Moonhor Ree

Pohang University of Science and Technology, Geijitsu, Gyeongsangbuk-do, South Korea

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Publications (335)1271.7 Total impact

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    ABSTRACT: Poly(oxy(11-(biotinyl)undecylthiomethyl)ethylene-co-oxy(11-phosphoryl-cholineundecylthiomethyl)ethylene)s (PECH-BTmPCn: m = 0~100 mol% biotin (BT) containing bristle; n = 100~0 mol% phosphorylcholine (PC) containing bristle) were newly synthesized. All polymers exhibited excellent solution processibility. They favorably self-assembled horizontal multibilayer structures in thin films with BT- and PC-enriched surface, which were driven by the lateral ordering of the fully extended upright bristles and the partial interdigitation between the BT and PC end groups of the bristles. Both hydrophilicity and water sorption of the films increased with the PC content. The PECH-BT100 films revealed remarkably distinctive sensitivity, selectivity, and adsorption ability for avidin against other proteins. Such remarkable performance was further significantly enhanced on the PECH-BTmPCn films in which PC moieties were incorporated to the BT-rich surface; in particular, the PECH-BT75PC25 films demonstrated the highest performance. Overall, the self-assembly brush copolymers of this study are very suitable for use in the high performance detection, adsorption, and separation of proteins and receptors, including avidin, which can reveal high affinity and selectivity to BT moiety.
    No preview · Article · Jan 2016 · Biomacromolecules
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    Full-text · Article · Dec 2015 · ACS Sustainable Chemistry & Engineering
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    ABSTRACT: Two series of well-defined brush polymers bearing a triazole moiety on each bristle were prepared from the click chemistry reactions of a poly(glycidyl azide) (PG) and a poly(4-azidomethylstyrene) (PS) with alkyne derivatives. The thin-film morphologies and properties, especially electrical memory performances, of these triazole-containing brush polymers were investigated in detail. The brush polymers with a triazole ring substituted with an alkyl or alkylenylphenyl group in the bristle exhibited only dielectric characteristics. By contrast, the other brush polymers bearing a triazole ring substituted with phenyl or its derivatives with a longer π-conjugation length in the bristle demonstrated excellent unipolar permanent memory behaviors with low power consumption, high ON/OFF current ratios and high stability and reliability under ambient air conditions. Furthermore, their memory type could be tuned to p- or n-type by the incorporation of an electron-donating or -accepting group into the phenyl unit linked to the triazole moiety. Overall, this study presents the first demonstration of the azide–alkyne click chemistry synthesis of triazole moieties with substituent(s) that exhibit a resonance effect; this approach is a very powerful synthetic route to develop electrical memory polymers suitable for the low-cost mass production of high-performance, polarity-free programmable memory devices.
    Preview · Article · Dec 2015
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    ABSTRACT: Amphiphilic poly(4-di(9,9-dihexylfluoren-2-yl)styrene)-b-poly(2-vinylpyridine)s (PStFl2m-b-P2VPn) in two different compositions and their homopolymers were synthesized: PStFl211-b-P2VP89 (50/50, volume ratio), PStFl212-b-P2VP33 (75/25), PStFl2, and P2VP. They were thermally stable up to around 350 °C. In nanoscale thin films, the diblock copolymers exhibited various phase-separated nanostructures depending on the composition and film process condition: random two phases, horizontal hexagonal P2VP cylinders, and hexagonally-close packed (HCP) P2VP spheres. Surprisingly, the hexagonal cylinder and HCP sphere structures are quite different from those of common diblock copolymers with similar compositions. The structural details of these thin film morphologies were investigated by synchrotron grazing incidence X-ray scattering. The thin film morphologies were found to make influences on the electrical memory performances of the polymers. In particular, the switching-ON voltage was influenced by the nanostructures and the film layer thickness as well as by the composition. Overall, the diblock copolymer films demonstrated excellent p-type permanent digital memory behaviors with unipolarity, long retention time, high ON/OFF current ratio and low power consumption. These memory behaviors were governed by a trap-limited space charge limited conduction mechanism combined with ohmic conduction and a hopping process.
    No preview · Article · Dec 2015 · European Polymer Journal
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    ABSTRACT: As integrated microelectronic circuit device dimensions continue to shrink, low dielectric constant (low-k) interlayer dielectrics are required for minimizing RC signal delay, capacitive coupling noise, and power consumption. The implementation of low-k materials in an interconnected structure, however, is known to be a very difficult task because of many criteria imposed by the structural functionality and the integration process. Here, we report structural reliability evaluation for the integration of low-k nanoporous organosillicate dielectrics into a multilayer structure, involving capping, chemical mechanical polishing (CMP), post-CMP cleaning, and thermal annealing processes. We have successfully investigated the structural reliability of the low-k dielectric layer subjected to such harsh processes using synchrotron grazing incidence X-ray scattering and reflectivity (GIXS and XR) analyses. This study additionally demonstrated that synchrotron GIXS and XR techniques are very powerful tools for providing valuable, accurate insight into the nanopore structure in low-k dielectric thin layers and the structural changes with the integration process conditions.
    No preview · Article · Oct 2015 · RSC Advances
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    ABSTRACT: Self-assembly characteristics of poly(oxy(11-phosphorylcholineundecylthiomethyl)ethylene) (PECH-C11-PC), a lipid-mimicking brush polymer, were investigated for the first time in nanoscale thin films as well as at the air-water interface using synchrotron grazing incidence X-ray scattering, X-ray reflectivity, and infrared spectroscopy. In thin films, the PECH-C11-PC molecules were found to form a well-ordered, in-plane-oriented molecular multibilayer structure in which the bristles made partial interdigitation in the neighbored layers via the favorable interactions of the PC end groups. The brush polymer molecules were further found to favorably form molecular assemblies at the water interface. They initially formed a monolayer assembly in which the hydrophilic backbones were in the extended conformation and the zwitterionic PC ends were anchored at the water interface and the hydrophobic alkylenyl linkers were present over the water surface. This phase underwent a surface pressure-driven structural transformation path way, ultimately forming a canonical bilayer structure similar to that commonly observed among natural lipids. These remarkable self-assembly behaviors were comprehended with consideration of the hydrophilic backbone, zwitterionic PC end, hydrophobic alkylenyl linker, and their selective interactions.
    Full-text · Article · Oct 2015 · Polymer
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    ABSTRACT: Poly(N-(1-hexylheptyl)-N′-(12-oxydodecyl)perylene-3,4,9,10-tetracarboxyldiimide acrylate) (PAcPDI), a perylene diimide (PDI) containing brush polymer, is synthesized, revealing good solubility in organic solvents, excellent thermal stability up to around 340 °C, and two melting transitions over 130−220 °C. The self-assembly and n-type memory characteristics of PAcPDI in nanoscale thin films are quantitatively investigated. As-cast films of PAcPDI are completely amorphous and the PDI units nevertheless formed π–π stacks favorably. However, the PAcPDI molecules can self-assemble via thermal annealing, developing a well-ordered horizontal lamellar structure with monomorphic or polymorphic monoclinic PDI crystals. The formation of monomorphic or polymorphic monoclinic crystals is attributed to various π–π stack modes of the PDI units, and is shown to be dependent on the film thickness. The differences in the thin film morphologies are directly reflected into the electrical memory behavior. The thermally annealed films demonstrate high-performance n-type unipolar volatile memory behavior within the thickness range of 12−31 nm. The as-cast films show n-type unipolar nonvolatile or volatile memory behavior in the range of 12−53 nm. The memory mode of PAcPDI films can be tuned by changing either the morphology or the film thickness.
    Full-text · Article · Aug 2015
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    ABSTRACT: Two series of crystalline−crystalline miktoarm star polymers were prepared and their thin film morphologies were investigated in detail by synchrotron grazing incidence X-ray scattering (GIXS): poly(n-hexyl isocyanate)(5000)−poly(ε-caprolactone) 1−3 (17000) (PHIC(5k)−PCL 1−3 (17k)) and poly(n-hexyl isocyanate)(10000)−poly(ε-caprolactone) 1−3 (10000) (PHIC(10k)−PCL 1−3 (10k)). In addition, their thermal properties were examined. All miktoarm star polymers revealed a two-step thermal degradation behavior where the PHIC arm was degraded first, followed by the PCL arm underwent degradation. Interestingly, all miktoarms were found to show a highly enhanced thermal stability, regardless of their molecular weight over 3k to 17k, which might be attributed to their one-end group capped with the counterpart arm(s) via arm-joint formation. Surprisingly, all miktoarm star polymers always developed only lamellar structure in toluene-and chloroform-annealed films via phase-separation, regardless of the length of PHIC arm as well as the length and number of PCL arm. Despite having highly imbalanced volume fractions, lamellar structure was constructed in the films of miktoarm star polymers through the override of volume fraction rule based on the rigid chain properties, self-assembling characteristics, conformational asymmetry, and compressibilities of PHIC and PCL arms. Furthermore, the orientation of such lamellar structures was controlled by the selection of either toluene or chloroform in the solvent-annealing process. The PHIC arm phases in the lamellar structures favorably formed a mixture of edge-on and face-on structures with fully extended backbone and bristle conformations even under the confined lamellar geometry and arm-joint. The PCL arm phases still crystallized, forming fringed-micelle like structures in which orthorhombic crystals were laterally grown along the in-plane direction of lamellae although their crystallization was somewhat suppressed by the confined lamellar geometry and arm-joint. Overall, crystalline−crystalline PHIC−PCL 1−3 miktoarm polymers demonstrated very interesting but unusual, very complex hierarchical structures in the solvent-annealed thin films.
    Full-text · Article · Aug 2015 · Macromolecules
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    ABSTRACT: A new approach for synthesizing well-defined hollow nanochanneled-silica nanosphere particles is demonstrated and the structural details of these particles are described for the first time. Positively charged styrene copolymer nanospheres with a clean, smooth surface and a very narrow size distribution are synthesized by surfactant-free emulsion copolymerization and used as a thermally sacrificial core template for the production of coreshell nanoparticles. A surfactant/silica composite shell with a uniform thickness is successfully produced and deposited onto the polymeric core template by charge density matching between the polymer nanosphere template surface and the negatively charged silica precursors and then followed by selective thermal decomposition of the polymeric core and the surfactant cylinder domains in the shell, producing the hollow nanochanneled-silica nanosphere. Comprehensive, quantitative structural analyses collectively confirm that the obtained nanoparticles are structurally well defined with a hollow core and a shell composed of cylindrical nanochannels that provide facile accessibility to the hollow interior space. Overall, the hollow nanochanneled-silica nanoparticles have great potential for applications in various fields.
    Full-text · Article · Aug 2015 · Nanoscale
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    ABSTRACT: We synthesized chemically well-defined brush (i.e., comb-like) polymers bearing guanine, cytosine, uracil, or thymine moieties at the bristle ends. The polymers were stable up to 220 °C and were readily solution-processable, yielding high-quality films. Interestingly, the brush polymers favorably self-assembled to form molecular multibilayer structures stabilized by hydrogen bonding interactions among the nucleobase moieties at the bristle ends, which provided nucleobase-rich surfaces. The multibilayer-structured polymer films showed high water affinity. They also displayed selective protein adsorption, suppressed bacterial adherence, facilitated cell adhesion, and exhibited good biocompatibility in mice. The brush polymer DNA-mimicking comb-like polymers are suitable as biomaterials and in protein separation applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015
    No preview · Article · Feb 2015 · Journal of Polymer Science Part A Polymer Chemistry
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    ABSTRACT: Covalent incorporations into polymers of fullerene were achieved via the Cu(I)-catalyzed azide–alkyne click polymerizations of a fullerene derivative monomer functionalized with 5-(trimethylsilyl)pent-4-yn-1-yl groups and a comonomer functionalized with azidomethyl groups, producing the novel fullerene polymers P1-C60 and P2-C60. Despite their extremely high fullerene loading levels, the polymers were soluble in common organic solvents and exhibited no aggregation of fullerene units in films. Moreover, devices containing these fullerene polymers were easily fabricated with common coating processes that exhibit excellent unipolar and bipolar flash memory characteristics as well as unipolar permanent memory characteristics, with high ON/OFF current ratios, long retention times, and low power consumption. These electrical switching behaviors were favorably operated by electron injection. Overall, these devices are the first n-type bipolar and unipolar digital polymer memory devices which can be operated in flash and write-once-read-many-times modes.
    Full-text · Article · Dec 2014 · Macromolecules
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    ABSTRACT: The electrical memory mechanism of carbazole-containing polyimides (PIs) in nanoscale thin films was investigated. For this investigation, a series of poly(3,3'-dihydroxy-4,4'-biphenylene-co-3,3'-bis(N-ethylenyloxycarbazole)-4,4'-biphenylene hexafluoroisopropylidenedi-phthalimide)s (6F-HAB-HABCZn PIs) with various compositions was synthesized as a model carbazole-containing polymer system. The thermal, optical, and electrochemical properties of the PIs were determined. Furthermore, the chemical compositions, as well as the nanoscale thin film morphologies and electron densities, were analyzed, providing detailed information on the population and positional distribution of carbazole moieties in thin films of the PIs. Devices with the polymers and aluminum top and bottom electrodes were fabricated and tested electrically. The PI thin film layers in the devices exhibited electrically permanent memory behavior, which was governed by trap-limited space-charge limited conduction and ohmic conduction. The memory characteristics were found to originate from the incorporated carbazole moieties rather than from the other chemical components. Furthermore, the memory characteristics depended significantly on the population and positional distribution of carbazole moieties in the PI layer, as well as the film thickness. Considering that the PI backbone is not conjugated, the present results collectively indicate that the electrical memory behavior of the PI films is driven by the carbazole moieties acting as charge traps and a hopping process using the carbazole charge-trap sites as stepping-stones.
    No preview · Article · Nov 2014 · ACS Applied Materials & Interfaces
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    ABSTRACT: A series of miktoarm star polymers, [poly(n-hexyl isocyanate)(12K)]–[poly(ε-caprolactone)1–3(5K)] (PHIC–PCL1–3) (composed of a rigid self-assembling PHIC arm and one to three flexible crystallizable PCL arms), were investigated to examine the polymers’ thermal properties and nanoscale thin film morphologies. The miktoarm polymers were stable up to 180 °C. The PHIC and PCL arm components underwent phase separation during the solution casting, drying, and post toluene-annealing processes, forming interesting but very complex thin film morphologies. The resulting thin film morphologies were examined in detail for the first time using synchrotron grazing incidence X-ray scattering (GIXS) measurements and quantitative data analysis. All of the miktoarm star polymer films formed vertically well-oriented lamellar structures, regardless of the number and length of PCL arms. These structures were quite different from the cylindrical structures commonly observed in conventional flexible diblock copolymer films having comparable volume fractions. The individual PHIC and PCL lamellar domains self-assembled to form their own respective morphological structures. The PHIC lamellae consisted of a mixture of horizontal and vertical multibilayer structure domains, as observed in the PHIC homopolymer film. The PCL lamellae formed fringed micelle-like crystals and/or highly imperfect folded crystals that differed significantly from the structures found in a PCL homopolymer film composed of typical folded lamellar crystals. These PCL crystals were formed with a mixture of vertical and horizontal orthorhombic lattices. Overall, the GIXS analysis revealed that the parameters that characterized the hierarchical structures in the thin films depended significantly on the number and length of the PCL arm and its crystallization characteristics as well as the chain rigidity and multibilayer structure formation characteristics of the PHIC arm.
    Full-text · Article · Nov 2014 · Macromolecules
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    ABSTRACT: Self-assembly characteristics of a well-defined brush polymer, poly(oxy(n-dodecyl-thiomethyl)ethylene) were in detail investigated at the air-water interface with surface–area isotherm, X-ray reflectivity, and infrared spectroscopy analyses. The brush polymer self-assembled at the air-water interface as a fully-extended chain via favorable lateral packing of the bristles in a fully extended conformation, forming highly ordered, oriented Langmuir monolayer. This well-ordered monolayer was produced via a five-regime structure formation with varying surface pressure. A Langmuir monolayer film with ≤1.92 nm thick was formed in the low surface pressure regime ≤18 mN/m and then converted to a highly dense, ordered monolayer with 3.65 nm thick in the high surface pressure regime ≥35 mN/m through monolayer-to-bilayer transition and bilayer-to-monolayer inversion. These Langmuir film formations and their ordering and orientation might be driven by the well-defined chemical architecture and the lateral orderings of the polymer backbones and the bristles in fully extended conformations.
    Full-text · Article · Nov 2014 · Science of Advanced Materials
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    ABSTRACT: The nanoscale thin film morphologies of a series of interesting miktoarm star polymers composed of a highly rigid and crystallizable poly(n-hexyl isocyanate) (PHIC) arm and one to three flexible and crystallizable poly(ε-caprolactone) (PCL) arms were investigated using synchrotron grazing incidence X-ray scattering methods. Nanoscale thin films of a PHIC and a PCL homopolymer were also characterized for comparison. The PCL homopolymer and star polymers formed horizontally oriented lamellar structures in toluene-annealed films. The horizontal lamellar structures formed in the miktoarm star polymer films were quite different from those observed in common flexible block copolymer specimens. Interestingly, the structural parameters associated with the star polymer films were significantly influenced by the exceptional rigidity of the PHIC arm chain and by the number and length of the PCL arms. This study demonstrated that a miktoarm star polymer system consisting of rigid and crystallizable arms could form thin films with a morphology that is suitable for specific target applications.
    No preview · Article · Nov 2014 · Science of Advanced Materials
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    ABSTRACT: In-situ synchrotron small-angle X-ray scattering measurements and quantitative data analysis were used to investigate isothermal self-assembly in a series of high-performance poly(1,4-cyclohexyldimethylene-co-ethylene terephthalate)s (PCETs) enriched with 1,4-cyclohexanedimethanol (CHDM). Interestingly, the bulky CHDM units, which assumed a kinked chair conformation, formed lamellar crystals. The self-assembly process was governed by a nucleation and growth mechanism that depended on the degree of supercooling. Isothermal self-assembly occurred through a four-regime process. The structural evolution was driven mainly by a primary crystallization process, which contributed to crystal layer thickening, and in part by a secondary crystallization process during the later stages, which did not contribute to crystal layer thickness, to produce a lamellar structure. In addition to the primary crystals, highly imperfect small secondary crystals distinct from the lamellar crystals were observed to form. The secondary crystals formed only in the amorphous phases, including in the amorphous layer of the lamellar structure. Surprisingly, the minor ethylene glycol (EG) units tended to be excluded from the primary lamellar crystals.
    No preview · Article · Nov 2014 · Science of Advanced Materials
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    ABSTRACT: The self-assembly characteristics in nanoscale thin films and digital memory behaviors of poly(5-phenyl-1,3,4oxadiazol-2-yl-[1,1 -biphenyl]carboxyloxy-n-nonyl acrylate), a well-defined brush polymer bearing oxadiazole moieties, were investigated. The synchrotron grazing incidence X-ray scattering analysis found that the brush polymer molecules in thin films always formed a multibilayer structure consisting of fully extended backbone and bristle conformations. In the structure, the bristles were interdigitated in part; In particular, the oxadiazole containing mesogens were fully interdigitated via the – interaction of the biphenyl linkers. The multibilayer structured film undergoes three phase transitions (glass, melting, and liquid crystal-to-isotropic transitions) below the degradation temperature of 350 °C. The film's overall crystallinity, as well as the orientation of the multibilayer structure was found to depend on the film formation process conditions. While the as-cast films had a relatively low crystallinity and formed a vertical multibilayer structure with a broad orientation distribution, the thermally annealed films had a high crystallinity and formed an almost perfect horizontally oriented multibilayer structure. These different morphologies led different digital memory modes in devices; the as-cast films revealed volatile memory behavior, whereas the thermally annealed films showed permanent memory characteristics. These memory modes originated from the oxadiazole moieties in the two different film morphologies. The memory modes were demonstrated for the polymer films in the thickness range 5–50 nm.
    No preview · Article · Nov 2014 · Science of Advanced Materials
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    ABSTRACT: The three-dimensional structures of the wild-type Pseudomonas putida ketosteroid isomerase (KSI-WT) and its single mutant KSI-Y57S were studied in solution for the first time using synchrotron X-ray scattering methods. The protein solutions were further analyzed using pulse field gradient nuclear magnetic resonance spectroscopy and ultracentrifugation analysis. The X-ray scattering profiles were extracted from the atomic crystal structures and analyzed. The KSI-WT solution structure differed in size and shape from the structure observed in the crystal form. In solution, the KSI-WT structure included an open cavity around the active site. This feature might be essential for the catalytic performance. The structure of KSI-WT changed upon introduction of a single mutation (the Tyr57 of KSI-WT was replaced with a serine residue). This single mutation was found to reduce the size and shape of the KSI-WT structure. However, the open cavity around the active site was abnormally enlarged in the presence of the single mutation. The changes in the size and shape might directly correlate with the large decrease in the catalytic performance of KSI-Y57S.
    No preview · Article · Nov 2014 · Science of Advanced Materials
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    ABSTRACT: The structural features of nanoscale thin films composed of a miktoarm (polystyrene)2-(polyisoprene)2 (PS2-PI2) star polymer were studied for the first time using synchrotron grazing incidence X-ray scattering (GIXS) and X-ray reflectivity (XR) analyses. The acetone-annealed thin films formed a horizontally oriented lamellar structure via phase separation. The lamellar structure displayed interesting and unique features not present in the corresponding diblock copolymer thin films. The thick interfacial layers formed by the PS and PI arm components were three times the thicknesses of the corresponding layers in the diblock copolymer films. The interfacial layers further displayed a relatively high degree of thermal expansion. The overall lamellar structure was thermally stable up to temperatures approaching the degradation temperature. These unique structural features could be understood in terms of the rigidity and bulkiness of the confined crowded environment surrounding the arm-jointer.
    No preview · Article · Nov 2014 · Science of Advanced Materials
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    ABSTRACT: Linear-brush diblock copolymers bearing carbazole moieties in the brush block were synthesized. Various phase-separated nanostructures were found to develop in nanoscale thin films of the copolymers, depending on the fabrication conditions including selective solvent-annealing. This variety of morphologies and orientations means that these block copolymers exhibit digital memory versatility in their devices. Overall, the relationship between the morphology and digital memory performance of these copolymers has several important features. In particular, the carbazole moieties in the vertical cylinder phase with a radius of 8 nm or less can trap charges and also form local hopping paths for charge transport, which opens the mass production of advanced digital memory devices with ultrahigh memory density. Charges can be transported through the layer when the dielectric linear block phase has a thickness of 10.6 nm; however, charge transport is not possible for a dielectric phase with a thickness of 15.9 nm. All the observed memory behaviors are governed by the trap-limited space-charge-limited conduction mechanism and local hopping path (i.e., filament) formation.
    No preview · Article · Jul 2014 · Macromolecules

Publication Stats

10k Citations
1,271.70 Total Impact Points

Institutions

  • 1994-2015
    • Pohang University of Science and Technology
      • • Department of Chemistry
      • • Division of Molecular and Life Sciences
      Geijitsu, Gyeongsangbuk-do, South Korea
  • 2008-2014
    • POSTECH POHANG UNIVERSITY OF SCIENCE AND TECHNOLOGY
      경산시, Gyeongsangbuk-do, South Korea
  • 2010-2012
    • Pohang Accelerator Laboratory
      Urusan, Ulsan, South Korea
  • 2011
    • Kyungpook National University
      • Department of Energy Chemical Engineering
      Daikyū, Daegu, South Korea