Publications by authors named "Young Moo Lee"

71 Publications

Poly(fluorenyl aryl piperidinium) membranes and ionomers for anion exchange membrane fuel cells.

Nat Commun 2021 Apr 22;12(1):2367. Epub 2021 Apr 22.

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul, Republic of Korea.

Low-cost anion exchange membrane fuel cells have been investigated as a promising alternative to proton exchange membrane fuel cells for the last decade. The major barriers to the viability of anion exchange membrane fuel cells are their unsatisfactory key components-anion exchange ionomers and membranes. Here, we present a series of durable poly(fluorenyl aryl piperidinium) ionomers and membranes where the membranes possess high OH conductivity of 208 mS cm at 80 °C, low H permeability, excellent mechanical properties (84.5 MPa TS), and 2000 h ex-situ durability in 1 M NaOH at 80 °C, while the ionomers have high water vapor permeability and low phenyl adsorption. Based on our rational design of poly(fluorenyl aryl piperidinium) membranes and ionomers, we demonstrate alkaline fuel cell performances of 2.34 W cm in H-O and 1.25 W cm in H-air (CO-free) at 80 °C. The present cells can be operated stably under a 0.2 A cm current density for ~200 h.
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http://dx.doi.org/10.1038/s41467-021-22612-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8062622PMC
April 2021

Blood Oxygenation Using Fluoropolymer-Based Artificial Lung Membranes.

ACS Biomater Sci Eng 2020 11 26;6(11):6424-6434. Epub 2020 Oct 26.

Innovation Center for Chemical Engineering, Incheon National University, Incheon 22012, Republic of Korea.

Artificial lung (AL) membranes are used for blood oxygenation for patients undergoing open-heart surgery or acute lung failures. Current AL technology employs polypropylene and polymethylpentene membranes. Although effective, these membranes suffer from low biocompatibility, leading to undesired blood coagulation and hemolysis over a long term. In this work, we propose a new generation of AL membranes based on amphiphobic fluoropolymers. We employed poly(vinylidene--hexafluoropropylene), or PVDF--HFP, to fabricate macrovoid-free membranes with an optimal pore size range of 30-50 nm. The phase inversion behavior of PVDF--HFP was investigated in detail for structural optimization. To improve the wetting stability of the membranes, the fabricated membranes were coated using Hyflon AD60X, a type of fluoropolymer with an extremely low surface energy. Hyflon-coated materials displayed very low protein adsorption and a high contact angle for both water and blood. In the hydrophobic spectrum, the data showed an inverse relationship between the surface free energy and protein adsorption, suggesting an appropriate direction with respect to biocompatibility for AL research. The blood oxygenation performance was assessed using animal sheep blood, and the fabricated fluoropolymer membranes showed competitive performance to that of commercial polyolefin membranes without any detectable hemolysis. The data also confirmed that the bottleneck in the blood oxygenation performance was not the membrane permeance but rather the rate of mass transfer in the blood phase, highlighting the importance of efficient module design.
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http://dx.doi.org/10.1021/acsbiomaterials.0c01251DOI Listing
November 2020

Poly(Alkyl-Terphenyl Piperidinium) Ionomers and Membranes with an Outstanding Alkaline-Membrane Fuel-Cell Performance of 2.58 W cm.

Angew Chem Int Ed Engl 2021 Mar 2;60(14):7710-7718. Epub 2021 Feb 2.

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

Aryl-ether-free anion-exchange ionomers (AEIs) and membranes (AEMs) have become an important benchmark to address the insufficient durability and power-density issues associated with AEM fuel cells (AEMFCs). Here, we present aliphatic chain-containing poly(diphenyl-terphenyl piperidinium) (PDTP) copolymers to reduce the phenyl content and adsorption of AEIs and to increase the mechanical properties of AEMs. Specifically, PDTP AEMs possess excellent mechanical properties (storage modulus>1800 MPa, tensile strength>70 MPa), H fuel-barrier properties (<10 Barrer), good ion conductivity, and ex-situ stability. Meanwhile, PDTP AEIs with low phenyl content and high-water permeability display excellent peak power densities (PPDs). The present AEMFCs reach outstanding PPDs of 2.58 W cm (>7.6 A cm current density) and 1.38 W cm at 80 °C in H /O and H /air, respectively, along with a specific power (PPD/catalyst loading) over 8 W mg , which is the highest record for Pt-based AEMFCs so far.
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http://dx.doi.org/10.1002/anie.202013395DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8048807PMC
March 2021

2D Nanosheets and Their Composite Membranes for Water, Gas, and Ion Separation.

Angew Chem Int Ed Engl 2019 Dec 18;58(49):17512-17527. Epub 2019 Jul 18.

Department of Energy Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

Two-dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal-organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long-term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes' excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.
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http://dx.doi.org/10.1002/anie.201814349DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6900107PMC
December 2019

Bio-Inspired Robust Membranes Nanoengineered from Interpenetrating Polymer Networks of Polybenzimidazole/Polydopamine.

ACS Nano 2019 01 8;13(1):125-133. Epub 2019 Jan 8.

School of Chemical Engineering and Analytical Science , The University of Manchester , The Mill, Sackville street , Manchester M13 9PL , United Kingdom.

Marine mussel inspired polydopamine (PDA) has received increased attention due to its good thermal and chemical stability as well as strong adhesion on most materials. In this work, high-performance nanofiltration membranes based on interpenetrating polymer networks (IPN) incorporating PDA and polybenzimidazole (PBI) were developed for organic solvent nanofiltration (OSN). Generally, in order to obtain solvent stability, polymers need to be covalently cross-linked under harsh conditions, which inevitably leads to losses in permeability and mechanical flexibility. Surprisingly, by in situ polymerization of dopamine within a PBI support, excellent solvent resistance and permeance of polar aprotic solvents were obtained without covalent cross-linking of the PBI backbone due to the formation of an IPN. The molecular weight cutoff and permeance of the membranes can be fine-tuned by changing the polymerization time. Robust membrane performance was achieved in conventional and emerging green polar aprotic solvents (PAS) in a wide temperature range covering -10 °C to +100 °C. It was successfully demonstrated that the in situ polymerization of PDA-creating an IPN-can provide a simple and green alternative to covalent cross-linking of membranes. To elucidate the nature of the solvent stability, a detailed analysis was performed that revealed that physical entanglement along with strong secondary interaction synergistically enable solvent resistance with as low as 1-3% PDA content.
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http://dx.doi.org/10.1021/acsnano.8b04123DOI Listing
January 2019

Functionalized Boron Nitride Nanosheets: A Thermally Rearranged Polymer Nanocomposite Membrane for Hydrogen Separation.

Angew Chem Int Ed Engl 2018 Dec 11;57(49):16056-16061. Epub 2018 Nov 11.

Department of Chemical Engineering, Monash University, Clayton, Victoria, 3800, Australia.

Amino functionalized boron nitride nanosheets (FBN) were incorporated into a crosslinked, thermally rearranged polyimide (XTR) to fabricate FBN-XTR nanocomposite membrane. The FBN-XTR membrane exhibited a small decrease in H permeability but demonstrated a remarkably increased H gas selectivity over other gases, compared with XTR. The XTR membrane heat-treated at 425 °C had a H permeability of 210 Barrers and a H /CH separation factor of 24.1, whereas the nanocomposite membrane with 1 wt % FBN exhibited a H permeability of 110 Barrers and H /CH separation factor of 275, an order of magnitude greater. At 1 wt % FBN loading, the FBN-XTR membrane showed three times higher tensile strength and 60 % higher elongation than pristine XTR membrane. In addition, FBN-XTR was found to be able to be readily processed into thin-film membranes for practical H separation applications.
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http://dx.doi.org/10.1002/anie.201809126DOI Listing
December 2018

Exploring and Exploiting the Effect of Solvent Treatment in Membrane Separations.

ACS Appl Mater Interfaces 2017 Mar 20;9(12):11279-11289. Epub 2017 Mar 20.

School of Chemical Engineering & Analytical Science, The University of Manchester , The Mill, Sackville Street, Manchester M13 9PL, United Kingdom.

It is well-known that solvent treatment and preconditioning play an important role in rejection and flux performance of membranes due to solvent-induced swelling and solvent adsorption. Investigations into the effect of solvent treatment are scarce and application specific, and were limited to a few solvents only. This study reveals the trend in solvent treatment based on solvent polarity in a systematic investigation with the aim to harness such effect for intensification of membrane processes. Nine solvents with polarity indices ranging from 0.1 to 5.8 (hexane to acetonitrile) were used as treatment and process solvents on commercial Borsig GMT-oNF-2, Evonik Duramem 300, and emerging tailor-made polybenzimidazole membranes. TGA-GCMS, HS-GC-FID, and NMR techniques were employed to better understand the effect of solvent treatment on the polymer matrix of membranes. In this work, apart from the solvent treatment's direct effect on the membrane performance, a subsequent indirect effect on the ultimate separation process was observed. Consequently, a pharmaceutical case study employing chlorhexidine disinfectant and antiseptic was used to demonstrate the effect of solvent treatment on the nanofiltration-based purification. It is shown that treatment of polybenzimidazole membranes with acetone resulted in a 25% increase in product recovery at 99% impurity removal. The cost of the process intensification is negligible in terms of solvent consumption, mass intensity, and processing time.
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http://dx.doi.org/10.1021/acsami.7b01879DOI Listing
March 2017

Hydrocarbon-Based Polymer Electrolyte Membranes: Importance of Morphology on Ion Transport and Membrane Stability.

Chem Rev 2017 Mar 3;117(6):4759-4805. Epub 2017 Mar 3.

Department of Energy Engineering, College of Engineering, Hanyang University , Seoul 04763, Republic of Korea.

A fundamental understanding of polymer microstructure is important in order to design novel polymer electrolyte membranes (PEMs) with excellent electrochemical performance and stabilities. Hydrocarbon-based polymers have distinct microstructure according to their chemical structure. The ionic clusters and/or channels play a critical role in PEMs, affecting ion conductivity and water transport, especially at medium temperature and low relative humidity (RH). In addition, physical properties such as water uptake and dimensional swelling behavior depend strongly on polymer morphology. Over the past few decades, much research has focused on the synthetic development and microstructural characterization of hydrocarbon-based PEM materials. Furthermore, blends, composites, pressing, shear field, electrical field, surface modification, and cross-linking have also been shown to be effective approaches to obtain/maintain well-defined PEM microstructure. This review summarizes recent work on developments in advanced PEMs with various chemical structures and architecture and the resulting polymer microstructures and morphologies that arise for potential application in fuel cell, lithium ion battery, redox flow battery, actuators, and electrodialysis.
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http://dx.doi.org/10.1021/acs.chemrev.6b00586DOI Listing
March 2017

Effect of cationic groups in poly(arylene ether sulfone) membranes on reverse electrodialysis performance.

Chem Commun (Camb) 2017 Feb;53(15):2323-2326

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

In this work, three functional groups were introduced in poly(arylene ether sulfone) membranes to investigate the effects of cationic functional groups in the membranes on reverse electrodialysis performance. Our results showed that controlling the swelling behaviour of the membranes was an important factor for increasing the permselectivity while maintaining their high conductivity.
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http://dx.doi.org/10.1039/c6cc08440kDOI Listing
February 2017

Thermally rearranged (TR) bismaleimide-based network polymers for gas separation membranes.

Chem Commun (Camb) 2016 Nov;52(93):13556-13559

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul 04763, Republic of Korea.

Highly permeable, thermally rearranged polymer membranes based on bismaleimide derivatives that exhibit excellent CO permeability up to 5440 Barrer with a high BET surface area (1130 m g) are reported for the first time. In addition, the membranes can be easily used to form semi-interpenetrating networks with other polymers endowing them with superior gas transport properties.
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http://dx.doi.org/10.1039/c6cc06609gDOI Listing
November 2016

Nanocrack-regulated self-humidifying membranes.

Nature 2016 Apr;532(7600):480-3

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul 133-791, South Korea.

The regulation of water content in polymeric membranes is important in a number of applications, such as reverse electrodialysis and proton-exchange fuel-cell membranes. External thermal and water management systems add both mass and size to systems, and so intrinsic mechanisms of retaining water and maintaining ionic transport in such membranes are particularly important for applications where small system size is important. For example, in proton-exchange membrane fuel cells, where water retention in the membrane is crucial for efficient transport of hydrated ions, by operating the cells at higher temperatures without external humidification, the membrane is self-humidified with water generated by electrochemical reactions. Here we report an alternative solution that does not rely on external regulation of water supply or high temperatures. Water content in hydrocarbon polymer membranes is regulated through nanometre-scale cracks ('nanocracks') in a hydrophobic surface coating. These cracks work as nanoscale valves to retard water desorption and to maintain ion conductivity in the membrane on dehumidification. Hydrocarbon fuel-cell membranes with surface nanocrack coatings operated at intermediate temperatures show improved electrochemical performance, and coated reverse-electrodialysis membranes show enhanced ionic selectivity with low bulk resistance.
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http://dx.doi.org/10.1038/nature17634DOI Listing
April 2016

Soluble, microporous, Tröger's Base copolyimides with tunable membrane performance for gas separation.

Chem Commun (Camb) 2016 Mar;52(19):3817-20

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul 04763, Republic of Korea.

A facile two-step synthesis beginning with commercial monomers to prepare copolyimides by Tröger's Base (TB) formation provides membranes for the first time with tunable gas transport relative to hydrogen separations, CO2 plasticization resistance, and good mechanical and thermal properties.
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http://dx.doi.org/10.1039/c5cc09783eDOI Listing
March 2016

A Promising Na3V2(PO4)3/Ag + Graphene Composites as Cathode Material for Hybrid Lithium Batteries.

J Nanosci Nanotechnol 2015 Nov;15(11):8937-42

The NASICON (sodium super ionic conductor) based Na3V2(PO4)3/Ag + graphene (NVP/Ag + G) was successfully synthesized through a sol-gel route using a silver nitrate and graphene as a raw material. The effects of the physical and electrochemical properties of the NVP/Ag + G composites have been evaluated with X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and electrochemical measurements. The graphene and Ag significantly influenced the morphology, structure and electrochemical performance of the Na3V2(PO4)3 material. In the electrochemical measurement, the (NVP/Ag + G) electrode showed the discharge capacity of 102 mAh g(-1) at 0.1 C rate, which was higher than the pristine Na3V2(PO4). At a current rate of 5 C, it still exhibits the discharge capacity of 73 mAh g(-1) and the capacity retention of 71.6%. The results of higher electrochemical performance of the NVP/Ag + G composites are mainly attributed to the synergetic effect of the graphene and the silver particles.
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http://dx.doi.org/10.1166/jnn.2015.11538DOI Listing
November 2015

Rational molecular design of PEOlated ladder-structured polysilsesquioxane membranes for high performance CO2 removal.

Chem Commun (Camb) 2015 Oct 4;51(83):15308-11. Epub 2015 Sep 4.

Center for Environment, Health and Welfare Research, Korea Institute of Science and Technology, Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea.

Poly(methoxy(polyethyleneoxy)propyl-co-methacryloxypropyl) silsesquioxane membranes with different copolymer ratios were successfully fabricated via UV-induced crosslinking with mechanical stability. By selectively introducing polyethylene oxide (PEO) groups covalently bound to the ladder-structured polysilsesquioxane, we effectively suppressed the PEO crystallization, allowing for excellent CO2/H2 and CO2/N2 separation under single as well as mixed gas conditions.
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http://dx.doi.org/10.1039/c5cc06269aDOI Listing
October 2015

Correction: Highly lithium-ion conductive battery separators from thermally rearranged polybenzoxazole.

Chem Commun (Camb) 2015 Feb;51(16):3474

School of Chemical Engineering, College of Engineering, Hanyang University, Seoul 133-791, Korea.

Correction for 'Highly lithium-ion conductive battery separators from thermally rearranged polybenzoxazole' by Moon Joo Lee et al., Chem. Commun., 2015, 51, 2068-2071.
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http://dx.doi.org/10.1039/c5cc90064fDOI Listing
February 2015

Highly lithium-ion conductive battery separators from thermally rearranged polybenzoxazole.

Chem Commun (Camb) 2015 Feb;51(11):2068-71

School of Chemical Engineering, College of Engineering, Hanyang University, Seoul 133-791, Korea.

High power density lithium ion battery (HLIB) separators were fabricated for the first time from thermally rearranged poly(benzoxazole-co-imide) (TR-PBOI) nanofibrous membranes coated with TR-PBOI nanoparticles, which show distinct thermal and dimensional stabilities as well as excellent cycle retention and rate capability.
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http://dx.doi.org/10.1039/c4cc09411eDOI Listing
February 2015

A simulation study on OH-containing polyimide (HPI) and thermally rearranged polybenzoxazoles (TR-PBO): relationship between gas transport properties and free volume morphology.

J Phys Chem B 2014 Mar 3;118(10):2746-57. Epub 2014 Mar 3.

Institute on Membrane Technology, ITM-CNR, Via P. Bucci Cubo 17/C, Rende (CS) 87036, Italy.

Recently, high free volume polymer materials have been regarded as high potential candidates for gas transport/separation membranes, since the amount of free volume in polymeric membrane can improve the diffusivity and solubility of gas molecules. In this study, we focused on how local changes in polymer structure can affect the performance of a membrane at the molecular level. The transport behavior was theoretically analyzed, and then the differences in the amount and morphology of free volume were characterized. Finally, we suggested how the "evolution of microcavities" affects the gas transport properties of hydroxyl-containing polyimide (HPI) and thermally rearranged (TR) polymers. In particular, using image analysis, we intuitively demonstrate the morphological difference between HPI and TR polymers that have been indirectly explained by experimental analyses using a wide-angle X-ray diffractometer (WAXD) and positron annihilation laser spectroscopy (PALS). Solubility results using the grand canonical Monte Carlo (GCMC) method showed marginal improvement in thermally rearranged polybenzoxazoles (TR-PBOs) from its precursor HPI, which is in good agreement with the experimental tendency. Moreover, higher diffusivities but lower selectivities of TR-PBO models compared with those of HPI models were observed, as reported experimentally. The difference in gas transport abilities between HPIs and TR-PBOs originates from the difference in their diffusion behavior, and this is strongly related to the free volume amount and morphology of polymeric materials. In addition to the higher amount of total free volume in TR-PBO, our image analysis revealed that TR-PBO has a higher amount of interconnected "hourglass-shaped free volume elements", which consist of larger and more elongated cavities with bottlenecks than the HPI model. In particular, the bottleneck diameters in the TR-PBO models are wider than those in the HPI models, enabling the larger gas molecules to diffuse through the cavities faster. However, the narrower and smaller bottleneck diameters in the HPI model can induce better selectivity for large gas molecules.
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http://dx.doi.org/10.1021/jp411612gDOI Listing
March 2014

One-pot template-free synthesis of monodisperse hollow hydrogel microspheres and their resulting properties.

Macromol Rapid Commun 2013 Aug 9;34(15):1243-8. Epub 2013 Jul 9.

Department of Chemical Engineering, College of Engineering, Hanyang University, Seoul, 133-791, Republic of Korea.

Monodisperse poly(methacrylic acid/ethyleneglycoldimethacrylate) (MAA/EGDMA) hollow microcapsules, which exhibit pH-responsive behavior, are prepared by diffusion of cationic surfactants and hydrophobic interaction. During the association of the negatively charged hydrogel microspheres and an oppositely charged surfactant (cetyltrimethylammonium bromide, CTA(+)B), the hydrophobic polymer-surfactant complexes that form are separated from the internal water; consequently, a hollow structure can be formed. Confocal laser scanning microscopy, UV spectro-scopy and zeta potential are employed to study the formation of the hollow structure during the diffusion of the cationic surfactant. The controlled release behavior of methylene blue as a model drug from the as-prepared poly(MAA/EGDMA) microcapsules with a hollow structure is investigated under different pH conditions. The hollow structure can be retained, even during repetitive pH changes.
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http://dx.doi.org/10.1002/marc.201300330DOI Listing
August 2013

Poly(acrylic acid)-grafted fluoropolymer films for highly sensitive fluorescent bioassays.

ACS Appl Mater Interfaces 2013 Mar 14;5(6):2155-60. Epub 2013 Mar 14.

Research Division for Industry and Environment, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup-si, Jeollabuk-do 580-185, Republic of Korea.

In this study, a facile and effective method for the surface functionalization of inert fluoropolymer substrates using surface grafting was demonstrated for the preparation of a new platform for fluorescence-based bioassays. The surface of perfluorinated poly(ethylene-co-propylene) (FEP) films was functionalized using a 150 keV ion implantation, followed by the graft polymerization of acrylic acid, to generate a high density of carboxylic acid groups on the implanted surface. The resulting functionalized surface was investigated in terms of the surface density of carboxylic acid, wettability, chemical structure, surface morphology, and surface chemical composition. These results revealed that poly(acrylic acid) (PAA) was successfully grafted onto the implanted FEP surface and its relative amount depended on the fluence. To demonstrate the usefulness of this method for the fabrication of bioassays, the PAA-grafted FEP films were utilized for the immobilization of probe DNA for anthrax toxin, followed by hybridization with Cy3-labeled target DNA. Liver cancer-specific α-feto-protein (AFP) antigen was also immobilized on the PAA-grafted FEP films. Texas Red-labeled secondary antibody was reacted with AFP-specific primary antibody prebound to the AFP antigen using an immunoassay method. The results revealed that the fluorescence intensity clearly depended on the concentration of the target DNA hybridized to the probe DNA and the AFP antigen immobilized on the FEP films. The lowest detectable concentrations of the target DNA and the AFP antigen were 10 fg/mL and 10 pg/mL, respectively, with the FEP films prepared at a fluence of 3 × 10(14) ions/cm(2).
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http://dx.doi.org/10.1021/am303197nDOI Listing
March 2013

Simultaneous microfabrication and tuning of the permselective properties in microporous polymers using X-ray lithography.

Small 2013 Jul 28;9(13):2277-82. Epub 2013 Feb 28.

CSIRO Division of Materials Science and Engineering (CMSE), Private Bag 33, Clayton South MDC, Victoria 3169, Australia.

Microchannels are fabricated using a photosensitive polymer to which microporosity is tuned with different X-ray doses. Using hard X-ray irradiation, the micropattern is positioned with various geometries in a multi-level, three-dimensional structure, while controlling the pore size and transport properties of small molecules. This highly reliable fabrication process has potential for use in microfluidic devices with enhanced transport properties through microchannels.
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http://dx.doi.org/10.1002/smll.201202735DOI Listing
July 2013

Materials science. Polymer rigidity improves microporous membranes.

Science 2013 Jan;339(6117):284-5

National Research Council Canada, Ottawa, Ontario, Canada.

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http://dx.doi.org/10.1126/science.1232714DOI Listing
January 2013

Thermal treatment effect on the structure and property change between hydroxy-containing polyimides (HPIs) and thermally rearranged polybenzoxazole (TR-PBO).

J Phys Chem B 2012 Oct 10;116(42):12864-77. Epub 2012 Oct 10.

Institute on Membrane Technology, ITM-CNR, Via P. Bucci Cubo 17/C, Rende (CS), 87036, Italy.

In this study, we report on the effect of thermal treatment on polyimide precursors (HPIs) and on the resulting thermally rearranged polybenzoxazole (TR-PBO) polymer membranes as investigated through the use of molecular dynamics (MD) simulations. For this purpose, we have first analyzed the structures of hydroxy-containing polyimides before thermal treatment and those of the thermally rearranged polybenzoxazoles after the thermal treatment, according to their temperature conditions. As expected, HPIs and TR-PBOs always show very limited motion of their polymer chains, indicated by the radius of gyration, due to their well-known thermal stability. In particular, the very rigid and stiff PBO linkages did not undergo significant change in their torsional angle distribution. On the other hand, in regards to intrachain movement, HPI chains were significantly affected by temperature. Their conformational changes were notably observed, which affected the distances between possible reaction sites, oxygen atoms in hydroxyl groups, and carbon atoms in the imido-ring. The free volume analysis, performed on both polymers and during thermal treatment, indicates that HPIs have a unimodal distribution of free volume areas, which partially coalesce in larger areas having, however, a relatively narrow size. Further, TR-PBO shows a bimodal cavity distribution, and after thermal treatment and TR reaction, the free volume structures in TR-PBO are maintained. The cavity size distributions determined by simulation were also consistent with free volume distributions determined by positron annihilation lifetime spectroscopy.
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http://dx.doi.org/10.1021/jp307365yDOI Listing
October 2012

Peri-implant soft tissue level secondary to a connective tissue graft in conjunction with immediate implant placement: a 2-year follow-up report of 11 consecutive cases.

Int J Periodontics Restorative Dent 2012 Apr;32(2):213-22

Department of Periodontology and Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea.

The purpose of this case series was to evaluate secondary soft tissue level changes of a single-stage surgical protocol combining immediate implant placement and connective tissue grafting in maxillary incisors associated with gingival recession defects. Ten patients underwent the proposed combined treatment consisting of 11 single-tooth implant restorations. Peri-implant soft tissue level and the width of keratinized gingiva were evaluated at baseline, the time of implant restoration connection, and 2 years postrestoration. All parameters used to assess esthetic outcomes showed improvements. The proposed clinical procedure can be considered an alternative approach to achieving an ideal esthetic anterior restoration.
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April 2012

Enhancement of proton transport by nanochannels in comb-shaped copoly(arylene ether sulfone)s.

Angew Chem Int Ed Engl 2011 Sep 24;50(39):9158-61. Epub 2011 Aug 24.

WCU Department of Energy Engineering, Hanyang University, Seoul 133-791, Republic of Korea.

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http://dx.doi.org/10.1002/anie.201102057DOI Listing
September 2011

Efficient immobilization and patterning of biomolecules on poly(ethylene terephthalate) films functionalized by ion irradiation for biosensor applications.

ACS Appl Mater Interfaces 2011 Jul 11;3(7):2235-9. Epub 2011 Jul 11.

Radiation Research Division for Industry and Environment, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup-si, Jeollabuk-do 580-185, Republic of Korea.

The surface of a poly(ethylene terephthalate) (PET) film was selectively irradiated with proton beams at various fluences to generate carboxylic acid groups on the surface; the resulting functionalized PET surface was then characterized in terms of its wettability, chemical structure, and chemical composition. The results revealed that (i) carboxylic acid groups were successfully generated in the irradiated regions of the PET surface, and (ii) their relative amounts were dependent on the fluence. A capture biomolecule, anthrax toxin probe DNA, was selectively immobilized on the irradiated regions on the PET surface. Cy3-labeled DNA as a target biomolecule was then hybridized with the probe DNA immobilized on the PET surface. Liver-cancer-specific α-fetoprotein (AFP) antigen, as a target biomolecule, was also selectively immobilized on the irradiated regions on the PET surface. Texas Red-labeled secondary antibody was then reacted with an AFP-specific primary antibody prebound to the AFP antigen on the PET surface for the detection of the target antigen, using an indirect immunoassay method. The results revealed that (i) well-defined micropatterns of biomolecules were successfully formed on the functionalized PET surfaces and (ii) the fluorescence intensity of the micropatterns was dependent mainly on the concentrations of the target DNA hybridized to the probe DNA and the target AFP antigen immobilized on the PET films. The lowest detectable concentrations of the target DNA and target AFP antigen in this study were determined to be 4 and 16 ng/mL, respectively, with the PET film prepared at a fluence of 5 × 10(14) ions/cm(2).
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http://dx.doi.org/10.1021/am200630pDOI Listing
July 2011

Metal-organic framework membranes fabricated via reactive seeding.

Chem Commun (Camb) 2011 Jan 8;47(2):737-9. Epub 2010 Nov 8.

State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, 5 Xinmofan Road, Nanjing 210009, P. R. China.

A facile reactive seeding (RS) method was developed for the preparation of continuous MOF membranes on alumina porous supports, in which the porous support acted as the inorganic source reacting with the organic precursor to grow a seeding layer.
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http://dx.doi.org/10.1039/c0cc03927fDOI Listing
January 2011

Phase separation and water channel formation in sulfonated block copolyimide.

J Phys Chem B 2010 Sep;114(37):12036-45

School of Chemical Engineering, Hanyang University, Seoul 133-791, Korea.

We compared experimental and simulated data to investigate the phase separation and water channel formation of proton exchange membranes (PEMs) for fuel cell. Sulfonated block copolyimides (SPIs) were adopted as model polymers for experiments and simulations, and Nafion was used as a reference. Nafion and SPIs were observed to have different microscopic structures such as constituent atoms, backbone rigidity, and the locations of sulfonic acid groups, all of which significantly affect phenomenological properties at the macroscopic level such as density, water uptake, and proton conductivity. In particular, SPIs show much weaker microphase separation than Nafion, mainly due to the lower mobility of sulfonic acid groups and the existence of acceptable sites for hydrogen bonding even in hydrophobic segments, which impedes water channel formation for proton transport. As a result, the phase separation behavior and the resulting water channel formation are the major factors affecting macroscopic properties of PEMs such as water uptake and proton transport.
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http://dx.doi.org/10.1021/jp105708mDOI Listing
September 2010

Surface-fluorinated proton-exchange membrane with high electrochemical durability for direct methanol fuel cells.

ACS Appl Mater Interfaces 2009 May;1(5):1113-21

School of Chemical Engineering, College of Engineering, Hanyang University, Seoul 133-791, Korea.

Random disulfonated poly(arylene ether sulfone)-silica nanocomposite (FSPAES-SiO2) membranes were physicochemically tuned via surface fluorination. Surface fluorination for 30 min converted about 20% of the C-H bonds on the membrane surface into C-F bonds showing hydrophobicity and electronegativity at the same time. The membranes with hydrophobic surface properties showed high dimensional stability and low methanol permeability when hydrated for direct methanol fuel cell applications. In particular, the surface enrichment of fluorine atoms led to anisotropic swelling behavior, associated with a stable electrode interface formation. Interestingly, in spite of the use of a random copolymer as a polymer matrix, the low surface free energy of the C-F bonds induced a well-defined continuous ionic channel structure, similar to those of multiblock copolymers. In addition to the morphological transition, fluorine atoms with high electron-withdrawing capability promoted the dissociation of sulfonic acid (-SO3H) groups. Consequently, FSPAES-SiO2 membranes exhibited improved proton conductivity. Thus, FSPAES-SiO2 membranes exhibited significantly improved single-cell performances (about 200%) at a constant voltage of 0.4 V in comparison with those of Nafion 117 and nonfluorinated membranes. Surprisingly, their good electrochemical performances were maintained with very low nonrecovery loss over the time period of 1400 h and interfacial resistances 380% times lower than those of conventional membrane-electrode assemblies comprising the control hydrocarbon membrane and a Nafion binder for the electrodes.
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http://dx.doi.org/10.1021/am900067qDOI Listing
May 2009

Chemically tuned anode with tailored aqueous hydrocarbon binder for direct methanol fuel cells.

Langmuir 2009 Jul;25(14):8217-25

School of Chemical Engineering, Hanyang University, Seoul 133-791, Korea.

An anode for direct methanol fuel cells was chemically tuned by tailoring an aqueous hydrocarbon catalyst (SPI-BT) binder instead of using a conventional perfluorinated sulfonic acid ionomer (PFSI). SPI-BT designed in triethylamine salt form showed lower proton conductivity than PFSI, but it was stable in the catalyst ink forming the aqueous colloids. The aqueous colloidal particle size of SPI-BT was much smaller than that of PFSI. The small SPI-BT colloidal particles contributed to forming small catalyst agglomerates and simultaneously reducing their pore volume. Consequently, the high filling level of binders in the pores, where Pt-Ru catalysts are mainly located on the wall and physically interconnected, resulted in increased electrochemical active surface area of the anode, leading to high catalyst utilization. In addition, the chemical affinity between the SPI-BT binder and the membrane material derived from their similar chemical structure induced a stable interface on the membrane-electrode assembly (MEA) and showed low electric resistance. Upon adding SPI-BT, the synergistic effect of high catalyst utilization, improved mass transfer behavior to Pt-Ru catalyst, and low interfacial resistance of MEA became greater than the influence of reduced proton conductivity in the electrochemical performance of single cells. The electrochemical performance of MEAs with SPI-BT anode was enhanced to almost the same degree or somewhat higher than that with PFSI at 90 degrees C.
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http://dx.doi.org/10.1021/la900406dDOI Listing
July 2009

Transplantation of mesenchymal stem cells within a poly(lactide-co-epsilon-caprolactone) scaffold improves cardiac function in a rat myocardial infarction model.

Eur J Heart Fail 2009 Feb;11(2):147-53

Division of Cardiology, College of Medicine, Hanyang University, 17 Haengdang-dong, Seongdong-ku, Seoul 133-791, South Korea.

Aims: Cardiac tissue engineering has been proposed as an appropriate method to repair myocardial infarction (MI). Evidence suggests that a cell with scaffold combination was more effective than a cell-only implant. Nevertheless, to date, there has been no research into elastic biodegradable poly(lactide-co-epsilon-caprolactone) (PLCL) scaffolds. The aim of this study was to investigate the effect of mesenchymal stem cells (MSCs) with elastic biodegradable PLCL scaffold transplants in a rat MI model.

Methods And Results: Ten days after inducing MI through the cryoinjury method, a saline control, MSC, PLCL scaffold, or MSC-seeded PLCL scaffold was transplanted onto the hearts. Four weeks after transplantation, cardiac function and histology were evaluated. Transplanted MSCs survived and differentiated into cardiomyocytes in the injured region. Left ventricular ejection fraction in the MSC+PLCL group increased by 23% compared with that in the saline group; it was also higher in the MSC group. The infarct area in the MSC+PLCL group was decreased by 29% compared with that in the saline group; it was also reduced in the MSC group.

Conclusion: Mesenchymal stem cells plus PLCL should be an excellent combination for cardiac tissue engineering.
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http://dx.doi.org/10.1093/eurjhf/hfn017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2639416PMC
February 2009