Browsing by Author "Dr. Mohamed Bourham, Committee Member"

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    The Effect of Atmospheric Pressure Plasma Treatments on Interfacial Bonding Strength of Ultrahigh Modulus Polyethylene Fibers to Epoxy Resin
    (2002-11-14) Jensen, Christina Louise; Dr. Marian McCord, Committee Member; Dr. Mohamed Bourham, Committee Member; Dr. Yiping Qiu, Committee Chair
    The surface modification of UHMPE fibers by atmospheric pressure plasma treatments was examined. In one study the aging effects of atmospheric plasma treatments were studied. UHMPE fibers were treated for 0.5 and 1 min with He/O2/air gas and for 2 and 4 min with He/air gas by atmospheric pressure plasma on a capacitively coupled device. The samples were tested for fiber/epoxy interfacial shear strength using the microbond technique at time intervals of 0, 3, 15 and 30 days after initial plasma treatment. Interfacial shear strengths (IFSS) for plasma treated fibers were 2 - 3 times as high as that of the control. The IFSS for the plasma treated fibers remained constant up to 15 days and then decreased afterwards. XPS Analysis and SEM photographs characterized the fiber surface modification. In a second study, delamination phenomena was studied by the transverse compression of seven-fiber bundle UHMPE microcomposites, a peeling test of laminated plain weave UHMPE fabric and tensile shear strength testing of a ten-layer plain weave UHMPE / Epoxy flat panel composite. Results showed a 49% increase in yield modulus of the plasma treated sample compared to the control in the transverse compression test. There was an 82.5% increase in bonding strength for the plasma treated sample during the peel test and a 25.7% increase in interlaminar shear strength of the ten-ply UHMPE composite proving that atmospheric plasma treatments are very effective in surface modification on a microscopic fiber level and a full-scale composite production level.
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    A High Resolution Study of p + 44Ca Reactions
    (2004-05-12) Lokitz, Stephen Jared; Dr. Gary E. Mitchell, Committee Co-Chair; Dr. John F. Shriner, Jr., Committee Co-Chair; Dr. Mohamed Bourham, Committee Member; Dr. John H. Kelley, Committee Member
    A high resolution measurement of the cross-sections of the 44Ca(p,p0) and 44Ca(p,p1) reactions was performed over the energy range E[subscript p] = 2.50--3.53 MeV to improve the purity and completeness of the 45Sc level sequences. A specific goal was the investigation of possible parity-dependence of the level densities of 45Sc. This research was performed at the High Resolution Laboratory at Triangle Universities Nuclear Laboratory. The data were measured at five angles and the observed cross-sections were fit with the multilevel, multichannel, R-matrix code MULTI6. Many levels were observed for the first time, and many levels were reassigned different quantum numbers. A total of ~800 resonances were observed. The purity and completeness of the 45Sc data were tested via several statistical analyses: the nearest-neighbor spacing distribution, the reduced width distribution, and the Dyson-Mehta Δ₃ statistic. The results of the statistical analyses were mixed. The s-wave resonance sequence compares very well with random matrix predictions. The other sequences do not agree well with GOE predictions, suggesting missing and/or misassigned levels. The experimental nearest-neighbor spacings were compared to the Wigner distribution to identify anomalously large (small) spacings which imply missing (misassigned) levels. The number of anomalous spacings has been reduced, indicating improved purity and completeness of the data. In particular the small spacing anomalies proved to be a very useful and practical analysis tool. The level densities were determined using two methods to correct for missing levels. Uncertainties in the level densities have been significantly reduced. No evidence of parity dependence in the level densities of 45Sc was observed.
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    A High Resolution Study of Proton Resonances in 51Mn
    (2004-08-16) Beal, William Chandler; Dr. Mohamed Bourham, Committee Member; Dr. Gary E. Mitchell, Committee Co-Chair; Dr. John F. Shriner, Jr., Committee Co-Chair; Dr. D. Ronald Tilley, Committee Member
    High-resolution measurements of the differential cross sections of the 50Cr(p,p0) and 50Cr(p,p1) reactions were performed over the energy range E[subscript p]=1.8045–3.5011 MeV at five different scattering angles. This experiment was performed at the High Resolution Laboratory (HRL) at Triangle Universities Nuclear Laboratory (TUNL); the system is capable of measuring proton-scattering data with an energy resolution of ~250 eV. The goal of this work is to improve the purity and completeness of the 51Mn level sequences in order to investigate average level properties. The observed cross sections were fit using the multi-level, multi-channel, R-matrix code MULTI, and resonance parameters were extracted from the data. Many resonances were observed for the first time, and several others were reassigned different quantum numbers compared to previous work. A total of 185 resonances were observed, 64 of which had not been observed in previous studies. Statistical analyses based on predictions of random matrix theory were performed on the nearest-neighbor spacing distributions and the reduced-width distributions, with mixed results. The s-wave resonance sequences are in good agreement with GOE predictions, while the p-wave resonance analyses show evidence of missing and misassigned levels. Separation of the d-wave, f-wave, and g-wave resonances into pure sequences is not feasible due to ambiguity in J assignments for these levels. Strength functions and level densities were determined for both the pure and mixed sequences.
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    The Plasma Flame: Development and Application of a Hybrid Plasma at Atmospheric Pressure
    (2009-06-01) King, Matthew Russell; Dr. Jerry Cuomo, Committee Chair; Dr. Mohamed Bourham, Committee Member; Dr. Joseph Tracy, Committee Member
    The focus of this work was to develop a hybrid plasma at atmospheric pressure, which we have deemed the “plasma flame†. This discharge is capable of facilitating the chemical reactivity associated with non-thermal (low energy) plasmas while operating at temperatures which can drive high energy reactions. Gas mixtures of nitrogen and oxygen were used as a model system for understanding the nature of the plasma flame. Multiple process variables and discharge characteristics were studied gas composition, applied power, driving frequency, electron density, gas temperature, plasma temperature, radical chemistry, and reaction kinetics. It was found that this discharge produces a significant amount of nitrogen dioxide (NO2) over 10^17 cm-3. The production of NO2 was found to depend predominately on the temperature differential between the plasma and ambient gas. The extent to which the NO2-forming reactions proceed also depends on the availability of atomic oxygen (O) and nitric oxide (NO). Given the level of NO2 formation in the plasma flame, a process was created for synthesizing nitric acid (HNO3) we call “Acid on Demand†. This process was then developed for application to the production of bioethanol and printed circuit boards (PCB’s). Furthermore, the formation of syngas (CO + H2) was also produced by introducing a different chemical system into the plasma flame (i.e. CH4 + H2O). This thesis establishes a framework for understanding the complex chemistries associated with the plasma flame. Such knowledge can be extended to a number of chemical systems and potential applications. Overarching themes of this work have implications for a variety of topics, from non-equilibrium chemistry to synthesis of alternative fuels.
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    Spherical Microwave Confinement and Ball Lightning
    (2010-04-14) Robinson, William Richard; Dr. David Aspnes, Committee Chair; Dr. Stephen Reynolds, Committee Member; Dr. Dean Lee, Committee Member; Dr. Mohamed Bourham, Committee Member
    This dissertation presents the results of research done on unconventional energy technologies from 1995 to 2009. The present civilization depends on an infrastructure that was constructed and is maintained almost entirely using concentrated fuels and ores, both of which will run out. Diffuse renewable energy sources rely on this same infrastructure, and hence face the same limitations. I first examined sonoluminescence directed toward fusion, but demonstrated theoretically that this is impossible. I next studied Low Energy Nuclear Reactions and developed methods for improving results, although these have not been implemented. In 2000 I began Spherical Microwave Confinement (SMC), which confines and heats plasma with microwaves in a spherical chamber. The reactor was designed and built to provide the data needed to investigate the possibility of achieving fusion conditions with microwave confinement. A second objective was to attempt to create ball lightning (BL). The reactor featured 20 magnetrons, which were driven by a capacitor bank and operated in a 0.2 s pulse mode at 2.45 GHz. These provided 20 kW to an icosahedral array of 20 antennas. Video of plasmas led to a redesign of the antennas to provide better coupling of the microwaves to the plasma. A second improvement was a grid at the base of the antennas, which provided corona electrons and an electric field to aid quick formation of plasmas. Although fusion conditions were never achieved and ball lightning not observed, experience gained from operating this basic, affordable system has been incorporated in a more sophisticated reactor design intended for future research. This would use magnets that were originally planned. The cusp geometry of the magnetic fields is suitable for electron cyclotron resonance in the same type of closed surface that in existing reactors has generated high-temperature plasmas. Should ball lightning be created, it could be a practical power source with nearly ideal characteristics that could solve many of our current energy-production problems.
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    Thermally Responsive Surfaces for Tissue Engineering and Apparel Applications
    (2006-11-05) Barcio, Sarah; Dr. Nancy Monteiro-Riviere, Committee Member; Dr. Marian McCord, Committee Chair; Dr. Mohamed Bourham, Committee Member
    Thermally responsive surfaces were created by grafting poly (N-isopropylacrylamide) (pNIPAM) onto polyester (PET) film and fabric using atmospheric pressure plasma treatment, which provided a quick, simple means of grafting that sufficiently sterilized the samples for cell culture. Grafting was achieved by a two-step process of surface activation with atmospheric pressure plasma followed by exposure of the substrate to a monomer solution in the presence of atmospheric pressure plasma. The plasma exposure time and monomer solution volume were optimized using cell culture studies. The graft was characterized by surface analysis techniques and cell culture studies. Contact angle measurements at different temperatures verified the thermally responsive nature of the graft on the PET film and fabric. Atomic force microscopy (AFM) was used to examine the surface topography and the effects of an aqueous environment on the surface. Scanning electron microscopy (SEM) was also used to examine the surface of the films and fabrics and to confirm the presence of the pNIPAM. AFM images showed the surface become significantly rougher and more variable when placed in water as the polymer chains became hydrated and a gel structure formed. The decrease in surface roughness seen with the grafted film and the SEM images confirm the graft coating the untreated film. The graft thickness on the PET film was found to be between 30 and 100 nm with AFM measurements. An acid dye test verified the presence of the graft on the filtration fabric. Cell culture studies were completed using human epidermal keratinocytes (HEKs), human lung fibroblasts (HFLs), and human hepatocellular carcinoma (Hep G2) cells to demonstrate thermally modulated cellular adhesion, growth and detachment on the films and fabrics. Viable cell sheets were successfully released from atmospheric plasma grafted pNIPAM on polyester film. Although no detachment was achieved with the grafted PET fabric, the treated fabrics could potentially be useful for tissue engineering scaffolds in bioreactors or for large-scale cell sheet engineering. Thermally responsive textiles were created using coat- and spray-grafting of pNIPAM onto woven cotton, nylon, and polyester with atmospheric pressure plasma treatment. Fourier transform infrared spectroscopy (FTIR) was used to examine the surface chemistry and confirm the presence and washfastness of the grafts produced from the two methods. Vertical wicking tests showed an increase in wettability with increasing temperature. Coat-grafted fabrics had the greatest resistance to wicking, and spray-grafted fabrics had the greatest wicking. An acid dye test also confirmed the presence of the graft showing the greatest uniformity and washfastness from the coat-grafting method. Once fully characterized, these fabrics could be used as responsive textiles for apparel applications.