Stable Horizontal Interface Formation and Separation of a Water/Oil Flow by Microfluidic Reactor Analyzed by Direct Observation and Numerical Simulation

Masaya Miyazaki*, 1, 2, 3, Yoshiko Yamaguchi+, 1, Takeshi Honda#, 1, Hideaki Maeda1, 3
1 National Institute of Advanced Industrial Science and Technology (AIST), Tosu, Saga 841-0052, Japan
2 Department of Advanced Technology Fusion, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan
3 Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan

© 2011 Miyazaki et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Measurement Solution Research Center, National Institute of Advanced Industrial Science and Technology, 807-1, Shuku, Tosu 841-0052, Japan; Tel: +81-942-81-4059; Fax: +81-942-81-3627; E-mail:
+ Deceased. This paper is dedicated to her memory.
# Present Address: Department of Pharmacology, Yamaguchi University Graduate School of Medicine, Japan


A microfluidic system with a wide surface area per unit volume has the potential for use in highly efficient chemical synthesis, separation, and extraction. In the case of efficient water/oil separation and material extraction, it becomes important to form a stable two-layer laminar flow interface. Previously, we developed a silicon/glass microfluidic reactor, in which microchannel inner walls were modified to produce hydrophilic/hydrophobic surface. In this work, flow behavior and separation of this microreactor was evaluated. This microfluidic chip made it possible to form a stable twolayer laminar flow interface between a flow of heavier water and lighter hexane, which were introduced into the upper and lower inlets, respectively. The efficiency in separation was examined using water and hexane. Under certain conditions including the pressure difference between the two outlet surfaces, complete phase separation was achieved. This result indicates that the highly efficient separation and stable interface formed by this microfluidic chip can be applied to immiscible liquid-liquid operations with the complete separation of the liquids at the outlets.

Keywords: Microfluidics, microreactor, surface modification, interface, separation, computational fluid dynamics.