초고속 원심방사에 의한 아세트산프로피온산 셀룰로오스/폴리부틸렌 숙시네이트 다공성 마이크론 섬유 제조

김태영(Tae Young Kim),김미경(Mi Kyung Kim),김진수(Jinsoo Kim),이정언(Jungeon Lee),정재훈(Jae Hoon Jung),김영권(Youngkwon Kim),김태현(Tae Hyeon Kim),김기영(Ki Young Kim),염정현(Jeong Hyun Yeum) 한국염색가공학회 2023 韓國染色加工學會誌 Vol.35 No.4

Cellulose is an abundant biodegradable material in nature with excellent properties, but due to its poor processability, it has been widely studied for processing through modification. Cellulose acetate propionate (CAP) is a cellulose derivative in which the hydroxyl group of cellulose is replaced by acetyl and propionyl groups. CAP has several advantages, such as excellent solubility, structural stability, light and weather resistance, and good transparency. Porous nanofibers with excellent specific surface area, which can be applied in various fields, can be easily formed by the phase separation method using highly volatile solvents. High speed centrifugal spinning is a nano/micro fiber preparation method with advantages such as fast spinning and easy alignment control. In this study, a CAP/polybutylene succinate (PBS) spinning solution with chloroform as solvent was prepared to prepare porous microfibers and the fiber morphology was examined as a function of the disk rotation speed in an high speed centrifugal spinning device.

Regioregular-<i>block</i>-Regiorandom Poly(3-hexylthiophene) Copolymers for Mechanically Robust and High-Performance Thin-Film Transistors

Park, Hyeonjung,Ma, Boo Soo,Kim, Jin-Seong,Kim, Youngkwon,Kim, Hyeong Jun,Kim, Donguk,Yun, Hongseok,Han, Junghun,Kim, Felix Sunjoo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2019 Macromolecules Vol.52 No.20

<P>In this work, we develop mechanically robust and high-performance organic thin-film transistors (OTFTs) based on poly(3-hexylthiophene) (P3HT) regioblock copolymers (<I>block</I>-P3HTs). These <I>block</I>-P3HTs consist of regioregular (<I>rre</I>) and regiorandom (<I>rra</I>) P3HTs, where the highly crystalline <I>rre</I> block allows efficient charge transport while the amorphous <I>rra</I> block provides mechanical robustness and interdomain connection. To examine the effects of the molecular architecture on the OTFT performance and stretchability, we prepare a series of <I>block</I>-P3HTs having different number-average molecular weight (<I>M</I><SUB>n</SUB>) values of <I>rra</I> blocks (from 0 to 32 kg mol<SUP>-1</SUP>) and a fixed <I>M</I><SUB>n</SUB> of <I>rre</I> blocks (11 kg mol<SUP>-1</SUP>). Thin films of all of the <I>block</I>-P3HTs exhibit a high charge-carrier mobility due to the formation of well-developed edge-on crystallites from the <I>rre</I> blocks confined within the <I>rra</I> domains, leading to a hole mobility of 1.5 × 10<SUP>-1</SUP> cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, which is superior to that of the <I>rre</I> P3HT homopolymer. In addition, the mechanical toughness of <I>block</I>-P3HT thin films is remarkably enhanced by the <I>rra</I> block. While the <I>rre</I> P3HT homopolymer thin film shows a brittle behavior with an elongation at break of only 0.3%, the elongation at break of the <I>block</I>-P3HT thin films increases by a factor of 100, yielding 30.2% with increasing <I>M</I><SUB>n</SUB> of the <I>rra</I> block, without sacrificing the electrical properties. In particular, a noticeable enhancement of both elongation at break and toughness is observed between <I>M</I><SUB>n</SUB> values of the <I>rra</I> block of 8 and 20 kg mol<SUP>-1</SUP>, indicating that the critical molecular weight of <I>rra</I> P3HT plays an important role in determining the mechanical response of the <I>block</I>-P3HT thin films. This study provides guidelines and strategies to improve the mechanical properties of organic electroactive materials without the disruption of optoelectrical properties, which is critical to fabricate high-performance soft electronics.</P> [FIG OMISSION]</BR>

Solution assembly behaviors of poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) amphiphilic rod-coil copolymer

Youngkwon Kim,Hyeong Jun Kim,Jin-Seong Kim,Bumjoon Kim 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

Aqueous Soluble Fullerene Acceptors for Efficient Eco-Friendly Polymer Solar Cells Processed from Benign Ethanol/Water Mixtures

Kim, Youngkwon,Choi, Joonhyeong,Lee, Changyeon,Kim, Youngwoong,Kim, Changkyun,Nguyen, Thanh Luan,Gautam, Bhoj,Gundogdu, Kenan,Woo, Han Young,Kim, Bumjoon J. American Chemical Society 2018 Chemistry of materials Vol.30 No.16

<P>We present a new series of fullerene derivatives that exhibit solubility in ethanol/water solvent mixtures and implement these materials to fabricate polymer solar cells (PSCs) using environmentally benign solvents. In order to simultaneously optimize the processability of the fullerenes in ethanol/water solvent mixtures and device performance, different fullerene mono-adducts were designed by introducing oligoethylene glycol side chains with different lengths and number of branches. As a result, we achieved power conversion efficiencies up to 1.4% for PSCs processed from benign ethanol/water mixtures in air. Significantly, the new alcohol/water-soluble fullerene derivatives displayed electron mobilities up to 1.30 × 10<SUP>-4</SUP> cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, 150 times higher than those of a previously reported alcohol-soluble fullerene bis-adduct, owing to efficient packing of the fullerenes. Femtosecond transient absorption spectroscopy revealed the acceptor side chain to markedly impact geminate and/or nongeminate charge recombination in the PSCs. In addition, side chain optimization of these fullerenes produced well-intermixed morphologies with high domain purity when blended with p-type polymer to provide hole and electron transport pathways. Our results provide important guidelines for the design of electroactive materials for safe and environmentally benign fabrication of PSCs and other organic electronic devices.</P> [FIG OMISSION]</BR>

Architectural Effects on Solution Self-Assembly of Poly(3-hexylthiophene)-Based Graft Copolymers

Kim, Youngkwon,Kim, Hyeong Jun,Kim, Jin-Seong,Hayward, Ryan C.,Kim, Bumjoon J. American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.3

<P>While solution assembly of conjugated block copolymers has been widely used to produce long 1-D nanowires (NWs), it remains a great challenge to provide a higher level of control over structure and function of the NWs. Herein, for the first time, we report the solution assembly of graft copolymers containing a conjugated polymer backbone in a selective solvent and demonstrate that their self assembly behaviors can be manipulated by the molecular structures of the graft copolymers. A series of poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP) copolymers was designed with two different architectural parameters: grafting fraction (f(g)) and molecular weight of P2VP chains (M-n,M-P2VP) on the P3HT backbone. Interestingly, crystallization of the P3HT-g-P2VP copolymers was systematically modulated by changes in f(g) and M-n,M-P2VP, thus allowing for control of the growth kinetics and curvatures of solution-assembled NWs. When M-n,M-P2VP (4.4 to 15.1 kg/mol) or fg (2.8 to 9.2%) of the P3HT-g-P2VP polymers was increased, the crystallinity of the copolymers was reduced significantly. Steric hindrance from the grafted P2VP chains apparently modified the growth of NWs, leading to shorter NWs with a greater degree of curvature for graft copolymers with more hindrance. Therefore, we envision that such conjugated chain-based graft copolymers can be versatile building blocks for producing NWs with controlled length and shape, which can be important for tailoring the optical and electrical properties of NW-based devices.</P>

Regioregularity controlled phase behavior for Poly(3-hexylthiophene): A combined study of simple coarse-grained simulation and experiment

Kim, Hyeong Jun,Kim, Jin-Seong,Kim, Youngkwon,Jung, Yeon Sik,Kim, Bumjoon J.,Kim, YongJoo Elsevier 2019 Polymer Vol.178 No.-

<P><B>Abstract</B></P> <P>In this study, we developed a simple coarse-grained simulation model framework to investigate the effect of regioregularity (RR) on the crystallization behavior of poly(3-hexylthiophene) (P3HT). To describe the regio-chemistry of P3HT, two different coarse-grained beads were designed to contain either regio-regularly substituted head-to-tail (HT) orientations or regio-irregularly substituted non-HT orientations, and two beads were randomly incorporated in a single polymer where the total RR was tuned from regio-random (RR = 50%) to regio-regular (RR = 100%). Based on our modeling, the crystallization behaviors in both bulk and solution states were investigated. As the number of irregularly substituted non-HT orientations increased, crystallization temperature in the bulk shifted to a lower temperature. When the RR of P3HT was lower than a critical RR value, which was 72.2% in our study, the crystallization of the P3HT chains was eventually suppressed. In the solution state, most of high RR P3HT chains stacked in parallel to produce nanowire (NW) structure to maximize the number of π-stackings in the system, whereas the P3HTs formed a globule structure when the RR value decreased below critical RR. To experimentally validate our simulation results, we synthesized a series of P3HTs having precisely controlled RRs from 66% to 95% with comparable molecular weights to the simulation. Well-matched experimental results suggested that our simplified model provides efficient computational guidance to describe the RR effect on crystalline feature of P3HTs for the various possible applications in organic optoelectronics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Simple coarse-grained model is developed to describe the effect of regioregularity (RR) on crystallization of P3HT. </LI> <LI> Experimental validation with a series of P3HTs having a wide range of RR from 66% to 95% is followed. </LI> <LI> Our model predicts critical RR value for crystallization of P3HT in bulk and solution. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Architectural Engineering of Rod–Coil Compatibilizers for Producing Mechanically and Thermally Stable Polymer Solar Cells

Kim, Hyeong Jun,Kim, Jae-Han,Ryu, Ji-Ho,Kim, Youngkwon,Kang, Hyunbum,Lee, Won Bo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2014 ACS NANO Vol.8 No.10

<P>While most high-efficiency polymer solar cells (PSCs) are made of bulk heterojunction (BHJ) blends of conjugated polymers and fullerene derivatives, they have a significant morphological instability issue against mechanical and thermal stress. Herein, we developed an architecturally engineered compatibilizer, poly(3-hexylthiophene)-<I>graft</I>-poly(2-vinylpyridine) (P3HT-<I>g</I>-P2VP), that effectively modifies the sharp interface of a BHJ layer composed of a P3HT donor and various fullerene acceptors, resulting in a dramatic enhancement of mechanical and thermal stabilities. We directly measured the mechanical properties of active layer thin films without a supporting substrate by floating a thin film on water, and the enhancement of mechanical stability without loss of the electronic functions of PSCs was successfully demonstrated. Supramolecular interactions between the P2VP of the P3HT-<I>g</I>-P2VP polymers and the fullerenes generated their universal use as compatibilizers regardless of the type of fullerene acceptors, including mono- and bis-adduct fullerenes, while maintaining their high device efficiency. Most importantly, the P3HT-<I>g</I>-P2VP copolymer had better compatibilizing efficiency than linear type P3HT-<I>b</I>-P2VP with much enhanced mechanical and thermal stabilities. The graft architecture promotes preferential segregation at the interface, resulting in broader interfacial width and lower interfacial tension as supported by molecular dynamics simulations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-10/nn503823z/production/images/medium/nn-2014-03823z_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn503823z'>ACS Electronic Supporting Info</A></P>

Modulating Regioregularity of Poly(3-hexylthiophene)-based Amphiphilic Block Copolymers To Control Solution Assembly from Nanowires to Micelles

Kim, Youngkwon,Kim, Hyeong Jun,Kim, Jin-Seong,Yun, Hongseok,Park, Hyeonjung,Han, Junghun,Kim, Bumjoon J. American Chemical Society 2018 Chemistry of materials Vol.30 No.21

<P>In selective solvents, poly(3-hexylthiophene) (P3HT)-based block copolymers (BCPs) assemble into one-dimensional nanowires (NWs) due to strong π-π stacking interactions of the P3HT block. Herein, we report the effect of P3HT regioregularity (RR) on the assembly of P3HT-based amphiphilic BCPs in solution. We synthesized a series of P3HT-<I>block</I>-poly(2-vinylpyridine) (P3HT-<I>b</I>-P2VP) copolymers with similar molecular weights and P3HT volume fractions but with different RRs, ranging from 55% to 95%, and studied their assembly in tetrahydrofuran/<I>n</I>-butanol mixtures. P3HT-<I>b</I>-P2VP copolymers with high RR (>80%) crystallized into well-ordered NWs with core widths consistent with fully extended P3HT chains. In BCP nanostructures with decreasing RR, more flexible P3HT chains produced gradual increases in the width of the NWs, from 12 to 24 nm. Eventually, a morphological transition to spherical micelle structures was observed at 55% RR. The structural differences were visualized by incorporating Au nanoparticles, which locate at the interface of P3HT and P2VP blocks, onto the NWs and imaging the resulting hybrid nanostructures by transmission electron microscopy. In addition, the crystalline behaviors of the assembled nanostructures were determined using differential scanning calorimetry and grazing incidence X-ray scattering. We elucidated important relationships between the solution assembly behaviors and the crystalline interactions of conjugated semicrystalline-coil BCPs, which will guide design of future versatile BCP nanostructures.</P> [FIG OMISSION]</BR>

Temperature Measurement Techniques for RAON Cryomodule

Kim, Heetae,Jung, Yoochul,Jo, Yong Woo,Lee, Min Ki,Choi, Jong Wan,Kim, Youngkwon,Kim, Juwan,Paeng, Won-Gi,Kim, Moo Sang,Jung, Hoechun,Kwon, Young Kwan The Korean Vacuum Society 2018 Applied Science and Convergence Technology Vol.27 No.2

Conducting and semiconducting temperature sensors are calibrated and applied to cryomodules. The definition of temperature is introduced and the pressure in vacuum is shown as a function of temperature. The resistance of Drude model is shown as a function of carrier density and mean free path. Temperature sensors are calibrated with Physical Property Measurement System (PPMS). The temperature sensors are applied to measure temperature accurately in RAON cryomodules.

방전 및 산화촉매 필터로 구성된 디젤 배기계의 성능평가

김영권(Youngkwon Kim),김태화(Taehwa Kim),김민우(Minwoo Kim),신귀수(Gwisu Shin),김근주(Keunjoo Kim),오영택(Young Taig Oh) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_1

The high-voltage discharge/oxidation catalyst filter was designed to reduce the particulate emission in automobile. The filter was located on the exhaust pipe of engine. The electrical power of low current which have the high voltage was applied. The experimental measurement on smoke density was performed by the implementation of the automobile named, "Carnival", a product of KIA Motor ㏇ at the uniform engine speed and brake on. The smoke opacity in optical absorption measurement showed that the high voltage discharge/oxidation catalyst filter leads to reduce the amount of emission. To characterize the performance of the filter, we used various experimental equipment. The results showed that the adoption of filter reduced the amount of the particulate matters.