Byoung-Ki Cho

Dankook University, Eidō, North Chungcheong, South Korea

Are you Byoung-Ki Cho?

Claim your profile

Publications (62)229.07 Total impact

  • Soyoung Park, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we report thermally induced intercolumnar transitions of C3-symmetric liquid crystals (LCs) bearing a triazole-based propeller-like aromatic mesogen. Since the constituting aromatic rings are conjugated through rotatable single bonds, the mesogenic shape is tuneable depending on the degree of the conformational motion. Molecule 1 with ninefold octyl peripheries shows a hexagonal columnar liquid crystalline phase transition from ordered mesogenic stacking to disordered mesogenic stacking upon heating. On the other hand, molecule 2 with sixfold octyl peripheries displays a helical hexagonal columnar phase with P6/mmm space group at ambient temperature as well as the ordered and disordered hexagonal columnar phases at higher temperatures. The intracolumnar helical order can be understood by an interdigitated stacking of the propeller-like mesogens along the columnar axis and the optimized space-filling. Notably, all the intercolumnar phase transformations in this study are revealed as second-order transitions. The thermodynamic nature agrees well with the fact that the conformational motions of the C3-symmetric aromatic mesogen change abruptly with each columnar transition.
    Soft Matter 10/2014; · 4.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We herein report the molecular assemblies of the click-derived amphiphiles bearing a triazole-based aromatic block and their heavy metal ion conjugates in a 100% water environment. The length and conformational rigidity of the aromatic block affected the aqueous assemblies of amphiphiles. In particular, the amphiphile 2N based on the rigid naphthalene unit formed a vesicular nanostructure above the CMC. Interestingly, the assembly power of the amphiphiles could be enhanced by Hg2+-capturing of the triazolyl units. Amphiphiles 2 and 2N formed micellar and vesicular aggregates with a fluorescence turn-off response, even below their CMCs, respectively, upon the addition of Hg2+. These aqueous morphologies were determined by the stoichiometry of the amphiphile-Hg2+ complexes which affects the interfacial curvature between hydrophilic and hydrophobic parts in the nanoassemblies. Therefore, the metal-amphiphile conjugates in this study would provide a useful and simple strategy for the detection of toxic heavy metals in aqueous medium. In addition, the resultant vesicular hybrids induced by the response to specific metal ion would open up the development of novel functional nanovehicles in response to specific chemical species.
    Chemical Communications 09/2014; · 6.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we report a C3-symmetric liquid crystal (LC) with sixfold alkyl peripheries exhibiting an unusual smectic E-like organization in the LC state. Based on conformational considerations, the smectic assembly is attributed to the formation of an endo-type Y conformer of asymmetric triazolyl and benzylic groups that cannot be accessed in other C3-symmetric molecules exclusively showing columnar assemblies. The Y conformers form a two-dimensional oblique lattice in the aromatic layers of the ordered smectic phase. In addition, the Y-shaped molecule in the smectic phases can change into a circular shape by the 1 : 1 hydrogen-bonding interaction with a gallic acid derivative, which leads to a hexagonal columnar LC phase. The triazole-based LC design concept proves the smectic LC assembly in the C3-symmetric system, and provides the supramolecular manipulation of LC morphologies.
    Soft Matter 06/2014; · 4.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A bent-shape triazolyl derivative was synthesized via click chemistry, and its photophysical property was investigated in various solvents. In contrast to the invisible ultraviolet emission of other solutions, the chloroform solution exhibited a blue light emission at 460 nm. Furthermore, the blue fluorescence intensified as the UV exposure time at 365 nm increased. On the basis of -NMR, pH paper, and acid-addition studies, we confirmed that chloroform was decomposed into HCl with the aid of the triazolyl derivative. The density functional theory calculations suggested that the eye-detectable blue fluorescence was attributed to an intramolecular charge transfer process of the protonated triazolyl derivative in the chloroform solution.
    Bulletin- Korean Chemical Society 01/2014; 35(1). · 0.84 Impact Factor
  • Macromolecular Research 12/2013; · 1.64 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The amphiphilic block codendrimer self-assembled into supramolecular vesicles with a bilayer membrane in both hydrophilic and hydrophobic solvents. Surface-modified quantum dots (QDs) were successfully entrapped within the wall of vesicles through a simple self-assembly process without any structural disruption.
    Chemical Communications 05/2013; · 6.38 Impact Factor
  • Sujin Choi, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: We synthesized three dendron–coil-dendron block copolymers consisting of ionophilic poly(ethylene oxide) (PEO) coils and mesogenic dendrons with four octadecyl peripheries via stepwise click reactions. The obtained polymers were doped with lithium triflate, whose concentration per ethylene oxide unit was 0.05. As characterized by optical polarized microscopy (POM) and X-ray scattering techniques, polymer 1 with the shortest PEO coil (Mn = 2000 g mol−1) did not show the liquid crystalline (LC) phase, while its ionic sample (1-Li+) exhibited a hexagonal columnar LC phase. On the other hand, 2 and 3 (with PEOs of Mn = 4000 and 8000 g mol−1, respectively) displayed identical LC morphologies to 2-Li+ and 3-Li+, respectively, although the phase transition temperatures increased upon salt doping. For 2 and 2-Li+, gyroid and lamellar LC phases were observed with increasing temperature, while 3 and 3-Li+ showed only a lamellar LC phase. The observed ion-transporting behavior was strongly dependent upon the connectivity of ion-conducting domain structures. The investigation of the morphology–conductivity correlation using a normalized conductivity (σ* = σ/f, where σ and f are the original conductivity and the PEO volume fraction) indicated that the 3-D gyroid LC phase showed the highest value, while the lowest conductivity was found in the 1-D columnar structure at identical temperatures. Additionally, the gyroid to lamellar phase transition temperature of 2-Li+ could be determined by the σ*, which was consistent with the X-ray data. Consequently, the results can be explained by the fact that the ionic pathway becomes complicated when going from higher to lower dimensional structures in polygrain samples.
    Soft Matter 03/2013; 9(16):4241-4248. · 4.15 Impact Factor
  • Source
    Jie Song, Byoung-Ki Cho
    Bulletin- Korean Chemical Society 01/2013; 34(1). · 0.84 Impact Factor
  • Jie Song, Eunji Lee, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: A well-defined (PEO-PS)2-PLA miktoarm terpolymer (1) was synthesized by stepwise click reactions of individually prepared poly(ethylene oxide) (PEO), polystyrene (PS, polymerized by atom transfer radical polymerization), and polylactide (PLA, polymerized by ring-opening polymerization) blocks. As characterized by differential scanning calorimetry and small-angle X-ray scattering techniques, the terpolymer self-assembled into a hexagonal columnar structure consisting of PLA/PEO cylindrical cores surrounded by PS chains. In contrast, the ion-doped sample (1-Li+) with lithium concentration per ethylene oxide = 0.2 exhibited a three-phase lamellar structure, which was attributed to the microphase separation between PEO and PLA blocks and to the conformational stabilization of the longest PLA chain. The two-phase columnar morphology before the ion doping was used to prepare a nanoporous material. PLA chains in the cylindrical core region were hydrolyzed by sodium hydroxide, producing nanopores with a pore diameter of about 14 nm. The resulted nanoporous material sank to the bottom in water, because of water-compatible PEO chains on the walls. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
    Journal of Polymer Science Part A Polymer Chemistry 01/2013; 51(2):446-456. · 3.54 Impact Factor
  • Jie Song, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study, we investigated the functionality- and size-dependent differentiation capability of bulk nanoporous polystyrene (PS) materials in aqueous environments. A three-arm star block copolymer (consisting of dibranched PS and linear polylactide (PLA) blocks) was employed to prepare PS nanochannels with the average pore diameter of 14.2 nm. Due to the ester group at the junction of the PS and PLA blocks, a negatively charged carboxylate group could be placed as the wall functional group automatically after the PLA etching. Based on specific electrostatic interactions, the bulk PS channels with the carboxylated wall could selectively capture a water-soluble cationic dye (rhodamine 6G) in the aqueous and methanolic solutions. Furthermore, the well-defined porous PS displayed excellent size-dependent selectivity, which was proved by a fluorescence quenching experiment using differently sized gold nanoparticles (AuNPs). Rhodamine 6G dyes on the pore wall were effectively quenched by 2 nm AuNPs. In contrast, the 16 nm AuNPs (larger than the pore diameter) did not affect the brightness of the rhodamine 6G-loaded PS.
    ACS Macro Letters 11/2012; 1(12):1375–1378. · 5.24 Impact Factor
  • Jie Song, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: We reported a synthetic protocol of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers via dehydrobromination and click coupling reactions. The PS block (acetylene-PS) was prepared by anionic polymerization and end-functionalized with an acetylene group. The other PMMA block was synthesized by an atom transfer radical polymerization (ATRP) of MMA using an azido-initiator. It was found, unexpectedly, that the click reaction of acetylene-PS and the bromide-ended PMMA using Cu(I)Br yielded a byproduct with double the molecular weight of the product (PS-b-PMMA). This was attributed to the coupling of the bromide ends of block copolymers. This problem could be avoided by a dehydrobromination of the PMMA block into the olefin end (azido-PMMA-ene) using tetra-n-butylammonium fluoride (TBAF) at room temperature. Due to the mild dehydrobromination condition and the weak basicity of TBAF, no hydrolysis of PMMA esters occurred. After the click coupling of acetylene-PS and azido-PMMA-ene, the excess PS was removed by further click reaction using insoluble PS resins surface-functionalized with azide groups.
    Macromolecular Research 10/2012; 20(10). · 1.64 Impact Factor
  • Jie Song, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: A micellar cubic LC phase consisting of a hydrophilic matrix exhibited enhanced ionic transport and mechanical properties without macroscopic orientation, which are attributed to the non-tortuous ionic transport and highly symmetric cubic lattice, respectively.
    Chemical Communications 05/2012; 48(54):6821-3. · 6.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In contrast to the known perpendicular ordering of conventional PS-b-PLA thin films, branched (PS)(2)-b-PLA thin films showed two different parallel orientations whose locations are strongly dependent upon film thickness.
    Chemical Communications 04/2012; 48(28):3418-20. · 6.38 Impact Factor
  • Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper reviews our recent research with regard to bulk self-assemblers based on well-defined branched building blocks. Branched molecules/polymers have been known to show different physical properties from conventional linear-shaped polymers. As well as thermal and solution properties, structural modification into branched building blocks also has a significant influence on self-assembling behavior in the bulk states, including solid and liquid crystalline (LC) phases. As a branched component, dendrons/dendrimers with well-defined structures can be ideal candidates for the construction of advanced self-assemblers. Recently, we worked on new assembling systems such as dendron-coils, block codendrimers and discotic LC molecules. In the design, we used aliphatic polyether dendrons in most cases and poly(benzyl ether) dendrons in part. Their bulk assembling and thermal properties were found to be distinct from conventional linear block copolymers and they were dependent upon their chain architectures. To self-assemble into ordered nanostructures, the hybrid assembers were designed to have incompatible blocks, for example, hydrophilic and hydrophobic parts. Furthermore, in some cases an ionic complexation was carried out to maximize the immiscibility between the two different blocks. This review describes the molecular manipulations to engineer the nanoassemblies in bulk and also the ionic transportation properties depending on the assembling morphology.
    Polymer Journal 03/2012; 44(6):475-489. · 1.50 Impact Factor
  • Jie Song, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: A series of self-assembling dendron-coil block copolymers with well-defined molecular structures were prepared via a divergent method. The hydrophilic and hydrophobic blocks are composed of PEO-like dendrons and poly(ethylene-alt-propylene) (PEP) linear coils, respectively. A dendron-coil, 2G-2400 (2G and 2400 indicate the dendron generation and PEP molecular weight, respectively), showed a melting transition of the peripheral PEO chains. In contrast, the dendron-coils containing the 3rd generation dendron did not show any melting transition because of the plasticization effect of the tri(ethylene oxide) branches. Due to the strong immiscibility between the PEO-like dendron and PEP blocks, diverse microphase-separated morphologies were observed. 2G-2400 displayed a lamellar mesophase with an interdigitated dendron packing structure. For the larger 3rd generation dendron series, A15 micellar cubic (Pm3n space group), hexagonal columnar, and lamellar morphologies were revealed depending on the PEP coil length and/or temperature. For the columnar mesophases, the molecular wedge angles (α) were calculated to be 46.8° and 34.6° for 3G-2400 and 3G-3400, respectively. This suggests that the longer PEP coil of 3G-3400 is conformationally more deformed in the columnar structure. As a consequence, the columnar phase was transformed into an interdigitated lamellar structure as the temperature increased. This order to order transition is a reversal of the well-known phase sequence of linear block copolymers. This unusual morphological behavior is mainly attributed to the unique molecular arrangement associated with non-conventional dendron-coil chain architecture.
    Soft Matter 02/2012; 8(12):3419-3428. · 4.15 Impact Factor
  • Angewandte Chemie International Edition 06/2011; 50(25):5737-40. · 11.34 Impact Factor
  • Jin‐Woo Choi, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: We studied the conducting and mesomorphic behavior of a dendritic-linear copolymer on adding hydrophilic additives and lithium salts. For the preparation of the pristine block copolymer (A), a click reaction of a hydrophobic Y-shaped dendron block and a hydrophilic linear poly(ethylene oxide) coil with Mn = 750 g mol−1 was performed. For ionic block copolymer samples (1–3), a hydrophilic compound (B) bearing two tri(ethylene oxide) chains was used as the additive. In all ionic samples, the lithium concentration per ethylene oxide was chosen to be 0.05. As characterized by polarized optical microscopy and small angle X-ray scattering techniques, copolymer A showed a hexagonal columnar mesophase. On addition of lithium-doped additives, ionic samples 1 and 2 with the additive weight fractions (fw) of 10 and 20%, columnar and bicontinuous structures coexisted in the liquid crystalline phase. On the other hand, ionic sample 3 with fw = 30% displayed only a bicontinuous cubic mesophase. Based on the impedance results, with increasing the amount of additives, the conductivity value increased from 3.80 × 10−6 to 2.34 × 10−5 S cm−1 at 35 °C. The conductivity growth could be explained by the interplay of the plasticization effect of the mobile additive and the morphological transformation from 1D to 3D of the ion-conducting cylindrical cores. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
    Journal of Polymer Science Part A Polymer Chemistry 04/2011; 49(11):2468 - 2473. · 3.54 Impact Factor
  • Jin-Woo Choi, Byoung-Ki Cho
    [Show abstract] [Hide abstract]
    ABSTRACT: We prepared two Janus dendrimers1 and 2 bearing a hydrophobic Percec-type minidendron (i.e., 3,4,5-tridodecyloxybenzylgroup) and hydrophilic aliphatic ether dendrons with different degrees of branching via stepwise click reactions. The obtained Janus dendrimers have the same hydrophilic volume fraction (f = 0.34), but a different number of hydrophilic chains, i.e., tetrabranched and dibranched oligo(ethylene oxide) coils for 1 and 2, respectively. Upon doping with lithium salt, liquid crystalline (LC) ionic samples 1-Li+ and 2-Li+ were obtained. As characterized by polarized optical microscopy (POM) and X-ray scattering techniques, 1-Li+ showed an optically isotropic cubic LC phase, while 2-Li+ displayed a birefringent hexagonal columnar LC structure with a bilayered cross-section. Interestingly, the conductivity values of the cubic phase were considerably higher than those of the columnar phase, with which the cubic phase could be assigned as a bicontinuous cubic structure rather than a micellar one. On the basis of the experimental observations, the morphological contrast between two ionic Janus dendrimers is strongly attributed to the degree of chain branching, which is one of the major parameters governing the morphological features in the Janus dendrimerassemblies.
    Soft Matter 04/2011; 7(8):4045-4049. · 4.15 Impact Factor
  • Source
    Bulletin- Korean Chemical Society 01/2011; 32(3). · 0.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: By employing a triblock copolymer, poly(styrene-b-ethylene oxide-b-caprolactone) copolymer, as a structure-directing agent, a series of silica-type hybrid materials were prepared via a sol-gel method of (3-glycidyloxypropyl) trimethoxy silane and aluminum sec-butoxide. Small angle X-ray scattering and transmission electron microscopy analyses demonstrated that ordered nanostructures, from lamellar to 2-dimensional hexagonal columnar with a disordered intermediate morphology, were exhibited as a function of the amount of loaded silica nanoparticles. Among the observed morphologies, the silica particles in the lamellar sample were localized at the PS/PEO interface, which could be elucidated by the dominant translational entropy of small silica particles.
    Polymer 09/2010; 51(19):4419-4423. · 3.77 Impact Factor

Publication Stats

263 Citations
229.07 Total Impact Points

Institutions

  • 2006–2014
    • Dankook University
      • Department of Chemistry
      Eidō, North Chungcheong, South Korea
  • 2013
    • Chungnam National University
      • Graduate School of Analytical Science and Technology
      Sŏngnam, Gyeonggi Province, South Korea
  • 1998–2007
    • Yonsei University
      • • Center for Supramolecular Nano-Assembly
      • • Department of Chemistry
      Seoul, Seoul, South Korea
  • 2004–2005
    • Cornell University
      • Department of Materials Science and Engineering
      Ithaca, NY, United States