Final report

1
Final report

• Department Institute of NEMS
• Student ID?d9635808
• Report? Yen - Liang Lin

2
Outline

• Introduction
• Design and Fabrication
• Experimental setup
• Results and discussion
• Conclusion
• Reference

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Introduction T-junction
The resulting instability that drives droplet
formation is a well-known competition between
surface tension and shear forces

• Effect of Flow Speed on Droplet Size
• Effect of Channel Size on Droplet Size
• Effect of Surfactant on the Stability of Droplets

T. Thorsen et al., Physical Review Letters, 2001.
T. Nisisako et al., Lab. Chip, 2002.
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Introduction Flow focusing

• Generation rate104/s for water-in-oil droplets
  and reaching 103/s for oil-in-water droplets
• The orifice with its cusp-like edge exerts a ring
  of maximized stress around the flow and ensures
  controlled breakup of droplets for a wide range
  of flow rates
• Focusing the flow into a 3-D profile.

• Janus particles ?both electrical and color
  anisotropy, for use in electronic paper.
• To produce bicolored particles, pigments of
  carbon black and titanium oxide are dispersed in
  an acrylic monomer (isobornyl acrylate, IBA)

T. Nisisako et al., Adv. Mater., 2006.
L. Yobas et al., Lab. Chip, 2006.
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Introduction Solidifying Choppers

• Solidifying these drops in situ either by
  polymerizing a liquid monomer or by lowering the
  temperature of a liquid that sets thermally.
• A range of materials can be applied, including
  heterogeneous multiphase liquids and suspensions.

• A novel combination of hydrodynamic-focusing and
  liquid-chopping techniques.
• The size of the droplets is tunable using three
  approaches including adjusting the relative
  sheath/sample flow velocity ratios, the applied
  air pressure and the applied chopping frequency.

S. Xu et al., Angew. Chem. Int. Ed., 2005.
G. B. Lee et al., JMEMS, 2006.
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Design
1. Two immiscible liquids, including a continuous
phase (sample A) with a velocity of V1 and
dispersed phase (sample B) with a velocity of V2
were injected into the T-junction channels to
generate the internal emulsion droplets. 2. The
internal emulsion droplets were hydrodynamically
focused into a narrow stream by the neighboring
sheath flows (Sample C) with a velocity of V3.
3. The pneumatic choppers were used to cut the
pre-focused emulsion flow into double emulsion
microdroplets with well-controlled sizes.
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Fabrication

• SU8 master mold
• Replication process of the PDMS structure

8
Experimental setup
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Results and discussion

• The deformation of controllable moving-wall
  structure squeezes the continuous phase flow
  locally and increase the continuous phase flow
  velocity near the intersection of the T-junction
  channels. It therefore increases the shear force
  to form droplets with smaller diameters.

• The coefficients of variation are 1.28, 2.78,
  1.61, and 3.53

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Results and discussion

• V1V2V3 1602000

• The external droplets size of double emulsion ?
  the applied pressure of pneumatic chopper.
• The internal droplets size of double emulsion ?
  the applied pressure of controllable moving-wall.

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Conclusion

• A new microfluidic chip capable of generating
  uniform double emulsion microdroplets utilizing
  the combination of a controllable moving-wall
  structure at the T-junction microchannels and
  pneumatic choppers was demonstrated.
• The controllable moving-wall can actively tune
  the size of the emulsion droplets without
  changing the syringe pumps flow rate.
• The deformation of the controllable moving-wall
  structure can physically change width of the
  microchannel. Therefore the flow velocity can be
  locally changed by applying compressed air
  pressure.
• The size of the external droplets can be
  fine-tuned by different applied air pressure of
  pneumatic choppers.
• The developed chip has the potential to be used
  for high-quality emulsification processes,
  including the analysis of pico-liter biochemical
  reactions, drug delivery systems, and cosmetic
  industry.

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Reference

• T. Thorsen, R. W. Roberts, F. H. Arnold and S. R.
  Quake, Dynamic pattern formation in a
  vesicle-generating microfluidic device, Physical
  Review Letters, vol. 86, pp. 4163-4166, 2001.
• T. Nisisako, T. Torii, T. Takahashi, and Y.
  Takizawa, Synthesis of monodisperse bicolored
  janus particles with electrical anisotropy using
  a microfluidic co-flow system, Adv. Mater., vol.
  18, pp. 1152-1156, 2006.
• T. Nisisako, T. Torii, and T. Higuchi, Droplet
  formation in a microchannel network, Lab. Chip,
  vol. 2, pp. 24-26, 2002.
• L. Yobas, S. Martens, W. L. Ong, and N.
  Ranganathan, High-performance flow-focusing
  geometry for spontaneous generation of
  monodispersed droplets, Lab. Chip, vol. 6, pp.
  1073-1079, 2006.
• S. Xu, Z. Nie, M. Seo, P. Lewis, E. Kumacheva, H.
  A. Stone, P. Garstecki, D. B. Weibel, I. Gitlin,
  and G. M. Whitesides, Generation of monodisperse
  particles by using microfluidics control over
  size, shape, and composition, Angew. Chem. Int.
  Ed., vol. 44, pp. 724-728, 2005.
• C. T. Chen, and G. B. Lee, Formation of
  micro-droplets in liquids utilizing active
  pneumatic choppers on a microfluidic chip,
  Journal of Microelectromechanical System, vol.
  15, pp. 1492-1498, 2006.

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Thank you for your attention !