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RISS 인기검색어
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- 저자 : Winey, Karen I. (검색결과 2 건)
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Polymer Diffusion from Attractive and Athermal Substrates
Choi, Jihoon,Clarke, Nigel,Winey, Karen I.,Composto, Russell J. American Chemical Society 2017 Macromolecules Vol.50 No.7
<P>Given the exceedingly high interfacial area-to-volume ratios in polymer nanocomposites and the ability to manipulate the polymer/nanoparticle interfacial interactions, manipulating the chain dynamics at these interfaces has immense potential for impacting macroscopic properties. There, the polymer center-of-mass tracer diffusion coefficient (D) from attractive (hydroxyl terminated) and athermal (phenyl-terminated or polymer-grafted) substrates was measured over a range of temperatures and tracer molecular weights using elastic recoil detection. The tracer polymer diffusion slows significantly relative to the bulk when polymers are in direct contact with an attractive substrate and exhibits a weaker molecular weight dependence, D M M. For polymers without direct contacts on the attractive substrates and for athermal substrates, the diffusion coefficients are similar to the bulk case. The temperature dependence of these diffusion coefficients indicates that the slower diffusion at the interfaces is coupled to differences in polymer conformation and smaller fractional free volumes. These deviations from bulk are more pronounced for higher molecular weights and more attractive interfaces.</P>
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Dynamics of Precise Ethylene Ionomers Containing Ionic Liquid Functionality
Choi, U Hyeok,Middleton, L. Robert,Soccio, Michelina,Buitrago, C. Francisco,Aitken, Brian S.,Masser, Hanqing,Wagener, Kenneth B.,Winey, Karen I.,Runt, James American Chemical Society 2015 Macromolecules Vol.48 No.2
<P>This paper presents the first findings on the molecular dynamics of the remarkable new class of linear and precisely functionalized ethylene copolymers. Specifically, we utilize broadband dielectric relaxation spectroscopy to investigate the molecular dynamics of linear polyethylene (PE)-based ionomers containing 1-methylimidazolium bromide (<B>ImBr</B>) pendants on exactly every 9th, 15th, or 21st carbon atom, along with one pseudorandom analogue. We also employed FTIR spectroscopy to provide insight into local ionic interactions and the nature of the ordering of the ethylene spacers between pendants. Prior X-ray scattering experiments revealed that the polar ionic groups in these ionomers self-assemble into microphase-separated aggregates dispersed throughout the nonpolar PE matrix. We focus primarily on the dynamics of the segmental relaxations, which are significantly slowed down compared to linear PE due to ion aggregation. Relaxation times depend on composition, the presence of crystallinity, and microphase-separated morphologies. Segmental relaxation strengths are much lower than predicted by the Onsager theory for mobile isolated dipoles but much higher than linear PE, demonstrating that at least some <B>ImBr</B> pendants participate in the segmental process. Analysis of the relaxation strengths using the Kirkwood <I>g</I> correlation factor demonstrates that ca. 10–40% of the <B>ImBr</B> ion dipoles (depending on copolymer composition and temperature) participate in the segmental motions of the precise ionomers under study, with the remainder immobilized or having net antiparallel arrangements in ion aggregates.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2015/mamobx.2015.48.issue-2/ma502168e/production/images/medium/ma-2014-02168e_0011.gif'></P>
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