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Title: Model Nanocatalysts with Tunable Reactivity: Tailoring the Structure and Surface Chemistry of Nanomaterials for Energy and Alternative Fuels Catalysis.
Creator: Mistry, Hemma, Roldan Cuenya, Beatriz, Chow, Lee, Stolbov, Sergey, Zhai, Lei, University of Central Florida
Abstract / Description: One of the most pressing challenges of our time is meeting growing global energy demands while limiting human impact on the environment. To meet this challenge, new catalysts are needed to enable carbon neutral energy production processes and low cost synthesis of alternative fuels. In order to design new catalysts for such processes, fundamental understanding is needed on how the structural and chemical properties of nanostructured materials influences their surface chemistry. In this...
Show moreOne of the most pressing challenges of our time is meeting growing global energy demands while limiting human impact on the environment. To meet this challenge, new catalysts are needed to enable carbon neutral energy production processes and low cost synthesis of alternative fuels. In order to design new catalysts for such processes, fundamental understanding is needed on how the structural and chemical properties of nanostructured materials influences their surface chemistry. In this dissertation, I explore how the properties of nanoparticles, such as particle size, shape, composition, and chemical state, can be used to tune their reactivity. For this work, model nanoparticles were synthesized with well-defined structural and chemical properties, and a variety of surface science approaches were used for catalyst characterization. In particular, emphasis was placed on understanding the changes which may occur in the catalyst structure and chemical state during a reaction using advanced in situ techniques and correlating these changes to reactivity. After exploring how nanostructuring the catalyst surface can be used to tune reactivity and how dynamic changes can occur to nanocatalysts in reactive environments, these general principles are applied to a model reaction, the electroreduction of carbon dioxide, which is a promising process for synthesizing valuable products using renewable energy while consuming waste carbon dioxide. I explore the mechanisms behind how catalyst particle size, composition, and oxidation state can be used to improve activity and tune selectivity towards different carbon dioxide reduction products. Such fundamental mechanistic insights are critically needed to design efficient catalysts for this reaction.
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Date Issued: 2016
Identifier: CFE0006482, ucf:51440
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006482

Title: Mechanochemical Synthesis of Fuels from Sustainable Sources Utilizing Solid Catalysts.
Creator: Todd, Jacob, Zhai, Lei, Blair, Richard, Hampton, Michael, Harper, James, Rahman, Talat, University of Central Florida
Abstract / Description: The transition to biofuels as a means of curbing the emissions of greenhouse gases has given rise to several questions such as what to use as the feedstock and how to cost effectively process them.(&)nbsp; The production of bio-derived chemicals presents challenges in synthesis and in use as a drop-in fuel replacement.(&)nbsp; Through the use of mechanochemistry reaction pathways can be utilized that allow the efficient production of biofuels and bioderived chemicals.(&)nbsp; To this end...
Show moreThe transition to biofuels as a means of curbing the emissions of greenhouse gases has given rise to several questions such as what to use as the feedstock and how to cost effectively process them.(&)nbsp; The production of bio-derived chemicals presents challenges in synthesis and in use as a drop-in fuel replacement.(&)nbsp; Through the use of mechanochemistry reaction pathways can be utilized that allow the efficient production of biofuels and bioderived chemicals.(&)nbsp; To this end mechanically driven esterification and transesterification reactions were studied.(&)nbsp; It was found that the acid base properties of solid catalysts was critical to efficient reactions.(&)nbsp; Further investigation into mechanocatalytic reaction resulted in a reaction scheme where glucose can be used as a feedstock for the production of propane from glucose through a retro aldol reaction followed by hydrodeoxygenation.(&)nbsp; The use of mechanochemistry facilitates the efficient synthesis of important energy molecules and allows new reaction pathways to be exploited.(&)nbsp; The efficient production of bio-derived chemicals will reduce our impact on the environment.(&)nbsp;(&)nbsp;
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Date Issued: 2017
Identifier: CFE0006809, ucf:51805
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006809

Title: Two-Component Covalent Inhibitors (TCCI) of the Human Immunodeficiency Virus Reverse Transcriptase (HIV-RT).
Creator: Ledezma, Carlos, Kolpashchikov, Dmitry, Yestrebsky, Cherie, Hernandez, Florencio, Zhai, Lei, Tatulian, Suren, University of Central Florida
Abstract / Description: The traditional design of nucleoside reverse transcriptase inhibitors (NRTI's) involves the synthesis of chain-terminated nucleoside analogs. HIV-RT has relatively low fidelity which facilitates mutations that confer resistance towards NRTI's, also, drug promiscuity from NRTI's result in various side-effects that lead to poor patient adherence to treatment. We designed and tested two-component covalent inhibitors against HIV-RT. Our inhibitor design results in higher specificity due to its...
Show moreThe traditional design of nucleoside reverse transcriptase inhibitors (NRTI's) involves the synthesis of chain-terminated nucleoside analogs. HIV-RT has relatively low fidelity which facilitates mutations that confer resistance towards NRTI's, also, drug promiscuity from NRTI's result in various side-effects that lead to poor patient adherence to treatment. We designed and tested two-component covalent inhibitors against HIV-RT. Our inhibitor design results in higher specificity due to its binary approach, which has previously been used in biosensing applications, where both components are necessary for therapeutic effect, and lower chances for mutagenesis because of its inhibitory action. The TCCI approach results in up to 93% inhibition of HIV-RT Furthermore, our inhibitor design is highly modular and can be adjusted towards the therapeutic targeting of other biopolymers.
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Date Issued: 2017
Identifier: CFE0006893, ucf:51712
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006893

Title: Development of enzyme-free hydrogen peroxide biosensor using cerium oxide and mechanistic study using in-situ spectro-electrochemistry.
Creator: Saraf, Shashank, Seal, Sudipta, Cho, Hyoung Jin, Zhai, Lei, Heinrich, Helge, Harper, James, University of Central Florida
Abstract / Description: During recent development, it has been demonstrated that cerium oxide nanoparticles (CNPs) have exhibited catalytic activity which mimics naturally existing enzymes such as superoxide dismutase (SOD) and catalase. The underlying mechanism is attributed to the modulation of oxygen vacancies on CNPs lattice by dynamic switching of the oxidation states between Ce3+ and Ce4+ due to the electron transfer resulting from the redox reaction between CNPs and reactive oxygen species such as hydrogen...
Show moreDuring recent development, it has been demonstrated that cerium oxide nanoparticles (CNPs) have exhibited catalytic activity which mimics naturally existing enzymes such as superoxide dismutase (SOD) and catalase. The underlying mechanism is attributed to the modulation of oxygen vacancies on CNPs lattice by dynamic switching of the oxidation states between Ce3+ and Ce4+ due to the electron transfer resulting from the redox reaction between CNPs and reactive oxygen species such as hydrogen peroxide (H2O2). Thereby the redox potential of CNPs is dependent on the surface chemistry i.e. the surface concentration of Ce3+ and Ce4+ Currently, the ratio of Ce3+/ Ce4+ in CNPs is characterized ex-situ using XPS or TEM which involves sample drying and exposure to high energy X-rays and electron beam, respectively. Sample drying and high energy beam exposure could lead to sample deterioration. The goal of the study is to explore a technique to characterize CNPs in-situ and identify the surface chemistry of CNPs. The in-situ investigation of CNPs was carried using spectroelectrochemistry wherein the electrochemical and optical measurements are carried out simultaneously. Detailed optical characterization of two different CNPs having different catalytic activity were carried under oxidation and reduction environments. Analysis of spectra revealed widely different redox potential for CNPs which was a function of pH and composition of buffer solution. In second part of dissertation a suitable surface chemistry of CNPs is investigated to replace the enzyme in biosensor assembly to allow amperometric detection of H2O2 in physiological conditions. Upon electrochemical investigation of the physio-chemical properties of CNPs, it was found that CNPs having higher surface concentration of Ce4+ as compared to Ce3+ oxidation states, demonstrated increased catalytic activity towards H2O2. The addition of CNPs resulted in 5 orders of increment in amperometric current with a response time of 400 msec towards detection of H2O2 and exhibited excellent selectivity in presence of interfering species. Additionally, cerium oxide was successfully integrated into the biosensor assembly through the anodic electrodeposition, which allowed the transfer of electron generated from the CNPs in the redox reaction to the electrode and demonstrated successful sensing of H2O2. Furthermore, to achieve detection of H2O2 in physiological conditions, CNPs were integrated with nanoporous gold (NPG) which exhibited anti-biofouling properties. The anti-biofouling property of NPG was investigated using electrochemical techniques and showed excellent signal retention in physiological concentration of albumin proteins. The novel study targets at developing robust enzyme free biosensor by integrating the detection ability of CNPs with the anti-biofouling activity of NPG based electrode.
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Date Issued: 2016
Identifier: CFE0006498, ucf:51404
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006498

Title: Redox-Active Solid State Materials and its Biomedical and Biosensing Applications.
Creator: Gupta, Ankur, Seal, Sudipta, Dong, Yajie, Cho, Hyoung Jin, Zhai, Lei, Schulte, Alfons, University of Central Florida
Abstract / Description: Reactive oxygen species (ROS) are byproducts of physiological processes in human body, and strengthened production of ROS is known to cause acute conditions such as inflammation, aging, Alzheimer's disease, melanoma and ovarian cancer, fibrosis and multiple sclerosis. Therefore, early detection of ROS at nanomolar concentration (at cellular level) and developing more potent antioxidants is essential for regular health monitoring. As an example, ROS are also responsible for inflammation...
Show moreReactive oxygen species (ROS) are byproducts of physiological processes in human body, and strengthened production of ROS is known to cause acute conditions such as inflammation, aging, Alzheimer's disease, melanoma and ovarian cancer, fibrosis and multiple sclerosis. Therefore, early detection of ROS at nanomolar concentration (at cellular level) and developing more potent antioxidants is essential for regular health monitoring. As an example, ROS are also responsible for inflammation reactions at orthopedic implants-tissue interface triggered by wear debris. Inflammation induced by ROS results in revision surgery. Coatings of redox-active materials exhibiting antioxidant properties on implants have potential to mitigate the inflammation and delay the need of revision surgery. This dissertation focus on developing advanced functional nanomaterials by tailoring the surface chemistry of existing materials. Surface chemistry of materials can be altered by introducing surface and edge defects in the lattice structure Three materials system doped cerium oxide nanoparticles (d-CNPs), cerium oxide thin films (CeOx) and molybdenum disulfide (MoS2) nanoparticles, have been studied for its surface and edge contributions in potential biomedical and biosensing applications. Surface (d-CNPs and CeOx thin films) and edge chemistry (MoS2) have been tailored to understand its role and specific response.Surface Ce3+/Ce4+ oxidation state in CNPs controls the bio-catalytic activity. Higher superoxide dismutase (SOD) is demonstrated by high Ce3+/Ce4+ oxidation state. On the other hand, improved catalase mimetic activity is observed for low Ce3+/Ce4+ CNPs. Different CNPs preparation results in different Ce3+ to Ce4+ ratio, particle size, surface coating, and agglomeration, thus significantly varying the antioxidant properties of CNPs. In the first section of the dissertation, sustainable one-step room temperature synthesis of rare earth element (La, Sm, and Er) d-CNPs have been developed to effectively control the Ce3+ to Ce4+ ratio for specific biological application. Substitution of Ce4+ ions by trivalent dopants from ceria lattice increases the oxygen vacancies and density of catalytic sites. Uniform distribution of trivalent dopant in ceria lattice confirmed by EFTEM is attributed to enhanced SOD mimetic activity, ROS scavenging and tuning surface Ce3+/Ce4+ oxidation state in CNPs. Surface chemistry of redox-active cerium oxide coating on orthopedic implants also plays a vital role in scavenging ROS and mitigating inflammation. Thus, surface chemistry of CeOx thin films deposited by atomic layer deposited (ALD), have also been tailored by controlling the film thickness. CeOx film of 2 nm thickness has high Ce3+/Ce4+ (ratio 1) whereas higher thickness films (6-33 nm) have lower Ce3+/Ce4+ (ratio 0.30-0.37). These films have been further tested for catalase mimetic activity and hydrogen peroxide (H2O2) detection. Sensor selectivity is always a key issue. Most often, ascorbic acid found in the biological system, interfere in the electrochemical detection of H2O2 resulting in selectivity issue, thus protective Nafion layer is required to prevent cerium oxide-ascorbic acid interaction.To improve the selectivity of electrochemical sensors, Sulfur-deficient redox-active MoS2 have been utilized for electrochemical detection of pharmaceutically relevant chemical species. S-deficient MoS2 nanoparticles have been prepared by liquid exfoliation method to increase Mo-edge density and tested as sensing materials for detection of pharmaceutically relevant H2O2, hypochlorous acid (HOCl) and reactive nitrogen (NO*) species. The addition of ascorbic acid and uric acid have shown no interference during H2O2 detection. Change in S to Mo ratio have been studied using x-ray photoelectron spectroscopy. Density functional theory (DFT) have been employed to understand the detection mechanism and size-dependent sensitivity of MoS2. DFT study further reveals the role of S-deficiency and Mo- and S-edges in the higher catalytic activity of 5-7 nm MoS2 particles.Through these studies, the importance of defects in nanomaterials and their exotic properties at the nanoscale have been demonstrated. Understanding developed from these studies have provided the framework to develop more advanced functional nanomaterials for biomedical and biosensing applications.
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Date Issued: 2017
Identifier: CFE0006944, ucf:51655
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006944

Title: Electrical properties of polymer-derived silicoaluminum carboxide ceramics and their applications in micro-sensors.
Creator: Cao, Yejie, An, Linan, Fang, Jiyu, Zhai, Lei, Chen, Quanfang, Orlovskaya, Nina, University of Central Florida
Abstract / Description: Polymer-derived ceramic (PDC) is a new kind of material which is directly synthesized by the thermal decomposition of polymer precursors. Due to their unique structure, which consists of the amorphous matrix phase and free-carbon phase, PDCs exhibit many distinguished properties even at high-temperature environment such as oxidation and creep resistance, amorphous semiconducting behavior as well as piezoresistive behavior. These outstanding properties make PDCs become promising candidates for...
Show morePolymer-derived ceramic (PDC) is a new kind of material which is directly synthesized by the thermal decomposition of polymer precursors. Due to their unique structure, which consists of the amorphous matrix phase and free-carbon phase, PDCs exhibit many distinguished properties even at high-temperature environment such as oxidation and creep resistance, amorphous semiconducting behavior as well as piezoresistive behavior. These outstanding properties make PDCs become promising candidates for various applications especially for high-temperature microsensors. However, most common used PDCs in the market now are SiC, SiCN and Si(M)CN ceramics, the high price and toxicity of their raw materials as well as strict operating requirements limit their applications. SiCO ceramics are appealing increasing attentions because they can cover these shortcomings of non-oxide ceramics, but their oxidation and corrosion resistance is so weak. In this dissertation, SiAlCO ceramics are chosen as main material. The addition of Al can improve the oxidation and corrosion resistance of SiCO ceramics. In this dissertation, the SiAlCO ceramics are synthesized by using silicone resin and aluminum tri-sec-butoxide (ATSB), then ceramic samples are obtained by pyrolyzing disk green bodies at 1000, 1100, 1200, 1300, 1400?C. Firstly, the composition, microstructure and structure evolution of SiAlCO ceramics are characterized via X-Ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Impedance spectroscopy (IS). The results indicate all ceramic samples pyrolyzed below 1400?C are amorphous and a sudden structure change point around 1100?C is observed due to the increase of degree of ordering. Si-C, Si-O, C-C/H, and C=C bonds are observed within the materials.Secondly, the room-temperature and temperature-dependent conductivity of the SiAlCO ceramics are studied. The optical absorption spectra are also measured. The conductivity increases by ~6 orders of magnitude when pyrolysis temperature increases from 1000 to 1400?C. A very high activation energy of 7.15eV is observed, and the redistribution of oxygen within the material is found to be responsible for it. Amorphous semiconductor behavior which follows the band-tail hopping (BTH) process is observed within this material. And the BTH process is resulted from unique electronic structures of the materials.Thirdly, SiAlCO ceramic exhibits extraordinary piezoresistive behavior with an extremely high gauge factor in range of 7000 ~16000, which is higher than that of any previously reported high-temperature materials. The coupling effect of pressure and temperature on the piezoresistive behavior is also studied. The piezoresistive stress coefficient increases with increasing temperature, which is contradictive to other reported materials. Such change of the piezoresistive stress coefficient is due to the change in the characteristic temperature, which is reversely related to the density of state within the band-tail level.In addition, SiAlCO also shows anomalous piezo-dielectricity with the positive pressure coefficient of the dielectric constant as high as 0.10-0.25 MPa-1, which is much higher than that of other high-temperature materials. The polarizability of the material also increases with increasing pressure. There behaviors are attributed to the unique cell-like structure of the materials.In the end, a pressure sensor is successfully developed. A supportive circuit is designed and the relationships among pressure, resistance and output voltage of the system are tested. The sensitivity of the sensor is calculated to be ?1 V=?15.125 Pa, indicating the SiAlCO ceramics are promising candidates for pressure sensor materials.
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Date Issued: 2016
Identifier: CFE0006275, ucf:51052
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006275

Title: Fabrication and Study of Graphene-Based Nanocomposites for Sensing and Energy Applications.
Creator: McInnis, Matthew, Zhai, Lei, Yestrebsky, Cherie, Zou, Shengli, Blair, Richard, Chen, Quanfang, University of Central Florida
Abstract / Description: Graphite is an allotrope of carbon made up of atomically thin sheets, each covalently bound together, forming a ?-conjugated network. An individual layer, called graphene, has extraordinary electrical, thermal and physical properties that provide the opportunity for innovating new functional composites. Graphene can be produced directly on a metallic substrate by chemical vapor deposition or by chemical oxidation of graphite, forming a stable aqueous suspension of graphene oxide (GO), which...
Show moreGraphite is an allotrope of carbon made up of atomically thin sheets, each covalently bound together, forming a ?-conjugated network. An individual layer, called graphene, has extraordinary electrical, thermal and physical properties that provide the opportunity for innovating new functional composites. Graphene can be produced directly on a metallic substrate by chemical vapor deposition or by chemical oxidation of graphite, forming a stable aqueous suspension of graphene oxide (GO), which allows for convenient solution processing techniques. For the latter, after thermal or chemical reduction, much of the properties of the starting graphene re-emerge due to the reestablishment of ?-conjugation. The ?-conjugated basal plane of graphene has been shown to influence the crystallization of ?-conjugated polymers, providing thermodynamically strong nucleation sites through the relatively strong ?-? interactions. These polymers can homocrystallize into 1-D filaments, but when nucleated from graphene, the orientation and geometry can be controlled producing hierarchical structures containing an electrical conductor decorated with wires of semi-conducting polymer. The resulting structures and crystallization kinetics of the conjugated polymer, poly(3-hexylthiophene-2,5-diyl) (P3HT) nucleated by graphene was studied. Further, field-effect transistors were developed using graphene as both the electrodes and the polymer crystallization surface to directly grow P3HT nanowires as the active material. This direct crystallization technique lead to higher charge mobility and higher on-off ratios, and this result was interpreted in terms of the morphology and polymer-graphene interface.Besides these thin-film technologies, neat GO suspensions can be lyophilized to produce monolithic, free-standing aerogels and then reduced to produce an electrically conductive porous material with a surface area greater than 1000 m2/g. The present research focuses on functionalizing the aerogel surfaces with metal nanoparticles to increase electrical conductivity and to impart functionality. Functionalization was carried out by adding a metal salt as a precursor and a chelating agent to inhibit GO flocculation. The GO and metal salt were simultaneously reduced to form rGO aerogels homogeneously loaded with metal nanoparticles. The size and distribution of these nanoparticles was controlled by concentration and chelating agent identity and abundance. Optimum aerogel formulations were used as a functioning and reversible conductometric hydrogen gas sensor and as an anode in an asymmetric supercapacitor with excellent properties.
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Date Issued: 2015
Identifier: CFE0006227, ucf:51066
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006227

Title: Electronic Transport Investigation of Chemically Derived Reduced Graphene Oxide Sheets.
Creator: Joung, Daeha, Khondaker, Saiful, Chow, Lee, Leuenberger, Michael, Zhai, Lei, University of Central Florida
Abstract / Description: Reduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is...
Show moreReduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is of great significance for determining its potential application. In this dissertation, I demonstrate fabrication of high-yield solution based graphene field effects transistor (FET) using AC dielectrophoresis (DEP) and investigate the detailed electronic transport properties of the fabricated devices. The majority of the devices show ambipolar FET properties at room temperature. However, the mobility values are found to be lower than pristine graphene due to a large amount of residual defects in RGO sheets. I calculate the density of these defects by analyzing the low temperature (295 to 77K) charge transport data using space charge limited conduction (SCLC) with exponential trap distribution. At very low temperature (down to 4.2 K), I observe Coulomb blockade (CB) and Efros-Shklovskii variable range hopping (ES VRH) conduction in RGO implying that RGO can be considered as a graphene quantum dots (GQD) array, where graphene domains act like QDs while oxidized domains behave like tunnel barriers between QDs. This was further confirmed by studying RGO sheets of varying carbon sp2 fraction from 55 (-) 80 % and found that both the localization length and CB can be tuned. From the localization length and using confinement effect, we estimate tunable band gap of RGO sheets with varying carbon sp2 fraction. I then studied one dimensional RGO nanoribbon (RGONR) and found ES VRH and CB models are also applicable to the RGONR. However, in contrast to linear behavior of decrease in threshold voltage (Vt) with increasing temperature (T) in the RGO, sub linear dependence of Vt on T was observed in RGONR due to reduced transport pathways. Finally, I demonstrate synthesis and transport studies of RGO/nanoparticles (CdS and CeO2) composite and show that the properties of RGO can be further tuned by attaching the nanoparticles.
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Date Issued: 2012
Identifier: CFE0004785, ucf:49743
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004785

Title: An Adhesive Vinyl-Acrylic Electrolyte and Electrode Binder for Lithium Batteries.
Creator: Tran, Binh, Zhai, Lei, Zou, Shengli, Kuebler, Stephen, Hernandez, Florencio, Gesquiere, Andre, University of Central Florida
Abstract / Description: This dissertation describes a new vinyl-acrylic copolymer that displays great potential for applications in lithium ion batteries by enabling novel, faster, safer and cost-effective processes. Understanding the chemistry of materials and processes related to battery manufacturing allows the design of techniques and methods that can ultimately improve the performance of existing batteries while reducing the cost. The first and second parts of this dissertation focuses on the free radical...
Show moreThis dissertation describes a new vinyl-acrylic copolymer that displays great potential for applications in lithium ion batteries by enabling novel, faster, safer and cost-effective processes. Understanding the chemistry of materials and processes related to battery manufacturing allows the design of techniques and methods that can ultimately improve the performance of existing batteries while reducing the cost. The first and second parts of this dissertation focuses on the free radical polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA), methyl methacrylate (MMA), and isobutyl vinyl ether (IBVE) monomers to afford a vinyl-acrylic poly(PEGMA-co-MME-co-IBVE) random copolymer and the investigation of its properties as a soluble, amorphous, and adhesive electrolyte that is able to permanently hold 800 times its own weight. Such material properties envision a printable battery manufacturing procedure, since existing electrolytes lack adhesion at a single macromolecular level. Electrolytes can also be used as an electrode binder so long as it has structural integrity and allows ion transfer to and from the active electrode material during insertion/extraction processes. In the third section, the use of this electrolyte as a water-soluble binder for the aqueous fabrication of LiCoO2 cathodes is presented. Results of this study demonstrated the first aqueous process fabrication of thick, flexible, and fully compressed lithium ion battery electrodes by using commercial nickel foam as a supporting current collector. This feat is rather impressive because these properties are far superior to other aqueous binders in terms of material loading per electrode, specific area capacity, durability, and cell resistance. Finally, the fourth section expands on this concept by using the poly(PEGMA-co-MMA-co-IBVE) copolymer for the aqueous fabrication of a low voltage Li4Ti5O12 anode type electrode. Altogether, results demonstrate as a proof of concept that switching the current toxic manufacturing of lithium-ion batteries to an aqueous process is highly feasible. Furthermore, new electrode manufacturing techniques are also deemed possible.
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Date Issued: 2013
Identifier: CFE0004761, ucf:49780
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004761

Title: Non-Oxide Porous Ceramics from Polymer Precursor.
Creator: Yang, Xueping, An, Linan, Fang, Jiyu, Zhai, Lei, Huo, Qun, Wu, Shintson, University of Central Florida
Abstract / Description: Non-oxide porous ceramics exhibit many unique and superior properties, such as better high-temperature stability, improved chemical inertness/corrosive resistance, as well as wide band-gap semiconducting behavior, which lead to numerous potential applications in catalysis, high temperature electronic and photonic devices, and micro-electromechanical systems. Currently, most mesoporous non-oxide ceramics (e.g. SiC) are formed by two-step templating methods, which are hard to adjust the pore...
Show moreNon-oxide porous ceramics exhibit many unique and superior properties, such as better high-temperature stability, improved chemical inertness/corrosive resistance, as well as wide band-gap semiconducting behavior, which lead to numerous potential applications in catalysis, high temperature electronic and photonic devices, and micro-electromechanical systems. Currently, most mesoporous non-oxide ceramics (e.g. SiC) are formed by two-step templating methods, which are hard to adjust the pore sizes, and require a harmful etching step or a high temperature treatment to remove the templates.In this dissertation, we report a novel technique for synthesizing hierarchically mesoporous non-oxide SiC ceramic from a block copolymer precursor. The copolymer precursors with vairing block length were synthesized by reversible addition fragmentation chain transfer polymerization. The block copolymers self-assemble into nano-scaled micelles with a core-shell structure in toluene. With different operation processes, hollow SiC nanospheres and bulk mesoporous SiC ceramics were synthesized after the subsequent pyrolysis of precorsur micelles. The resultant SiC ceramics have potential applications in catalysis, solar cells, separation, and puri?cation processes.The polymer synthesis and pyrolysis process will investigated by NMR, FTIR, GPC, TEM, and TGA/DSC. The morphology and structure of synthesised SiC hollow spheres and mesoporous ceramics were analyzed by SEM, TGA/DSC and BET/BJH analysis.Besides forming core shell micelles in selective solvent Toluene, we found that PVSZ-b-PS could also exhibit this property in the air water interface. By inducing the Langmuir-Blodgett deposition, a precursor monolayer with homogeously distributed povinylsilazane particles deposited on silicon wafer synthesized by spreading the diblock copolymer PVSZ-b-PS in the air water interface. After the pyrolysis process, orderly arranging SiC nano particles formed from the polymer precursor monolayer doped on the surface of silicon wafer, which shows great potential as an optoelectronic material. The deposition process and the relationship between compress pressure and monolayer morphology were studies, and the structure of monolayer and SiC dots were investigated by AFM, SEM.
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Date Issued: 2014
Identifier: CFE0005564, ucf:50274
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005564

Title: Light-Matter Interactions of Plasmonic Nanostructures.
Creator: Reed, Jennifer, Zou, Shengli, Belfield, Kevin, Zhai, Lei, Hernandez, Eloy, Vanstryland, Eric, University of Central Florida
Abstract / Description: Light interaction with matter has long been an area of interest throughout history, spanning many fields of study. In recent decades, the investigation of light-matter interactions with nanostructures has become an intense area of research in the field of photonics. Metallic nanostructures, in particular, are of interest due to the interesting properties that arise when interacting with light. The properties are a result of the excitation of surface plasmons which are the collective...
Show moreLight interaction with matter has long been an area of interest throughout history, spanning many fields of study. In recent decades, the investigation of light-matter interactions with nanostructures has become an intense area of research in the field of photonics. Metallic nanostructures, in particular, are of interest due to the interesting properties that arise when interacting with light. The properties are a result of the excitation of surface plasmons which are the collective oscillation of the conduction electrons in the metal. Since the conduction electrons can be thought of as harmonic oscillators, they are quantized in a similar fashion. Just as a photon is a quantum of oscillations of an electromagnetic field, the plasmon is a quantum of electron oscillations of a metal. There are three types of plasmons:1. Bulk plasmons, also called volume plasmons, are longitudinal density fluctuations which propagate through a bulk metal with an eigenfrequency of ?_p called the plasma frequency.2. Localized surface plasmons are non-propagating excitations of the conduction electrons of a metallic nanoparticle coupled to an electromagnetic field. 3. Surface plasmon polaritons are evanescent, dispersive propagating electromagnetic waves formed by a coupled state between a photon and the excitation of the surface plasmons. They propagate along the surface of a metal-dielectric interface with a broad spectrum of eigenfrequencies from ?=0 to ?= ?_p??2. Plasmonics is a subfield of photonics which focuses on the study of surface plasmons and the optical properties that result from light interacting with metal films and nanostructures on the deep subwavelength scale. In this thesis, plasmonic nanostructures are investigated for optical waveguides and other nanophotonic applications through computational simulations primarily base on electrodynamic theory. The theory was formulated by several key figures and established by James Clerk Maxwell after he published a set of relations which describe all classical electromagnetic phenomena, known as Maxwell's equations. Using methods based on Maxwell's equations, the optical properties of metallic nanostructures utilizing surface plasmons is explored. In Chapter 3, light propagation of bright and dark modes of a partially and fully illuminated silver nanorod is investigated for waveguide applications. Then, the origin of the Fano resonance line shape in the scattering spectra of a silver nanorod is investigated. Next, in Chapter 4, the reflection and transmission of a multilayer silver film is simulated to observe the effects of varying the dielectric media between the layers on light propagation. Building on the multilayer film work, metal-insulator-metal waveguides are explored by perforating holes in the bottom layer of a two layer a silver film to investigate the limits of subwavelength light trapping, confinement, and propagation. Lastly, in Chapter 5, the effect of surface plasmons on the propagation direction of electromagnetic wave around a spherical silver nanoparticle which shows an effective negative index of refraction is examined. In addition, light manipulation using a film of silver prisms with an effective negative index of refraction is also investigated. The silver prisms demonstrate polarization selective propagation for waveguide and optical filter applications. These studies provide insight into plasmonic mechanisms utilized to overcome the diffraction limit of light. Through better understanding of how to manipulating light with plasmonic nanostructures, further advancements in nanophotonic technologies for applications such as extremely subwavelength waveguides, sensitive optical detection, optical filters, polarizers, beam splitters, optical data storage devices, high speed data transmission, and integrated subwavelength photonic circuits can be achieved.
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Date Issued: 2013
Identifier: CFE0005049, ucf:49964
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005049

Title: Photophysical and photochemical factors affecting multi-photon direct laser writing using the cross-linkable epoxide SU-8.
Creator: Williams Jr., Henry, Kuebler, Stephen, Elsheimer, Seth, Zhai, Lei, Liao, Yi, Heinrich, Helge, University of Central Florida
Abstract / Description: For the past decade, the epoxy based photoresist SU-8 has been used commercially and in the lab for fabricating micro- and nano-structures. Investigators have studied how processing parameters such as pre- and post-exposure bake temperatures affect the resolution and quality of SU-8 structures patterned using ultraviolet or x-ray lithography. Despite the advances in understanding the phenomena, not all of them have been explored, especially those that are specific to multi-photon direct laser...
Show moreFor the past decade, the epoxy based photoresist SU-8 has been used commercially and in the lab for fabricating micro- and nano-structures. Investigators have studied how processing parameters such as pre- and post-exposure bake temperatures affect the resolution and quality of SU-8 structures patterned using ultraviolet or x-ray lithography. Despite the advances in understanding the phenomena, not all of them have been explored, especially those that are specific to multi-photon direct laser writing (mpDLW). Unlike conventional exposure techniques, mpDLW is an inherently three-dimensional (3D) process that is activated by nonlinear absorption of light.This dissertation reports how several key processing parameters affect mpDLW using SU-8 including pre-exposure bake duration, focal depth, incident laser power, focal-point scan speed, and excitation wavelength. An examination of solvent content of films at various stages in the mpDLW by 1H-NMR shows that even moderate solvent content (over 1 wt-%) affects film viscosity and photoacid diffusion lengths, and can greatly affect the overall fidelity of small features. A study of micro-fabricated feature size versus writing depth in the material shows that even slight refractive index mismatch between SU-8 and the medium between it and the focusing objective introduces spherical aberration that distorts the focus, causing feature size to decrease or even increase in size with writing depth, depending on the average exposure power used. Proper adjustment of the average exposure power was demonstrated as a means to fabricate more uniform features with writing depth. Third, when varying the power and scan speed, it was observed that the feature-size scales with these two parameters in a manner that is consistent with a three-photon absorption mechanism at an excitation wavelength of 800 nm. When aniiiexcitation wavelength of 725 nm is used, the feature-size scaling becomes consistent with that of two photon absorption. This shows that the photoinitiators in the SU-8 can be activated by either two- or three-photon absorption over this wavelength range. Using an irradiance of ~2 TW cm-2 and elongated femtosecond pulses resulted in an observed fourth order power dependence. This observation is in agreement with the literature and suggests that the effective absorptive nonlinearity is also sensitive to pulse duration. These findings will be useful for creating accurate models of the process of mpDLW in SU-8. These models could be used to optimize the processing parameters and develop new processing methods and materials for high-resolution fabrication of robust 3D microstructures. Some of the findings were used to develop a method for fabricating functional microlenses on the tip of optical fibers. This approach opens a new route to functional integrated photonic devices.
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Date Issued: 2013
Identifier: CFE0005441, ucf:50403
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005441

Title: TAILORING THE PROPERTIES OF POLYELECTROLYTE COATED CERIUM OXIDE NANOPARTICLES AS A FUNCTION OF MOLECULAR WEIGHT.
Creator: Saraf, Shashank, Seal, Sudipta, Cho, Hyoung, Zhai, Lei, Heinrich, Helge, Harper, James, University of Central Florida
Abstract / Description: The application of Cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. This was achieved by coating CNPs with polyacrylic acid (PAA)which increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA...
Show moreThe application of Cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. This was achieved by coating CNPs with polyacrylic acid (PAA)which increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA coating was analysed using the change in the Gibbs free energy computed by Langmuir adsorption model. The adsorption isotherms were determined using soft particle electrokinetics which overcomes the challenges presented by other techniques. The Gibbs free energy was highest for PAA coated CNPs by 250 kg/mole indicating the most stable coating. The free energy for PAA 100 kg/mole coated CNPs is 85% lower than the PAA250 coated CNPs. This significant difference is caused by the strong adsorption of PAA100 on CNPs. Catalytic activity of PAA-CNPs is accessed by the catalase enzymatic activity of nanoparticles. The catalase activity was higher for PAA coated CNPs as compared to bare CNPs which indicated preferential adsorption of hydrogen peroxide induced by coating. Apart from PAA coating the catalase activity is also affected by the structure of the coating layer.
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Date Issued: 2013
Identifier: CFE0005410, ucf:50410
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005410

Title: Three-phase contact line phenomena in droplets on solid and liquid surfaces: electrocapillary, pinning, wetting line velocity effect, and free liquid surface deformation.
Creator: Shabani, Roxana, Cho, Hyoung, Kumar, Ranganathan, Kapat, Jayanta, Chow, Louis, Zhai, Lei, University of Central Florida
Abstract / Description: In this dissertation, physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wettingline) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL)phenomena, which encompass the wetting line energy (WLE), the wetting line velocity (WLV), and the contact anglehysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the air filmlubrication...
Show moreIn this dissertation, physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wettingline) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL)phenomena, which encompass the wetting line energy (WLE), the wetting line velocity (WLV), and the contact anglehysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the air filmlubrication effect and the liquid free surface deformation were taken into account to explain the dual equilibrium states ofwater droplets on liquid free surfaces. A micropump based on droplet/meniscus pressure gradient generated by EWOD was designed and fabricated. By alteringthe contact angle between liquid and solid using an electric field a pressure gradient was induced and a small droplet waspumped into the channel. The flow rate in the channel was found to be constant in spite of the changes in the droplet'sradius. The WL phenomena were studied to unravel the physical concept behind the micropump constant flow rate. Theobservation and measurement reveal that the shrinking input droplet changes its shape in two modes in time sequence: (i)its contact angle decreases, while its wetting area remains constant, and (ii) its WL starts to move while its contact anglechanges. Contact angles were measured for the advancing and receding WLs at different velocities to capture a full pictureof contact angle behavior. The effects of the WLE on the static contact angle and the WLV on the dynamic contact angle inthe pump operation were investigated. Also the effect of EWOD voltage on the magnitude and uniformity of the micropumpflow rate was studied. Dynamic contact angles were used to accurately calculate the pressure gradient between the dropletand the meniscus, and estimate the flow rate. It was shown that neglecting either of these effects not only results in aconsiderable gap between the predicted and the measured flow rates but also in an unphysical instability in the flow rateanalysis. However, when the WLE and WLV effects were fully taken into account, an excellent agreement between thepredicted and the experimental flow rates was obtained.For the study of the TCL between three fluids, aqueous droplets were formed at oil-air interface and two stableconfigurations of (i) non-coalescent droplet and (ii) cap/bead droplet were observed. General solutions for energy and forceanalysis were obtained and were shown to be in good agreement with the experimental observations. Further the energybarrier obtained for transition from configuration (i) to (ii) was correlated to the droplet release height and the probability ofnon-coalescent droplet formation. Droplets formed on the solid surfaces and on the free surface of immiscible liquids have various applications indroplet-based microfluidic devices. This research provides an insight into their formation and manipulation.
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Date Issued: 2013
Identifier: CFE0005253, ucf:50598
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005253

Title: 1, 2, and 3 Dimension Carbon/Silicon Carbon Nitride Ceramic Composites.
Creator: Calderon Flores, Jean, Zhai, Lei, Campiglia, Andres, Yestrebsky, Cherie, Zou, Shengli, Khondaker, Saiful, University of Central Florida
Abstract / Description: Polymer-derived ceramics (PDCs) are exceptional ultra-high temperature and stable multifunctional class of materials that can be synthesized from a polymer precursor through thermal decomposition. The presented research focuses on 1-D nanofibers, 2-D films and 3-D bulk, carbon-rich silicon carbon nitride (SiCN) ceramics. 1-D nanofibers were prepared via electrospinning for light weight, flame retardant and conductive applications. The commercially available CerasetTM VL20, a liquid...
Show morePolymer-derived ceramics (PDCs) are exceptional ultra-high temperature and stable multifunctional class of materials that can be synthesized from a polymer precursor through thermal decomposition. The presented research focuses on 1-D nanofibers, 2-D films and 3-D bulk, carbon-rich silicon carbon nitride (SiCN) ceramics. 1-D nanofibers were prepared via electrospinning for light weight, flame retardant and conductive applications. The commercially available CerasetTM VL20, a liquid cyclosilazane pre-ceramic precursor, was mixed with polyacrylonitrile (PAN) in order to make the cyclosilazane electrospinnable. Carbon-rich PDC nano?bers were fabricated by electrospinning various ratios of PAN/cyclosilazane solutions followed by pyrolysis. Surface morphology of the electro spun nanofibers characterized by SEM show PDC nano?bers with diameters ranging from 100-300 nm. Also, thermal stability towards oxidation showed a 10% mass loss at 623oC. 2-D carbon/SiCN films were produced by drop-casting a mixture of PAN/cyclosilazane onto a glass slide followed by pyrolysis of the film. Samples ranging from 10:1 to 1:10 PAN:cyclosilazane were made by dissolving the solutes into DMF to produce solutions ranging from 1% to 12% by weight. Green, heat-stabilized, and pyrolyzed 8% films were examined with FTIR to monitor the change in chemical structure at each step of the ceramization. SEM shows that high PAN samples produced films with ceramic embedded spheroid components in a carbon matrix, while high cyclosilazane samples produced carbon embedded spheroid.Finally, this research focuses on the challenge of making fully dense, 3-D bulk PDCs materials. Here we present a composite of SiCN with reduced graphene oxide (rGO) aerogels as a route for fully dense bulk PDCs. Incorporation of the rGO aerogel matrix into the SiCN has its pros and cons. While it lowers the strength of the composite, it allows for fabrication of large bulk samples and an increase in the electrical conductivity of the PDC. The morphology, mechanical, electrical properties and thermal conductivity of graphene-SiCN composite with varying rGO aerogel loading (0.3-2.4%) is presented. The high temperature stability, high electrical conductivity and low thermal conductivity of these composites make them excellent candidates for thermoelectric applications. Generally, carbon-rich SiCN composites with improved thermal and electrical properties are of great importance to the aerospace and electronics industries due to their expected harsh operating environments.
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Date Issued: 2015
Identifier: CFE0005768, ucf:50095
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005768

Title: Advanced Nanoscale Characterization of Plants and Plant-derived Materials for Sustainable Agriculture and Renewable Energy.
Creator: Soliman, Mikhael, Tetard, Laurene, Vaidyanathan, Raj, Kang, Hyeran, Santra, Swadeshmukul, Zhai, Lei, Chumbimuni Torres, Karin, University of Central Florida
Abstract / Description: The need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced...
Show moreThe need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced worldwide.Here we will present our advanced characterization approach to study the effects of external stresses on plants, and resulting opportunities for biomass valorization with an impact on the food-energy-water nexus.First, the adaption of plants to the pressure imposed by gravity in poplar reaction wood will be discussed. We will show that a multiscale characterization approach is necessary to reach a better understanding of the chemical and physical properties of cell walls across a transverse section of poplar stem. Our Raman spectroscopy and statistical analysis reveals intricate variations in the cellulose and lignin properties. Further, we will present evidence that advanced atomic force microscopy can reveal nanoscale variations within the individual cell wall layers, not attainable with common analytical tools. Next, chemical stresses, in particular the effect of Zinc-based pesticides on citrus plants, will be considered. We will show how multiscale characterization can support the development of new disease management methods for systemic bacterial diseases, such as citrus greening, of great importance for sustainable agriculture. In particular, we will focus on the study of new formulations, their uptake and translocation in the plants following different application methods. Lastly, we will consider how plant reactions to mechanical and chemical stresses can be controlled to engineer biomass for valorization applications. We will present our characterization of two examples: the production of carbon films derived from woody lignocellulosic biomass and the development of nanoscale growth promoters for food crop. A perspective of the work and discussion of the broader impact will conclude the presentation.
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Date Issued: 2018
Identifier: CFE0007415, ucf:52717
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007415

Title: Synthesis and Properties of Self-Assembled C/SiCN Nanocomposite Derived from Polymer Precursors.
Creator: Li, Cheng, An, Linan, Fang, Jiyu, Coffey, Kevin, Liao, Yi, Xu, Chengying, Zhai, Lei, University of Central Florida
Abstract / Description: The properties of C/SiCN nanocomposites synthesized by thermal decomposition of polymer precursors were studied in this work. The novel polymer-to-ceramic process enables us to tailor the ceramic structure in atomic level by designing the starting chemicals and pyrolysis procedures. It is of both fundamental and practical significance to investigate the properties and structures relationship of the nanocomposites. In this work, we explored their application potential in using as anode of...
Show moreThe properties of C/SiCN nanocomposites synthesized by thermal decomposition of polymer precursors were studied in this work. The novel polymer-to-ceramic process enables us to tailor the ceramic structure in atomic level by designing the starting chemicals and pyrolysis procedures. It is of both fundamental and practical significance to investigate the properties and structures relationship of the nanocomposites. In this work, we explored their application potential in using as anode of lithium-ion secondary batteries. The structure and structural evolution of C/SiCN nanocomposite were investigated by using XRD, FTIR, SEM, TEM, Solid state NMR and Raman spectroscopy. The results revealed the nanocomposites consisted of amorphous SiCxNx-4 matrix and carbon nanoclusters distributed within it. The size of the carbon was measured by Raman spectroscopy, varied with starting chemicals and pyrolysis temperature. The electronic properties of the C/SiCN nanocomposite were studied by measuring the I-V curves and a.c. impedance. The d.c. conductivity increased with carbon content and pyrolysis temperatures. The impedance spectra and fitted equivalent circuit results confirmed the existence of two phases in the nanocomposite. The possibility of using C/SiCN as anode in lithium-ion secondary batteries was investigated by electrochemical measurements, namely cyclic voltammetry, galvanostatic cyclic test and electrochemical impedance spectroscopy. The galvanostatic measurements showed that the nanocomposite with 26% of carbon nanoclusters exhibited a specific capacity of 480 mAh/g, which is 30% higher than that of commercial graphite anode. The high capacity of the nanocomposites is attributed to the formation of a novel structure around C/SiCN interface. The excellent electrochemical properties, together with the simple, low-cost processing, make the nanocomposites very promising for Li-ion battery applications.
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Date Issued: 2012
Identifier: CFE0004194, ucf:49028
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004194

Title: Structure and Properties of Polymer-Derived SiBCN Ceramics.
Creator: Chen, Yaohan, An, Linan, Fang, Jiyu, Xu, Chengying, Zhai, Lei, Huo, Qun, Gong, Xun, University of Central Florida
Abstract / Description: Polymer-derived ceramics (PDCs) are a unique class of multifunctional materials synthesized by thermal decomposition of polymeric precursors. Due to their unique and excellent properties and flexible manufacturing capability, PDC is a promising technology to prepare ceramic fibers, coatings, composites and micro-sensors for high-temperature applications. However, the structure-property relationships of PDCs have not been well understood. The lack of such understandings drastically limited the...
Show morePolymer-derived ceramics (PDCs) are a unique class of multifunctional materials synthesized by thermal decomposition of polymeric precursors. Due to their unique and excellent properties and flexible manufacturing capability, PDC is a promising technology to prepare ceramic fibers, coatings, composites and micro-sensors for high-temperature applications. However, the structure-property relationships of PDCs have not been well understood. The lack of such understandings drastically limited the further developments and applications of the materials.In this dissertation, the structure and properties of amorphous polymer-derived silicon carbonitride (SiCN) and silicoboron carbonitride (SiBCN) have been studied. The SiCN was obtained using commercially available polysilazane as pre-ceramic precursor, and the SiBCN ceramics with varied Si-to-B ratio were obtained from polyborosilazanes, which were synthesized by the hydroboration and dehydrocoupling reaction of borane and polysilazane. The structural evolution of polymer-derived SiCN and SiBCN ceramics from polymer to ceramics was investigated by NMR, FTIR, Raman, EPR, TG/DTA, and XRD. The results show a phase-separation of amorphous matrix and a graphitization of (")free(") carbon phase, and suggest that the boron doping has a great influence on the structural evolution. The electric and dielectric properties of the SiCN and SiBCNs were studied by I-V curves, LCR Meter, and network analyzer. A new electronic conduction mechanism and structure model has been proposed to account for the relationships between the observed properties and microstructure of the materials. Furthermore, the SiBCN ceramics showed the improved dielectric properties at characterization temperature up to 1300 (&)#186;C, which allows the fabrication of ultrahigh-temperature wireless microsensors for extreme environments.
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Date Issued: 2012
Identifier: CFE0004195, ucf:49014
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004195

Title: Multifunctional and Responsive Polyelectrolyte Nanostructures.
Creator: Malhotra, Astha, Zhai, Lei, Kolpashchikov, Dmitry, Ye, Jingdong, Chumbimuni Torres, Karin, Santra, Swadeshmukul, Fang, Jiyu, University of Central Florida
Abstract / Description: A polyelectrolyte complex is formed by mixing two oppositely charged polyelectrolytes in a solution. The electrostatic interactions between partially charged polymeric chains lead to the formation of a stable complex while avoiding the use of covalent cross linkers. Since complex formation can improve the stability of polyelectrolyte and metal ions in polyelectrolyte can provide various functionalities, PECs incorporated with metal ions are promising candidates for manufacturing stable and...
Show moreA polyelectrolyte complex is formed by mixing two oppositely charged polyelectrolytes in a solution. The electrostatic interactions between partially charged polymeric chains lead to the formation of a stable complex while avoiding the use of covalent cross linkers. Since complex formation can improve the stability of polyelectrolyte and metal ions in polyelectrolyte can provide various functionalities, PECs incorporated with metal ions are promising candidates for manufacturing stable and multifunctional structures. While the coordination of metal ions and polyelectrolytes has been extensively investigated in solutions and multilayer films, to our knowledge, no research has been performed to study the effect of metal ion/polyelectrolyte interactions on PECs structures and properties. The following research demonstrates the impact of different metal ions in controlling PEC structure morphology and applications. These discoveries indicate great potential of metal ions in PECs to fabricate functional PEC nanostructures.The research investigates the effect of the interactions between different metal ions and polyelectrolytes on the morphology and properties of PECs, explore the fabrication of different structures using embedded metal ions and understand the impact of metal ion/polyelectrolyte interactions on the nanoparticle structures. The research concludes: 1) incorporating metal ions of different valence into PECs introduces metal ion/polyelectrolyte interactions that can tune the morphology of PECs; 2) metal ion/polyelectrolyte interactions can be used to control the PECs swelling properties and stability in aqueous solutions; 3) the release of embedded metal ions from PECs to aqueous solutions is affected by metal ion/polyelectrolyte interactions; and 4) the embedded metal ions function as a reagent reservoir for various applications to produce functional structures. ?
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Date Issued: 2014
Identifier: CFE0005833, ucf:50918
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005833

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anode (2)	+ -
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Advancing and receding wetting-lines (1)	+ -
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