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A Free-Standing Self-Assembled Tubular Conjugated Polymer Sensor
Oh, Seungwhan,Uh, Kyungchan,Jeon, Seongho,Kim, Jong-Man American Chemical Society 2016 Macromolecules Vol.49 No.16
<P>Tubular materials created by self-assembly of small organic molecules have gained great attention recently. Fabrication of tubular structures that have precise dimensions by using conventional self-assembly approaches is extremely challenging. Herein we describe fabrication of a free-standing tubular polydiacetylene (PDA) sensor based on the meniscus guided self-assembly and polymerization of diacetylene (DA) Microtube monomers. The free-standing single PDA tube can be utilized as an unprecedented microcapillary-based sensor system, which requires only a minimum amount (70-140 nL) of an analyte solution. We have observed 4 orders of magnitude more sensitive to analytes than is a conventional PDA sensor when a biotinfunctionalized PDA tube is exposed to streptavidin. The microcapillary-based analytical method developed in this study should find great utility not only for PDA sensors but also for other free-standing wire sensor systems.</P>
트리아진 코어를 지니는 초분자 고분자의 광화학적 상전이 거동
오승환(Seungwhan Oh),Yashwardhan R. Malpani,정영식(Young-Sik Jung),김종만(Jong-Man Kim) 한국고분자학회 2016 폴리머 Vol.40 No.4
트리아진(triazine) 코어를 중심으로 아조벤젠을 말단기로 갖는 광 감응성 화합물을 합성하고, 초분자 구조체를 제조하여 용매에 따른 구조적 특성을 조사하였다. 트리아진 유도체 N2,N4,N6-tris(4-((E)-phenyldiazenyl) phenyl)-1,3,5-triazine-2,4,6-tricarboxamide(Azo-TA)를 디메틸설폭사이드와 디메틸포름아마이드 용매에 녹인 후, 증류수를 첨가해 섬유상의 초분자 고분자구조체를 만들었다. 아조벤젠의 광이성질화에 의해, 365 nm 파장의 자외선을 조사하면 초분자 구조의 분해가 일어나고, 400 nm 파장 이상의 가시광선을 조사하면 초분자 구조의 재조립이 일어나는 것을 확인하였다. A photoresponsive azobenzene derivative having a triazine core moiety was prepared. Self-assembly of the triazine containing azobenzene derivative (Azo-TA) in aqueous dimethylsulfoxide and N,N-dimethylformamide afforded fibrous supramolecular polymers. Melting and regeneration of the supramolecular polymer were observed with alternative 365 nm UV and visible light irradiation by reversible cis-trans isomerization of azobenzene moieties.
백승환(Seungwhan Baek),유이상(Isang Yu),신재현(Jaehyun Shin),박광근(Kwangkun Park),정영석(Youngsuk Jung),조기주(Kiejoo Cho),오승협(Seunghyub Oh) 한국추진공학회 2021 한국추진공학회지 Vol.25 No.4
Understanding the liquid propellant transport phenomena in low gravity is essential for developing Korea Space Launch Vehicle (KSLV) upper-stage for the diversity of space missions. A low-gravity environment can be simulated via the free-fall method on the ground; however, the air drag is inevitable. To reduce air resistance during free fall, air-drag shield is usually adopted. In this study, the free-fall method was performed with an air-drag shield from a 7-m height tower. The acceleration of a falling object was measured and analyzed. Low gravity below 0.01 g was achieved during 1.2-s free fall with the air-drag shield. The minimum gravitational acceleration value at 1.2-s after free fall was ±0.005 g, which is comparable to the value obtained from Bremen drop tower experiments, ±0.002 g. A prolonged free-fall duration may enhance the low-gravity quality during the drop tower experiments.
한국형발사체 축소형 추진기관 시험 설비(R-PSTC) 현황
백승환(Seungwhan Baek),유이상(Isang Yu),박광근(Kwangun Park),정영석(Yungsuk Jung),조기주(Kiejoo Cho),오승협(Seunghyub Oh) 한국추진공학회 2021 한국추진공학회 학술대회논문집 Vol.2021 No.5
한국형발사체 누리호(KSLV-II)는 액체산소와 케로신을 이용한 우주운송수단이다. 발사체의 추진기관 검증 모델 개발을 위하여 축소형 추진기관 시험 설비가 개발되었다. 축소형 추진기관 시험설비는 액체 추진제의 배출 과정을 관찰하는 시험 설비로 액체 추진제 저장탱크와 부수 설비로 이루어져 있다. 추진기관 운용을 위한 추진제 수위 계측 장치, 추진제 소진 감지 장치 또한 검증할 수 있도록 시험 장치를 개발하였다. 고온 헬륨 열교환기가 구비되어 있어 액체 추진기관의 가압 과정을 최대한 유사하게 모사할 수 있다. 본 논문에서는 추진기관 축소형 시험설비의 현황과 운용 결과에 대하여 요약한다. The Korean launch vehicle Nuri is a space transportation vehicle that uses liquid oxygen and kerosene. In order to develop a propulsion engine verification model for a launch vehicle, a reduced propulsion system test complex was developed. The reduced propulsion system test complex is a facility that observes the charge/discharge process of the liquid propellant, and consists of a cryogenic liquid propellant tank and ancillary facilities. Moreover, it can verify the propellant level measurement device and liquid depletion detect device for the operation of the propulsion system. The high-temperature helium heat exchanger allows the simulate the pressurization process of propulsion system as closely as possible. This paper summarizes the current status and operation results of the propulsion engine scale-down test facility.
백승환(Seungwhan Baek),유이상(Isang Yu),박광근(Kwangkeun Park),정영석(Youngsuk Jung),조기주(Kiejoo Cho),오승협(Seunghyub Oh) 한국추진공학회 2020 한국추진공학회 학술대회논문집 Vol.2020 No.11
KSLV 상단의 임무의 다각화를 위해서는 저중력 환경에서 액체 추진제의 거동을 정확히 파악하고 있어야 한다. 지상에서 저중력 환경을 모사하는 방법은 자유낙하 방법이 있지만, 공기저항이 항상 동반된다. 공기 저항을 제거하기 위하여 공기 저항 보호막을 이용한 낙하 시험을 진행하였다. 공기 저항 보호막 내부에 시험체를 위치하고 7 m 높이에서 1.2초 동안 낙하하여 시험체의 저중력 환경을 조성하였다. 낙하하는 동안 0.01g 이하의 중력가속도를 측정하였다. 지표면에 도달하기 전 최소 가속도는 약 0.005g였다. 이는 Bremen drop tower에 비하여 0.003g 높은 값이지만, 추후 낙하 높이 및 낙하 시간이 증가한다면 개선될 수 여지가 있다. Understanding of liquid propellant transport phenonma in the low gravity is essential for the development of KSLV upper-stage for the diversity of space mission. The low gravity environment can be simulated by free-fall method on the ground, however, the air-drag is inevitabble. To reduce the air resistance during the free fall, the air-drag shield adopted. In this study, free fall method performed with air-drag shield from 7 m height tower. The acceleration of falling object was measured and analyzed. The low gravity below 0.01g achieved during 1.2 seconds of free fall with the drag shield. The lowest gravitational acceleration value was 0.005g. The minimum gravitational acceleration value was compared with Bremen drop tower experiments, and experimental showed 0.003g higher value. The longer free fall duration may enhance the low gravity quality during the drop experimental.
A light-driven supramolecular nanowire actuator
Lee, Junho,Oh, Seungwhan,Pyo, Jaeyeon,Kim, Jong-Man,Je, Jung Ho The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.15
<P>A single photomechanical supramolecular nanowire actuator with an azobenzene-containing 1,3,5-tricarboxamide derivative is developed by employing a direct writing method. Single nanowires display photoinduced reversible bending and the bending behavior follows first-order kinetics associated with azobenzene photoisomerization. A wireless photomechanical nanowire tweezers that remotely manipulates a single micro-particle is also demonstrated.</P>
Stimulus-Responsive Azobenzene Supramolecules: Fibers, Gels, and Hollow Spheres
Lee, Sumi,Oh, Seungwhan,Lee, Joosub,Malpani, Yashwardhan,Jung, Young-Sik,Kang, Baotao,Lee, Jin Yong,Ozasa, Kazunari,Isoshima, Takashi,Lee, Sang Yun,Hara, Masahiko,Hashizume, Daisuke,Kim, Jong-Man American Chemical Society 2013 Langmuir Vol.29 No.19
<P>Novel, stimulus-responsive supramolecular structures in the form of fibers, gels, and spheres, derived from an azobenzene-containing benzenetricarboxamide derivative, are described. Self-assembly of tris(4-((<I>E</I>)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxamide (<B>Azo-1</B>) in aqueous organic solvent systems results in solvent dependent generation of microfibers (aq DMSO), gels (aq DMF), and hollow spheres (aq THF). The results of a single crystal X-ray diffraction analysis of <B>Azo-1</B> (crystallized from a mixture of DMSO and H<SUB>2</SUB>O) reveal that it possesses supramolecular columnar packing along the <I>b</I> axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the <B>Azo-1</B> fibers. UV irradiation of the microfibers, formed in aq DMSO, causes complete melting while regeneration of new fibers occurs upon visible light irradiation. In addition to this photoinduced and reversible phase transition, the <B>Azo-1</B> supramolecules display a reversible, fiber-to-sphere morphological transition upon exposure to pure DMSO or aq THF. The role played by amide hydrogen bonds in the morphological changes occurring in <B>Azo-1</B> is demonstrated by the behavior of the analogous, ester-containing tris(4-((<I>E</I>)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxylate (<B>Azo-2</B>) and by the hydrogen abstraction in the presence of fluoride anions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2013/langd5.2013.29.issue-19/la400159m/production/images/medium/la-2013-00159m_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la400159m'>ACS Electronic Supporting Info</A></P>