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Spatiotemporally Defining Biomolecule Preconcentration by Merging Ion Concentration Polarization
Kwak, Rhokyun,Kang, Ji Yoon,Kim, Tae Song American Chemical Society 2016 ANALYTICAL CHEMISTRY - Vol.88 No.1
<P>The ion concentration polarization (ICP) phenomenon at micronanofluidic interfaces has been extensively utilized to preconcentrate low-abundance biological samples. Although preconcentration by ICP is robust, its multiphysics phenomenon does not permit a clear prediction of the preconcentration conditions and sites. Here, we present a new method for spatiotemporally defining preconcentration, which can generate target-condensed plugs in a very specific region (< 100 mu m) regardless of the operating conditions (time, applied voltage, ionic strength, and pH). In contrast to previous devices that use only ion depletion, this device uses merged ICP zones with opposite polarity, i.e., ion depletion and ion enrichment. In this regard, ICP is initiated between two line-patterned cation exchange membranes. When voltage is applied across two membranes, an ion depletion (enrichment) zone occurs on the anodic (cathodic) side of the membranes. Two ICP zones are then merged and confined between the membranes. Consequently, the preconcentration action is also confined between the membranes. We demonstrate that fluorescent dyes are always preconcentrated at the designated location at all lengths of operating time and at broad voltage (0.5-100 V), ionic strength (I-100 mM KCI), and pH (3.7-10.3) ranges. This device successfully condenses proteins up to 10000-fold in a specific region of the channel (100 X SO X 10 mu m(3)) in 10 min. This Work not only characterizes the unique scientific phenomenon of ICP overlapping but also opens the possibility of integrating ICP preconcentrators into commercial analysis equipment, which requires a known, stationary preconcentration site.</P>
이온농도분극에 의한 와류현상에서 관찰된 유동전단응력-이동장벽 효과
곽노균(Rhokyun Kwak),Van Sang Pham,강지윤,한종윤(Jongyoon Han) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Rotating shear flow is a common tool to suppress turbulence and control transport in plasma physics. Despite the desires to apply this phenomenon to other fields, it has rarely been observed in non-ionized fluids. Here, we visualize this effect on a generic neutral-fluid situation in electro-membrane systems: electroconvective vortex (EC) under Hagen-Poiseuille (HP) flow, which initiated by ion concentration polarization (ICP) on ion exchange membranes. This is the first demonstration of “flow-shear-induced transport barrier” in electrochemical systems, which was found only in magnetized flow previously. Combining scaling analysis and experiment, we capture the effect by pinpointing the threshold for shear suppression. Selected by balancing velocity fluctuation (with EC vortices) and flow shear (with noslip walls), the threshold is scaled as the dimensionless EC height dec/w=0.618. Stable EC occurs under the threshold, while chaotic EC occurs over the threshold by velocity fluctuation overwhelming flow shear. The threshold we identify here has wide applications to prevent chaotic flows in various electro-membrane systems.
UV 나노임프린팅을 이용한 단일(單一) 나노 브리지 구조의 제작
곽노균(Rhokyun Kwak),정훈의(Hoon Eui Jeong),서갑양(kahp Y. Suh) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
In this paper, a simple vacuum-assisted UV nanoimprint lithography (NIL) method is presented for fabricating well-defined monolithic nanobridges. A droplet of UV-curable resin of polyurethane acrylate (PUA) is dispensed and imprinted to form microscale structures with PDMS mold and subsequent curing for several seconds. Under proper conditions, the top layer is partially cured by the trapped air and provides further nanofabrication upon application of a nanoscale PUA mold at vacuum. It is noted that a pressure gradient is generated between a contacting and a non-contacting parts with the mold, resulting in a flow of the partial cured pre-polymer into the void regions. Finally, monolithic nanobridges is fabricated with high aspect ratio in large area. These nanobridges are potentially useful for smart optical and electronic devices.
전단흐름 하에 이온교환막 위에서 발생하는 전기수력학적 와류
곽노균(Rhokyun Kwak) 한국가시화정보학회 2018 한국가시화정보학회지 Vol.16 No.1
Ion exchange membrane can transfer only cation or anion in electrically conductive fluids. Recent studies have revealed that such selective ion transport can initiate electroconvective instability, resulting vortical fluid motions on the membrane. This so-called electroconvective vortex (a.k.a. electroconvection (EC)) has been in the spotlight for enhancing an ion flux in electrochemical systems. However, EC under shear flow has not been investigated yet, although most related systems operate under pressure-driven flows. In this study, we present the direct visualization platform of EC under shear flow. On the transparent silicone rubber, microscale channels were fabricated between ion exchange membranes, while allowing microscopic visualization of fluid flow and ion concentration changes on the membranes. By using this platform, not only we visualize the existence of EC under shear flow, its unique characteristics are also identified: i) unidirectional vortex pattern, ii) its advection along the shear flow, and iii) shear-sheltering of EC vortices.
Solvent-Assisted Decal Transfer Lithography by Oxygen-Plasma Bonding and Anisotropic Swelling
Kim, Pilnam,Kwak, Rhokyun,Lee, Sung Hoon,Suh, Kahp Y. WILEY-VCH Verlag 2010 Advanced Materials Vol.22 No.22
<B>Graphic Abstract</B> <P>Solvent-assisted decal transfer lithography (DTL) enables the formation of well-defined micro-/nanostructures over a large area (∼4 in. wafer) by combining irreversible oxygen bonding and anisotropic swelling of poly(dimethoxylsiloxane) (PDMS). Such swelling-induced stress gradient allows for cohesion failure of the skin layer upon removal of the stamp, leaving behind a highly uniform layer (∼100 nm). <img src='wiley_img_2010/09359648-2010-22-22-ADMA200903440-content.gif' alt='wiley_img_2010/09359648-2010-22-22-ADMA200903440-content'> </P>
Two-step capillary force lithography for fabricating biomimetic, superhydrophobic surfaces
Hoon Eui Jeong(정훈의),Rhokyun Kwak(곽노균),Jae Kwan Kim(김재관),Kahp Y. Suh(서갑양) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Inhibition effects in UV radiation curing by oxygen were utilized for fabricating monolithic, micro/nanoscale hierarchical polymer structures via two-step UV-assisted capillary force lithography. It was found that the UV exposure time for the partial curing of microstructure was a crucial parameter; a shorter exposure time induced collapse of the underlying microstructure while a longer time gave rise to non-fluidity of the microstructure. The partial curing is attributed to inhibition of UV cross linking by trapped or permeated oxygen within mold cavities. Using this method, various dual-scale hierarchical structures were fabricated with minimum resolution to 50 nm over a large area (5×5 ㎠) in a fast and reproducible manner.
대류-확산 모델과 막 변형을 고려한 역전기투석 시스템 최적화
김성훈(Sunghoon Kim),곽노균(Rhokyun Kwak) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Reverse electrodialysis (RED) with ion exchange membranes is one of the promising renewable energy that can create no byproducts. Previous works tested various RED systems with different geometries and flow conditions. Despite those trials could cause the considerable deformation of membranes, no one consider the membrane deformation and corresponding effects on RED yet, even RED prefers to use very thin membranes to reduce the electric resistance of the cell. In this study, we revisit RED system by considering membrane deformation and hydrodynamic characteristics simultaneously. To do this, we solved the governing equations of fluid flows between the membranes and that of solid mechanics of the membrane. As the first step, the optimal ratio of channel’s velocities were evaluated. Here, we found that the net power density was maximized when the velocity ratio of concentrate to dilute is 4 with membrane deformation, while it was maximized when the ratio of 2.33 without the deformation.
마이크로 전기탈이온 시스템: 이온 농도 분석 및 유체 유동 가시화
박수동(Sudong Park),곽노균(Rhokyun Kwak) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Electrodeionization (EDI) is a membrane-based desalination utilizing ion exchange membranes and ion exchange resins. By combining Electrodialysis and Ion exchanger, EDI can produce ultrapure water. Although its theoretical mechanisms are well documented, there is no experimental platform which can observe microscopic details inside of the system. In this paper, we present the microscale EDI that can visualize in situ ion concentration, pH, and fluid flows. This visualization platform was fabricated by filling ion exchange resins as a monolayer in the transparent polydimethylsiloxane channel between cation/anion exchange membranes. According to operating voltages (0-15 V), distinct behaviors of ion concentration profile, pH shift, and fluid flows were observed in Ohmic, limiting, and overlimiting regimes. It is noteworthy that overlimiting regimes can be sub-categorized as a water-splitting and electroconvection regimes, which is a clear departure from the dynamics in electrodialysis and ion exchanger. Although such dynamic behaviors have been predicted previously, this is the first time that they were clearly visualized in a realistic EDI model.