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Exploring Periodic Bicontinuous Cubic Network Structures with Complete Phononic Bandgaps
Hur, Kahyun,Hennig, Richard G.,Wiesner, Ulrich American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.40
<P>Controlling the phononic properties of materials provides opportunities for better thermal insulation, reduction of sound noise, and conversion of wasted heat into electricity. Phononic crystals are periodically structured media composed of two or more dissimilar materials offering a unique pathway to control the transmission of phonons, responsible for sound and heat transport. In particular, phononic crystals with cubic network structure possessing complete phononic bandgaps are highly desirable for energy applications but have not been thoroughly investigated, hampering progress in this field. Here we computationally obtained phononic band structures of 16 cubic network structures that could be made by fabrication techniques including block copolymer self-assembly and identified six structures that exhibit complete phononic bandgaps. The champion phononic bandgap structure is the so-called I-WP structure with a bandgap width of 0.41. On the basis of simulation results, design rules to tailor network structures for larger phononic bandgaps are elucidated. We expect that our results will provide guidance to develop novel materials for sonic and thermal devices.</P>
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>
Block copolymer-nanoparticle hybrid self-assembly
Hoheisel, Tobias N.,Hur, Kahyun,Wiesner, Ulrich B. Elsevier 2015 Progress in polymer science Vol.40 No.-
<P><B>Abstract</B></P> <P>Polymer-inorganic hybrid materials provide exciting opportunities as they may display favorable properties from both constituents that are desired in applications including catalysis and energy conversion and storage. For the preparation of hybrid materials with well-defined morphologies, block copolymer-directed nanoparticle hybrids present a particularly promising approach. As will be described in this review, once the fundamental characteristics for successful nanostructure formation at or close to the thermodynamic equilibrium of these nanocomposites are identified, the approach can be generalized to various materials classes. In addition to the discussion of recent materials developments based on the use of AB diblock copolymers as well as ABC triblock terpolymers, this review will therefore emphasize progress in the fundamental understanding of the underlying formation mechanisms of such hybrid materials. To this end, critical experiments for, as well as theoretical progress in the description of these nanostructured block copolymer-based hybrid materials will be discussed. Rather than providing a comprehensive overview, the review will emphasize work by the Wiesner group at Cornell University, US, on block copolymer-directed nanoparticle assemblies as well as their use in first potential application areas. The results provide powerful design criteria for wet-chemical synthesis methodologies for the generation of functional nanomaterials for applications ranging from microelectronics to catalysis to energy conversion and storage.</P>
Hwang, Jongkook,Jo, Changshin,Hur, Kahyun,Lim, Jun,Kim, Seongseop,Lee, Jinwoo American Chemical Society 2014 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.136 No.45
<P>Hierarchically porous oxide materials have immense potential for applications in catalysis, separation, and energy devices, but the synthesis of these materials is hampered by the need to use multiple templates and the associated complicated steps and uncontrollable mixing behavior. Here we report a simple one-pot strategy for the synthesis of inorganic oxide materials with multiscale porosity. The inorganic precursor and block copolymer are coassembled into an ordered mesostructure (microphase separation), while the in situ-polymerized organic precursor forms organic-rich macrodomains (macrophase separation) around which the mesostructure grows. Calcination generates hierarchical meso/macroporous SiO<SUB>2</SUB> and TiO<SUB>2</SUB> with three-dimensionally interconnected pore networks. The continuous 3D macrostructures were clearly visualized by nanoscale X-ray computed tomography. The resulting TiO<SUB>2</SUB> was used as the anode in a lithium ion battery and showed excellent rate capability compared with mesoporous TiO<SUB>2</SUB>. This work is of particular importance because it (i) expands the base of BCP self-assembly from mesostructures to complex porous structures, (ii) shows that the interplay of micro- and macrophase separation can be fully exploited for the design of hierarchically porous inorganic materials, and therefore (iii) provides strategies for researchers in materials science and polymer science.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2014/jacsat.2014.136.issue-45/ja5091172/production/images/medium/ja-2014-091172_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5091172'>ACS Electronic Supporting Info</A></P>
Optically Switchable Smart Windows with Integrated Photovoltaic Devices
Kwon, Hyun-Keun,Lee, Kyu-Tae,Hur, Kahyun,Moon, Sung Hwan,Quasim, Malik M.,Wilkinson, Timothy D.,Han, Ji-Young,Ko, Hyungduk,Han, Il-Ki,Park, Byoungnam,Min, Byoung Koun,Ju, Byeong-Kwon,Morris, Stephen M Wiley Blackwell (John Wiley Sons) 2015 Advanced energy materials Vol.5 No.3
Soft self-assembly of Weyl materials for light and sound
Fruchart, Michel,Jeon, Seung-Yeol,Hur, Kahyun,Cheianov, Vadim,Wiesner, Ulrich,Vitelli, Vincenzo National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.16
<P>Soft materials can self-assemble into highly structured phases that replicate at the mesoscopic scale the symmetry of atomic crystals. As such, they offer an unparalleled platform to design mesostructured materials for light and sound. Here, we present a bottom-up approach based on self-assembly to engineer 3D photonic and phononic crystals with topologically protected Weyl points. In addition to angular and frequency selectivity of their bulk optical response, Weyl materials are endowed with topological surface states, which allow for the existence of one-way channels, even in the presence of time-reversal invariance. Using a combination of group-theoretical methods and numerical simulations, we identify the general symmetry constraints that a self-assembled structure has to satisfy to host Weyl points and describe how to achieve such constraints using a symmetry-driven pipeline for self-assembled material design and discovery. We illustrate our general approach using block copolymer self-assembly as a model system.</P>
Label-free bacterial detection using polydiacetylene liposomes
Park, Jimin,Ku, Seul Kathy,Seo, Deokwon,Hur, Kahyun,Jeon, Hojeong,Shvartsman, Dmitry,Seok, Hyun-Kwang,Mooney, David J.,Lee, Kangwon The Royal Society of Chemistry 2016 Chemical communications Vol.52 No.68
<P>Polydiacetylene (PDA) liposomes were prepared to selectively capture target released from bacteria. Specific interplay between released-surfactin and PDA resulted in a conformal change in the structure of PDA, highlighting the potential of indirect interactions between bacteria and PDA in the construction of new label-free bacterial sensors.</P>
Intrinsic photonic wave localization in a three-dimensional icosahedral quasicrystal
Jeon, Seung-Yeol,Kwon, Hyungho,Hur, Kahyun Nature Publishing Group 2017 Nature physics Vol.13 No.4
Wave transport is one of the most interesting topics related to quasicrystals. This is due to the fact that the translational symmetry strongly governs the transport properties of every form of wave. Although quasiperiodic structures with or without disorder have been studied, a clear mechanism for wave transport in three-dimensional quasicrystals including localization is missing. To study the intrinsic quasiperiodic effects on wave transport, the time invariance of the lattice structure and the loss-free condition must be controlled. Here, using finite-difference methods, we study the diffusive-like transport and localization of photonic waves in a three-dimensional icosahedral quasicrystal without additional disorder. This result appears at odds with the well-known theory of wave localization (Anderson localization), but we found that in quasicrystals the short mean free path of the photonic waves makes localization possible.