Surface-Tension-Based Micromechanical Engineering
While a regular volume of liquids needs to be bounded by solid walls (such as in a bottle), a small volume can stay as a droplet, which is bounded by the surface tension of its meniscus. However, surface tension has rarely been used in mechanical designs because the sub-millimeter world has been irrelevant until the advent of MEMS. Our lab has long been exploring mechanical engineering based on surface tension, establishing fundamental knowledges and developing unique microdevices. To demonstrate the effectiveness of proper mechanical engineering in microscale, this talk will present three examples that started with a completely new design concept but reached commercialization. (1) By designing a virtual check valve using the surface tension of vapor bubbles in a microchannel, we have developed a high-performance inkjet printhead, which was later commercialized. (2) By actuating liquid droplets with only voltage signals, we have developed electrowetting-on-dielectric (EWOD) technology, which led to the field of digital microfluidics (DMF) and multiple commercial products today. (3) By repelling water with surface tension, a superhydrophobic (SHPo) surface prevents water from spreading and instead letting its droplets roll on it. The SHPo surface can even be designed to repel “all” available liquids. Although hydrodynamic drag reduction has been the most highly anticipated application of the SHPo surfaces, the success has remained elusive in practical conditions. Identifying and solving the key problems using MEMS, we have obtained a drag reduction of about 30% under a motorboat speeding on open sea. This is a rare example of applying microfluidics to a large-scale application.
Professor CJ Kim is a Distinguished Professor and holds the Volgenau Endowed Chair in Engineering in the Mechanical and Aerospace Engineering Department of the University of California, Los Angeles (UCLA). He received B.S. from Seoul National University, M.S. from Iowa State University, and Ph.D. from the University of California, Berkeley, and had a postdoctoral visit to the University of Tokyo before joining UCLA in 1993. Directing the Micro and Nano Manufacturing Lab, Prof. Kim performs research in MEMS with a focus on utilizing surface tension. The recipient of Research Excellence Award (Iowa State Univ.), TRW Outstanding Young Teacher Award (UCLA), CAREER Award (NSF), Achievement Award (ALA), Samueli Outstanding Teacher Award (UCLA), Ho-Am Prize in Engineering (the Ho-Am Foundation), Robert Bosch Micro and Nano Electro Mechanical Systems Award (IEEE), he has been involved with numerous professional activities, including General Chair of the 2014 IEEE International Conference on MEMS. An ASME Fellow, IEEE Fellow, and AIMBE Fellow, he is currently serving on the International Steering Committee of Transducers, on the International Steering Committee of Electrowetting Conference, on the Editorial Board of Micro and Nano Systems Letters, on the Editorial Advisory Board for the IEEJ Transactions on Electrical and Electronic Engineering, as Co-Editor-in-Chief of Functional Composites and Structures, and as Co-Editor-in-Chief for Droplet. Prof. CJ Kim has also been active in the commercial sector as a consultant, advisor, and startup founder.