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- 저자 : Lacevic, Naida (검색결과 2 건)
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Yeom, Bongjun,Sain, Trisha,Lacevic, Naida,Bukharina, Daria,Cha, Sang-Ho,Waas, Anthony M.,Arruda, Ellen M.,Kotov, Nicholas A. Nature Publishing Group 2017 Nature Vol. No.
<P>Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix(1-3). This structural motif is unusually consistent across all species from all geological eras(4-6). Such invariability-especially when juxtaposed with the diversity of other tissues-suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels-we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that lightweight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth's normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.</P>
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Chain Dynamics of Ring and Linear Polyethylene Melts from Molecular Dynamics Simulations
Hur, Kahyun,Jeong, Cheol,Winkler, Roland G.,Lacevic, Naida,Gee, Richard H.,Yoon, Do Y. American Chemical Society 2011 Macromolecules Vol.44 No.7
<P>The dynamical characteristics of ring and linear polyethylene (PE) molecules in the melt have been studied by employing atomistic molecular dynamics simulations for linear PEs with carbon atom numbers <I>N</I> up to 500 and rings with <I>N</I> up to 1500. The single-chain dynamic structure factors <I>S</I>(<I>q</I>,<I>t</I>) from entangled linear PE melt chains, which show strong deviations from the Rouse predictions, exhibit quantitative agreement with experimental results. Ring PE melt chains also show a transition from the Rouse-type to entangled dynamics, as indicated by the characteristics of <I>S</I>(<I>q</I>,<I>t</I>) and mean-square monomer displacements <I>g</I><SUB>1</SUB>(<I>t</I>). For entangled ring PE melts, we observe <I>g</I><SUB>1</SUB>(<I>t</I>) ∼ <I>t</I><SUP>0.35</SUP> and the chain-length dependence of diffusion coefficients <I>D</I><SUB><I>N</I></SUB> ∝ <I>N</I><SUP>−1.9</SUP>, very similar to entangled linear chains. Moreover, the diffusion coefficients <I>D</I><SUB><I>N</I></SUB> remain larger for the entangled rings than the corresponding entangled linear chains, due to about a 3-fold larger chain length for entanglement. Since rings do not reptate, our results point toward other important dynamical modes, based on mutual relaxations of neighboring chains, for entangled polymers in general.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2011/mamobx.2011.44.issue-7/ma102659x/production/images/medium/ma-2010-02659x_0008.gif'></P>
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