Title page for ETD etd-04262011-153424

Type of Document Dissertation
Author Ok, Jeong Tae
Author's Email Address jok1@lsu.edu
URN etd-04262011-153424
Title Droplet Motion on Miniaturized Ratchets
Degree Doctor of Philosophy (Ph.D.)
Department Engineering Science (Interdepartmental Program)
Advisory Committee
Advisor Name Title
Park, Sunggook Committee Chair
Choi, Jin-Woo Committee Member
Murphy, Michael C. Committee Member
Nikitopoulos, Dimitris E. Committee Member
Wong, Harris Committee Member
Kundu, Sukhamay Dean's Representative
  • Superhydrophobic
  • Ratchets
  • Micro/nanofabrication
  • Leidenfrost
Date of Defense 2011-04-06
Availability unrestricted
The main objective of this study is to evaluate the feasibility of using miniaturized asymmetric structures to move liquid droplets and understand the driving mechanism. We developed the fabrication process for large area topological ratchets with the period ranging from millimeter down to sub-micrometer using micromachining techniques. Non-wetting superhydrophobic surfaces were successfully fabricated using soft UV or thermal nanoimprint lithography, reactive ion etching by oxygen plasma, and chemical surface modification by fluorinated silane vapor deposition. An accurate and reproducible experimental setup equipped with high speed camera and automatic injection system was established. Image processing tools allowed us to obtain various critical information related droplet motion and behavior along the ratchets surface. Various influences on the motion such as the surface temperature, ratchets dimension, surface wettability, droplet volume, kind of liquid, initial impact speed of droplet, polymer additive, and surface slope were systematically investigated for miniaturized non-wetting asymmetric ratchets. It is observed that the droplet motion on the ratchets is strongly dependent on the ratchets dimensions as well as the surface temperature. Extremely fast water droplet motion was achieved from the sub-micrometer ratchets near the Leidenfrost temperature. Even though the Leidenfrost-miniaturized ratchets system can be considered as an efficient pumping and cooling component, further intensive study to reduce the operating temperature and drive the liquid motion within microchannel is required for the broad range of applications.
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