Jae-Ryung Cha

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

New blue fluorescent spirobenzoanthracene-type dopant materials, 3,9-di(di(p-tolyl))aminospiro[benzo[de]anthracene-7,9′-fluorene] (DTSBAF) and 3,9-di(di(4-biphenyl))aminospiro[benzo[de]anthracene-7,9′-fluorene] (DBSBAF), were designed and successfully prepared by an amination reaction of 3-bromo-9-chlorospiro[benzo[de] anthracene-7,9′-fluorene] with di(p-tolyl)amine and di(4-biphenyl)amine, respectively. The EL characteristics of 1,10-dinaphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (DNSBTF) as the blue host material doped with the above blue dopant materials was evaluated. The electroluminescence spectra of indium tin oxide (150 nm)/N,N′-diphenyl-N,N′-bis[4-(phenyl-m-tolyl-amino)phenyl]-biphenyl-4,4′-diamine (DNTPD, 60 nm)/N,N,N′,N′-tetra(1-biphenyl)-biphenyl-4,4′-diamine (TBB, 30 nm)/SBTF hosts: SBAF dopant (20 nm, 5%)/9,10-di(naphthalene-2-yl)anthracen-2-yl-(4,1-phenylene)(1-phenyl-1H-benzo[d]imidazole) (LG201, 20 nm)/LiF (1 nm)/Al (200 nm) with DNSBTF as a host material show a blue emission band with a full width at half maximum of 50 nm and λmax = 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−1 at 5 V) and high external quantum efficiency (6.02%).

Preparation of Silver-Coated Silk Fabrics with Antibacterial Activity Using Silver Carbamate and Hydrogen Reduction

A new method was studied to efficiently metallize silk fabrics, and silver-coated silk fabrics were prepared and characterized. In this study, silver 2-ethylhexylcarbamate was used as the silver precursor, and a hydrogen atmosphere was used to reduce the precursors, thus forming silver nanoparticles on the surface of silk fabric. The silver-coated silk fabric was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy, and the results confirmed that 20-70 nm silver nanoparticles were uniformly generated without damaging the silk fabric. The silver-coated silk fabric showed excellent ultraviolet blocking properties and antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This method provides a way to improve the antibacterial ability of silk fabrics while avoiding damage to the silk.

Facile procedure for producing silver nanocoated cotton gauze and antibacterial evaluation for biomedical applications

We present a rapid, simple, convenient and cost-effective method for producing nanosized stable silver particles on cotton fibers with complete control of the silver loading level using a thermal reducing silver carbamate complex. Cotton gauze was coated with silver 2-ethylhexylcarbamate solution. Silver nanoparticles on the cotton gauze were characterized by energy dispersive X-ray spectroscopy and X-ray diffraction. Particle size and lattice image of the silver nanoparticles were studied by scanning electron microscopy. The antibacterial activity of the silver coated cotton gauze against Escherichia coli and Staphylococcus aureus, whole blood clotting and physical properties including vertical wicking test, water retention time and absorption of 0.9 % (w/v) saline were studied. Silver coated cotton gauze showed a faster blood clotting rate than the untreated cotton gauze. Cotton gauzes treated with two different silver concentrations (0.01 %, 0.1 %) showed slightly better saline absorption and they had better vertical wicking and water retention time than pristine cotton gauze.

Surface modification of polyester fibers by thermal reduction with silver carbamate complexes

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 0.12 kΩ·cm.

Bio-based chiral dopants having an isohexide skeleton for cholesteric liquid crystal materials

Chiral dopants were synthesized from bio-based epimeric isohexides (glucose-derived isosorbide and mannose-derived isomannide) and their phase transition behaviors and abilities for developing cholesteric liquid crystal (CLC) films were examined with a consideration of the core structure. In spite of lower reactivity of the endo hydroxy group of isomannide caused by the steric hindrance and intermolecular hydrogen bonding, final synthetic yields of chiral dopants bearing an isomannide core (64.5% for IH-2 and 65.0% for IH-4) did not show conspicuous difference compared with chiral dopants bearing isosorbide (68.4% for IH-1 and 74.0% for IH-3). On the other hand, in phase transition behaviors, chiral dopants bearing an isomannide core showed lower crystalline and melting temperatures than IH-1, IH-3 despite of the same substituents. The helical twisting power (HTP) of chiral dopants bearing isosorbide (IH-1 and IH-3) was higher than that of chiral dopants bearing isomannide (IH-2 and IH-4). The calculated HTPs of IH-1 and IH-3 were 26.6 and 42.1 μm−1, respectively. In the case of IH-3, the helical pitch length of CLC could be adjusted to reflect visible light by controlling its amount and showed best performance in the range 5.0 to 7.0 mol%. In contrast to IH-1 and IH-3, it was found that IH-2 and IH-4 could not induce CLC films that reflect visible light.

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

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.