Brown University School of Engineering

Fluids at Brown, Division of Applied Mathematics Fluids and Thermal Sciences, School of Engineering Joint Seminar Series

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Tuesday, April 17, 2018 3:00pm - 4:00pm

Experimental Reaseaches on Interfacial Flow : 1. Double emulsion droplet under high electric field; 2. Tree-inspired pump and actuator Jinkee Lee, PhD School of Mechanical Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea ABSTRACT: In this presentation, I want to show the research results focus on (1) emulsion under high electric field and (2) development of tree mimicking mechanical devices. (1) We investigate numerically, theoretically, and experimentally how EHD deformation and breakup of double emulsion droplet can occur under DC electric fields. Based on comprehensive experiments, we observe four different breakup modes for double emulsion droplet depending on various physical constraints, i.e. viscosity, conductivity, permittivity, and volume fraction between the core and shell fluid. The breakup modes are classified such as a unidirectional breakup mode, two different bidirectional breakup modes, and tip-streaming continuous breakup mode. We obtained phase diagram to depict the different breakup modes which can contribute to control the emulsion droplet shape. Furthermore, we employed a theoretical study to predict the core droplet migration inside the shell. (2) An artificial leaf mimicking structure using hydrogel, which has a nanoporous structure is fabricated. The cryogel method is used to develop a hierarchy structure on the nano- and microscale in the hydrogel media that is similar to the mesophyll cells and veins of a leaf, respectively. The suction pressure of the artificial leaf is affected by several variables (e.g., pore size, wettability of the structure, nano particle modification). Finally, by decreasing the pore size and increasing the wettability, the maximum negative pressure of the artificial leaf, 7.9 kPa is obtained. Also, We have developed a hygromorphic metallic oxide monolayer film capable of actuation by electrochemically producing superhydrophilic free-standing nano-capillary forest of titanium oxide with an anatase crystal structure of high aspect ratio (~80) nano capillaries. This hygromorphic metallic monolayer is activated by the generation of forces from the spreading and capillary-driven imbibing into nano gaps during hydration and evaporation. This system possesses a great stability and repeatability for long time usage and has a high bending energy density of ~1250 kJ/m3. The results suggest that these hygromorphic structures could possibly exhibit high energy densities and therefore potentially play important roles for external stimuli-responsive materials that are efficient energy converters and actuators. Biography: Prof. Jinkee Lee received B.S. and M.S. degrees in Mechanical Engineering from Korea Advanced Institute of Science and Technology (KAIST), Korea in 1997 and 1999, respectively, and Ph.D. degree from Brown University in 2008, where he held the prestigious Simon Ostrach Fellowship. Following his graduate studies, he was a Postdoctoral Research Fellow at jointly in School of Engineering and Applied Science and Department of Organismic and Evolutionary Biology in Harvard University from 2008 to 2009, then moved back to Brown University as an Assistant Professor (Research) in School of Engineering from 2009 to 2011. In 2012, he joined Sungkyunkwan University (SKKU), where he is currently Associate Professor and Director of Multiscale Fluid Mechanics Laboratory in School of Mechanical Engineering. His research interests is the Interfacial Flow & Transport Phenomena and their Applications falls under the area of Mechanical Engineering, Chemical Engineering, Material Science, Physics and Micro-/Nano-Technologies. He has published 48 peer-reviewed journal articles. He was a recipient of the SKKU Teaching Award 2016 awarded by President of SKKU, which is chosen by evaluating level of contribution, innovation for education and passions for teaching.