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Isolated Mesoporous Microstructures Prepared by Stress Localization-Induced Crack Manipulation
Wooh, Sanghyuk,Lee, Soojin,Lee, Yunchan,Ryu, Ji Ho,Lee, Won Bo,Yoon, Hyunsik,Char, Kookheon American Chemical Society 2016 ACS NANO Vol.10 No.10
<P>Cracks observed in brittle materials are mostly regarded as defects or failures. However, they can be a valuable tool when implemented in a controlled way. Here, we introduce a strategy to control the crack propagation of mesoporous micropatterns (prisms and pyramids), which leads to the isolation of well-defined microstructures. Mesoporous micropatterns were fabricated by the soft imprinting technique with wet TiO2 nanoparticle (NP) pastes, followed by sintering to remove organic components. Since the volume of the paste significantly shrinks during the sintering step, stress is localized at the edge of micropatterns, in good agreement with finite element method simulations, creating well-defined cracks and their propagation. It was demonstrated that the degree of stress localization is determined by the thickness of residual layers, NP size, and heating rate. After controlled crack propagation and delamination of microparticles from the substrates, mesoporous microwires and microparticles were successfully produced and functionalized from the isolated mesoporous prisms and pyramids. The method proposed in this study for controlled crack manipulation and delamination opens a door for straightforward and economical fabrication of well-defined mesoporous microparticles.</P>
Wooh, Sanghyuk,Kim, Tea-Yon,Song, Donghoon,Lee, Yong-Gun,Lee, Tae Kyung,Bergmann, Victor W.,Weber, Stefan A. L.,Bisquert, Juan,Kang, Yong Soo,Char, Kookheon American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.46
<P>Dye aggregation and electron recombination in TiO<SUB>2</SUB> photoanodes are the two major phenomena lowering the energy conversion efficiency of dye-sensitized solar cells (DSCs). Herein, we introduce a novel surface modification strategy of TiO<SUB>2</SUB> photoanodes by the fluorinated self-assembled monolayer (F-SAM) formation with 1<I>H</I>,1<I>H</I>,2<I>H</I>,2<I>H</I>-perfluorooctyltriethoxysilane (PFTS), blocking the vacant sites of the TiO<SUB>2</SUB> surface after dye adsorption. The F-SAM helps to efficiently lower the surface tension, resulting in efficient repelling ions, e.g., I<SUB>3</SUB><SUP>–</SUP>, in the electrolyte to decrease the electron recombination rate, and the role of F-SAM is characterized in detail by impedance spectroscopy using a diffusion–recombination model. In addition, the dye aggregates on the TiO<SUB>2</SUB> surface are relaxed by the F-SAM with large conformational perturbation (i.e., helix structure) seemingly because of steric hindrance developed during the SAM formation. Such multifunctional effects suppress the electron recombination as well as the intermolecular interactions of dye aggregates without the loss of adsorbed dyes, enhancing both the photocurrent density (11.9 → 13.5 mA cm<SUP>–2</SUP>) and open-circuit voltage (0.67 → 0.72 V). Moreover, the combined surface modification with the F-SAM and the classical coadsorbent further improves the photovoltaic performance in DSCs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-46/acsami.5b07211/production/images/medium/am-2015-072114_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b07211'>ACS Electronic Supporting Info</A></P>
Evaporation Driven Supraparticle Syntheses on Liquid Repellent Surfaces
Sanghyuk Wooh(우상혁) 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.1
Supraparticles have been synthesized by solution process which is difficult to control shapes, sizes and materials. Even though supraparticles have great functionalities and potentials, this limited shape, size and material have been serious huddles of supraparticle researches. Recently we have developed a strategy to synthesize spherical supraparticles on superamphiphobic surfaces with various sizes and components. Due to the strong liquid repellency of superamphiphobic surface, spherical supraparticles could be formed by drying of nanoparticle dispersion with constant contact angle. During the process, no energy consumption and wasting chemicals were applied. By applying magnetic colloids and tuning dispersity of the drop, shapes and porosities of the supraparticles can be controlled. In addition, drying dispersion drop by using Ouzo effect is introduced that allows supraparticle synthesis on normal flat hydrophobic surface by self-lubricating colloidal dispersion evaporation.
Breivogel, Aaron,Wooh, Sanghyuk,Dietrich, Jan,Kim, Tea Yon,Kang, Yong Soo,Char, Kookheon,Heinze, Katja Wiley-VCH 2014 European journal of inorganic chemistry Vol. No.
<P><B>Abstract</B></P><P>Stable push‐pull substituted heteroleptic bis(tridentate) ruthenium(II) polypyridine complexes with COOH or 2,2′‐bipyridine anchor groups have been prepared and characterized by <SUP>1</SUP>H, <SUP>13</SUP>C and <SUP>15</SUP>N NMR 1D and 2D spectroscopy, infrared spectroscopy, elemental analysis, high‐resolution ESI mass spectrometry, electrochemistry, UV/Vis absorption spectroscopy, luminescence spectroscopy, and density functional calculations. The complexes feature a pronounced electronic directionality and high absorption wavelengths up to <I>λ</I><SUB>max</SUB> = 544 nm extending to 720 nm as a result of favorable push‐pull substitutions. A remarkable photostability in the presence of water and coordinating ions (I<SUP>–</SUP>) was discovered for the tridentate complexes when compared with the standard ruthenium sensitizer N719 and tris(bidentate) [Ru(bpy)<SUB>3</SUB>](PF<SUB>6</SUB>)<SUB>2</SUB>, which are highly photolabile under the same conditions (photodissociation/photosubstitution). The complexes were studied as photosensitizers in dye‐sensitized solar cells. The incident photon‐to‐current conversion efficiency follows the absorption spectra into the NIR region. However, the high positive charge of the complexes (2+) favors the recombination of the injected electrons with I<SUB>3</SUB><SUP>–</SUP> of the redox electrolyte, which is evidenced by high dark currents and short electron recombination lifetimes, leading to low cell performances compared with cells with the negatively charged N719 dye.</P>
Mechanoresponsive Tuning of Anisotropic Wetting on Hierarchically Structured Patterns
Kwon, Dokyeong,Wooh, Sanghyuk,Yoon, Hyunsik,Char, Kookheon American Chemical Society 2018 Langmuir Vol.34 No.16
<P>Here, we propose a simple mechanoresponsive system on patterned soft surfaces to manipulate both anisotropy and orientation of liquid wetting. On the poly(dimethylsiloxane) embedding line patterned structures, additional topographies, such as wrinkles and cracks, can be provided by applying compressive and tensile stress, respectively. This tunable hierarchy of structures with the different scales and directions of lines, wrinkles, and cracks allow the mechanoresponsive control of anisotropic wetting in a single platform. In addition, the wetting behavior on those surfaces is precisely investigated based on the concept of critical contact angle to overcome the ridges in a step flow.</P> [FIG OMISSION]</BR>
Orientation Control of Block Copolymer Thin Films Placed on Ordered Nanoparticle Monolayers
Kim, Taehee,Wooh, Sanghyuk,Son, Jeong Gon,Char, Kookheon American Chemical Society 2013 Macromolecules Vol.46 No.20
<P>We investigate orientation and lateral ordering of poly(styrene-<I>block</I>-methyl methacrylate) (PS-<I>b</I>-PMMA) diblock copolymer (diBCP) thin films placed on ordered nanoparticle (NP) monolayers. The densely packed NP monolayers were prepared on silicon substrates with the Langmuir–Blodgett (LB) deposition technique. The perpendicular domain orientation of BCP thin films is obtained on the ordered NP monolayers due to the nanoscale regular roughness which exerts the elastic deformation on the BCP nanodomains and suppresses the substrate-induced parallel orientation. The effect of BCP film thickness as well as the NP size on the orientation of BCP nanodomains was systematically investigated. We also demonstrate the defect-tolerant ordering of the perpendicular orientation of BCP thin films on the NP-vacant sites.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2013/mamobx.2013.46.issue-20/ma401601f/production/images/medium/ma-2013-01601f_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma401601f'>ACS Electronic Supporting Info</A></P>
Fluorocarbon lubricant impregnated nanoporous oxide for omnicorrosion-resistant stainless steel
Lee, Junghoon,Wooh, Sanghyuk,Choi, Chang-Hwan Elsevier 2020 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.558 No.-
<P><B>Abstract</B></P> <P>Corrosion protection coatings have been required for long-term uses of metallic materials applied in various environments incorporating liquid and/or vapor phase corrosion reactants. In this study, we introduce a fluorocarbon lubricant impregnated nanoporous oxide (FLINO) coating on stainless steel for realizing effective resistances against corrosive media in both liquid and vapor phases. The FLINO layer on stainless steel significantly enhances corrosion resistances with superior durability and self-healing capability. The combination of nanoporous structure and fluorocarbon lubricant layer provides an outstanding atmospheric corrosion resistance, which has been a serious issue to be overcome on corrosion-resistant coatings. Therefore, the FLINO coating exhibiting stable and remarkable corrosion resistance against both liquid and vaporized corrosive media, called omnicorrosion-resistance, gives a new route for the versatile protection of metallic materials in various environments encompassing both underwater and atmospheric applications.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>