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Title: PRODUCTION OF BULK CERAMIC SHAPES FROM POLYMER DERIVED CERAMICS.
Creator: Hill, Arnold Hill, An, Linan, University of Central Florida
Abstract / Description: A method has been developed to produce bulk ceramic components from a class of ceramics known as polymer derived ceramics. In the past polymer derived ceramics have been limited to thin film applications or in the fabrication of MEMS devices. The reason being that when the polymer is into a ceramic, large quantities of gas are generated which produce internal pressure that fractures the ceramic components. The method developed here solves that issue by casting into the polymer a 3 dimensional...
Show moreA method has been developed to produce bulk ceramic components from a class of ceramics known as polymer derived ceramics. In the past polymer derived ceramics have been limited to thin film applications or in the fabrication of MEMS devices. The reason being that when the polymer is into a ceramic, large quantities of gas are generated which produce internal pressure that fractures the ceramic components. The method developed here solves that issue by casting into the polymer a 3 dimensional network of polymer fibers in the form of a foam which, during pyrolysis, burns out and leaves a network of open channels that allows decomposition gases to escape thus preventing pressure from building up. The inclusion of the polymer foam allows for the formation of strong plastic like green bodies which can be machined into any shape. The green bodies are then pyrolized into ceramic components. This process allows for the simple and inexpensive fabrication of complex ceramic components that have the potential to replace current components that are made with traditional methods.
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Date Issued: 2008
Identifier: CFE0002037, ucf:47605
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002037

Title: PRESSURE AND TEMPERATURE RESPONSE OF A STIMULI-RESPONSIVE POLYMER PROBED WITH RAMAN MICROSCOPY.
Creator: Cariker, Coleman, Schulte, Alfons, University of Central Florida
Abstract / Description: Poly(N-isopropylacrylamide) (PNIPAM) is a thermo-responsive hydrogel; that is, it is a macromolecule which exists in a hydrated state beneath its lower critical solution temperature (LCST). Polymers such as PNIPAM undergo a phase transition in response to changes in temperature, pressure, pH, salt concentration, and the addition of co-solvents. Previously, visible-light microscopic measurements of the pressure-induced phase transition have been hindered by the lack of a pressurization...
Show morePoly(N-isopropylacrylamide) (PNIPAM) is a thermo-responsive hydrogel; that is, it is a macromolecule which exists in a hydrated state beneath its lower critical solution temperature (LCST). Polymers such as PNIPAM undergo a phase transition in response to changes in temperature, pressure, pH, salt concentration, and the addition of co-solvents. Previously, visible-light microscopic measurements of the pressure-induced phase transition have been hindered by the lack of a pressurization apparatus with the short working distance and optical transmission properties necessary for high resolution microscopy. We employ a high pressure setup which uses a fused silica micro-capillary to contain the sample. Our experiment reveals differences in the spatial evolution of the phase change across the temperature and pressure thresholds, and Raman measurements allude to conformational differences in the evolution of the phase transitions. The Raman peaks positions are in agreement with previous FTIR measurements, and due to a difference in selection rules additional vibrational bands are observed in the Raman spectra.
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Date Issued: 2014
Identifier: CFH0004694, ucf:45246
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004694

Title: Effects of Surfactant Concentrations on Perovskite Emitters Embedded in Polystyrene.
Creator: Calkins, Eric, Dong, Yajie, Tetard, Laurene, Zhai, Lei, University of Central Florida
Abstract / Description: With their simple fabrication, narrow light spectrum, and color tunability, a class of materials known as perovskites are emerging as promising candidates for light emission applications. These materials, when exposed to normal atmospheric conditions show significant degradation. Improved protection has been demonstrated by embedding perovskites in polymers. Furthermore, the addition of a surfactant into the precursor solution has been shown to increase stability and allow for color tuning by...
Show moreWith their simple fabrication, narrow light spectrum, and color tunability, a class of materials known as perovskites are emerging as promising candidates for light emission applications. These materials, when exposed to normal atmospheric conditions show significant degradation. Improved protection has been demonstrated by embedding perovskites in polymers. Furthermore, the addition of a surfactant into the precursor solution has been shown to increase stability and allow for color tuning by exploiting quantum confinement effects. However, the effects of surfactants typically used to stabilize perovskites in solution have not been explored in this polymer embedding strategy. Here we determine the physical and optical emission changes produced by modifying the concentration of octylamine, butylamine, and oleylamine in the perovskite precursor solution prior to embedding into a polystyrene substrate. Using optical emission spectroscopy, we measure emission spectra of perovskite nanocrystals embedded in the polymer. Changes in morphology and dispersion of the perovskite particles within the polymer are observed using UV illuminated optical microscopy. XRD data suggests increased crystallinity with the addition of short chain surfactant. Our measurements in emission show that the location of the emission peak and overall shape of the emission spectra change when longer chain surfactant is added while short chain surfactant reduces nanorod formation without a significant change in particle dispersion or emission. The work suggests that increased long chain surfactant concentration prohibits perovskite crystal growth within the polymer leading to increased optical transparency and quantum confinement effects observable through photo luminescent emission.
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Date Issued: 2017
Identifier: CFE0007119, ucf:51940
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007119

Title: LIQUID CRYSTAL MATERIALS AND TUNABLE DEVICES FOR OPTICAL COMMUNICATIONS.
Creator: Du, Fang, Wu, Shin-Tson, University of Central Florida
Abstract / Description: In this dissertation, liquid crystal materials and devices are investigated in meeting the challenges for photonics and communications applications. The first part deals with polymer-stabilized liquid crystal (PSLC) materials and devices. Three polymer-stabilized liquid crystal systems are developed for optical communications. The second part reports the experimental investigation of a novel liquid-crystal-infiltrated photonic crystal fiber (PCF) and explores its applications in fiber-optic...
Show moreIn this dissertation, liquid crystal materials and devices are investigated in meeting the challenges for photonics and communications applications. The first part deals with polymer-stabilized liquid crystal (PSLC) materials and devices. Three polymer-stabilized liquid crystal systems are developed for optical communications. The second part reports the experimental investigation of a novel liquid-crystal-infiltrated photonic crystal fiber (PCF) and explores its applications in fiber-optic communications. The curing temperature is found to have significant effects on the PSLC performance. The electro-optic properties of nematic polymer network liquid crystal (PNLC) at different curing temperatures are investigated experimentally. At high curing temperature, a high contrast, low drive voltage, and small hysteresis PNLC is obtained as a result of the formed large LC micro-domains. With the help of curing temperature effect, it is able to develop PNLC based optical devices with highly desirable performances for optical communications. Such high performance is generally considered difficult to realize for a PNLC. In fact, the poor performance of PNLC, especially at long wavelengths, has hindered it from practical applications for optical communications for a long time. Therefore, the optimal curing temperature effect discovered in this thesis would enable PSLCs for practical industrial applications. Further more, high birefringence LCs play an important role for near infrared photonic devices. The isothiocyanato tolane liquid crystals exhibit a high birefringence and low viscosity. The high birefringence LC dramatically improves the PSLC contrast ratio while keeping a low drive voltage and fast response time. A free-space optical device by PNLC is experimentally demonstrated and its properties characterized. Most LC devices are polarization sensitive. To overcome this drawback, we have investigated the polymer-stabilized cholesteric LC (PSCLC). Combining the curing temperature effect and high birefringence LC, a polarization independent fiber-optical device is realized with over 30 dB attenuation, ~12 Vrms drive voltage and 11/28 milliseconds (rise/decay) response times. A polymer-stabilized twisted nematic LC (PS TNLC) is also proposed as a variable optical attenuator for optical communications. By using the polarization control system, the device is polarization independent. The polymer network in a PS TNLC not only results in a fast response time (0.9/9 milliseconds for rise/decay respectively), but also removes the backflow effect of TNLC which occurs in the high voltage regime.
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Date Issued: 2005
Identifier: CFE0000485, ucf:46361
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000485

Title: POLYMER-DERIVED SI-AL-C-N CERAMICS:OXIDATION, HOT-CORROSION, AND STRUCTURAL EVOLUTION.
Creator: Wang, Yiguang, An, Linan, University of Central Florida
Abstract / Description: Polymer-derived ceramics are a new class of materials synthesized by thermal decomposition of polymer precursors. Previous studies have shown that the materials exhibit excellent thermo-mechanical properties and can be stable at temperatures up to 2000oC. Furthermore, the novel polymer-to-ceramics process enables the manipulation of the ceramic structures at the atomic/nano level by designing the chemistry of polymer precursors and controlling the pyrolysis conditions, thereby, the properties...
Show morePolymer-derived ceramics are a new class of materials synthesized by thermal decomposition of polymer precursors. Previous studies have shown that the materials exhibit excellent thermo-mechanical properties and can be stable at temperatures up to 2000oC. Furthermore, the novel polymer-to-ceramics process enables the manipulation of the ceramic structures at the atomic/nano level by designing the chemistry of polymer precursors and controlling the pyrolysis conditions, thereby, the properties of ceramics. In this dissertation, oxidation/hot-corrosion behavior and the structural evolution of Si-Al-C-N ceramics have been studied. The structural evolution and crystallization behavior of the SiCN and SiAlCN ceramics are investigated using FT-IR, XRD, and NMR. The results revealed that aluminum could greatly affect the structural evolution and crystallization behavior of polymer-derived ceramics, resulting to better stability. The oxidation kinetics of the SiCN and SiAlCN ceramics in air is determined by directly measuring the thickness of the oxide scale with SEM as a function of oxidation time. The results revealed that while the oxidation of the SiCN ceramics follows parabolic kinetics in all of the ranges of testing temperatures, oxidation of the SiAlCN ceramics is complicated: their oxidation rates are similar to that of SiCN ceramics at the earlier stage, but they decrease to very low levels after a certain time. The oxidation rate of the SiAlCN ceramics is more than an order of magnitude lower than any other silicon based ceramics previously reported. The transportation behavior of oxygen through the oxide scales is studied by 18O diffusion. The results indicate that oxidation is controlled by molecular oxygen diffusing through the oxides for both SiCN and SiAlCN ceramics; however, the oxygen diffusion rate in the oxides on SiAlCN ceramics is remarkably retarded. The structures of the oxides are characterized by XRD and NMR. A structural model is advanced to account for the aluminum effect on the oxygen diffusion in the oxide. The oxidation and hot-corrosion kinetics of the SiCN and SiAlCN ceramics in water vapor are determined by measuring their weight changes as a function of annealing time. The kinetic constants, kp and kl, are obtained by fitting the weight-change data with a paralinear model. The results reveal that the SiAlCN ceramics have a much better corrosion resistance than the SiCN and CVD SiC/Si3N4. After annealing at 1400oC for 300 hours, the SiAlCN-20 still retains more than 70% of its original strength, while the SiCN only retains about 20% of its original strength. The improvement in oxidation/hot-corrosion resistance of the SiAlCN ceramics is attributed to the low activity of the SiO2 in the Al2O3-containing silica. In summary, I have developed a new class of high-temperature materials, Si-Al-C-N ceramics. It is demonstrated that these new materials have excellent oxidation and corrosion resistance and thermal stability. Together with their easy processability, the materials will find many high temperature applications such as environmental barrier coatings, ceramic matrix composites, and MEMS for harsh environments.
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Date Issued: 2006
Identifier: CFE0001017, ucf:46810
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001017

Title: SYNTHESIS AND CHARACTERIZATION OF POLYMER-DERIVED POROUS SICN CERAMICS.
Creator: wei, yun, An, Linan, University of Central Florida
Abstract / Description: The synthesis and characterization of porous SiCN ceramics produced by the method of polymer-derived ceramics were studied in this work. The polymer-to-ceramic conversion technique is a novel revolution in the methods for fabricating porous materials with controlled morphologies and tailored properties. The porous SiCN ceramics can be successfully prepared from thermal decomposition of polymeric precursors (polysilazane) and the pore former (polyvinyl alcohol (PVA)). The fabrication...
Show moreThe synthesis and characterization of porous SiCN ceramics produced by the method of polymer-derived ceramics were studied in this work. The polymer-to-ceramic conversion technique is a novel revolution in the methods for fabricating porous materials with controlled morphologies and tailored properties. The porous SiCN ceramics can be successfully prepared from thermal decomposition of polymeric precursors (polysilazane) and the pore former (polyvinyl alcohol (PVA)). The fabrication procedures involved the mixing of the pre-ceramic precursor with appropriate concentration of the PVA, curing, pyrolysis and subsequent PVA removal, leaving pores in the ceramic matrix. The material obtained revealed a homogeneous amorphous microstructure consisting of Si, C and N elements. The effects of the concentration and the particle size of PVA on the bulk density, open porosity, line shrinkage, microstructure, pore size, permeability, mechanical behavior, oxidation behavior and thermal stability were examined in this thesis. An increase in both concentration and particle size of PVA contribute to a decrease in the bulk density and an increase in the open porosity and line shrinkage. The morphology development, in particular, was investigated by scanning electron microscopy (SEM). The properties in terms of the pore size and permeability were measured by the water expulsion method. The mechanical behavior of the porous SiCN ceramic was characterized by the three- point bending strength test, thermal shock strength test and hertzian indentation strength test. The flexural strength and hertzian indentation strength of these porous ceramics at room temperature decrease with an increase in porosity. However, the flexural strength after thermal shock was significantly improved by increasing the temperature change. The oxidation behavior and thermal stability of porous SiAlCN ceramics were also explored by the mass change versus oxidation time and temperature. The phase evolution at different temperatures was also investigated by XRD analysis.
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Date Issued: 2008
Identifier: CFE0002359, ucf:47792
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002359

Title: INFRARED SURFACE PLASMON POLARITONS ON SEMICONDUCTOR, SEMIMETAL AND CONDUCTING POLYMER.
Creator: Shahzad, Monas, Peale, Robert, Heinrich, Helge, Coffey, Kevin, Diaz, Diego, University of Central Florida
Abstract / Description: Conductors with IR (infrared) plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPPs) with subwavelength mode confinement for sensing applications. The underlying aim of this work is to identify such conductors that also have sharp SPP excitation resonances for biosensor applications at infrared (3-11 ?m) wavelengths, where biological analytes are strongly differentiated by their IR absorption spectra. In this work, various materials were investigated such as a...
Show moreConductors with IR (infrared) plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPPs) with subwavelength mode confinement for sensing applications. The underlying aim of this work is to identify such conductors that also have sharp SPP excitation resonances for biosensor applications at infrared (3-11 ?m) wavelengths, where biological analytes are strongly differentiated by their IR absorption spectra. In this work, various materials were investigated such as a heavily doped semiconductor, a semimetal, a conducting polymer and its composite.Heavily doped silicon was investigated by tuning its plasma frequency to the infrared region by heavily doping. The measured complex permittivity spectra for p-type silicon with a carrier concentration of 6 (&)#215; 1019 and 6 (&)#215; 1020 cm-3 show that these materials support SPPs beyond 11 and 6 ?m wavelengths, respectively. SPP generation was observed in angular reflection spectra of doped-silicon gratings. Photon-to-plasmon coupling resonances, a necessary condition for sensing, were demonstrated near 10 ?m wavelength for the heaviest doped, and the observed resonances were confirmed theoretically using analytic calculations. The permittivity spectra were also used to calculate SPP mode heights above the silicon surface and SPP propagation lengths. Reasonable merit criteria applied to these quantities suggest that only the heaviest doped material has sensor potential, and then mainly within the wavelength range of 6 to 10 ?m. The semimetal bismuth (Bi) has an infrared plasmon frequency less than the infrared plasma frequency of noble metals such as gold and silver, which is one order of magnitude lower than their plasma frequencies. The excitation of IR surface plasmons on Bi lamellar gratings in the wavelength range of 3.4 (&)#181;m to 10.6 (&)#181;m was observed. Distinct SPP resonances were observed although the usual condition for bound SPP is not satisfied in this wavelength range because the real part of the permittivity is positive. The excitation of these resonances agrees theoretically with the electromagnetic surface waves called surface polaritons (SPs). The measured permittivity spectra were used to calculate the SP mode heights above the bismuth surface and SP propagation length, which satisfied our criteria for sensors.A conducting polymer and its composite with graphite were also investigated since their plasma frequency may lie in the infrared region. Polyaniline was chemically synthesized and doped with various acids to prepare its salt form. A composite material of polyaniline with colloidal and nano-graphite was also prepared. Optical constants were measured in the long wave infrared region (LWIR) and were used to calculate SPP propagation length and penetration depth. SPP resonance spectra were calculated and suggested that polyaniline and its composite can be used as a host with sufficient mode confinement for IR sensor application.
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Date Issued: 2012
Identifier: CFE0004598, ucf:49215
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004598

Title: Turbidity Removal Efficiency and Toxicity Issues Associated with the Chitosan-Based Dual Bio-Polymer Systems.
Creator: Hernandez, Rylee, Chopra, Manoj, Wanielista, Martin, Randall, Andrew, University of Central Florida
Abstract / Description: Stormwater runoff can be a great concern in the State of Florida due to the impact the quality of the runoff water can have on the natural water bodies. Stormwater runoff can carry pollutants and sediments which can cause both physical and biological risks in an aquatic ecosystem such as a lake, river, or pond. Polymers, namely the chitosan-based dual polymer system, can be used remove the sediment from this runoff to ensure the safety of the state's water bodies. Three soils are used in this...
Show moreStormwater runoff can be a great concern in the State of Florida due to the impact the quality of the runoff water can have on the natural water bodies. Stormwater runoff can carry pollutants and sediments which can cause both physical and biological risks in an aquatic ecosystem such as a lake, river, or pond. Polymers, namely the chitosan-based dual polymer system, can be used remove the sediment from this runoff to ensure the safety of the state's water bodies. Three soils are used in this testing: AASTO soil classifications A-3(sandy soil) and A-2-4 (silty-sand), and a soil with a fine-grained limerock component. An optimum dose of the chitosan-based dual polymer system is first determined using jar testing. The optimum dose is the dose that reduces the final turbidity to 29 NTUS or below and creates significant flocs. The under dose and over dose are calculated based on the optimum dose. Using these dosages, field scale tests are conducted using two different treatment methods: a semi-passive treatment method and a passive treatment method. Whole effluent toxicity and residual chitosan tests are then conducted on the effluent from the field scale treatment methods. The passive treatment method is the best field scale treatment method when using the silty-sand and the soil with a fine-grained limerock component. The semi-passive treatment method is the best field scale treatment method when using the sandy soil. The passive treatment method with the silty-sand achieves a final turbidity of 123.9 NTUS (88.45% removal). The passive treatment method with the soil with a fine-grained limerock component achieves a final turbidity of 132 NTUS (83.86% removal). The semi-passive treatment method with the sandy soil achieves a final turbidity of 31.43 NTUS (82.04% removal). There is only significant toxicity associated with the tests using the effluent from the passive treatment method with the soil with a fine-grained limerock component which only uses the cationic polymer.
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Date Issued: 2012
Identifier: CFE0004301, ucf:49482
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004301

Title: Printable Carbon Nanotube Based Multifunctional Nanocomposites for Strain Sensing and Self-heating.
Creator: Wang, Xin, Gou, Jihua, Challapalli, Suryanarayana, Xu, Yunjun, University of Central Florida
Abstract / Description: The unique properties of carbon nanotubes (CNTs) represent a potential for developing a piezo-resistive strain sensor and a resistive heating sheet with a smart structure. Conventional fabrication techniques of CNT based nanocomposites such as molding, casting or spray coating lack the ability to control the geometry and properties of fabricated composites. In order to meet the various requirements of strain sensing or self-heating applications, nanocomposites with complex geometry and...
Show moreThe unique properties of carbon nanotubes (CNTs) represent a potential for developing a piezo-resistive strain sensor and a resistive heating sheet with a smart structure. Conventional fabrication techniques of CNT based nanocomposites such as molding, casting or spray coating lack the ability to control the geometry and properties of fabricated composites. In order to meet the various requirements of strain sensing or self-heating applications, nanocomposites with complex geometry and controllable properties are in high demand. Digital printing technique is able to fabricate CNT films with precisely controlled geometry with the help of computer aided design, and their properties could also be controlled by adjusting the printing parameters. The objective of this study is to investigate the printing-structure-property relationship of CNT based multifunctional nanocomposites fabricated by digitally controlled spray deposition process for strain sensing and self-heating. A spray deposition modeling (SDM) printer that uses a 12-array inkjet nozzle attached to an x-y plotter was developed for the fabrication of CNT layers. Most of previously-reported CNT based nanocomposite strain sensors only have limited stretchability and sensitivity for measuring diverse human motions. Additionally, strain sensors fabricated by traditional techniques are only capable of measuring strain in a single direction, but for monitoring human motion with complicated strain condition, strain sensors that can measure strain from multi-direction are favorable. In this dissertation, highly stretchable (in excess of 45% strain) and sensitive (gauge factor of 35.75) strain sensors with tunable strain gauge factors were fabricated by incorporating CNT layers into polymer substrate using SDM printing technique. The cyclic loading-unloading test results revealed that the composite strain sensors exhibited excellent long-term durability. Due to the flexibility of the printing technique, rosette-typed sensors were fabricated to monitor complicated human motions. These superior sensing capabilities of the fabricated nanocomposites offer potential applications in wearable strain sensors. Resistive heating properties of CNT based nanocomposites were also investigated. The electrically resistive heating of these composites can be a desirable stimulus to activate the shape memory effect of polymer matrix. CNT based nanocomposites fabricated by traditional techniques showed a slow heating rate and same shape recovery ratio at different locations in nanocomposites. However, from the practical applications like smart skin or smart tooling perspective, programmable shape recovery ratio at specified locations are desirable. In this dissertation, the CNT based nanocomposites with a fast heating rate and controllable maximum surface temperature were fabricated using SDM technique. The study on the shape memory effect of nanocomposites showed that their shape recoverability was approximately 100% taking 30s under a low voltage of 40V. It is worth noting that through programming the number of printed CNT layers at different locations, the shape recovery rate could be controlled and localized actuation with the desired recovery ratio was achieved. The high efficiency of heating coupling with wide adjustability of surface temperature and shape recovery ratio at specified locations make the fabricated nanocomposites a promising candidate for electrical actuation applications.
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Date Issued: 2017
Identifier: CFE0006819, ucf:52892
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006819

Title: PROCESSING AND STUDY OF CARBON NANOTUBE / POLYMER NANOCOMPOSITES AND POLYMER ELECTROLYTE MATERIALS.
Creator: Harish, Muthuraman, Huo, Qun, University of Central Florida
Abstract / Description: The first part of the study deals with the preparation of carbon nanotube/polymer nanocomposite materials. The dispersion of multi-walled carbon nanotubes (MWNTs) using trifluoroacetic acid (TFA) as a co-solvent and its subsequent use in polymer nanocomposite fabrication is reported. The use of carbon nanotube/ polymer nanocomposite system for the fabrication of organic solar cells is also studied. TFA is a strong but volatile acid which is miscible with many commonly used organic solvents....
Show moreThe first part of the study deals with the preparation of carbon nanotube/polymer nanocomposite materials. The dispersion of multi-walled carbon nanotubes (MWNTs) using trifluoroacetic acid (TFA) as a co-solvent and its subsequent use in polymer nanocomposite fabrication is reported. The use of carbon nanotube/ polymer nanocomposite system for the fabrication of organic solar cells is also studied. TFA is a strong but volatile acid which is miscible with many commonly used organic solvents. Our study demonstrates that MWNTs can be effectively purified and readily dispersed in a range of organic solvents including dimethyl formamide (DMF), tetrahydrofuran (THF), and dichloromethane when mixed with 10 vol% trifluoroacetic acid (TFA). X-ray photoelectron spectroscopic analysis revealed that the chemical structure of the TFA-treated MWNTs remained intact without oxidation. The dispersed carbon nanotubes in TFA/THF solution were mixed with poly(methyl methacrylate) (PMMA) to fabricate polymer nanocomposites. A good dispersion of nanotubes in solution and in polymer matrices was observed and confirmed by SEM and optical microscopy study. Low percolation thresholds of electrical conductivity were observed from the fabricated MWNT/PMMA composite films. A carbon nanotube/ polymer nanocomposites system was also used for the fabrication of organic solar cells. A blend of single-wall carbon nanotubes (SWNTs) and poly3-hexylthiophene (P3HT) was used as the active layer in the device. The device characteristics showed that the fabrication of the solar cells was successful without any shorts in the circuit. The second part of the study deals with the preparation and characterization of electrode and electrolyte materials for lithium ion batteries. A system of lithium trifluoroacetate/ PMMA was used for its study as the electrolyte in lithium battery. A variety of different processing conditions were used to prepare the polymer electrolyte system. The conductivity of the electrolyte plays a critical role in the high power output of a battery. A high power output requires fast transport of lithium ions for which the conductivity of the electrolyte must be at least 3 x 10^-4 S/cm. Electrochemical Impedance Spectroscopy (EIS) was used to determine the conductivity of the polymer electrolyte films. Among the different processing conditions used to prepare the polymer electrolyte material, wet films of PMMA/salt system prepared by using 10vol% of TFA in THF showed the best results. At about 70wt% loading of the salt in the polymer, the conductivity obtained was about 1.1 x 10^-2 S/cm. Recently, the use of vanadium oxide material as intercalation host for lithium has gained widespread attention. Sol-gel derived vanadium oxide films were prepared and its use as a cathode material for lithium ion battery was studied. The application of carbon nanotubes in lithium ion battery was explored. A carbon nanotube /block copolymer (P3HT-b-PS) composite was prepared and its potential as an anode material was evaluated.
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Date Issued: 2007
Identifier: CFE0001941, ucf:47436
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001941

Title: INVESTIGATION OF GROUND PENETRATING RADAR FOR DETECTION OF LEAKING PIPELINES UNDER ROADWAY PAVEMENTS AND DEVELOPMENT OF FIBER-WRAPPING REPAIR TECHNIQUE.
Creator: Suarez, Pedro, Kuo, Shiou-San, University of Central Florida
Abstract / Description: Nowadays, it has become a common practice to observe urban roadways undergo severe distress characterized by substantial depressions. In some cases, these pavement depressions are caused by leakages in the connecting joints of sewage pipelines laid beneath the roadway pavement. Manual inspection of pipe leakages has become costly and complex since sewage pipes with relative small diameters do not allow inspection from inside and digging may be required. On the other hand, pipes with large...
Show moreNowadays, it has become a common practice to observe urban roadways undergo severe distress characterized by substantial depressions. In some cases, these pavement depressions are caused by leakages in the connecting joints of sewage pipelines laid beneath the roadway pavement. Manual inspection of pipe leakages has become costly and complex since sewage pipes with relative small diameters do not allow inspection from inside and digging may be required. On the other hand, pipes with large diameters, in which inspection can be made from pipe interior, inspector can not remain inside of the pipe for long periods of time because of toxic fumes. In order to overcome this problem, a geophysical technique known as ground penetrating radar (GPR) has been proposed as a candidate to detect the leakages. GPR is a nondestructive reflection technique, which uses high frequency electromagnetic waves to acquire subsurface information. GPR contributes to detect leaks in sewer pipes either by detecting underground voids surrounding the faulty pipe, or by detecting anomalies in the depth of the pipe as the radar propagation velocity varies due to the saturation of the soil near the leak. Once the leakage is detected, on site-repair technique to restore the damaged pipe is not an easy task. In this study, fiber reinforced polymer (FRP) composite created by saturating a fiber sheet with an epoxy resin matrix is proposed to be applied in several layers of overlay to the faulty structure surface. This fiber sheet is typically made of carbon or glass and saturated with the chemical resin matrix and makes the repaired structure even stronger than originally constructed. For the last twenty years, FRP has been used to repair and strengthen concrete columns by employing a practice known as "fiber wrapping technique". This method involves the wrapping of unidirectional fiber composite sheets around concrete columns. FRP wrapping approach can be extended to sewage pipelines for repairing and strengthening the distressed pipeline. The purpose of this study is to detect leakages in sewer pipelines using GPR, and develop an on-site fiber-wrapping technique for repairing and strengthening sewage pipes. In detecting sewer leakages, one case study is presented. The case involves the use of GRP for leakage detection in a sewer pipeline overlaid by flexible pavement that already shows signs of subsidence. Moreover, in developing a repair technique, a gypsum cement mold wrapped with carbon fiber composite material is placed around a large-scale faulty pipe joint, and tested using a MTS servo-controlled hydraulic actuator. In addition, both free ends of the pipes are capped and filled with water to determine the effectiveness of the technique in stopping leaks along the repaired joint. During the GPR survey performed in the area of study, no clear indications of leakages were observed along the buried sewer pipeline. This lack of traceable signals from the subsurface was the result of the significant attenuation of the radar signal with depth that made impossible to discern effectively any anomaly along the designated pipeline. Although different antennas having center frequencies of 300 and 80 MHz were used and a variety of settings on the GPR unit were tried, the buried pipeline was barely detectable. Nevertheless, signal reflections generated by buried pipelines in other areas such as stormwater pipes on UCF campus and drainage pipelines at road side of University Boulevard were clearly detected, which makes to believe that the significant attenuation of the radar signal at the area of study is due to the extreme high conductivity of soils which have been severely contaminated by the leakage of sewage from the distressed pipeline. In contrast, favorable results were obtained in the development of the repair technique since the two-component system, Hydro-stone Gypsum Cement and FRP composite material, wrapped around the faulty joint effectively increased its structural capacity even higher than the pipe original strength.
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Date Issued: 2004
Identifier: CFE0000290, ucf:46215
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000290

Title: Nanoscale Characterization and Mechanism of Electroless Deposition of Silver Metal.
Creator: Grabill, Christopher, Kuebler, Stephen, Beazley, Melanie, Zou, Shengli, Frazer, Andrew, Bhattacharya, Aniket, University of Central Florida
Abstract / Description: This dissertation is an investigation of the nanoscale characteristics and mechanism of electrolessly deposited silver metal seeded by gold nanoparticles. The process of growing seed-nanoparticles on a polymer surface was studied. Several bifunctional amines and organic reducing agents were used to explore how these chemical factors affect the size and distribution of gold nanoparticles formed at the interface. The nanoparticles were characterized by transmission electron microscopy (TEM) and...
Show moreThis dissertation is an investigation of the nanoscale characteristics and mechanism of electrolessly deposited silver metal seeded by gold nanoparticles. The process of growing seed-nanoparticles on a polymer surface was studied. Several bifunctional amines and organic reducing agents were used to explore how these chemical factors affect the size and distribution of gold nanoparticles formed at the interface. The nanoparticles were characterized by transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). An electroless deposition (ED) bath developed by Danscher was selected to study electroless deposition of silver in detail. The chemical species in the bath were varied to determine how concentration, nature of the carboxylate buffering species, and the presence and absence of gum arabic affect the morphology of silver metal formed by ED and the overall rate of deposition at the surface. The kinetics of deposition using the Danscher bath was studied in detail to elucidate the mechanism of ED. Knowledge generated from this investigation can be used to expand applications of silver ED where strict control over the nanoscale morphology of the deposited metal is required to obtain specific chemical and physical properties.
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Date Issued: 2018
Identifier: CFE0007009, ucf:52051
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007009

Title: IMAGING AND SPECTROSCOPY OF CONDUCTING POLYMER-FULLERENE COMPOSITE MATERIALS.
Creator: Tenery, Daeri, Gesquiere, Andre, University of Central Florida
Abstract / Description: Since the development and optical study of conjugated (conducting) polymers it has become apparent that chain conformation and aggregation at the molecular scale result in complex heterogeneous nanostructured bulk materials for which a detailed insight into morphological, spectroscopic as well as optoelectronic properties and mechanisms is overwhelmingly difficult to obtain. Nanoparticles composed of the conjugated polymer poly (MEH-PPV) and nanocomposite nanoparticles consisting of MEH-PPV...
Show moreSince the development and optical study of conjugated (conducting) polymers it has become apparent that chain conformation and aggregation at the molecular scale result in complex heterogeneous nanostructured bulk materials for which a detailed insight into morphological, spectroscopic as well as optoelectronic properties and mechanisms is overwhelmingly difficult to obtain. Nanoparticles composed of the conjugated polymer poly (MEH-PPV) and nanocomposite nanoparticles consisting of MEH-PPV doped with 1-(3-methoxycarbonylpropyl)-1-phenyl-C61 (PCBM) were prepared as model systems to study these materials at the length scale of one to a few domains. The MEH-PPV and PCBM doped nanoparticles were analyzed by single imaging/particle spectroscopy (SPS) and revealed molecular scale information on the structure-property relationships of these composite materials. The data obtained from SPS were investigated in terms of spectral difference between doped and undoped nanoparticles. The doped nanoparticles are blue shifted by approximately 5-10 nm, have an additional blue shoulder, and show different vibronic structure than the undoped nanoparticles. Specifically, relative intensity of the 0-1 transition is lower than for the undoped nanoparticles. These data are indicative of differences in molecular order between both nanoparticle systems, detected at the molecular scale. In addition, the effect of electrical fields present in devices on the interfacial charge transfer properties was evaluated. Furthermore, these nanoparticles were incorporated into the lipid nanotubes to study the diffusion process of the single MEH-PPV nanoparticles inside the lipid nanotubes. Our data shows a clear proof of concept that diffusion of nanoparticles inside the hollow lipid nanotubes can be studied on a single particle basis, which will allow us to study diffusion processes quantitatively and mechanistically within the framework of developing a biocompatible drug and gene delivery platform.
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Date Issued: 2009
Identifier: CFE0002708, ucf:48155
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002708

Title: ELECTRONIC PROPERTIES AND MICROSTRUCTURES OF AMORPHOUS SICN CERAMICS DERIVED FROM POLYMER PRECURSORS.
Creator: JIANG, TAO, An, Linan, University of Central Florida
Abstract / Description: Polymer-derived ceramics (PDCs) are a new class of high-temperature materials synthesized by thermal decomposition of polymeric precursors. These materials possess many unique features as compared with conventional ceramics synthesized by powder metallurgy based processing. For example, PDCs are neither amorphous nor crystalline. Instead, they possess nano-domain structures. Due to the direct chemical-to-ceramic processing, PDCs can be used for making components and devices with complex...
Show morePolymer-derived ceramics (PDCs) are a new class of high-temperature materials synthesized by thermal decomposition of polymeric precursors. These materials possess many unique features as compared with conventional ceramics synthesized by powder metallurgy based processing. For example, PDCs are neither amorphous nor crystalline. Instead, they possess nano-domain structures. Due to the direct chemical-to-ceramic processing, PDCs can be used for making components and devices with complex shapes. Thus, understanding the properties and structures of these materials are of both fundamental and practical interest. In this work, the structures and electronic behavior of polymer-derived amorphous silicon carbonitrides (SiCNs) were investigated. The materials were synthesized by pyrolysis of a commercially available liquid precursor. Ceramic materials with varied structures/properties were successfully synthesized by modifying the precursor and using different pyrolysis temperatures. The structures of the obtained materials were studied using XRD, solid state NMR, EPR, FTIR and Raman Spectroscope. The electronic behavior of the materials was investigated by measuring I-V curves, Hall effects, temperature dependent conductivity. The experiments were also performed to measure UV-Visible absorption and dielectric properties of the materials. This work leads to the following significant progresses: (i) developed quantitative technique for measuring free carbon concentration; (ii) achieved better understanding of the electronic conduction mechanisms and measured electronic structures of the materials for the first time; and (iii) demonstrated that these materials possess unusual dielectric behavior and provide qualitative explanations.
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Date Issued: 2009
Identifier: CFE0002702, ucf:48174
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002702

Title: Nano and nanostructured materials for optical applications.
Creator: Chantharasupawong, Panit, Thomas, Jayan, Hagan, David, Kik, Pieter, Gaume, Romain, Chanda, Debashis, University of Central Florida
Abstract / Description: Nano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical...
Show moreNano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical applications are investigated in the context of optical limiting, three dimensional displays, and optical sensing. Nanomaterials with nonlinear optical responses are promising candidates for self-activating optical limiters. In the first part of this study, optical limiting properties of unexplored nanomaterials are investigated. A photoacoustic detection technique is developed as an alternative characterization method for studying optical nonlinearities. This was done with an indigenously developed setup for measuring the photoacoustic signals generated from samples excited with a pulse laser. A theoretical model for understanding the experimental observations is presented. In addition, the advantages of this newly developed technique over the existing methods are demonstrated. Blending optical sensitizers with photoconducting polymers and chromophores results in a polymer composite that is able to record a light grating. This composite can be used as recording media in 3D holographic display technology. Here, 2D nano materials, like graphenes, are used as optical sensitizers to improve the response time of a photorefractive polymer. The addition of graphenes to a PATPD/ECZ/7-DCST composite results in a three-fold enhancement in response time and therefore faster recording speed of the medium. The faster build-up time is attributed to better charge generation and mobility due to the presence of graphenes in the composite. Lastly, a facile nanofabrication technique is developed to produce metallic nanostructures with a tunable plasmonic response. The enhancement of the light-matter interactions due to these nanostructures in sensing an analyte is demonstrated.
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Date Issued: 2015
Identifier: CFE0006029, ucf:51016
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006029

Title: Development of 3D Vision Testbed for Shape Memory Polymer Structure Applications.
Creator: Thompson, Kenneth, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: As applications for shape memory polymers (SMPs) become more advanced, it is necessary to have the ability to monitor both the actuation and thermal properties of structures made of such materials. In this paper, a method of using three stereo pairs of webcams and a single thermal camera is studied for the purposes of both tracking three dimensional motion of shape memory polymers, as well as the temperature of points of interest within the SMP structure. The method used includes a stereo...
Show moreAs applications for shape memory polymers (SMPs) become more advanced, it is necessary to have the ability to monitor both the actuation and thermal properties of structures made of such materials. In this paper, a method of using three stereo pairs of webcams and a single thermal camera is studied for the purposes of both tracking three dimensional motion of shape memory polymers, as well as the temperature of points of interest within the SMP structure. The method used includes a stereo camera calibration with integrated local minimum tracking algorithms to locate points of interest on the material and measure their temperature through interpolation techniques. The importance of the proposed method is that it allows a means to cost effectively monitor the surface temperature of a shape memory polymer structure without having to place intrusive sensors on the samples, which would limit the performance of the shape memory effect. The ability to monitor the surface temperatures of a SMP structure allows for more complex configurations to be created while increasing the performance and durability of the material. Additionally, as compared to the previous version, both the functionalities of the testbed and the user interface have been significantly improved.
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Date Issued: 2015
Identifier: CFE0005893, ucf:50860
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005893

Title: ADSORPTION BEHAVIOUR OF POLYACRYLIC ACID ON CERIUM OXIDE NANOSTRUCTURES: EXPERIMENTAL AND PREDICTIVE MODEL.
Creator: Haghighat Mesbahi, Ali, Seal, Sudipta, Fang, Jiyu, Bai, Yuanli, University of Central Florida
Abstract / Description: Cerium oxide-based slurries are crucial for chemical mechanical polishing (CMP) in electronic industry. For these slurry systems, poly(acrylic acid) (PAA) is heavily utilized to provide colloidal stability. Some of the important parameters in the colloid stability are molecular weight (MW) and concentration of stabilizer, size of the nanoparticle in the slurry and the pH of system. By determining the colloidal stability of a discrete number of slurry formulations and relating these to certain...
Show moreCerium oxide-based slurries are crucial for chemical mechanical polishing (CMP) in electronic industry. For these slurry systems, poly(acrylic acid) (PAA) is heavily utilized to provide colloidal stability. Some of the important parameters in the colloid stability are molecular weight (MW) and concentration of stabilizer, size of the nanoparticle in the slurry and the pH of system. By determining the colloidal stability of a discrete number of slurry formulations and relating these to certain slurry component parameters, a possible model can be produced to predict the influence of these parameters on the particle stability. Direct quantification of colloidal stability is difficult, however, polymer adsorption has been well established to correlate with the stability and therefore it can be used to quantify the colloidal stability.For the current thesis, surface area of cerium oxide, molecular weight of PAA, and the relative weight fraction of PAA were varied in two different nanomaterial systems, such as nanocubes and nanorods. To obtain the best fit of these variables, as they relate to polymer adsorption, fittings were performed using two advanced modeling techniques; namely, artificial neural network and adaptive neuro-fuzzy inference system. The precision of these techniques were compared each other and with the more simple, though largely imprecise, multi-variable linear regression. It was determined that the GENFIS-3 model shows the best performance for describing polymer adsorption on the nanocube and nanorod systems with an average relative deviation of only 6.5%. Additionally, these models suggest that the relative fraction of PAA has the most significant effect on the stability of cerium oxide-based CMP slurries. The greater precision of these advanced modeling methods can explain the better slurry performance with greater colloidal stability.
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Date Issued: 2015
Identifier: CFE0006315, ucf:51542
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006315

Title: Characterization of mechanical properties in nanoparticle reinforced hybrid carbon fiber composites using photoluminescence piezospectroscopy.
Creator: Jahan, Sanjida, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, University of Central Florida
Abstract / Description: Carbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Hybrid carbon fiber reinforced polymer (HCFRP) composites with alumina nanoparticles reinforcement display improved material properties such as fracture toughness, resistance to crack propagation and improved fatigue life. However, homogeneous dispersion of nanoscale materials in the matrix is important for even distribution of the improved...
Show moreCarbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Hybrid carbon fiber reinforced polymer (HCFRP) composites with alumina nanoparticles reinforcement display improved material properties such as fracture toughness, resistance to crack propagation and improved fatigue life. However, homogeneous dispersion of nanoscale materials in the matrix is important for even distribution of the improved properties. Implementing silane coupling agents (SCAs) improves dispersion by acting as a bridge between organic and inorganic materials, which increases interfacial strength and decreases sedimentation by bonding the particulate filler to the fiber reinforcement. This research is aimed at quantifying the improvement in dispersion of nanoparticles and elucidating the effects on the mechanical property of HCFRP samples through the novel use of photoluminescent characteristic peaks emitted by the alumina reinforcement particles. Photo-luminescene emission from secondary reinforcement particles of alumina embedded within the hybrid carbon fiber composites is leveraged to reveal microstructural effects of functionalization and particle weight fraction as it relates to overall composite mechanics.6, 9 and 12 weight percentage of alumina particle loading with Reactive Silane Coupling Agents, Non-reactive Silane Coupling Agent surface treatments and untreated condition are investigated in this research. Uniaxial tensile tests were conducted with measurements using piezospectroscopy (PS) and concurrent digital image correlation (DIC) to quantify the mechanical property and load distribution between the carbon fiber/epoxy and the reinforcing nanoparticles. The piezospectroscopic data were collected in an in-situ configuration using a portable piezospectroscopy system while the sample was under tensile load. Photoluminescence results show the dispersion and sedimentation behavior of the nanoparticles in the material for different surface treatment and weight percentage of the alumina nanoparticles. The piezospectroscopic maps capture and track the residual stress and its change under applied load. The results reveal the effect of varying particle loading on composite mechanical properties and how this changes with different functionalization conditions. The role of the particles in load transfer in the hybrid composite is further investigated and compared with theory. This work extends the capability of spectroscopy as an effective non-invasive method to study, at the microstructural level, the material and manufacturing effects on the development of advanced composites for applications in aerospace structures and beyond.
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Date Issued: 2017
Identifier: CFE0006886, ucf:51715
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006886

Title: Conformations and Dynamics of Semi-Flexible Polymers.
Creator: Huang, Aiqun, Bhattacharya, Aniket, Kokoouline, Viatcheslav, Tatulian, Suren, Campiglia, Andres, University of Central Florida
Abstract / Description: In this dissertation, we investigate the conformations, transverse fluctuations and dynamics of two-dimensional (2D) semi-flexible polymers both in the bulk and under channel confinement. We present unified scaling relations in regard to various quantities of interest for a broad range of combinations of chain length and chain stiffness using Langevin dynamics simulation. We also present a three-dimensional (3D) heterogeneous semi-flexible chain model for a double stranded DNA (dsDNA). Our...
Show moreIn this dissertation, we investigate the conformations, transverse fluctuations and dynamics of two-dimensional (2D) semi-flexible polymers both in the bulk and under channel confinement. We present unified scaling relations in regard to various quantities of interest for a broad range of combinations of chain length and chain stiffness using Langevin dynamics simulation. We also present a three-dimensional (3D) heterogeneous semi-flexible chain model for a double stranded DNA (dsDNA). Our model not only confirms the established findings for homogeneous dsDNA, but also predicts new physical phenomenon for heterogeneous dsDNA. The problems studied in this dissertation are relevant to analysis of the conformations and dynamics of biopolymers (such as DNA) in living organisms, and also offer insights for developing devices which operate on the single-molecule level.In particular, we present a unified description for the dynamics of building-blocks (monomers) of a semi-flexible chain. We consider the full range of flexibility from the case where the chain is fully flexible (no stiffness at all) to the case where the chain behaves like a rod (infinite stiffness). Our theory predicts qualitatively different sub-diffusive regimes for the monomer dynamics originating from the chain stiffness by studying the mean square displacement (MSD) of the monomers before the chain dynamics become purely diffusive.For the conformations in the bulk, we present results confirmed and agreed by two completely different models of semi-flexible polymers, with one of which is the bead-spring model (studied by Langevin dynamics) in the continuum space, the other (studied by Monte Carlo) is a self-avoiding walk chain on the square lattice, where only discrete bond angles are possible. We point out the universal features of chain conformations and fluctuations which are independent of the models.For the conformations under channel confinement, we discover qualitatively different conformations and dynamics of the chain as a function of the channel width and chain stiffness, and show how globule like shapes ((")de Gennes blobs(")) for more flexible chains continuously go over to shapes in the form of deflections from the wall ((")Odijk limit(")) for more stiff chains. We provide theoretical arguments how these regimes occur and interpolate among each other as one varies different parameters of the model. We also demonstrate the effect of physical dimensions (either 2D or 3D) on these regimes and argue that since in 2D the excluded volume (EV) effect is more severe compared to 3D, certain regimes do not exist in 2D.Finally, we study a model of a dsDNA , where both base-pairing and base-stacking interactions are accounted for albeit at a low computational cost compared to the other existing models. Our model correctly recovers the stiffness for dsDNA and ssDNA at different temperatures. Under most conditions of interest, a dsDNA can locally denature and form bubbles due to thermal fluctuations. At a critical temperature, a dsDNA undergoes a phase transition, in which the two strands of dsDNA completely melt to two single strands (two ssDNA). By considering EV interactions and calculating the bubble size distribution, recent studies have shown that this denaturation process is a first order transition. We show that for a homogeneous dsDNA made of only AT or GC pairs, our simulation results agree with the previous conclusion of first order transition, however, for sequences of periodic AT and GC regions, when the periodic size is relatively large compared to the sequence length, we show that the bubble size distribution exhibits peaks expressing the sequence pattern, and more importantly, the denaturation is no longer a first order transition.All these studies reported in the dissertation are relevant to the physics of living systems.
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Date Issued: 2016
Identifier: CFE0006464, ucf:51429
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006464

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

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conjugated polymer (3)	+ -
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carbon nanotube (2)	+ -
graphene oxide (2)	+ -
nanocomposites (2)	+ -
poly(3-hexylthiophene) (2)	+ -
shape memory polymer (2)	+ -
(Solid phase microextraction) SPME (1)	+ -
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Accelerated durability (1)	+ -
Adaptive Optics (1)	+ -
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An, Linan (11)	+ -
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