaled reel-to-reel filamentization process allowing the production of long length multifilamentary tapes has been developed. The process uses laser ablation followed by oxygenation and selective electroplating. The AC losses of reel-to-reel produced multifilamentary tapes was significantly reduced by preventing copper growth on their back side. To address the coupling losses over long length, a new transposition pattern was also proposed and implemented. Finally, the striation process was modified to allow the integration of the multifilamentary tapes into the STAR wires. STAR wires with various number of filaments per tape were fabricated and their AC losses characterized. Results showed exceptional AC losses reduction over a broad range of frequencies and fields compared to a normal REBCO tape.Item Atomistic Modeling of Nanostructures via Molecular Dynamics and Time-Scaling Methods(2016-08) Hammami, Farah; Kulkarni, Yashashree; Sharma, Pradeep; Ardebili, Haleh; Willam, Kaspar J.; Mavrokefalos, AnastassiosNanostructures are emerging as novel materials with revolutionary application in electronics, nuclear reactors, structures, aerospace, and energy. Nanocrystalline structures owe their outstanding mechanical properties to their nanoscale grain size and high density of crystalline interfaces called grain boundaries. Recently, nanotwinned structures, containing special grain boundaries called twin boundaries, have become quite attractive as optimal motifs for strength, ductility, and grain stability in metals. This dissertation presents our atomistic study of the role of these grain boundaries and twin boundaries in governing the mechanical response of nanostructures by way of different atomistic simulation methods. Nanopillar compression is first used to investigate the interplay between size effects associated with the twin spacing and the finite size of nanopillars by molecular dynamics. Simulations reveal that there exists an optimal aspect ratio for which the yield strength of twinned nanopillars is higher than even single crystal nanopillars. In addition, it is observed that twin boundaries facilitate dislocation-starvation as defects glide along twin boundaries and are annihilated at the free surface. Approaching experimentally-relevant strain rates has been a long-standing bottleneck for molecular dynamics. In this study, shearing of a nanopillar with a grain boundary is used as a paradigmatic problem to investigate the rate dependence of grain boundary sliding in nanostructures. A combination of time-scaling approaches is used including the recently developed autonomous basin climbing method, the nudged elastic band method, and kinetic Monte Carlo, to access strain rates ranging from 0.5s-1 to 107s-1. Although grain boundary sliding is the primary mechanism observed in all simulations, at lower strain rate, sliding initiates at significantly lower stress and occurs on the time-scale of seconds which is beyond the reach of conventional molecular dynamics. Finally the time scaling approach is used to investigate the diffusion of radiation-induced point defects through nanotwinned metals. The simulations reveal that dumbbell interstitials can cross coherent twin boundaries in three low energy barrier steps which can occur even at room temperature. Furthermore, the method shows that Frenkel pairs have greater probability to recombine in the vicinity of coherent twin boundaries which is consistent with observations reported by other computational studies.Item Atomistic Simulations of Particle Reinforced Nanocrystalline Materials(2018-12) Kadiyala, Janakiram Kaushal; Kulkarni, Yashashree; Ardebili, Haleh; Feng, QianmeiNanocrystalline materials have applications in numerous fields due to their high strength. Grain growth is prevalent in nanocrystalline materials and leads to a decrease in material strength. Zener pinning has proven to be effective in hindering grain growth and thus, maintain the strength of the material. In this work, atomistic simulations were performed to understand and visualize the effect of Zener pinning in restricting grain boundary motion, and hence grain growth. The simulations were performed on two different grain boundary structures, ∑ 5 and ∑ 17 by varying the particle diameter and distance between the particles and compare these results with that of structures without any particles. The impact of adding high particle volume fraction (up to 50%) in Ag polycrystals to produce ultrahigh strength materials is also discussed. The yield strength of these nanocomposites was evaluated by varying particle volume fraction, particle size and inter-particle spacing. The highest yield strength observed in Ag nanocomposites was found to be about 5 times the strength of nanocrystalline Ag. The possible strengthening mechanisms responsible for this huge increase are discussed based on molecular dynamics results.Item Automatic First Break Detection by Spectral Decomposition Using Minimum Uncertainty Wavelets(2012-12) Kapur, Sunil 1988-; Kouri, Donald J.; Rao, Jagannatha R.; Ardebili, HalehSeismic Signal Processing can be effectively utilized to determine micro- seismic events. With the advances in hydraulic fracturing techniques, first break detection has become really important in locating micro-seismic events. The measured data collected gathers far more information than can be extracted by human operators and whose interpretation can consume a lot of time. The transforma- tion in the computational efficiency suggests the involvement of computers in interpreting the measured data. We suggest a new method of first break detec- tion that is based on time-frequency spectral decomposition method and utilizes the Cn Transform and the Super-Gaussian μ wavelets. We tested our method on lab data with various signals and first arrival time was determined. The results were compared to the manual detection and our method had an accuracy of 0.6 μ seconds. The results indicate that our method is robust and is successful in detecting the first arrival time automatically.Item Blending PLA(Poly-lactic acid) with layered silicates(2013-05) Heo, Yoo Rang 1986-; Krishnamoorti, Ramanan; Robertson, Megan L.; Ardebili, HalehLayered silicates are used for organic/inorganic hybrid fillers to reinforce the polymers. Dispersion of polymer and layered silicate is important because phase separation leads to weak interaction which makes poor property at polymer-layered silicate nanocomposites. In this work, PLA(Poly-lactic acid) is synthesized from cyclic L-lactide with layered silicates through in-situ ring opening reaction with varying concentrations of layered silicate. PLA is an attractive biomaterial and is used for packaging due to high strength and high-modulus properties. Its shortcomings such as barrier property, brittleness can be enhanced by mixing it with organic modified layered silicate. The polymer-layered silicate nanocomposites are characterized by x-ray diffraction, thermal gravimetric analysis and optical microscopy. In this work, intercalated or exfoliated polymer layered silicate nanocomposites could be achieved. The analysis of samples shows that crystallinity is decreased with increasing inorganic concentration. In addition, thermal stability and morphology also depend on dispersibility and inorganic concentration.Item Bottlebrush Polymers: A Pathway to Engineering Surfaces and Interfaces(2018-05) Mah, Adeline; Ruchhoeft, Paul; Stein, Gila E.; Robertson, Megan L.; Ardebili, Haleh; Verduzco, RafaelBottlebrush polymers are macromolecules with a linear backbone and densely-grafted polymeric side-chains. Steric repulsion between the side chains forces the backbone to extend, leading to a rod or wormlike conformation. Therefore, bottlebrush polymers resemble both comb polymers and polymer-grafted particles. Our goal is to develop an in-depth understanding on the thermodynamics of bottlebrush polymer additives for linear hosts, with an emphasis on understanding interface and surface attraction for the design of compatibilizers and functional coatings. First, we studied the phase behavior of bottlebrush polymers with random copolymer poly (styrene-r-methyl methacrylate) side-chains in a blend of two immiscible homopolymers, polystyrene and polymethyl methacrylate. We determined that bottlebrush composition and architecture will control the morphology of the blends and identified the conditions that lead to the formation of a bottlebrush-rich interphase that suppresses coarsening of the blend microstructures. Second, we studied the segregation behavior of bottlebrush polystyrene in a blend with linear polystyrene by systematically changing the bottlebrush side-chain length, bottlebrush backbone length, and length of the linear host. We developed a scaling law and generated a phase diagram that describes the segregation behaviors of bottlebrush polymers in a thin film. Finally, we investigated the stability and swelling response of bottlebrush networks that were crosslinked using atom beam lithography. We found that swelling declines as the number of side-chains is increased, which is consistent with a simple Flory model for equilibrium swelling of networks.Item Computational Modeling of Structural Energy Storage(2020-05) Aderyani, Sarah; Ardebili, Haleh; Sharma, Pradeep; Kulkarni, Yashashree; Ryou, Jae-Hyun; Rodrigues, Debora F.Flexible structural energy storage is a rapidly emerging area with tantalizing applications such as integrated devices in textiles and smart suits, portable electronic devices and electric vehicles (EV). Due to several outstanding properties, graphene oxide (rGO)/ aramid nanofiber (ANF) composite material has emerged as a compelling choice as a structural electrode for supercapacitors and batteries. A key question of significant technological relevance pertains to what kind of nanoscale architecture motifs may lead to enhanced ionic diffusivity — the key characteristic dictating the overall performance of the electrode. In this work, we attempt to address this precise question, through multiphysics computational modeling in the context of several experimentally realizable nanoarchitectures, namely, “layered” and “house of cards” nanostructures. We investigate different arrangements (staggered, aligned and square) with various degrees of waviness of the rGO nanosheets inside the ANF polymer matrix. Nanoarchitecture modeling results indicate that decreasing waviness of the rGO sheets can enhance the ion diffusivity in the staggered and aligned arrangements of the electrode material, while this effect is stronger in staggered arrangement than aligned arrangement. The results obtained from nanoarchitecture computational modeling are compared to the porous media approach. It is shown that the widely used porous electrode theory such as Bruggeman or Millington-Quirk relations, overestimates the effective diffusion coefficient. Also, the results from nanoarchitecture modeling are validated with experimental measurements obtained from impedance spectroscopy (EIS) and cyclic voltammetry (CV). The effective diffusion coefficients obtained from nanoarchitectural modeling show better agreement with experimental measurements. The effective properties obtained from nanoarchitecture modeling is used to simulate cyclic voltammetry (CV) of rGO/ANF structural supercapacitors. Various electrochemical kinetics evaluated to characterize structural supercapacitors. The insights obtained from this study can lead to a more effective design of electrode architectures. Finally, the effect of temperature on solid polymer Li-ion batteries is investigated through a 1D model that predicts the discharge behavior of flexible pouch cells at different temperatures. The simulations results show a good agreement with experimental measurements and yields fundamental insight which is essential for future developments in flexible solid polymer Li-ion batteries.Item Cooling System Design for a Fully Superconducting Machine Used in Future Aircrafts(2015-12) Bidad, Pejman; Masson, Philippe J.; Ardebili, Haleh; Nikolaou, MichaelConsidering developments in superconducting machines (motors and generators), modern methods and innovations required for optimization in this field like any other energy-based systems. Meanwhile, some improvements in superconducting technologies has been drawn to flying sciences such as future turbo-electric aircrafts. Thus, companies and pioneers in this industry like NASA have been investing many resources on the aim of future aircrafts working based upon Turboelectric distributed propulsion (TeDP), Hybrid and/or electric propulsion systems. Based on the fact that superconducting machines could make gigantic saves in energy waste, they came into spotlight. This promising technology also requires demanding attentions in the area of ahead obstacles such as novel cooling methods; there have been some analyzes in this area, though. Regarding to this issue, this study is aimed to design cooling systems for superconducting machines working with liquid hydrogen (LH2) as coolant. The indirect cooling system, which is based on both convection and conduction, has been employed. Having all sort of designs and ideas, a meander and helical shape design is recommended for rotor and stator, respectively. The results should comprise two important goals: 1) providing cryogenic temperature for system 2) evaluating pressure and outlet phase of LH2 working in a loop. Hence, different conventional materials in cryogenic sciences have been analyzed and compared to the famous metallic mate like aluminum.Item DERIVATION OF SEISMIC DESIGN PARAMETERS FOR HIGH-PERFORMANCE FIBER REINFORCED CONCRETE (HPFRC) AND MULTI-MATERIAL BUILDINGS(2013-12) Kaymaz, Ibrahim 1981-; Gencturk, Bora E.; Belarbi, Abdeldjelil; Ardebili, HalehOver the past decade, various experimental studies have demonstrated the advantages of high-performance fiber reinforced concrete (HPFRC) for seismic applications, most importantly high ductility, energy absorption capacity and damage tolerance. However, large-scale applications of HPFRC are still rare today, mainly resulting from two facts: lack of explicit design guidelines and high cost. In this study, seismic design parameters; namely, response modification, system overstrength and displacement amplification factors (R, Ω0, Cd) are derived for reinforced concrete moment resisting frames based on the procedure outlined in FEMA P695. Two different buildings designs are considered. In one of these designs, the concrete is entirely replaced with HPFRC. In the second design, to address the cost issue, only the plastic hinge regions are built from HPFRC while reinforced concrete is used for the rest of the buildings. The seismic design factors are quantified using the current code concepts, with the help of incremental dynamic analyses and finally by means of risk assessment techniques. The results are proposed as a basis for further research on seismic design of HPFRC and multi-material buildings.Item Developing Magnetic Tweezers for Magnetic Material Manipulation(2013-08) Liu, Yun; Sun, Li; Ardebili, Haleh; Mavrokefalos, AnastassiosSingle-molecule research has stimulated the development of a wide range of technologies that are capable of manipulating very small structures and materials. Among current available methods, the magnetic tweezers show high efficiency and cost effectiveness in generating strong and direction adjustable interactions with magnetic materials. Since our research group has extensive experience in synthesizing magnetic nanostructures, it is of great interest to develop magnetic force-based nanomaterials manipulation techniques. In this thesis, we describe the design and construct of tip based electromagnetic tweezers. We focused on the investigation and quantification of interactions between a soft magnetic tip and a superparamagnetic bead suspended in liquid. We studied the effects of tip taper length and current in the solenoid surrounding the tip on resulted forces. An axisymmetric 2D model using COMSOL Multiphysics has also been developed to analyze the magnetic field and force acting on the superparamagnetic beads based on experimental design.Item Development of Analytical Models for Evaluating the Mechanical and Electrochemical Response of Flexible and Stretchable Lithium Ion Battery Materials(2016-12) Berg, Sean; Ardebili, Haleh; Ryou, Jae-Hyun; Yu, Cunjiang; Sharma, Pradeep; Kulkarni, YashashreeFlexible and stretchable batteries have become a highly active area of research in recent years due to a new demand for mechanically compliant energy storage devices for a wide range of flexible applications including wearable and implantable electronics, touch-screens, and smart technology. Lithium ion batteries are leading candidates for flexible and stretchable energy storage devices due to their high energy density and efficiency. Considerable research has been related to developing flexible and stretchable materials, and solid polymer electrolyte lithium ion batteries show promise, offering many mechanical and safety advantages. While much experimental work has been in the development of these batteries, considerably less analytical modeling and numerical work has been a part of the development, which would elucidate experimental observations and provide enhanced understanding of the materials behavior in these new batteries. The work presented in this dissertation includes results of computational modeling and simulation of the mechanical and electrochemical behavior of flexible and stretchable battery materials under normal operating conditions and applied deformations resulting from mechanical loads. Additionally, analytical multiphysics models in the form of series of differential equations were derived to explain experimental observations of changes in battery performance and material properties due to applied loads and deformations. These models can be used to predict materials behavior and to relate key design parameters of flexible and stretchable batteries. The battery materials and designs that are assessed in this work were developed in our lab. Objectives of this work include understanding relationships between mechanical loading and certain key controllable fabrication parameters such as layer interface contact properties to predict the influence on flexible battery performance, and exploring how deformation occurring in the polymer electrolyte due to an applied mechanical load influences electrochemical performance. The effect of loading on other performance parameters, including battery impedance, is further studied, and all analytical work is compared to experimental data. An important aspect of this development is the consideration of nonlinearity in the models. Novel approaches are taken to include and address nonlinearity within the systems considered. While these models can be simplified through linearization, limitations of linear solutions are also discussed.Item DEVELOPMENT OF FLEXIBLE TRIBOELECTRIC NANOGENERATORS AND SOLID-STATE LITHIUM-ION POLYMER BATTERIES FOR ENERGY CONVERSION AND STORAGE PURPOSES(2022-12) Cheng, Kuan; Ardebili, Haleh; Karim, Alamgir; Ghasemi, Hadi; Bao, Jiming; Ryou, Jae-HyunConventional techniques to harvest and store energy are challenged by the ever-increasing demand for versatile forms of electrical energy caused by the rapid expansion of the Internet of Things (IoTs). As emergent solutions, flexible triboelectric nanogenerators (TENGs) and lithium-ion batteries (LIBs) have been invented and extensively studied in recent years. Different TENGs are fabricated to scavenge mechanical energy from most natural sources and human motions, making them portable solutions to energy generation on-demand. On the other hand, rechargeable LIBs play critical roles in the evolution of energy over 50 years, owing to its abilities to store massive amount of energy, lay the foundation for portable smart devices, and make possible a fossil fuel-free world. At the beginning of this dissertation, latest efforts that incorporating low-dimension carbon materials with TENG systems will be systematically reviewed. Carbon materials, including graphene and carbon nanotube, can bring many synergistic properties to TENGs, such as output enhancement and multifunctionality. They are poised to further the reach of TENG applications and make a positive impact on common issues related to TENG technology. The second section is to present a robust route to fabricate flexible TENGs with multifunctionality by nano-patterning thermoplastic polyurethane (TPU) thin films. Topographically optimized TENGs could promote higher power generation while preventing biofilm formation without using any chemical additives. Analysis of pattern amplitude and wavelength correlation to output power is uniquely provided for a deeper understanding of how patterned TENGs enable peak performance. The last part of this work presents the fabrication and characterization of lithium-ion batteries based on solid-state polymer electrolytes. Efforts made to substitute conventional liquid electrolyte and plastic separators make a great accomplishment on mechanical properties and safety aspects of LIBs. Fluoroethylene carbonate (FEC) has been proved as an effective electrolyte additive, which helps building LIB systems with ultra-high capacity and low self-discharge. Comprehensive electrochemical properties along with thermal properties of LIBs will be closely scrutinized in this work.Item Development of Multi-Electrode Neural Probe on Optical Fiber Substrate for Brain-Machine Interfaces(2018-05) Tisa, Tamanna Afrin; Wolfe, John C.; Shih, Wei-Chuan; Zagozdzon-Wosik, Wanda; Charlson, Earl J.; Wood, Lowell T.; Ardebili, HalehBrain-machine interfaces (BMIs) aim to restore communication and control of prosthetic devices to individuals with neurological injury or disease, by recording the neural activity, and mapping or decoding it in to a motor command. One of the great challenges in this effort is to develop reliable neural probes that are capable of processing the activity of large ensembles of cortical neurons. In this dissertation, we reported a method for fabricating highly reliable neural probes with integrated, thin film conductor and dielectric coatings on the cylindrical surface of fine optical fibers for brain-machine interfacing. The use of optical fibers as probe substrates provide the strength and stiffness required for deep-brain applications, as well as the high intensity, multi-spectral light delivery with essentially no coupling loss is useful for optogenetics application in neuroscience. Early probes were fabricated on 65 µm optical fiber substrates with polyimide jackets. Electrodes were defined over this jacket, and high quality in-vivo recordings were acquired in area V1 of the Greater Northern Galago (Galago garnetti). Microscopic examination of the probes after extraction from the brain, showed that the jacket had cracked and delaminated; the glass itself may have cracked. Invariably this happened near the probe tip, suggesting that micro-cracking of the unprotected fiber end was the cause of the problem. So, a new jacket of cross-linked plasma-deposited styrene was developed. This layer was impervious to water vapor, as well as hot acids and bases. Single channel probes fabricated with this jacket survived a battery of reliability tests, including continuous soaking in PBS for 30 days, multiple insertions in agar gel and cannulas, disinfection, and marinating overnight in a whole mouse brain in the Dragoi lab. Moreover, test-to-test and lot-to-lot variation of the 2 kHz impedance was less than 1 % (3). High quality, in-vitro spike recordings were acquired in a living mouse brain slice at the Dragoi lab. Thus, reliability of the contact fabrication process has been established. In this dissertation, we also reported the extension of the technology that we developed for single channel prototypes to probes with a large number (>30) of micrometer-scale contacts that are needed to map laminar circuits in the brain. For fabricating those multi-electrode neural probes, significant advancement in alignment technology was required. The near-atomic straightness of fiber holder and accurate registration of the mask pattern with the V-grooves ensures that the printed pattern will be centered on the bottom of the fiber. The overlay of patterns on the fiber was ensured, a) longitudinally by using fiber stops, high precision ball bearings which were hold to lithographically defined pits at the tip-end of each V-groove, b) rotationally by using a high precision cubic bead glued to the end of the fiber as the reference. SEM images showed that longitudinal and lateral pattern overlay error was always below 2 µm without any outliers.Item Development of REBCO Tapes on Non-Metallic Flexible Substrates for RF Applications(2019-05) Zhang, Yuan; Selvamanickam, Venkat; Wosik, Jarek; Ardebili, Haleh; Ryou, Jae-Hyun; Meen, James K.RE-Ba-Cu-O (REBCO, RE = rare earth) films on a flexible, low-cost, and low-thermal-expansion substrate offer a unique advantage for radio-frequency (RF) applications such as surface receiver coils for magnetic resonance imaging (MRI). Second-generation high-temperature superconductors (2G-HTS) are well developed for direct current (DC) applications. However, alternating current (AC) losses because of eddy currents in Hastelloy dominate at microwave frequencies. This work aims to develop REBCO on inexpensive and non-metallic flexible substrates for RF applications. Two methods have been developed in this work—exfoliation and transfer and direct growth. In the exfoliation and transfer method, the metallic substrate was peeled away from a standard 2G-HTS tape and the exfoliated REBCO film was transferred to a polyimide tape. Scanning Hall Probe Microscopy (SHPM) showed uniform trapped fields on the exfoliated tapes. For the growth method, polycrystalline, inexpensive, lightweight, and flexible yttria-stabilized zirconia (YSZ) with low thermal conductivity, low RF loss, and a relatively low dielectric constant was used as a substrate for epitaxial REBCO films. The YSZ substrate surface was planarized to a surface roughness Rq of about 1 nm, as measured by atomic force microscopy (AFM). Ion-beam assisted deposition (IBAD) was used to obtain highly-oriented single-crystalline-like buffer templates on planarized, polycrystalline YSZ substrates. Homo-epitaxial MgO and epitaxial LaMnO3 (LMO) thin films were deposited via reel-to-reel medium-frequency magnetron sputtering and radio-frequency magnetron sputtering, respectively. The out-of-plane and in-plane texture of homo-epitaxial MgO were optimized to 2° full-width-at-half-maximum (FWHM) and 5.5° FWHM, respectively. LMO out-of-plane and in-plane texture values were optimized to 2.6° and 6.8° FWHM, respectively. Epitaxial GdYBCO was grown by an Advanced Metal Organic Chemical Vapor Deposition (A-MOCVD) on the buffered-YSZ substrates with an in-plane texture average of about 3.8° FWHM. Magnetization critical current density (Jc) at 77 K, 0 T measured by a physical property measurement system (PPMS) was 1.21 MA/cm2. The quality factor (Q factor) measured at 77 K, 12.9 GHz was comparable to that of high quality epitaxial REBCO films on single crystal rigid substrates. Epitaxial REBCO films on the YSZ polycrystalline substrates can be used to construct RF coils for MRI and other RF, microwave applications.Item Development of Sustainable Thermoplastic Elastomers(2015-05) Wang, Shu; Robertson, Megan L.; Krishnamoorti, Ramanan; Conrad, Jacinta C.; Ardebili, Haleh; Yao, YanSustainable poly(styrene-b-(lauryl-co-stearyl acrylate)-b-styrene) (SAS) triblock copolymers containing a rubbery midblock derived from fatty acids were designed with targeted properties appropriate for thermoplastic elastomer applications. Well-defined polymers with desired compositions and controlled molecular weight distributions were successfully synthesized using reversible addition fragmentation chain transfer (RAFT) polymerization. SAS exhibited elastomeric behavior at room temperature and were processable above the order-disorder transition (ODT) temperature. The alkyl side-chain length of the polyacrylates (as well as the related midblock composition of SAS) was utilized as a convenient parameter for tuning the physical properties of SAS, including the melting temperature and viscosity of the midblock polyacrylate, melt viscosity of SAS above the ODT, and tensile properties. The thermodynamic interactions between the components of SAS, polyacrylates and polystyrene, were explored through determination of the Flory-Huggins interaction parameter through cloud point measurements on binary polymer blends and measurement of the ODT of the triblock copolymers. It was shown that the Flory-Huggins interaction parameter was independent of the length of the alkyl side-chain of the polyacrylates, in the limit of large alkyl side-chains (i.e., more than 10 carbon atoms), in stark contrast to theoretical predictions using group contribution methods and solubility parameter theory. The morphology of SAS was probed by transmission electron microscopy, showing the presence of spherical polystyrene domains in the polyacrylate matrix, as well as small angle X-ray scattering, indicating the presence of randomly oriented grains upon compression molding. Large amplitude oscillatory shear was employed at a temperature below ODT to align the randomly oriented grains. The predominant orientation was determined to be hexagonally close-packed spherical domains with the {0001} planes parallel to the shear plane, with a small population of face-centered cubic spherical domains with the {1-10} planes parallel to the shear plane. Fully sustainable triblock copolymers with midblocks derived from fatty acids and endblocks derived from salicylic acid were also successfully synthesized with RAFT polymerization. The properties of the resulting poly(acetylsalicylic ethyl methacrylate-b-lauryl methacrylate-b-acetylsalicylic ethyl methacrylate) (ALA) triblock copolymers were examined for their utility as thermoplastic elastomers. Poly(acetylsalicylic ethyl methacrylate) was found to be a suitable replacement for polystyrene, with a glass transition temperature above room temperature. The morphology and mechanical properties of ALA were comparable to that observed in the partially sustainable SAS triblock copolymers.Item Diffusion in Reduced Graphene Oxide/Aramid Nanofiber Electrode in Li-ion Batteries(2017) Aderyani, Sarah; Ardebili, HalehItem Direct Patterning Of Conductive Polymer Domains For Photovoltaic Devices(2012-08) Moungthai, Suchanun 1983-; Stein, Gila E.; Donnelly, Vincent M.; Doxastakis, Manolis; Ruchhoeft, Paul; Ardebili, HalehIn the developed world, the demand for energy is increasing tremendously. In this day and age, the main sources of energy are natural resources like oil and coal, and their supply could run out in the near future. In addition, burning fossil fuel produces large amounts of carbon dioxide which are linked to global warming. We need an alternative source of energy that is clean, renewable and sustainable. Photovoltaics are one of the most interesting alternative energy sources for future energy, as this technology could potentially generate clean, e cient, and reliable electricity. Most products in the marketplace are based on silicon, and these devices require a lot of energy for the fabrication process, driving up their cost and reducing the bene t. Polymer solar cells can be made at a very low cost, and o er additional advantages such as exible, light weight modules that can be made in a variety of sizes and shapes. A typical polymer solar cell is made from a partially phase-separated polymer/fullerene blend. The main problem for polymer solar cell is their low powerconversion e ciency, which is partly controlled by active layer morphology. The objective of this work is to develop a system to study the e ects of active layer morphology on device function. The approach developed in this work uses electron-beam patterning of polymer semiconductors to build model polymer/ fullerene devices. Electron-beam patterning generates conductive nanostructures or microstructures through an in-situ cross-linking reaction, where the size, shape and density of polymer domains are all tunable parameters. Cross-linked polymer structures are thermally-stable and solvent-resistant, so they can be incorporated into devices that require thermal annealing or solution-based processing. This method was validated by building gradient and nanostructured poly(3-hexylthiophene)/fullerene solar cells. These model devices exhibit good power-conversion e ciencies, which are explained by a polymer cross-linking mechanism that largely preserves the -bonds responsible for light absorption, charge generation, and charge transport. The exible methodology can be used to study the e ects of domains size and interfacial area on optoelectronic function.Item Dispensing Nano-Pico Droplets of Ferrofluids(2016-12) Irajizad, Peyman; Ghasemi, Hadi; Yang, Di; Ardebili, HalehDispensing miniature volumes of a ferrofluid is of fundamental and practical importance for diverse applications ranging from biomedical devices, optics, and self-assembly of materials. Current dispensing systems are based on microfluidics flow-focusing approaches or acoustic actuation requiring complicated structures. A simple method is presented to continuously dispense the miniature droplets from a ferrofluid reservoir. Once a jet of the ferrofluid is subjected to a constrained flux through a membrane and an inhomogeneous magnetic field, the jet experiences a curvature-driven instability and transforms to a droplet. Ferrofluid droplets in the range of 0.1–1000 nl are dispensed with tunable dispensing frequencies. A model was developed, which predicts the dispensed volume of the ferrofluid droplets with an excellent agreement with the measurements.Item Elastomer Degradation in Chemically Reactive Environment under Elevated Temperature and Pressurized Condition(2017-08) Lu, Min; Sun, Li; Franchek, Matthew A.; Mo, Yi-Lung; Ardebili, Haleh; Yu, CunjiangMechanical properties of elastomer undergo accelerated degradation when immersed in chemically active environment, especially at elevated temperature and/or under high pressure. Beside physical relaxation due to the viscoelastic nature of polymers, diffusion-reaction process plays an important role in accelerating elastomer deterioration. In a previous research, Fickian diffusion was often used to model the small molecule ingression in bulk elastomeric materials. Under high temperature and high pressure, chemical reaction accelerates and some of the processes that are negligible under standard temperature and pressure can have significant impacts on elastomer properties. For example, water near or above its critical state, can react with some relatively stable functional groups in elastomers. To study elastomer degradation under HPHT and chemical environment, sealed mechanical testing apparatuses have been designed and manufactured so that real time mechanical performance of elastomer under compression after ageing in chemicals, at elevated temperature, and under pressurized conditions, can be quantitatively studied. It is found that for elastomer stress relaxation, additional lateral confinement induced by environmental stress can effective reduce elastomer relaxation along the axial direction. In addition to the development of experimental elastomer characterization methodology, we also built a quantitative model to investigate the diffusion-reaction process between chemical diffusant and elastomer at elevated temperature and under pressurized condition. The PDE developed in this study uses the Vrentus-Duda free volume theory to quantify the diffusion between small molecules and macromolecular matrices. Current model allows us to study temperature, pressure, and chemical kinetic effects through the quantification of diffusant concentration profile evolvement numerically by solving the PDE problem. Finally, we also studied the electromechanical properties of an elastomer-carbon nanocomposite. The nanocomposite are fabricated by a solution casting technique based on a patent from our research group to achieve high quality interfacial bonding and uniform filler distribution. Electromechanical behavior in such elastomer nanocomposite is studied, repeatable piezoresistive response is confirmed after training cycles, and their potential applications as large deformation strain sensor are discussed.