AC Complex Impedance Study on the Resistive Humidity Sensors with Ammonium Salt-Containing Polyelectrolyte using a Different Electrode Pattern

Cha, Jae-Ryung,Gong, Myoung-Seon Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.9

We examined the effect of electrode fingers and gaps of coplanar interdigitated electrode (IDE) structures to characterize the ammonium salt-containing polyelectrolyte film of resistance-based humidity sensors. IDEs designed for this purpose were flexible gold electrodes deposited on a polyimide substrate using a printing process because the geometry presents a potential for tunable sensitivity over other electrode designs. The basic design of the sensors consisted of IDEs with a different number of electrode fingers such as 3, 4, and 5 and gap sizes of 310, 360, 410, and $460{\mu}m$. Details of the AC complex impedance characteristics such as the Nyquist plot, Bode plot, and activation energy based on electrode construction were investigated.

New efficient fused-ring spiro[benzoanthracene-fluorene] dopant materials for blue fluorescent organic light-emitting diodes

Cha, Jae-Ryung,Lee, Chil-Won,Gong, Myoung-Seon The Royal Society of Chemistry 2015 NEW JOURNAL OF CHEMISTRY Vol.39 No.5

<P>New blue fluorescent spirobenzoanthracene-type dopant materials, 3,9-di(di(<I>p</I>-tolyl))aminospiro[benzo[<I>de</I>]anthracene-7,9′-fluorene] (<B>DTSBAF</B>) and 3,9-di(di(4-biphenyl))aminospiro[benzo[<I>de</I>]anthracene-7,9′-fluorene] (<B>DBSBAF</B>), were designed and successfully prepared by an amination reaction of 3-bromo-9-chlorospiro[benzo[<I>de</I>] anthracene-7,9′-fluorene] with di(<I>p</I>-tolyl)amine and di(4-biphenyl)amine, respectively. The EL characteristics of 1,10-dinaphthylspiro[benzo[<I>ij</I>]tetraphene-7,9′-fluorene] (<B>DNSBTF</B>) as the blue host material doped with the above blue dopant materials was evaluated. The electroluminescence spectra of indium tin oxide (150 nm)/<I>N</I>,<I>N</I>′-diphenyl-<I>N</I>,<I>N</I>′-bis[4-(phenyl-<I>m</I>-tolyl-amino)phenyl]-biphenyl-4,4′-diamine (DNTPD, 60 nm)/<I>N</I>,<I>N</I>,<I>N</I>′,<I>N</I>′-tetra(1-biphenyl)-biphenyl-4,4′-diamine (TBB, 30 nm)/<B>SBTF</B> hosts: <B>SBAF</B> dopant (20 nm, 5%)/9,10-di(naphthalene-2-yl)anthracen-2-yl-(4,1-phenylene)(1-phenyl-1<I>H</I>-benzo[<I>d</I>]imidazole) (LG201, 20 nm)/LiF (1 nm)/Al (200 nm) with <B>DNSBTF</B> as a host material show a blue emission band with a full width at half maximum of 50 nm and <I>λ</I><SUB>max</SUB> = 472 nm. The device obtained from DNSBTF doped with DTSBAF showed a good color purity (0.141, 0.254), high luminance efficiency (10.12 cd A<SUP>−1</SUP> at 5 V) and high external quantum efficiency (6.02%).</P> <P>Graphic Abstract</P><P>Novel fused-ring spirobenzoanthracene-fluorene blue dopants have been successfully designed and synthesized for the fluorescent sky-blue OLEDs using <B>SBTF</B> host and <B>SBAF</B> dopants. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5nj00143a'> </P>

<i>In vivo</i> corrosion mechanism by elemental interdiffusion of biodegradable Mg–Ca alloy

Jung, Jae‐,Young,Kwon, Sang‐,Jun,Han, Hyung‐,Seop,Lee, Ji‐,Young,Ahn, Jae‐,Pyoung,Yang, Seok‐,Jo,Cho, Sung‐,Youn,Cha, Pil‐,Ryung,Kim, Yu‐,Chan,Seo Wiley Subscription Services, Inc., A Wiley Company 2012 Journal of biomedical materials research. Part B, Vol.b100 No.8

<P><B>Abstract</B></P><P>We elucidated the <I>in vivo</I> corrosion mechanism of the biodegradable alloy Mg–10 wt % Ca in rat femoral condyle through transmission electron microscope observations assisted by focused ion beam technique. The alloy consists of a primary Mg phase and a three‐dimensional lamellar network of Mg and Mg<SUB>2</SUB>Ca. We found that the Mg<SUB>2</SUB>Ca is rapidly corroded by interdiffusion of Ca and O, leading to a structural change from lamellar network to nanocrystalline MgO. In contrast to the fast corrosion rate of the lamellar structure, the primary Mg phase slowly changes into nanocrystalline MgO through surface corrosion by O supplied along the lamellar networks. The rapid interdiffusion induces an inhomogeneous Ca distribution and interestingly leads to the formation of a transient CaO phase, which acts as a selective leaching path for Ca. In addition, the outgoing Ca with P from body fluids forms needle‐type calcium phosphates similar to hydroxyl apatite at interior and surface of the implant, providing an active biological environment for bone mineralization. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.</P>

Rapid <i>In Vitro</i> Corrosion Induced by Crack-Like Pathway in Biodegradable Mg-10% Ca Alloy

Jung, Jae-Young,Kwon, Sang-Jun,Han, Hyung-Seop,Yang, Gui Fu,Lee, Ji-Young,Yang, Seok-Jo,Cho, Sung-Youn,Cha, Pil-Ryung,Kim, Young-Yul,Kim, Yu-Chan,Seok, Hyun-Kwang,Ahn, Jae-Pyoung Cambridge University Press 2013 Microscopy and Microanalysis Vol.19 No.5

<B>Abstract</B><P>The <I>in vitro</I> corrosion mechanism of the biodegradable cast Mg-10% Ca binary alloy in Hanks' solution was evaluated through transmission electron microscopy observations. The corrosion behavior depends strongly on the microstructural peculiarity of Mg2Ca phase surrounding the island-like primary Mg phase and the fast corrosion induced by the interdiffusion of O and Ca via the Mg2Ca phase of lamellar structure. At the corrosion front, we found that a nanosized crack-like pathway was formed along the interface between the Mg2Ca phase and the primary Mg phase. Through the crack-like pathway, O and Ca are atomically exchanged each other and then the corroded Mg2Ca phase was transformed to Mg oxides. The <I>in vitro</I> corrosion by the exchange of Ca and O at the nanosized pathway led to the rapid bulk corrosion in the Mg-Ca alloys.</P>

Preparation of sintered silver nanosheets by coating technique using silver carbamate complex

Ahn, Hee-Yong,Cha, Jae-Ryung,Gong, Myoung-Seon Elsevier 2015 Materials chemistry and physics Vol.153 No.-

<P><B>Abstract</B></P> <P>This study describes a coating technique approach for large-scale preparation of sintered silver nanosheets whose lateral dimensions were controlled in the thickness range of 50–65 nm. These procedures involved coating water-soluble poly (vinyl alcohol) (PVA) and silver 2-ethylhexylcarbamate (Ag-EHC), as well as thermal reduction of a silver precursor by heating at 150 °C, followed by dissolving away the PVA layer with alcoholic water. When the silver carbamate layer on the PVA layer was heated to 150 °C, the silver carbamate layer was thermally reduced and directed to grow into uniform sintered nanosheets with aspect ratios as high as 1000. The multi-stacked PVA/Ag structures and sintered silver nanosheets were confirmed by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Measurements of the conductive property at room temperature indicated that these nanosheets were electrically continuous with a resistivity of approximately 7.3 × 10<SUP>−6</SUP> Ω cm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A coating technique is used to make sintered Ag nanosheets. </LI> <LI> PVA and silver carbamate act as a separation layer and a silver precursor. </LI> <LI> The Ag nanosheets have thickness width 50–60 nm and width up to hundred μm. </LI> <LI> The Ag nanosheets showed a resistivity of ca. 7.3 × 10<SUP>−6</SUP> Ω cm. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Phase Field Model Simulation of Grain Growth in Three Dimensions under Isotropic and Anisotropic Grain Boundary Energy Conditions

Ko, Kyung Jun,Cha, Pil Ryung,Park, Jong Tae,Kim, Jae Kwan,Hwang, Nong Moon Trans Tech Publications, Ltd. 2007 Materials science forum Vol.558 No.-

<P>Phase-field model (PFM) in multiple orientation fields was used to simulate the grain growth in three-dimensions (3-D) for isotropic and anisotropic grain boundary energy. In the simulation, the polycrystalline microstructure was described by a set of non-conserved order parameters and each order parameter describes each orientation of grains. For isotropic grain boundary energy, the simulation showed the microstructure evolution of normal grain growth. For anisotropic grain boundary energy, however, the simulation showed that certain grains which share a high fraction of low energy grain boundaries with other grains have a high probability to grow by wetting along triple junctions and can grow abnormally with a growth advantage of solid-state wetting. The PFM simulation shows the realistic microstructural evolution of island and peninsular grains during abnormal grain growth by solid-state wetting.</P>

Biodegradable shape-memory polymers using polycaprolactone and isosorbide based polyurethane blends

Joo, Yoon-Suk,Cha, Jae-Ryung,Gong, Myoung-Seon Elsevier 2018 Materials Science and Engineering C Vol.91 No.-

<P><B>Abstract</B></P> <P>Thermally responsive shape-memory polymers have received widespread attention in the biomedical field. In this study, biocompatible and biodegradable polyurethane (PU) and polycaprolactone (PCL) were blended to obtain shape-memory properties. Highly crystalline PCL was used as a hard segment, and PU synthesized from isosorbide, which is non-toxic and chemically and thermally stable, was used as a soft segment. The obtained PU/PCL blends containing the 30%, 50%, and 70% PU by weight were investigated for their thermal properties, mechanical properties, and shape-memory behavior. The 30%PU/PCL polymer has the best shape-memory characteristics and can be knotted by itself in the hot water bath, indicating that it can be applied in smart suture applications. The degradation test performed at 37 °C in phosphate buffered solution showed a mass loss of 2–4% for the obtained PU/PCL blends after 6 weeks. Finally, MC3T3-E1 cells cultured on PU/PCL blends showed high biocompatibility due to high adhesion and proliferation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We synthesized bio-based isosorbide-containing biodegradable PU. </LI> <LI> Thermally responsive shape-memory polymer was successfully prepared. </LI> <LI> MC3T3-E1 cells cultured on PU/PCL blends showed high biocompatibility. </LI> <LI> PU/PCL blends have potential for smart suture applications. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Surface Modification of Polyester Fibers by Thermal Reduction with Silver Carbamate Complexes

Kwak, Wan-Gyu,Cha, Jae-Ryung,Gong, Myoung-Seon 한국섬유공학회 2016 Fibers and polymers Vol.17 No.8

In this study, the surface of polyester fiber was modified by means of thermal treatment with a silver carbamate complex. We used scanning electron microscopy (SEM), an X-ray diffraction technique (XRD), and X-ray photoelectron spectroscopy (XPS) to allow a detailed characterization of the silver-coated polyethylene terephthalate (PET) fibers. The results revealed remarkable changes in the surface morphology and microstructure of the silver film after thermal reduction. On SEM, the silver nanoparticles (AgNPs) were seen to be uniformly and densely deposited on the fiber surface. The XRD pattern of the silver-coated fiber indicated that the film has a crystalline structure. A continuous layer of AgNPs, between 30 and 100 nm in size, was assembled on the PET fibers. The PET/Ag composite was found to impart high conductivity to the fibers, with an electrical resistivity as low as <TEX>$0.12k{\Omega}{\cdot}cm$</TEX>.

Facile Preparation of Silver Nanoparticles and Application to Silver Coating Using Latent Reductant from a Silver Carbamate Complex

Kim, Kyung-A,Cha, Jae-Ryung,Gong, Myoung-Seon Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.2

A low temperature ($65^{\circ}C$) thermal deposition process was developed for depositing a silver coating on thermally sensitive polymeric substrates. This low temperature deposition was achieved by chemical reduction of a silver alkylcarbamate complex with latent reducing agent. The effects of acetol as a latent reducing agent for the silver 2-ethylhexylcarbamate (Ag-EHCB) complex and their blend solutions were investigated in terms of reducing mechanism, and the size and shape of silver nanoparticles (Ag-NPs) as a function of reduced temperature and time, and PVP stabilizer concentration were determined. Low temperature deposition was achieved by combining chemical reduction with thermal heating at $65^{\circ}C$. A range of polymer film, sheet and molding product was coated with silver at thicknesses of 100 nm. The effect of process parameters and heat treatment on the properties of silver coatings was investigated.

Arthroscopic mattress locking suture technique for the repair of small- and medium-sized rotator cuff tears

Sang-Hun Ko,Yun Jae Cho,Chang-hyun Youn,Hye-Yong Cho,Jae-Ryung Cha 대한정형외과 스포츠의학회 2015 Arthroscopy and Orthopedic Sports Medicine Vol.2 No.1

Background: To prospectively compare the outcomes of an arthroscopic mattress locking (ML) suture repair and a simple suture repair of small or medium-sized rotator cuff tears. Methods: The 92 patients who had received an unsuccessful conservative treatment of small or medium-sized rotator cuff tears between April 2007 and October 2010 and who required an additional arthroscopic treatment were enrolled in the study. The patients were arbitrarily divided into the type of arthroscopic repair they received; 27 patients who received the arthroscopic ML suture were put into group 1, and 65 patients who received the simple suture were put into group 2. The mean age of patients at the time of surgery was 58 years, and the mean duration to final follow-up was 30 months. To measure the outcome of the treatment, visual analogue scale (VAS) for pain (clinical score), UCLA, American Shoulder and Elbow Surgeons (ASES) and Korean shoulder scoring (KSS) for the range of motion (functional scores) were measured for each patient. Lastly, the magnetic resonance imaging (MRI) scans of the patient’s shoulder were taken at the final follow-up. Results: Although the mean scores for clinical and functional outcomes (VAS, KSS, UCLA, and ASES scores) had improved from after the operation in both groups (P < 0.001), we found no significant differences in these improvements between the two groups (P > 0.001). Through MRI scans at the follow-up, we found that the proportion of re-tears was significantly lower in group 1 (2 patients, 7.41%) than in group 2 (12 patients, 18.46%). Conclusion: We found no significant difference in the clinical or functional outcomes of an arthroscopic ML suture repair and the simple suture repair of small-sized or medium-sized rotator cuff tears after a follow-up period of at least one year. However, the proportion of re-tears was significantly lower in patients who received ML sutures than in patients who received simple sutures.