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

3. Effect of Flow Speed on Droplet Size Effect of Channel Size on Droplet Size Effect of Surfactant on the Stability of Droplets Solid water stream Ribbon layer Pearl necklace Single droplets Solid oil stream Introduction – T-junction The resulting instability that drives droplet formation is a well-known competition between surface tension and shear forces T. Thorsen et al., Physical Review Letters, 2001. T. Nisisako et al., Lab. Chip, 2002.

4. Introduction – Flow focusing • Generation rate：104/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.

5. Flow focusing Chopper 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.

6. 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.

7. SU8 mold PDMS structure 50 µm 500 µm 50 µm 400 µm 50 µm Fabrication • SU8 master mold • Replication process of the PDMS structure

8. Experimental setup

9. 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 %

10. 165.21/80.43 μm , 10 psi 135.71/81.03 μm , 20 psi Moving wall：0 psi Moving wall：0 psi 164.87/60.38 μm , 10 psi 85.81/61.09 μm , 30 psi Moving wall：20 psi Moving wall：20 psi Results and discussion • V1:V2:V3 = 1:60:2000 • 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.

11. 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.

12. 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.

13. Thank you for your attention !