Final report

Department ： Institute of NEMS

Student ID ︰ d9635808

Report ︰ Yen - Liang Lin

Outline

Introduction Design and Fabrication Experimental setup Results and discussion Conclusion Reference

Solid water stream

Ribbon layer

Pearl necklace

Single droplets

Solid oil stream

Introduction – T-junction

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.

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

Introduction – Flow focusing

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

“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)

Generation rate ： 104/s for water-in-oil droplets and reaching 103/s for oil-in-water dropletsThe 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 ratesFocusing the flow into a 3-D profile.

Introduction – Solidifying & Choppers

S. Xu et al., Angew. Chem. Int. Ed., 2005. G. B. Lee et al., JMEMS, 2006.

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.

Flow focusing Chopper

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.

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.

Fabrication

SU8 master moldReplication process of the PDMS structure

500 µm

50 µm

400 µm50 µm

50 µm

SU8 mold PDMS structure

Experimental setup

Results and discussion

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

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.

Results and discussion

V1:V2:V3 = 1:60:2000

165.21/80.43 μm , 10 psi 135.71/81.03 μm , 20 psi

164.87/60.38 μm , 10 psi 85.81/61.09 μm , 30 psi

Moving wall： 0 psi Moving wall： 0 psi

Moving wall： 20 psi Moving wall： 20 psi

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.

Conclusion A new microfluidic chip capable of generating uniform double emuls

ion 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.

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.

Thank you for your attention !