Master of Science in Polymer Engineering, University of Akron, 2006, Polymer Engineering

The main goal of this research is to develop anintegrated uniaxial stretching system that allows simultaneousmeasurement of electrical conductivity, true stress and true strainduring free-width uniaxial deformation of electrically conductivepolymers. Percolation curve for biodegradable Poly lactic acidfilled with high structure carbon black was constructed and thepercolation curve was found to be precipitously increased andsensitive at the critical percolation concentration (5 wt% forbinary system). In order to reduce this, organically modifiednanoclay was introduced at small concentrations and this was foundto partially block the electron conducting pathways thereby causingthe reduction of the sensitivity of the percolation curve. This,then allows for development of conductive compositions to beobtained at intermediate conductivity levels (10-5 - 10-10 S/cm)that are needed for electrostatic discharge applications includingelectronic packaging. Using the newly developed real timemeasurement system, we have investigated the temperature dependencyof electrical conductivities of selected binary nanocomposites.Positive temperature coefficient (PTC) behavior (decrease ofconductivity with increase of temperature) was observed from roomtemperature to Tg+20. This is attributed to increase of gapseparation in the conductive pathways established by the carbonblack due to much higher thermal expansion coefficient of the PLAmatrix as compared to those of the fillers. Above this temperaturerange the originally amorphous matrix begins to crystallize andthis resulted in increase of electrical conductivity. The expulsionof dispersed CB particles by the growing crystallites to theirboundaries leading to formation of added branches in the conductivenetwork could cause such an increase during the coldcrystallization process. Heating beyond this range resulted inaccelerated increase in conductivity when the matrix melts. Sinceall parameters are continuously monitored before, during and (open full item for complete abstract)

Committee: Mukerrem Cakmak (Advisor) Subjects:

Doctor of Philosophy, Miami University, 2023, Chemistry and Biochemistry

In the future, well-engineered and optimized flexible electronic devices will be woven into everyday accessories such as clothes, furniture, safety, and healthcare monitoring devices. Dynamic polymer nanocomposites (DPNs) are an excellent class of materials that have a huge potential in the future of flexible electronics. DPNs are achieved through macromolecular engineering of dynamic polymers enhanced with electrically conductive nanofillers or nanocomposites with self-healing capabilities enabled via dynamic chemical linkages. Integration of multiple types of dynamic linkages into one polymer network is challenging and not well understood especially in the design and fabrication of DPNs. This dissertation presents facile methods for synthesizing flexible, healable, conductive, recyclable, and thermoresponsive DPNs using three dynamic chemistries playing distinct roles. Dynamic hydrogen bonds account for material flexibility and recycling character. Thiol-Michael exchange accounts for thermoresponsive properties. Diels-Alder reaction leads to covalent bonding between polymer matrix and nanocomposite. Overall, the presence of multiple types of orthogonal dynamic bonds provided a solution to the trade-off between enhanced mechanical performance and material elongation in DPNs. Efficient reinforcement was achieved using <1 wt.% carbon nanotubes (CNT) as nanofillers. Increased mechanical strength, electrical conductivity, and re-processability were achieved all while maintaining material flexibility and extensibility, hence highlight the strong promise of these DPNs in the rapidly growing fields of flexible compliant electrodes. Additionally, structure-property relationships highlighting the impact of network architecture, chain-length, cross-link density, and CNT loading are explored. Controlled addition of CNT as nanofiller produces electrically conductive and mechanically enhanced DPNs with demonstrated application in the regulation of current flow towards a (open full item for complete abstract)

Committee: Dominik Konkolewicz d.konkolewicz@miamioh.edu (Advisor) Subjects: Chemistry; Materials Science; Nanoscience; Organic Chemistry; Physical Chemistry

Master of Science, University of Toledo, 2022, Geology

Wetlands' water and nutrient retention functions depend on their soil properties, hence the need to understand the spatial-temporal variation of these properties. The use of soil cores and in situ sensors to assess soil properties distribution is limited due to their high cost, field efforts, and disturbances. This study seeks to advance the use of non-invasive geophysical methods using soil electrical conductivity via electromagnetic imaging (EMI) for estimating wetlands' soil properties distribution. First, I acquired spatial distribution of soil apparent electrical conductivity (ECa) and magnetic susceptibility (MSa) via EMI over a 162,000 m2 restored wetland using an EM-38-MK2 instrument towed behind a utility terrain vehicle equipped with a differential ground positioning system. I collected twenty-two undisturbed soil samples and analyzed them in the laboratory for soil moisture (SMC), organic matter (SOM), porosity, bulk density, and texture. A linear regression model was used to compare the correlation between each soil property with measured ECa and MSa, while ECa was used to predict the distribution of SMC and SOM using the statistical model validated using a leave-one-out technique. Measured ECa correlates strongly with soil texture, SMC, and SOM, with SOM showing a slightly dominant control. These results show that ECa can predict the distribution of SMC and SOM in wetland soils to an accuracy of ~67-70% for these datasets. While these results validate the potential for extending EMI to characterize wetland soils, reliance on statistical correlation is limited to the study site and data range. Cross-correlation between the soil properties also limits understanding of the contribution of each soil property to the measured bulk conductivity. Decoupling this requires a mechanistic understanding of the current conduction processes within wetland soils, considering electromigration via the soil pore fluid and surface conduction at the grain-fluid interface. T (open full item for complete abstract)

Committee: Kennedy Doro Prof. (Committee Chair); Richard Becker Prof. (Committee Member); Michael Weintraub Prof. (Committee Member) Subjects: Agriculture; Aquatic Sciences; Electromagnetics; Environmental Science; Environmental Studies; Geology; Geophysics; Hydrologic Sciences; Hydrology; Natural Resource Management; Soil Sciences; Water Resource Management

Doctor of Philosophy (PhD), Ohio University, 2022, Mechanical and Systems Engineering (Engineering and Technology)

In this study, it was hypothesized that graphene aluminum alloys can be engineered for improved bulk electrical properties by establishing a form of coherency with aluminum valance and graphene π electrons. To this end, the effects of graphene concentration and process parameters were assessed, and thus shown that improvements in the electrical performance of bulk aluminum alloys is possible. Al/graphene composites were manufactured under varying thermo-mechanical process conditions with varying graphene content embedded into three different aluminum alloy systems, namely AA1100 (commercially pure, non-heat treatable), AA3003 (alloyed, non-heat treatable), and AA6101 (alloyed, heat treatable) alloys. Electrical conductivity and temperature coefficient of resistance were determined for the 10 - 12 AWG composite wires manufactured via solid phase processing techniques, hot extrusion and shear assisted processing and extrusion. Microstructural characterizations were performed through optical and scanning electron microscopy to identify the process-structure-property relationships for the composites. Results showed that hot-extruded AA1100 composites with 0.25 wt.% graphene showed the highest improvement of 2.32% in electrical conductivity as well as the TCR lower by 23.4% compared to control samples manufactured under similar conditions. Enhanced conductivity was seen in composites with higher semimetallic graphene while lower TCR was observed in samples with higher semiconductor graphene concentration. Extrusion pressures played a key role in the exfoliation and deformation of agglomerated graphene nanoparticle precursors. Second phase solubility was affected by hot pressing conditions, extrusion temperature and ShAPE parameters, and not the presence of graphene in the composite microstructures. On the other hand, graphene affected precipitation dynamics during aging of hot-extruded AA6101 composites. Finally, composite grain morphology and distribution as well as pre (open full item for complete abstract)

Committee: Frank Kraft (Advisor); Keerti Kappagantula (Advisor); Muhammad Ali (Advisor); Brian Wisner (Committee Member); Jay Wilhelm (Committee Member); Zaki Kuruppalil (Committee Member); Eric Stinaff (Committee Member) Subjects: Materials Science; Mechanical Engineering

MS, Kent State University, 2021, College of Arts and Sciences / Department of Earth Sciences

The Huff Run Watershed, located in Mineral City, Ohio, was mined for coal, limestone, and clay from 1853 to the late 1970s. Mine spoil is left scattered on the surface of about one third of the watershed, contributing to metal leaching to the watershed. Although the mine spoil has had time to become vegetated, camouflaging itself among the native landscape, the disturbed pyrite from coal layers is exposed to water and oxygen leading to a chain of chemical reactions, resulting in the production of potentially acidic and metal-rich porewater, which can infiltrate into the groundwater and streams. Remediation efforts for this watershed have totaled around 4.5 million dollars, but most of the remediation is focused on the point sources of contamination. Runoff from the spoil is a nonpoint source of contamination, and most areas are left untreated. These untreated areas can affect the immediate area and many kilometers downstream of the leaching. For this project, soil samples were collected from a vegetated mine spoil hill and a vegetated shale hill in this watershed, to make a physical and chemical comparison of the soils and their pore water. Solid phase characterization included particle size analysis, bulk X-ray powder diffraction, and loss on ignition (LOI). Soil pore water was collected from suction lysimeters installed at different depths (10, 40, 80, and 120 cm) at the two sites. Field-based water quality analyses included pH, dissolved oxygen (DO), electrical conductivity, and temperature; collected samples were analyzed for metals by inductively coupled plasma-optical emission spectrometry (ICP-OES), anions by ion chromatography, and dissolved organic carbon (DOC). The speciation of Al, Fe, and Mn was also determined by a sequential extraction procedure. The particle size distribution showed a sandy loam, with an overall average of 4.4% clay, 47.7% silt, and 47.9% sand in the high wall (HW) and 6.3% clay, 41.8% silt, and 51.9% sand in the mine spoil (open full item for complete abstract)

Committee: David Singer (Advisor); Elizabeth Herndon (Committee Member); David Costello (Committee Member) Subjects: Geochemistry; Geology

Doctor of Philosophy, Case Western Reserve University, 2020, Physics

Within the past decade or so, semiconductor physics has turned a keen eye on two dimensional systems, with the pivotal investigation of atomically thin carbon films. The remarkable figures of merit produced by graphene in electronic and electrochemical applications, in contrast to bulk carbon properties, are indicative of the potential that layered materials might possess in their own right. Transition metal oxides offer a relatively unexplored facet of 2D semiconductor technology; these materials are often overlooked due to their wide band gaps when considering new subjects for nanostructure study. However, oxides offer a library of interesting properties, many of which are still not fully understood, and can be easily modified through doping to engineer new characteristics. Herein, three studies are discussed, where characterization of layered oxides, modified via various methods of doping, result in unique behaviors. The first study involves varying oxygen stoichiometry in α-MoO3, where transport is controlled by quantifiable reduction of grown α-MoO3 nanoflakes. The second details the study of LixCoO2, the staple cathode material used in lithium-ion batteries. This material exhibits unique charge-ordering phenomena as a function of lithium content, and is explored in its few-layer, single-crystal form for the first time. Finally, V2O5 is investigated, which displays p-type characteristics and a surface scattering effect when partially doped with sodium. The band structure is analyzed to explain these behaviors. The findings of these studies may play a key role in engineering thin oxide systems for future electronics applications.

Committee: Xuan Gao Professor (Advisor); Walter Lambrecht Professor (Committee Member); Jesse Berezovsky Associate Professor (Committee Member); Alp Sehirlioglu Associate Professor (Committee Member) Subjects: Condensed Matter Physics; Materials Science; Physics

Master of Science (MS), Ohio University, 2019, Mechanical Engineering (Engineering and Technology)

Aluminum alloys with improved electrical and mechanical performance are a highly sought-after due to their potential use as energy efficient conductors in power transmission, electronics, and aerospace systems. In this thesis, a novel hot extrusion alloying (HEA) process was used to synthesize aluminum/graphite nano-alloys using commercially available AA1100 and graphite nanoparticles (GNP) as precursors to improve electrical properties. The effects of GNP content from 0 – 1 wt.%, on the electrical and mechanical properties were evaluated. Results showed that the addition of 0.25 wt.% GNPs to the Al substrate improved its electrical conductivity by 2.1%, current density by 7.9%, ultimate tensile strength by 6.1% and yield strength by 30.3% compared to the control sample with no GNP additives. Improvements in electrical conductivity and current density were observed for all Al/GNP formulation at 60 °C and 90 °C. Ductility of the Al/GNP nano-alloys decreased with increasing GNP content. The improvement in Al/GNP electrical performance is attributed to GNP exfoliation at the temperatures and shear stresses experienced during hot extrusion, leading to the formation of highly conductive graphene particles.

Committee: Keerti Kappagantula (Advisor) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2018, Electrical Engineering

This work presents a fully-integrated multi-sensor system based on CMOS technology that contains pH, electrical conductivity (EC), and temperature sensors, as well as an extended-counting analog-to-digital converter (EC-ADC). The pH sensor is implemented using an ion-sensitive field-effect transistor (ISFET) where two low-power, compact pH readout circuits have been designed to overcome the nonidealities of ISFETs. In addition, a novel electrode structure for the EC sensor has been implemented, which eliminates the conventional post-processing steps, thus reducing the cost and fabrication difficulties. Using different frequencies generated by a variable frequency oscillator, the detection range of the proposed EC sensor spans three orders of magnitude, from 20 µS/cm to 10 mS/cm. Furthermore, a complementary to absolute temperature (CTAT) current source with diode-connected transistors was used as the temperature sensor. The measurement range is from 18◦C to 35◦C. The core area, including all three sensors and readout circuits is 2.1 mm2. The EC-ADC is a combination of an incremental sigma-delta and a time-mode ADC. By sharing the OTA and the comparator between two ADCs, the implemented circuit allows the smallest core area amongst state-of-the-art ADCs with similar resolution and bandwidth. The core area of the proposed ADC is 0.0625 mm2, and the measured differential nonlinearity (DNL) and integral nonlinearity (INL) are +0.4/-0.4 and +0.84/-0.88 LSB, respectively.

Committee: Kye-shin Lee Dr. (Advisor); Joan E. Carletta Dr. (Committee Member); Ryan C. Toonen Dr. (Committee Member); Truyen Van Nguyen Dr. (Committee Member); Chelsea Monty Dr. (Committee Member) Subjects: Electrical Engineering

MS, University of Cincinnati, 2018, Engineering and Applied Science: Aerospace Engineering

Carbon nanotubes (CNTs) have extraordinary mechanical, thermal and electrical properties. However, the macroscopic products of CNTs such as sheet and thread, lack these extraordinary physical properties. This reduction in properties for the macroscopic products of CNT is due to the presence of structural defects (disorder-induced symmetry-breaking effects in the sp2 hybridized carbon products), impurities, slipping apart of the short nanotubes in bundles, and random orientation of the CNT strands in sheet and thread. Transferring the physical properties of individual CNTs to the macroscopic scale is a challenging task. To use carbon nanotubes in different applications, intensive research is being performed to improve the mechanical, thermal and electrical properties of CNT sheet and thread. The goal of this work is to investigate methods to improve the mechanical and electrical properties of CNT sheet and thread. The research starts with tuning the CNT synthesis process to produce CNT sheet with fewer structural defects. Also, the effect of this synthesis optimization process on the mechanical and electrical properties of the CNT sheet is investigated. Towards the goal of improving the properties of CNT sheet, further post-processing techniques are studied to improve the orientation of the CNT strands in CNT sheet. It is observed that the mechanical and electrical properties improved due to improved alignment and packing of the CNT strands in the sheet. From the perspective of the application, the hydrophilicity of the CNT sheet is also studied for integrating CNT sheet into textiles. Acid treatment of CNT sheet promoted the hydrophilicity of the CNT sheet. For acid treatment of CNT sheet, hydrogen peroxide and a mixture of H2SO4+HNO3 in 3:1 ratio is used. After analyzing the IG/ID ratio from Raman analysis before and after acid treatment, hydrogen peroxide treated CNT sheet for 48 h showed the best result. Hydrogen peroxide treatment of CNT sheet for 48 h s (open full item for complete abstract)

Committee: Peter Nagy Ph.D. (Committee Chair); Yao Fu (Committee Member); Mark Schulz Ph.D. (Committee Member) Subjects: Nanotechnology

Doctor of Philosophy, University of Akron, 2018, Electrical Engineering

First part of this research presents a fully-integrated multi-sensor chip using standard CMOS technology that contains three key components: pH, electrical conductivity (EC), and temperature. Two novel low-power, compact pH readout circuits have been proposed to overcome the nonidealities of ISFETs. In addition, a novel electrode implementation as EC sensor which eliminates the conventional post-processing steps is proposed. From a circuit point of view, a fully-integrated on-chip approach has been proposed to measure EC. In this method, a new variable-frequency oscillator stimulates the electrodes, and two variable-gain instrumentation amplifiers measure the equivalent voltage and current between the electrodes that are converted into EC. The detection range of the proposed EC sensor spans three orders of magnitude, from 0.02 to 10 mS/cm. Furthermore, a CTAT current source with diode connected transistors was used as temperature sensor. The total core area including all three sensors and readout circuits is 2.1 mm2. In the second part of this research, a novel 10-bit, 20 kHz bandwidth extended-counting ADC (EC-ADC) for our multi-sensor system has been proposed. This hybrid ADC is a combination of incremental sigma-delta and time-mode ADCs. By sharing the OTA and the comparator between two ADCs, the proposed approach shows the smallest core area amongst state-of-the-art ADCs with similar resolution and bandwidth. The core area of the proposed ADC is 0.0625 mm2, and the measured DNL and INL are +0.4/-0.4 and +0.84/-0.88 LSB, respectively.

Committee: Kye-shin Lee Dr. (Advisor); Joan Carletta Dr. (Committee Member); Ryan Toonen Dr. (Committee Member); Truyen Van Nguyen Dr. (Committee Member); Chelsea Monty Dr. (Committee Member) Subjects: Electrical Engineering

Master of Science, University of Akron, 2018, Physics

The flow of current in response to an electric field, or conductivity, of materials, depends on properties such as the electron density, band structure of the material, temperature and presence of external fields. For this work, we assume the presence of conduction electrons in a perfect hexagonal crystalline lattice. The sample experiences a small, uniform in-plane electric field and a perpendicular magnetic field. An external electric field accelerates electrons, but scattering causes them to lose energy and momentum. Electrons interact with other electrons and collective lattice vibrations, via electron-electron and electron-phonon scattering. We study this phenomenon using the Boltzmann transport equation. In graphene-like materials with linear bands, for a model with a constant electron-phonon relaxation time, the conductivity decreases as the temperature is increased from absolute zero. Furthermore, in linear band materials, the electron-electron interaction decreases the conductivity. This is in contrast to parabolic band materials with constant electron-phonon relaxation time, where the conductivity does not depend on temperature or the electron-electron scattering rate. We also calculate the magneto-conductance for linear band materials in the absence of electron-electron scattering.

Committee: Ben Yu-Kuang Hu Prof. (Advisor); Jutta Jutta Luettmer-Strathmann Prof. (Committee Member); Alper Buldum Prof. (Committee Member) Subjects: Materials Science; Physics; Solid State Physics; Theoretical Physics

Master of Science in Renewable and Clean Energy Engineering (MSRCE), Wright State University, 2018, Mechanical Engineering

With the rise of electric vehicles and increasing dependence on mobile electronics, the demands for lithium-ion batteries have followed in tandem for their high energy and power densities. However, traditional lithium-ion batteries consisting of liquid electrolytes have limited operating temperatures and are susceptible to ignition and subsequent fires. Recently, battery research has diverged into solid state chemistry to address the aforementioned issues. In this research, we systematically investigate a series of ceramic/polymer lithium-ion conducting composite electrolytes, i.e. Li1.4Al0.4Ge1.6(PO4)3 /lithiated polyethylene oxide (LAGP/PEO). Lithiated PEO was prepared with two different lithium salts, LiBF4 and LITFSI. The impacts of the LAGP on the electrical, thermal, and mechanical properties of the two lithiated PEO systems are assessed. When LAGP is homogenously distributed in PEO-LiTFSI films, ionic conductivities and thermal properties remain relatively uninhibited; the elastic modulus and ultimate strength increased up to 450% and 200%, respectively. When LAGP was added to PEO-LiBF4 films, it increased the elastic strength nearly 200% without compromising the ultimate strength and thermal properties, but at the sacrifice of ionic conductivity. The ceramic/polymeric electrolytes have potential applications to flexible all solid state lithium-ion batteries.

Committee: Hong Huang Ph.D. (Committee Chair); James Menart Ph.D. (Committee Member); Thomas Howell Ph.D. (Committee Member); Michael Rottmayer Ph.D. (Committee Member) Subjects: Alternative Energy; Energy; Engineering; Materials Science; Solid State Physics; Technology

Doctor of Philosophy, University of Akron, 2015, Mechanical Engineering

Thermoelectric materials exhibit a significant coupling between thermal and electrical transport. Devices made from thermoelectric materials can convert between thermal and electrical energy. System reliability is extremely high but widespread use of the technology is hindered by low conversion efficiency. To increase the practicality of thermoelectric devices improvements are required in both (i) device design and (ii) thermoelectric materials. Advanced thermoelectric analysis developed in this work provides general guidelines for device design by introducing a new set of design factors. The new analytic factors include Device Design Factor, Fin Factor, Inductance Factor, and Thermal Diffusivity Factor. The advanced analysis is applied to two material systems developed in this work. The first system investigated was a composite of WSi2 precipitates in a Si/Ge matrix. The composite was investigated through both solidification techniques and powder processing. The system has a 30% higher figure of merit, a material parameter relating to conversion efficiency, than traditional zone-leveled Si/Ge. The second system investigated was a novel quaternary CoxNi4-xSb12-ySny skutterudite. The system was found to achieve both n- and p-type conduction with tuning of the Co level.

Committee: Celal Batur Dr. (Advisor); Alp Sehirlioglu Dr. (Committee Member); Minel Braun Dr. (Committee Member); Guo-Xiang Wang Dr. (Committee Member); Jerry Young Dr. (Committee Member); Bob Viellette Dr. (Committee Member) Subjects: Aerospace Materials; Materials Science; Mechanical Engineering

Doctor of Philosophy, University of Toledo, 2014, Engineering

The electrical conductivity of polymers can be changed by adding conductive fillers, such as, metal fibers, and carbon fibers. The resulting materials can be used as conductive coating, where metals were traditionally used. From the engineering viewpoint, the advantages of conductive composites over metals are light weight, resistance to corrosion and ease of processing. Conductive composite is useful in electronic circuits and packaging applications such as, flexible electronics, organic electronic devices, and printable circuits and antennas. An innovative method of making graphene filled polymer nanocomposites is proposed in this dissertation. Graphene/polymer nanocomposites were obtained by directly exfoliating graphite into graphene using organic solvent, and solution phase mixing with a polymer. The feasibility of this one-pot approach was studied for making graphene/poly(methyl methacrylate) (PMMA) nanocomposite and graphene/polypyrrole (PPy) nanocomposite. To make graphene/PMMA nanocomposite, two kinds of solvents, 1-methyl-2-pyrrolidinone (NMP) and acetonitrile, were investigated to be used to exfoliate graphite. The conductivity of PMMA has been increased after the addiction of graphene. The conductivity of graphene/PMMA nanocomposite reached to 6×10-3 S/cm at graphene concentration of 20 wt%. The oxygen plasma was used to treat the surface of resultant graphene/PMMA film, and was found to be improved the electrical conductivity. Tensile tests conducted on graphene/PMMA nanocomposite suggested that there was no improvement in mechanical properties after adding the graphene additives to PMMA. The graphene/PPy nanocomposite was processed using in-situ polymerization. During polymerization, PPy tends to grow on the surface of graphene sheets. The resultant graphene/PPy nanocomposite has a core-shell structure. Dependence of resistivity of graphene/PPy nanocomposite on temperature was measured and analyzed with the Arrhenius theory. The Raman spectroscopy, x (open full item for complete abstract)

Committee: Ahalapitiya H. Jayatissa (Committee Chair); Matthew Franchetti (Committee Member); Sorin Cioc (Committee Member); Manish Kumar (Committee Member); Weiqing Sun (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2008, Food, Agricultural, and Biological Engineering

High pressure process and product development efforts are largely limited to post pressurization characterization. Measuring food properties in-situ under pressure can characterize chemical and physical changes and contribute to safety and quality optimization of products and processes. The purpose of this research was to develop in-situ methods to measure and calculate density, compressibility, and electrical conductivity of foods and reaction volume and pH of weak acid buffers under pressure. A custom variable volume piezometer was calibrated with water and measured volume change of 17 solid and liquid foods as a function of pressure to 700 MPa at 25°C. Piston movement, characterizing volume change, was detected by changing impedance in a magnet wire inductance coil. Solution compressibility decreased as a function of concentration. Compressibility of fats and slightly porous solids were large compared to water from 0.1 to 100 MPa. Density of all samples increased as a function of pressure at a rate that decreased with pressure. Reaction volumes for protonic ionization of citric acid, phosphoric acid, 2-(N-morpholino) ethanesulfonic acid (MES), and sulfanilic acid buffers were measured in-situ to 400 MPa at 25°C. Phosphoric acid and citric acid showed negative reaction volumes that decreased as a function of pressure due to increased ionization and consequent electrostriction. Sulfanilic acid and MES had relatively pressure stable, slightly positive reaction volumes. Equilibrium constants and pH were calculated as a function of pressure; pH changes from 0.1 to 400 MPa at 25°C were -0.57 for citric acid, -1.24 for phosphoric acid and 0.18 for MES, and to 200 MPa, -0.07 for sulfanilic acid. Electrical conductivity of juices and salt solutions was measured in-situ with a custom conductivity cell at 25°C and 50°C to 800 MPa. Cell constants at atmospheric pressure were calculated from KCl measurements and standard values; cell constants under pressure were estimated as (open full item for complete abstract)

Committee: Sudhir Sastry (Advisor); V.M. Balasubramaniam (Committee Member); G&#246;n&#252;l Kaletun&#231; (Committee Member) Subjects: Agricultural Engineering; Food Science

Doctor of Philosophy, The Ohio State University, 2008, Food, Agricultural, and Biological Engineering

Ohmic heating has potential applications for continuous sterilization processing of low-acid foods containing particulates. The main challenge is to establish a credible safety assurance protocol through experimental and modeling studies. This research aims to create a base of knowledge necessary to be developed before ohmic heating can become commercially acceptable. Electrical conductivities of six different fresh fruits and several different cuts of three types of meat were determined over entire sterilization temperature range. Electrical conductivity of all products increased linearly with the temperature during ohmic heating at constant voltage gradient. A simple blanching method was developed to increase the electrical conductivity of solid components in chicken chowmein which is a low-acid food product containing particulates. On adjusting the electrical properties of different components it was possible to ensure more uniform heating while still maintaining product quality. A simple method was developed to measure diffusivity of salt in water chestnut tissue under different levels of sodium chloride concentration and temperature. The apparent diffusion coefficient of salt in water chestnut did not change significantly with salt concentration, but as expected it increased significantly with temperature. After blanching, it was possible to increase the overall electrical conductivity and heat the solid more rapidly during ohmic heating. Residence time distribution (RTD) of particles in the ohmic heater in a continuous sterilization process was measured using Radio Frequency Identification (RFID). Mean particle residence time increased with the rotational speed of agitators in the ohmic heaters while there was no significant effect of solids concentration. The velocity of the fastest particle was 1.62 times the mean product velocity which is less than that associated with Newtonian fluid in tubular flow.

Committee: Sudhir Sastry (Advisor) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2007, Physics (Arts and Sciences)

Electro spinning is a technique used for the production of thin continuous fibers from a variety of materials including polymers, composites and ceramics [1-3]. The extremely small diameters (~ nm) and high surface to volume and aspect ratios found in electrospun fibers can not be achieved through conventional spinning. Electrically conducting polymers are materials which simultaneously possess the physical and chemical properties of organic polymers and the electronic characteristics of metals. In this work fibers were electrospun from polymer blends of polyaniline doped with Camphorsulfonic acid (PAn.HCSA) and polyethylene oxide (PEO) in chloroform. Electrical conductivities of the fibers were measured using the four-point-probe method. The conductivities of the cast films were measured for comparison purposes. It was noticed that the conductivity of both the fibers and films increase exponentially with the concentration of (PAn.HCSA), the conductivity of the film however is higher than that of the mat for any given concentration of PAn.HCSA in PEO. Electrical conductivities of single fibers containing different PAn: HCSA concentrations were measured for the first time and were found to be the highest (3.2S/cm) among the mats and films. The effect of the non-conductive PEO on the conductivity of the polyaniline fibers was studied. Keeping the PAn.HCSA concentration constant films and fibers were obtained from blends containing PEO (300,000 g/mol) and PEO (900,000 g/mol). Higher electrical conductivities were recorded in fibers and mats containing PEO (900,000 g/mol) than those containing PEO (300,000 g/mol). Silicon Carbide (SiC) fibers were obtained by electrospinning a blend of SiC and PEO in chloroform and sintering the as spun fibers at temperatures of 800°C and 1000°C. The compositional analysis of the annealed samples confirmed the presence of (30-40) µm long SiC fibers with diameters in the range (1-3) µm. Optical spectra of the fibers show red emission ext (open full item for complete abstract)

Committee: Martin Kordesch (Advisor) Subjects: Physics, Condensed Matter

Doctor of Philosophy (Ph.D.), University of Dayton, 2009, Mechanical Engineering

This dissertation describes the design and development of a new high-resolution electrical conductivity imaging technique combining the basic principles of eddy currents and atomic force microscopy (AFM). An electromagnetic coil is used to generate eddy currents in an electrically conducting material. The eddy currents induced in the sample are detected and measured with a magnetic tip attached to the AFM cantilever. The interaction of eddy currents with the magnetic tip-cantilever is theoretically modeled. The model is then used to estimate the eddy current forces generated in a typical metallic material placed in induced current field. The magnitude of the eddy current force is directly proportional to the electrical conductivity of the sample. The theoretical eddy current forces are used to design a magnetic tip-cantilever system with appropriate magnetic field and spring constant to facilitate the development of a high-resolution, high sensitivity electrical conductivity imaging technique. The technique is used to experimentally measure eddy current forces in metals of different conductivities and compared with theoretical and finite element models. The experimental results show that the technique is capable of measuring pN range eddy current forces. The experimental eddy current forces are used to determine the electrical resistivity of a thin copper wire and the experimental value agrees with the bulk resistivity of copper reported in literature. The imaging capabilities of the new technique are demonstrated by imaging the electrical conductivity variations in a composite sample and a dual-phase titanium alloy in lift mode AFM. The results indicate that this technique can be used to detect very small variations in electrical conductivity. The spatial resolution of the technique is determined to be about 25 nm by imaging carbon nanofibers reinforced in polymer matrix. Since AFM is extensively used to characterize nanomaterials, the newly developed technique is (open full item for complete abstract)

Committee: Sathish Shamachary PhD (Committee Chair); P. Terrence Murray PhD (Committee Member); Donald Klosterman PhD (Committee Member); Chakrapani Varanasi PhD (Committee Member); Mark Blodgett PhD (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, Case Western Reserve University, 1990, Materials Science and Engineering

The defect structure and the dc electrical conductivity of TiO2-NbO2 solid solution have been studied by using time-of-flight neutron diffraction, Nb K-edge x-ray absorption spectroscopy, and dc electrical conductivity measurement as a function of composition. The oxygen content in the solid solutions was determined using thermogravimetric analysis, and the results of other experiments were analyzed and correlated to establish a defect structure that controls the dc electrical conductivity. The lattice parameters and the interstitial defect occupancy were determined using the Rietveld method applied to neutron diffraction results. The valence and the coordination state of Nb ions were determined through XANES and EXAFS analyses of Nb K-edge x-ray absorption data. The formation of Nb-Nb pairs postulated by other researchers was directly observed by Nb K-edge EXAFS analysis. The formation of Nb-Nb pairs was also noticed in the results of neutron diffraction analysis and dc electrical conductivity measurement. A conductivity maximum was observed at Nb0.1Ti0.9O2, after which the conductivity decreases with increasing Nb concentration. The decreasing conductivity with increasing Nb concentration is attributed to the pair formation, by which charge car riers are localized between the two Nb ions.

Committee: Hisao Yamada (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2008, Polymer Engineering

In this work, highly conductive carbon-filled epoxy composites were developed for manufacturing bipolar plates in proton exchange membrane (PEM) fuel cells. These composites were prepared by solution intercalation mixing, followed by compression molding and curing. The in-plane and through-plane electrical conductivity, thermal and mechanical properties, gas barrier properties, and hygrothermal characteristics were determined as a function of carbon-filler type and content. For this purpose, expanded graphite and carbon black were used as a synergistic combination. Mixtures of aromatic and aliphatic epoxy resin were used as the polymer matrix to capitalize on the ductility of the aliphatic epoxy and chemical stability of the aromatic epoxy. The composites showed high glass transition temperatures (Tg ~ 180°C), high thermal degradation temperatures (T2 ~ 415°C), and in-plane conductivity of 200-500 S/cm with carbon fillers as low as 50 wt%. These composites also showed strong mechanical properties, such as flexural modulus, flexural strength, and impact strength, which either met or exceeded the targets. In addition, these composites showed excellent thermal conductivity greater than 50 W/m/K, small values of linear coefficient of thermal expansion, and dramatically reduced oxygen permeation rate. The values of mechanical and thermal properties and electrical conductivity of the composites did not change upon exposure to boiling water, aqueous sulfuric acid solution and hydrogen peroxide solution, indicating that the composites provided long-term reliability and durability under PEM fuel cell operating conditions. Experimental data show that the composites developed in this study are suitable for application as bipolar plates in PEM fuel cells.

Committee: Sadhan Jana (Advisor) Subjects: Engineering, Chemical