High Throughput Size Controlled Microdroplet Generation�Shuichi Shoji1, Dong Hyun Yoon2, Daiki Tanaka2and Tetsushi Sekiguchi2�1)Faculty of Science and Engineering, Waseda University, Tokyo, JAPAN�2)The Research Organization for Nano & Life Innovation, Waseda University, Tokyo JAPAN���Published in: 2021 21st International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers)�

Presented By: Ajitesh Dhal

Power Mechanical Department

Instructors: Cheng- Hsien Liu

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1

Outline

• Introduction
• Methodology
• Result Analysis
• Conclusion

2

Introduction

• Droplet-based microfluidics is the technology that deals with the formation and manipulation of uniform and micron-sized droplets at extremely high rates
•  A three step half and half size/volume division of source droplet device using three stage cascade channel is introduced
• Passive and active size/volume ratio controllable source droplet division devises are reported next. Finally, two types of microdroplet (daughter) generation devices using hydrodynamic droplet breakup of source droplet (mother) are described

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3

Methodology

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• Developed a multi-step divergence micro flow device which has a three

stage cascade channel structure

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• To achieve uniform division, micro pillars and a separate channel wall are

located at the center of each inlet of the bifurcation points

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• The device was fabricated by Si Deep RIE and Si-Pyrex glass anodic

bonding

4

1)Passive Division/Separation�

Cont..

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Concept of uniform division/separation by the pillars and wall

• In order to achieve uniform division, micro pillars and a separate channel wall are located at the center of each inlet of the bifurcation points

• The dispersed phase liquid of water containing 3 % polyvinyl alcohol and the contentious phase fluid of butyl acetate are introduced to T-junction to generate source droplets.
• High throughput microdroplet generation is achieved by the fact that one droplet is uniformly divided into 16 pieces. The maximum generation rate was about 1760 droplets/sec and the average diameter of the droplets was about37µm. The deviation of the droplet diameter was smaller than 3 %

Cont.…

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SEM image of the shifted pillar of 4th stage bifurcation point

• By modifying pillars and wall bifurcation structure, droplet size/volume ratio controlled division is possible. The concept of the droplet division is shown in Figure. The position of the pillar structures is shifted upper from the center of the channel while the separate channel wall is located at the center

• In actual device, this structure was fabricated at the inlet of final step of a four stage cascade channel whose 1st to 3rd stages have 1:1 division structures
• The inlet flow rate ratio of the continuous phase (Qw) and the dispersed phase (Qo) were fixed at 1:1. Under low flow rate, separated droplet size/volume difference is small
• The maximum droplet generation rate was about 1800 droplet/sec

Cont.…

2)Active Division/Separation

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• If upper channel resistance R1 and lower channel resistance R2 are same, separated droplet volume V1 and V2 is uniform. When channel resistance R1 is much larger than R2, droplet volume V1 is much smaller than V2. The valuable channel resistance is performed with microchannels and horizontal type pneumatic microvalves fabricated by molded PDMS structures

• An actual devise consists of a Y-shaped channel and two microvalves located at outlet channels was fabricated as shown in Figure 7. The divided droplet volume ratio was changed from 1:1 (Valve 1: 0 kPa) to 1:145 (Valve 1: 150 kPa). Constant microdroplet generation of approximately 800 drops/min with volume from 8.62 pl to 1.25 nl was obtained

Result Analysis

• Hydrodynamic droplet division or breakup was applied to generate uniform small droplet using parallel straight side channels
• By employing this structure, the generated daughter droplet returns to the main channel and the device needs only one inlet and one outlet.
• Two types of multi droplet breakup devices of five D-shaped bypass channels connected in series were fabricated using molded PDMS.
• Type A has same bypass channel entrance gaps of 30μm while type B has those of 20, 25, 30, 35 and 40 μm.
• Type A enables uniform daughter droplet generation from 25 μm to 35 μm in diameter under different flow rate ratio of the continuous phase (Qw) and the dispersed phase (Qo), The maximum relative standard deviation of the droplet diameters was 7.8%
• Wide variety of daughter droplets whose sizes ranged from 10 μm to 65 μm was generated at the same time by type B device

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Principles of droplet breakup by the vertical side flow

Conclusion

• Under high flow rate condition, shear-induced tailing of a droplet and tail breakup is occurred, which generates satellite droplet

• By optimizing flow conditions of water and oil flow rates, an appropriate length tail was formed and daughter droplets of a few μm in diameter were generated

• This phenomenon was appeared by suction flow generated in a main and side channel structure as shown in Figure . We enhanced this effect by the parallel straight side channel structure

• In order to control the tailing of the droplet, we employed surfactants, Tween 20 (dispersed phase: water) and Span 80 (continuous phase: oil)

Reference

1)C. N. Baroud, F. Gallaire and R. Dangla, "Dynamics of Microfluidic Droplets", Lab on a Chip, vol. 10, pp. 2032-2045, 2010.

2)P. Zhu and L. Wang, "Passive and Active Droplet Generation with Microfluidics: a Review", Lab on a Chip, vol. 17, pp. 34-75, 2017.

3)D. R. Link, S. L. Anna, D. A. Weitz and H. A. Stone, "Geometrically mediated breakup of droplets in microfluidic device", Physical Review Letters, vol. 92, pp. 054503, 2004.

4)M. Fujii, K. Kawai, D.H. Yoon and S. Shoji, "Volume Controlled High Throughput Picoliter Droplet Generation System Using Cascade Multi-Stage Separation Channel", Digest Tech Papers IEEE MEMS 2011 conference, pp. 1201-1204, January 23–27, 2011.

5)T. Moritani, M. Yamada and M. Seki, "Generation of uniform-size droplets by multistep hydrodynamic droplet division in microfluidic circuits", Microfluid Nanofluidles, vol. 11, pp. 601-610, 2011.