Department of Chemistry

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Browsing Department of Chemistry by Department "Materials Science and Engineering"

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    Dissolution and Diffusion-Based Reactions within YBa2Cu3O7-x Glass Fibers
    Heyl, Hanna; Yang, Shuo; Homa, Daniel S.; Slebodnick, Carla; Wang, Anbo; Pickrell, Gary R. (MDPI, 2019-12-20)
    This work presents a thorough identification and analysis of the dissolution and diffusion-based reaction processes that occur during the drawing of YBa2Cu3O7-x (YBCO) glass-clad fibers, using the molten-core approach, on a fiber draw tower in vacuum and in oxygen atmospheres. The results identify the dissolution of the fused silica cladding and the subsequent diffusion of silicon and oxygen into the molten YBCO core. This leads to a phase separation due to a miscibility gap which occurs in the YBCO–SiO2 system. Due to this phase separation, silica-rich precipitations form upon quenching. XRD analyses reveal that the core of the vacuum as-drawn YBCO fiber is amorphous. Heat-treatments of the vacuum as-drawn fibers in the 800–1200 °C range show that cuprite crystallizes out of the amorphous matrix by 800 °C, followed by cristobalite by 900 °C. Heat-treatments at 1100 °C and 1200 °C lead to the formation of barium copper and yttrium barium silicates. These results provide a fundamental understanding of phase relations in the YBCO–SiO2 glass-clad system as well as indispensable insights covering general glass-clad fibers drawn using the molten-core approach.
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    Influence of nucleobase stoichiometry on the self-assembly of ABC triblock copolymers
    Zhang, Keren; Talley, Samantha J.; Yu, Ya Peng; Moore, Robert Bowen; Murayama, Mitsuhiro; Long, Timothy E. (Royal Society of Chemistry, 2016-05-11)
    ABC triblock copolymers bearing adenine- and thymine-functionalized external blocks self-assembled into long-range, ordered lamellar microphase-separated morphologies on non-patterned substrates. Intermolecular hydrogen bonding formed thymine–adenine triplets and promoted self-assembly into well-defined lamellae consisting of poly(n-butyl acrylate) soft domains and complementary nucleobase hard domains, while thymine–adenine duplets contributed to superior mechanical properties.
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    Ion transport and storage of ionic liquids in ionic polymer conductor network composites
    Liu, Yang; Liu, Sheng; Lin, Junhong; Wang, Dong; Jain, Vaibhav; Montazami, Reza; Heflin, James R.; Li, Jing; Madsen, Louis A.; Zhang, Q. M. (AIP Publishing, 2010-05-01)
    We investigate ion transport and storage of ionic liquids in ionic polymer conductor network composite electroactive devices. Specifically, we show that by combining the time domain electric and electromechanical responses, one can gain quantitative information on transport behavior of the two mobile ions in ionic liquids (i.e., cation and anion) in these electroactive devices. By employing a two carrier model, the total excess ions stored and strains generated by the cations and anions, and their transport times in the nanocomposites can be determined, which all depend critically on the morphologies of the conductor network nanocomposites. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432664]
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    Transience of plasma surface modification as an adhesion promoter for polychlorotrifluorethylene
    Subrahmanyan, Sumitra; Dillard, John G.; Love, B. J.; Romand, M.; Charbonnier, M. (American Institute of Physics, 2002-05-01)
    Poly (chlorotrifluoroethylene) (PCTFE) and other fluoropolymers are increasingly used as inner layer dielectrics. However, these polymers have low surface energies and correspondingly poor adhesive proper-ties. Results are presented on the use of a low-pressure ammonia plasma to enhance the surface bondability of PCTFE. The plasma modified PCTFE film surfaces were characterized by x-ray photoelectron spectroscopy and contact angle measurements, Surface modified films exhibited improved adhesion to electroless copper deposits (180degrees peel test) compared to coated PCTFE controls and that underwent no plasma exposure. Annealing studies were conducted between 30 and 100 degreesC to examine the stability of the plasma-modified surfaces. For samples annealed below T-g. contact angle measurements indicated that the plasma-introduced groups remained bound on the surface for four weeks. For specimens annealed above Tg, the surface functionalities were absorbed within the bulk and surface rearrangement occurred within 10 h of annealing time. As a result of rearrangement, the benefit of adhesion enhancement by plasma is lost and the adhesion to copper is reduced. (C) 2002 American Vacuum Society.