현재 멀티스케일전달현상 연구실은 함께 일할 대학원생, 학부 연구생을 모집하고 있습니다. 기계공학의 전통 분야인 열,유체, 열전달 분야와 최근 활발하게 연구가 이루어지고 있는 에너지/나노 분야의 융복합 연구에 관심이 있는 학생들의 연락을  기다리고 있습니다. (wojchoi@korea.ac.kr)
We are currently looking for postdoc, graduate students, undergraduate students who are interested in the convergence research between thermal-fluid engineering and energy/nano research.  Interested applicants should contact Professor Choi by email.

자가 전파 연소반응을 이용한 망간산화물 기반 전기화학 축전지 성능 향상 및 최적화

금 나노입자 기반 어닐링 공정에 의한 원뿔형 나노포어 어레이의 제작 방법

구조기반 연소파를 활용한 탄소막 코팅 망간 산화물 나노구조체 제작 및 전기화학적 응용

전기장을 이용한 미소채널 내부 이멀젼 기반 이상유체 액적 생성 및 동시 모니터링 기술 개발

조립형 다기능 열메타물질을 통한 국부 열전달 제어

열전물질의 기하학적 구조를 이용한 플렉서블 온도-유속 센서

조립형 열메타물질 기반 점 열원의 국부지역 내 제어

원형 히트 파이프의 성능을 향상시키기 위한 자기조립 다층박막 코팅을 이용한 이중 다공 코팅 층 하이브리드 구조

Mechanical metamaterials as broadband electromagnetic wave absorbers: investigating relationships between geometrical parameters and electromagnetic response

구조 기반 연소 반응을 통한 대면적 마이크로/나노 물질의 간단한 단일 변형 방법

고속 연소 공정 기반 다종금속 활물질을 함유한 다공성 탄소 구조 이중기능 촉매 제작 및 이를 적용한 고성능 아연 공기 전지 전극 개발

MWCNTs/PEI-MWCNTs 자기조립 다층박막 코팅을 통한 원형 히트 파이프의 성능 향상

구조유도 연소반응 기반 금속 폼 내부의 탄소막 코팅 및 슈퍼 커패시터 전극 응용

Boosted thermogalvanic thermopower upon solid-to-liquid phase transition

연소반응 전파를 활용한 마이크로/나노구조 금속산화물의 고속 상변화 구현

Waste Heat-Driven Thermomagnetic Agitator for Advanced Immersion Cooling

멀티스케일 복합 구조 기반 열-유체-에너지 전달 현상 제어

One-step transformation of MnO 2 into MnO 2− x@ carbon nanostructures for high-performance supercapacitors using structure-guided combustion waves

Voltage amplification of thermopower waves via current crowding at high resistances in self-propagating combustion waves

Simultaneous electric production and sizing of emulsion droplets in microfluidics

CNT-형상기억폴리머 복합재 Resin 기반 3D 프린팅 제작 구조체의 열물성 향상

전열 공정 기반 결함 엔지니어링을 이용한 ZIF-67 와 코발트 산화물 나노 구조의 결합 기술 개발 및 아연 공기 배터리의 고성능 산소 촉매 응용

Electrically Assisted Thermal Stamping of Tunable Carbon‐Based Nanofilms for Direct Fabrication of Hydrophobic, Energy Harvesting, and Sensing Devices

고속 줄히팅 전열공정 기반 공기-아연 배터리 양극 소재 내부 3 중 전이금속 나노 구조의 이중 기능 산소 촉매 제작 및 삼상 계면 확장

Manipulation of combustion waves in carbon-nanotube/fuel composites by highly reactive Mg nanoparticles

Arbitrary-Shape Transformation Multiphysics Cloak by Field-Coupling Topology Optimization

나노튜브/화학연료의 동축 구조에서 생성되는 열동력 파도를 이용한 전기 에너지 생성

열동력 파도 기반 복합 자가 충전 시스템

DC-field-driven combustion waves for one-step fabrication of reduced manganese oxide/multi-walled carbon nanotube hybrid nanostructures as high-performance …

One-step fabrication of silver nanosphere-wetted carbon nanotube electrodes via electric-field-driven combustion waves for high-performance flexible supercapacitors

Scalable fabrication of nanopores in membranes via thermal annealing of Au nanoparticles

Thermoelectric–pyroelectric hybrid energy generation from thermopower waves in core–shell structured carbon nanotube–PZT nanocomposites

가열된 금속 와이어 표면에 충돌하는 유체 액적의 거동: 웨버수와 유체의 물리화학적 특성이 충돌 거동에 미치는 영향: 웨버수와 유체의 물리화학적 특성이 충돌 거동에 …

Tunable fabrication of core–shell Ni–MnO 2 hybrid foams through structure-guided combustion waves for binder-free high-performance supercapacitor electrodes

Effects of chemical fuel composition on energy generation from thermopower waves

Enhanced thermopower wave via nanowire bonding and grain boundary fusion in combustion of fuel/CuO–Cu 2 O–Cu hybrid composites

상변화형 박막 구조의 슈퍼렌즈 응용 모델

Combustion-assisted sintering for tunable densification of manganese cobalt oxide layers

Energy and Mass Transport within Hybrid Nanostructures

마이크로파 연소 공정을 통한 3 중 전이금속 나노 구조의 이중 기능 아연 공기 배터리 촉매 연구

structure-guided combustion waves for binder-free high

Soft robotic manipulation and locomotion with a 3d printed electroactive hydrogel

Coherence resonance in a single-walled carbon nanotube ion channel

4D Printing Reconfigurable, Deployable and Mechanically Tunable Metamaterials

Chemically driven carbon-nanotube-guided thermopower waves

Diameter-dependent ion transport through the interior of isolated single-walled carbon nanotubes

The effect of fuel utilization on heat and mass transfer within solid oxide fuel cells examined by three-dimensional numerical simulations

Reactions and mass transport in high temperature co-electrolysis of steam/CO 2 mixtures for syngas production

Evidence for high-efficiency exciton dissociation at polymer/single-walled carbon nanotube interfaces in planar nano-heterojunction photovoltaics

Tunable multifunctional thermal metamaterials: manipulation of local heat flux via assembly of unit-cell thermal shifters

Excess thermopower and the theory of thermopower waves

Sodium-chloride-assisted synthesis of nitrogen-doped porous carbon shells via one-step combustion waves for supercapacitor electrodes

Carbon nanotube-guided thermopower waves

Broadband mechanical metamaterial absorber enabled by fused filament fabrication 3D printing

Combustion-driven synthesis route for tunable TiO2/RuO2 hybrid composites as high-performance electrode materials for supercapacitors

Multiscale porous architecture consisting of graphene aerogels and metastructures enabling robust thermal and mechanical functionalities of phase change materials

Thermal conditions and heat transfer characteristics of high-temperature solid oxide fuel cells investigated by three-dimensional numerical simulations

Scalable Synthesis of Triple‐Core–Shell Nanostructures of TiO 2 @MnO 2 @C for High Performance Supercapacitors Using Structure‐Guided Combustion Waves

Thermo-Chemo-Mechanically Robust, Multifunctional MXene/PVA/PAA-Hanji Textile with Energy Harvesting, EMI Shielding, Flame-Retardant, and Joule Heating Capabilities

Layer-by-layer carbon nanotube coatings for enhanced pool boiling heat transfer on metal surfaces

Rational Design for Optimizing Hybrid Thermo-triboelectric Generators Targeting Human Activities

Wonjoon Choi

Electroactive hydrogels (EAH) that exhibit large deformation in response to an electric field have received great attention as a potential actuating material for soft robots and artificial muscle. However, their application has been limited due to the use of traditional two-dimensional (2D) fabrication methods. Here we present soft robotic manipulation and locomotion with 3D printed EAH microstructures. Through 3D design and precise dimensional control enabled by a digital light processing (DLP) based micro 3D printing technique, complex 3D actuations of EAH are achieved. We demonstrate soft robotic actuations including gripping and transporting an object and a bidirectional locomotion.

Biological ion channels are able to generate coherent and oscillatory signals from intrinsically noisy and stochastic components for ultrasensitive discrimination with the use of stochastic resonance, a concept not yet demonstrated in human-made analogs. We show that a single-walled carbon nanotube demonstrates oscillations in electroosmotic current through its interior at specific ranges of electric field that are the signatures of coherence resonance. Stochastic pore blocking is observed when individual cations partition into the nanotube obstructing an otherwise stable proton current. The observed oscillations occur because of coupling between pore blocking and a proton-diffusion limitation at the pore mouth. The result illustrates how simple ionic transport can generate coherent waveforms within an inherently noisy environment and points to new types of nanoreactors, sensors, and nanofluidic channels based …

The exotic properties of mechanical metamaterials emerge from the topology of micro-structural elements. Once manufactured, however, the metamaterials have fixed properties without the ability to adapt and adjust. Here, we present geometrically reconfigurable, functionally deployable, and mechanically tunable lightweight metamaterials created through four-dimensional (4D) printing. Using digital micro 3D printing with a shape memory polymer, dramatic and reversible changes in the stiffness, geometry, and functions of the metamaterials are achieved.

Theoretical calculations predict that by coupling an exothermic chemical reaction with a nanotube or nanowire possessing a high axial thermal conductivity, a self-propagating reactive wave can be driven along its length. Herein, such waves are realized using a 7-nm cyclotrimethylene trinitramine annular shell around a multiwalled carbon nanotube and are amplified by more than 10 4 times the bulk value, propagating faster than 2 m s −1 , with an effective thermal conductivity of 1.28±0.2 kW m −1 K −1 at 2,860 K. This wave produces a concomitant electrical pulse of disproportionately high specific power, as large as 7 kW kg −1 , which we identify as a thermopower wave. Thermally excited carriers flow in the direction of the propagating reaction with a specific power that scales inversely with system size. The reaction also evolves an anisotropic pressure wave of high total impulse per mass (300 N s kg −1 …

Nanopores that approach molecular dimensions demonstrate exotic transport behaviour and are theoretically predicted to display discontinuities in the diameter dependence of interior ion transport because of structuring of the internal fluid. No experimental study has been able to probe this diameter dependence in the 0.5–2 nm diameter regime. Here we observe a surprising fivefold enhancement of stochastic ion transport rates for single-walled carbon nanotube centered at a diameter of approximately 1.6 nm. An electrochemical transport model informed from literature simulations is used to understand the phenomenon. We also observe rates that scale with cation type as Li + >K + >Cs + >Na + and pore blocking extent as K + >Cs + >Na + >Li + potentially reflecting changes in hydration shell size. Across several ion types, the pore-blocking current and inverse dwell time are shown to scale linearly at low electric field …

The thermo-fluid reacting environment and local thermodynamic state in solid oxide fuel cell (SOFC) stacks were examined by using three-dimensional numerical simulations. Enhancing the performance and durability of the SOFC stacks is essential when a high fuel utilization scheme is implemented to increase the system efficiency and lower system operating costs. In this study, numerical simulations were conducted to elucidate the effect of fuel utilization on heat and mass transfer as the fuel utilization is raised. A high-fidelity three-dimensional physical model was developed incorporating elementary electrochemical reaction kinetics by assuming rate-limiting steps and spatially-resolved conservation equations. The model considers planar anode-supported SOFC stacks and is validated against their electrochemical performance experimentally measured. A parametric study with respect to fuel utilization was …

High temperature co-electrolysis of steam/CO 2 mixtures using solid oxide cells has been proposed as a promising technology to mitigate climate change and power fluctuation of renewable energy. To make it viable, it is essential to control the complex reacting environment in their fuel electrode. In this study, dominant reaction pathway and species transport taking place in the fuel electrode and their effect on the cell performance are elucidated. Results show that steam is a primary reactant in electrolysis, and CO 2 contributes to the electrochemical performance subsequently in addition to the effect of steam. CO 2 reduction is predominantly governed by thermochemical reactions, whose influence to the electrochemical performance is evident near limiting currents. Chemical kinetics and mass transport play a significant role in co-electrolysis, given that the reduction reactions and diffusion of steam/CO 2 mixtures are …

There is significant interest in combining carbon nanotubes with semiconducting polymers for photovoltaic applications because of potential advantages from smaller exciton transport lengths and enhanced charge separation. However, to date, bulk heterojunction (BHJ) devices have demonstrated relatively poor efficiencies, and little is understood about the polymer/nanotube junction. To investigate this interface, we fabricate a planar nano-heterojunction comprising well-isolated millimeter-long single-walled carbon nanotubes underneath a poly(3-hexylthiophene) (P3HT) layer. The resulting junctions display photovoltaic efficiencies per nanotube ranging from 3% to 3.82%, which exceed those of polymer/nanotube BHJs by a factor of 50−100. The increase is attributed to the absence of aggregate formation in this planar device geometry. It is shown that the polymer/nanotube interface itself is responsible for …

Thermal metamaterials, designed by transformation thermodynamics are artificial structures that can actively control heat flux at a continuum scale. However, fabrication of them is very challenging because it requires a continuous change of thermal properties in materials, for one specific function. Herein, we introduce tunable thermal metamaterials that use the assembly of unit-cell thermal shifters for a remarkable enhancement in multifunctionality as well as manufacturability. Similar to the digitization of a two-dimensional image, designed thermal metamaterials by transformation thermodynamics are disassembled as unit-cells thermal shifters in tiny areas, representing discretized heat flux lines in local spots. The programmed-reassembly of thermal shifters inspired by LEGO enable the four significant functions of thermal metamaterials—shield, concentrator, diffuser, and rotator—in both simulation and experimental …

Self-propagating exothermic chemical reactions can generate electrical pulses when guided along a conductive conduit such as a carbon nanotube. However, these thermopower waves are not described by an existing theory to explain the origin of power generation or why its magnitude exceeds the predictions of the Seebeck effect. In this work, we present a quantitative theory that describes the electrical dynamics of thermopower waves, showing that they produce an excess thermopower additive to the Seebeck prediction. Using synchronized, high-speed thermal, voltage, and wave velocity measurements, we link the additional power to the chemical potential gradient created by chemical reaction (up to 100 mV for picramide and sodium azide on carbon nanotubes). This theory accounts for the waves’ unipolar voltage, their ability to propagate on good thermal conductors, and their high power, which is up to 120 …

Heteroatom-doped, multiporous carbon structures are of considerable interest as high-performance electrochemical electrodes. However, their complex and time-consuming synthetic procedures impede a scalable production. Herein, a combustion-driven sodium-chloride-assisted synthesis route of nitrogen-doped, cube-like hierarchical porous carbon shells (N-C-HPCS) is developed for the electrode materials of supercapacitors. Free-standing hybrid films composed of nitrocellulose and NaCl particles serving as the chemical fuel layer and templates are prepared, and self-propagating combustion waves passing through the films within a few seconds fabricate controllable nitrogen-doped porous carbon (N-PC) after the simple removal of the templates by washing. The optimal tuning of thermochemical reactions through the nitrocellulose loadings leads to synthesizing the N-C-HPCS, while other precursors …

Thermopower waves are a new concept for the direct conversion of chemical to electrical energy. A nanowire with large axial thermal diffusivity can accelerate a self-propagating reaction wave using a fuel coated along its length. The reaction wave drives electrical carriers in a thermopower wave, creating a high-power pulse of as much as 7 kW/kg in experiments using carbon nanotubes. We review nanomaterials designed to overcome limitations of thermoelectricity and explore the emerging scientific and practical outlook for devices using thermopower waves.

Rationally designed porous structures are promising as broadband electromagnetic (EM) wave absorbers for counteracting military radar signal or reducing EM interference between electronic components. However, their poor mechanical properties associated with low density limit the scalability. Here, we report a three-dimensional printed, broadband mechanical metamaterial absorber (BMMA) that implements a dual-function of EM wave absorption and reinforced relative stiffness. Based on tuning the lattice unit-cells and comprising materials, the proposed BMMAs feature a multilayered design comprising geometrically optimized octet-truss structures composed of carbon black-based backbone composites. Three-dimensionally printed BMMAs achieve > 90% absorbance (~98.66% on average) for frequencies spanning 5.8–18 GHz, while maintaining nearly constant stiffness per unit mass density of 1.37 at a low …

Hybrids of micro/nanostructured metals/metal oxides have great potential to provide high performance in electrochemical applications such as supercapacitors. However, their synthesis routes involve complex procedures that limit scalable fabrication. Herein, we report a combustion-driven synthesis route for tunable TiO 2 /RuO 2 hybrid composites as high-performance electrode materials for supercapacitors. Self-propagating combustion waves passing through precursors consisting of TiO 2 nanoparticles and combustible nitrocellulose directly fabricated carbon templates as sacrificial layers for the outermost functional metal oxides, while the initial mass loading of nitrocellulose manipulated the residual hybrids. Through substituting the pre-formed carbon templates with RuO 2 , tunable TiO 2 /RuO 2 hybrid composites of core–shell TiO 2 @RuO 2 nanostructures or RuO 2 clusters with embedded TiO 2 nanoparticles were …

Passive thermal energy storage systems using phase change materials (PCMs) are promising for resolving temporal‐spatial overheating issues from small‐ to large‐scale platforms, yet their poor shape stability due to solid–liquid transition incurs PCM leakage and weak resistance against mechanical disturbance, limiting practical applications. While foam‐stable templates for PCMs have shown complement, they reveal massive leakage and collapse of liquefied PCMs under external loads or impacts. Herein, a multiscale porous architecture consisting of graphene aerogels (GAs) and meta structures enabling robust thermal‐mechanical functionalities of PCMs (3D‐MPGA) toward sustainable phase change thermal energy storage composites is reported. 3D‐printed mechanical metamaterials employing octet‐truss cells provide supportive strength and directionally‐assisted leakage reduction, while GAs serve as …

Elucidating internal thermal conditions of high-temperature solid oxide fuel cell (SOFC) stacks is essential for obtaining a substantial thermal efficiency and reliability for long-term operations prior to their commercialization. To examine simultaneous heat transfer and its generation and their effect on the local thermodynamic state, a high-fidelity physical model that resolves spatially the three-dimensional structure of planar, anode-supported SOFC stacks is used in this study. Results show that thermal conduction through metallic interconnects plays a key role in transferring the heat produced by joule heating and electrochemical reactions and thus determining the internal thermal conditions. The heat generated from the electrolyte and thin reactive electrode layers is transferred to the interconnect predominantly by gaseous convection and conduction through materials in the anode and cathode, respectively. The …

Core–shell nanostructures of metal oxides and carbon‐based materials have emerged as outstanding electrode materials for supercapacitors and batteries. However, their synthesis requires complex procedures that incur high costs and long processing times. Herein, a new route is proposed for synthesizing triple‐core–shell nanoparticles of TiO 2 @MnO 2 @C using structure‐guided combustion waves (SGCWs), which originate from incomplete combustion inside chemical‐fuel‐wrapped nanostructures, and their application in supercapacitor electrodes. SGCWs transform TiO 2 to TiO 2 @C and TiO 2 @MnO 2 to TiO 2 @MnO 2 @C via the incompletely combusted carbonaceous fuels under an open‐air atmosphere, in seconds. The synthesized carbon layers act as templates for MnO 2 shells in TiO 2 @C and organic shells of TiO 2 @MnO 2 @C. The TiO 2 @MnO 2 @C‐based electrodes exhibit a greater specific capacitance …

The rapid development of wearable electronics, personal mobile equipment, and Internet of Things systems demands smart textiles that integrate multiple functions with enhanced durability. Herein, the study reports robust and multifunctional textiles with energy harvesting, electromagnetic interference (EMI) shielding, flame resistance, and Joule heating capabilities, fabricated by a facile yet effective integration method using the deposition of cross‐linked MXene (Ti 3 C 2 T x ), poly(vinyl alcohol) (PVA), and poly(acrylic acid) (PAA) onto traditional Korean paper, Hanji via vacuum filtration. Comprehensive analyses confirm robust cross‐linking, structural integrity, and interface stability in the MXene/PVA/PAA‐Hanji (MPP‐H) textiles, which synergistically boost their multifunctional performance. The MPP‐H textiles exhibit remarkable power generation lasting over 60 min with a power density of 102.2 µW cm −3 and an …

Micro/nanotextured coatings have enabled the manipulation of thermal characteristics in pool boiling heat transfer such as the heat transfer coefficient (HTC) and critical heat flux (CHF) because of the ability to optimize bubble formations and departures. However, fabricating such coatings on substrates involves high cost-bulky setup, and is limited by the materials and adhesion properties. Herein, we report layer-by-layer (LbL)-assembled polyethylenimine (PEI)-multi-walled carbon nanotube (MWCNTs) coatings on stainless steel (SS316) to enhance HTC and CHF in pool boiling heat transfer. LbL-assembled PEI-MWCNTs coatings (10, 20, 40 bi-layers) on SS316 were fabricated, whereas bare SS316 substrate and vacuum-filtered MWCNTs coating were prepared as controls. Because of the nano-cavities and the inner-nanoporous structures, LbL coatings showed significant enhancement of HTCs and CHFs …

Despite the rise in Internet of Things devices and mobile electronics, devising an energy harvester with sufficient time-averaged power remains a challenge when targeting human activities. Here, we report a hybrid thermo-triboelectric generator targeting human motion with systematic optimization strategies in frequency feature-size variable spaces. The device consists of bismuth telluride (Bi 2 Te 3 ) tiles with polydimethylsiloxane (PDMS) layers filled in between, thereby harvesting both thermal energy and triboelectricity from human touch. Detailed heat transport analyses reveal that optimal operational frequency for thermoelectrics may be tuned on the basis of the insulation property of PDMS. Meanwhile, triboelectricity exhibits strong feature-size dependence when PDMS is interfaced with high-dielectric thermoelectric materials. The analyses establish the design guidelines for a hybrid energy harvester that …

Platform Development Team Assistant Engineer

MTL @ Korea University

교수님 소개

최원준

연구실 소개

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Electrically Assisted Thermal Stamping of Tunable Carbon‐Based Nanofilms for Direct Fabrication of Hydrophobic, Energy Harvesting, and Sensing Devices

고속 줄히팅 전열공정 기반 공기-아연 배터리 양극 소재 내부 3 중 전이금속 나노 구조의 이중 기능 산소 촉매 제작 및 삼상 계면 확장

마이크로파 연소 공정을 통한 3 중 전이금속 나노 구조의 이중 기능 아연 공기 배터리 촉매 연구

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

최원준

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Electrically Assisted Thermal Stamping of Tunable Carbon‐Based Nanofilms for Direct Fabrication of Hydrophobic, Energy Harvesting, and Sensing Devices

고속 줄히팅 전열공정 기반 공기-아연 배터리 양극 소재 내부 3 중 전이금속 나노 구조의 이중 기능 산소 촉매 제작 및 삼상 계면 확장

마이크로파 연소 공정을 통한 3 중 전이금속 나노 구조의 이중 기능 아연 공기 배터리 촉매 연구

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

우리 연구실 모집