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Micromachines (Basel). 2018 Oct 20;9(10). pii: E533. doi: 10.3390/mi9100533.

Numerical Demonstration of In-Tube Liquid-Column Migration Driven by Photoisomerization.

Author information

1
Department of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan. 7517651@ed.tus.ac.jp.
2
Department of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan. tsuka@rs.tus.ac.jp.
3
Water Frontier Science & Technology Research Center (W-FST), Research Institute for Science & Technology, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan. tsuka@rs.tus.ac.jp.

Abstract

Droplet manipulation by light-induced isomerization was numerically demonstrated and investigated regarding the driving mechanism. Such a non-invasive manipulation of a droplet in a microchannel can be realized, for example, by the use of watery solution of photoresponsive surfactant that exhibits the isomerization. Due to variable fluid properties between the cis and trans isomers, one-side light irradiation on a liquid column in a tube would lead to some kind of imbalance between the two ends of the liquid column and then drive droplet migration. The present numerical simulations of air⁻liquid two-phase flow and its scalar transport of the isomer, considering the variable static contact angle, agreed quantitatively with the experimental results in terms of the migration speed. This fact supports the contention that the droplet migration is more likely to be driven by an imbalance in the wettability, or the contact angle. The migration speed was found to be less dependent on the liquid-column length, but proportional to the tube diameter.

KEYWORDS:

computational fluid dynamics; droplet manipulation; lab-on-a-chip; microfluidics; non-invasive control; photochemical reaction; photoresponsible surfactant; surface tension; two-phase flow; wettability

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