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. 2018 Sep 14;9(9):468.
doi: 10.3390/mi9090468.

Structural Formation of Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) Droplets in PDMS Device Using Protrusion Channel without Hydrophilic Surface Treatment

Dong Hyun Yoon  1 , Daiki Tanaka  2 , Tetsushi Sekiguchi  3 , Shuichi Shoji  4
Affiliations

Structural Formation of Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) Droplets in PDMS Device Using Protrusion Channel without Hydrophilic Surface Treatment

Dong Hyun Yoon et al. Micromachines (Basel). .

Abstract

This paper presents a simple method of droplet formation using liquids that easily wet polydimethylsiloxane (PDMS) surfaces without any surface treatment. Using only structural features and uniform flow focusing, Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) droplets were formed in the full PDMS structure. Extrusion channel and three-dimensional flow focusing resulted in effective fluidic conditions for droplet formation and the droplet size could be precisely controlled by controlling the flow rate of each phase. The proposed structure can be utilized as an important element for droplet based research, as well as a droplet generator.

Keywords: double emulsion; microdroplet; polydimethylsiloxane; three-dimensional structure.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Principle of droplet formation for highly wettable liquid using protrusion channel and three-dimensional focusing.
Figure 2
Figure 2
Flow distribution at the junction for droplet formation. (A) Protrusion-end structure; and, (B) Flat-end structure. (C) Velocity distributions in the axial direction at the junction area.
Figure 3
Figure 3
Images of three-dimensional device. (A) Schematic view and detailed dimensions of the units; (B) Microscopic images of the polydimethylsiloxane (PDMS) units and stacked structure.
Figure 4
Figure 4
Visualization of the oil droplet (Oil-in-Water (O/W)) formation at the protrusion junction and the outside device.
Figure 5
Figure 5
(A) Droplet formation result without protrusion structure; (B) Recovered formation of oil droplet via oil washing at the junction area with protrusion structure.
Figure 6
Figure 6
Control of the droplet size via flow rates of continuous phase flow (A) and dispersed phase flow (B).
Figure 7
Figure 7
Visualization of the double layer (Water-in-Oil-in-Water (W/O/W)) droplet formation at the protrusion junction.
Figure 8
Figure 8
Control of the droplet size via flow rates of core phase flow (A,D), shell phase flow (B,E), and continuous phase flow (C).
See this image and copyright information in PMC

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