Look through the object in nano(micro)scale
Prof. Jung Ho Je
Department of Materials Science
Date & Time
Tuesday, 8 January 2019
Room 7-37, Haking Wong Building, HKU
Despite recent advanced science and technology, the visualization through bulk objects in nano or micro-scale is a challenge. Here we develop x-ray imaging that enables us to visualize through bulk drops the micro/nano ultrafast dynamics, contributing to solving out many long-standing scientific issues.
When a liquid drop impacts a solid surface, air is generally entrapped underneath. Using ultrafast x-ray imaging, we directly visualize the profile of an entrapped air film and its evolution into a bubble during drop impact. We identify a complicated evolution process that consists of three stages .
A bubble reaching an air-liquid interface usually bursts and forms a liquid jet. Jetting has been mostly observed for large bubbles (R >> 100μm) but rarely for small bubbles (R < 100μm). Here we show that jet formation is inhibited by bubble size, which results in elucidating jetting mechanism . A vortex is a flow phenomenon that is very commonly observed in nature.
Despite long studies more than a century, the origin of the vortices and their dynamics remain unclear. With ultrafast X-ray phase-contrast imaging, we show that the formation of vortex rings originates from the energy transfer by capillary waves generated at the moment of the drop impact .
One of the most questionable issues in wetting is the force balance that includes the vertical component of liquid surface tension. On soft solids, the vertical component leads to a microscopic protrusion of the contact line, that is, a ‘wetting ridge’. The wetting principle determining the tip geometry of the ridge is at the heart of the issues over the past half century. Here we reveal a universal wetting principle from the ridge tips directly visualized with high spatio-temporal resolution of x-ray imaging .
Finally, a unique method of nanowire growth with position-selectivity that has been developed from using x-ray imaging is demonstrated with a few of striking applications [5,6].
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 J.H. Lee et al, Adv. Mater. 28, 4071 (2016).
Prof. Jung Ho Je is a professor of Materials Science Engineering at POSTECH Korea and director of X-ray Imaging Center (http://xic.postech.ac.kr/). He received his Ph.D. in Materials Science and Engineering from KAIST in 1983. Prof. Je’s research interests include X-ray imaging for soft matter dynamics and biomedical science, nanowire-based optoelectronics, and nanowire cell endoscopy. He has published 6 book chapters and over 300 SCI papers. He is currently a Section Editor-In-Chief in Materials and Editorial board in Scientific Reports. He is a recipient of POSTECHIAN Prize in Research (2015.12), Su-Dang Award (2015.05), Nam-go Chair Professor (2014.03 ~ 2017.02), Excellent Class Award for Deriving Active Learning (2012), Gyungbuk Provincial Science and Technology Grand Prize (2005. 04.), Korea Industry and Technology Grand Prize (2004. 10.), Shim-Gyeh Science Award (KOSUA) (2003. 11.), Outstanding Swiss-Korea Researcher Award (SSA/MOST) (2003. 05.), Scientist of the Month Award (KOSEF) (2002. 12.)
Advanced Materials and Thermofluids