Hyun Ji Kim

Novel Polymer Nanowire Crystals of Diketopyrrolopyrrole‐Based Copolymer with Excellent Charge Transport Properties

The first demonstration of polymer nanowire (PNW) crystals based on a diketopyrrolopyrrole-based copolymer (i.e., PDTTDPP), and their application to field-effect transistors (FETs) is reported. Remarkably, transmission electron microscopy and selected area electron diffraction analyses of the PNW reveal its single-crystalline (SC) nature. FETs fabricated of a SC PNW exhibit a maximal charge carrier mobility of ≈7.00 cm(2) V(-1) s(-1) , which is almost one order of magnitude higher than that of the thin-film transistors made of the same polymer (PDTTDPP).

PDMS/MWCNT nanocomposite actuators using silicone functionalized multiwalled carbon nanotubes via nitrene chemistry

We demonstrate that covalently functionalized multiwalled carbon nanotubes (MWCNT) with a silicone copolymer via nitrene chemistry can be used as efficient conductive fillers for silicone dielectric elastomer actuators. The MWCNTs were covalently functionalized with poly(azidopropylmethyl)-co-(dimethylsiloxane) (silicone-N3) bearing an azide group through a nitrene addition reaction. The incorporation of a small amount of the uniformly silicone grafted MWCNTs (silicone-g-MWCNTs) in silicone dielectric elastomer strongly enhanced the mechanical, dielectric, and electromechanical properties of the resulting nanocomposites. This reinforcing effect is attributed to the homogeneous dispersion of silicone-g-MWCNTs in the silicone elastomer matrix due to the large degree of compatibility between the matrix and the passivation layers of the functionalized MWCNT.

An efficient re-coloring method with information preserving for the color-blind

In this paper, a fast re-coloring method with information preserving is proposed for the color-blind (CB) who experiences difficulty to discriminate some color differences. In the proposed algorithm, we utilize a new color transform that can enhance the perceptibility for the CB while maintaining the re-colored image as natural as possible for the normal viewer. In addition, an improved method which effectively detects the CB unperceivable (CBU) colors to be re-colored is introduced. Experimental results show that the proposed method can produce more comprehensible images for CB viewers while preserving the naturalness of the recolored images for standard viewers with reduced complexity.

Control of hard block segments of methacrylate-based triblock copolymers for enhanced electromechanical performance

A series of well-defined hard–soft–hard triblock copolymers were synthesized by Ru-based atom transfer radical polymerization (ATRP) (MWD < 1.26) in order to examine their electromechanical properties under electric fields. The obtained methacrylate based triblock copolymers consisted of poly(dodecyl methacrylate) (PDMA) soft middle block segments and three different hard block segments with poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PtBMA), and their random copolymers (PMTDTMTs). Polar acidified triblock copolymers were also prepared by deprotecting tert-butyl groups in tBMA-incorporating hard block segments through simple thermal treatment at 200 °C for 120 min, which in situ gave poly(methacrylic acid) (PMAA) and its random copolymers (PAMDMA) in the hard block segments. SAXS and AFM studies indicated that these triblock copolymers showed well-organized phase separations with different domain sizes, which were strongly dependent on the amount of bulky PtBMA or polar PMAA in the hard block segments. In addition, these triblock copolymers had a variety of morphologies affecting their mechanical (elastic modulus) and electrical (dielectric constant) properties, leading to a tuning of their electromechanical properties. The transverse strains of these triblock random copolymers as a function of an applied electric field indicated that the PTMDMT series possessed the best electromechanical properties, exhibiting an 11-fold enhancement relative to the corresponding acidified polymer PAMDMA at 50 Vpp μm−1 due to a dramatic decrease of the elastic modulus from 4.04 to 0.05 MPa in spite of an increase of the dielectric constant from 3.6 to 5.1. In situ SAXS analysis under an electric field showed that these bulk strains originated from nano-structured microdomain changes.

Color modification for color-blind viewers using the dynamic color transformation

Daltonization is a procedure of color adaptation in an image to improve the color perception for a color-blind viewer. This paper presents a fast daltonization algorithm for protanopes who cannot distinguish the color between red and green. In the proposed algorithm, the protanope-unperceptible (PU) colors are identified in an image and then converted into new protanope-perceptible (PP) colors by a fast daltonization method that utilizes the color clustering to rapidly measure the color similarity. Experimental results indicate that the proposed algorithm performs better than the conventional method in terms of both color perceptibility and computational complexity.

Controlled synthesis of multi-armed P3HT star polymers with gold nanoparticle core

Well-defined multi-armed P3HT star polymers with a gold nanoparticle (NP) core were synthesized by an arm-first method based on a ligand exchange reaction between linear end-functionalized P3HT (P3HT-SH) and gold NPs. A high loading amount of gold NPs to P3HT-SH with a relatively lower molecular weight gave a higher yield of star polymers (∼70%) with a high molecular weight (Mw = 2867k, PDI = 2.1), and the number of P3HT arm chains on one gold NP was 119. The P3HT star polymer with a gold NP core was well-dispersed both in solution and in solid, which was interestingly not crystalline because of the unique 3-dimenstional structure. In addition, surface plasmon resonance (SPR) absorption from the gold NP, as the core of the star polymer, was more enhanced both in solution and in solid, in comparison to those with non end-functionalized P3HT arm chains (P3HT-allyl); however, PL emission was more diminished because of the molecularly contacted P3HT arm chain and gold NP core. This was then introduced in an active layer consisting of P3HT:PCBM in an organic solar cell to increase optical absorption by the SPR effect from the gold NP, however, the device efficiency was rather decreased compared to that of the reference device without gold NPs, which was probably due to direct electron transfer between the gold NP and P3HT.

Highly purified cyclic olefin polymer by ROMP and In situ hydrogenation with ruthenium supported catalyst

Abstract

IFNγ induces PD-L1 overexpression by JAK2/STAT1/IRF-1 signaling in EBV-positive gastric carcinoma

Programmed death-ligand 1 (PD-L1) acts as an immune checkpoint inhibitor in various cancers. PD-L1 is known to be more frequently expressed in EBV (+) gastric cancer (GC). However, the mechanisms underlying the regulation of PD-L1 expression in EBV (+) GC remain unclear. We investigated the basal and inducible PD-L1 expressions in GC cells. PD-L1 expression was upregulated upon treatment with IFNγ in both EBV (−) and EBV (+) GC cells. Upon stimulation with the same concentration of IFNγ for 24 h, EBV (+) SNU-719 cells showed dramatically higher PD-L1 expression levels by activating JAK2/STAT1/IRF-1 signaling than those of EBV (−) AGS cells. PD-L1 promoter assays, chromatin immunoprecipitation, and electrophoretic mobility shift assays revealed that IFNγ-inducible PD-L1 overexpression is primarily mediated by the putative IRF-1α site of the PD-L1 promoter in EBV (+) SNU-719 cells. Moreover, EBNA1 knockdown reduced both constitutive and IFNγ-inducible PD-L1 promoter activity by decreasing the transcript and protein levels of JAK2 and subsequently STAT1/IRF-1/PD-L1 signaling. EBNA1 is suggested to be moderately enhance both constitutive and IFNγ-inducible PD-L1 expression in EBV (+) GC cells. Thus, the signaling proteins and EBNA1 that regulate PD-L1 expression are potential therapeutic targets in EBV (+) GC.

Hybrid Nanocomposite of CdSe Quantum Dots and a P3HT-b-PDMAEMA Block Copolymer for Photovoltaic Applications

We synthesized a new hybrid nanocomposite consisting of CdSe quantum dot (QD) and regioregular poly (3-hexylthiophene)-b-poly (N,N-dimethylamino-2-ethylmethacrylate) rod-coil block copolymer to investigate the effects of nanoscale morphology to the photovoltaic properties in inorganic-organic hybrid solar cell. Well-defined conducting rod-coil block copolymers, P3HT-b-PDMAEMA, were synthesized by combination of Grignard metathesis polymerization (GRIM) and atom transfer radical polymerization (ATRP) methods. These rod-coil block copolymers were then mixed with oleic acid capped CdSe QDs through ligand exchange and characterized their nanoscale morphology and optoelectronic properties. These results can be explained by the effects of the bicontinuous electron-donor/electron-acceptor networks in active layer based on rod-coil P3HT-b-PDMAEMA block copolymers blended with CdSe QDs.

Enhanced re-coloring method with an information preserving property for color-blind person

Various image re-coloring methods have been developed to enhance the perceptibility of the image for the color-blind. Recently, some methods have been proposed to produce the re-colored images that are not only visually perceptible for color deficient viewers but also look natural for normal observer. However, the methods are impractical to apply to the consumer devices due to its high complexity. Therefore, in this paper, an efficient re-coloring method that utilizes color clustering is proposed. The proposed method detects visually important region to further enhance perceptibility of re-colored images. Experimental results show that the proposed method can provide more comprehensible images for the color-blind person while maintaining the original color information.