Droplet Formation in a Microchannel Network

Keyword: Microchannel, Lab on a Chip, µTAS, Micro Chemical Reactor, T-junction, Emulsion, Emulsification, Microcapsule, DDS

Abstract

A novel method is given for generating droplets in a microchannel network. With oil as the continuous phase and water as the dispersed phase, water droplets can be generated in a continuous phase flow. The droplet size is controllable in the range from 380 µm (29 nl) to 100 µm (0.5 nl) when the velocity of a continuous phase flow is changed from 0.01 m/s to 0.15 m/s. Our method is applicable to the preparation of chemical samples, emulsification processes, and drug delivery systems (DDS), for example.

Microchannel Device

Microchannels for generating droplets are fabricated on a polymetyl metacrylate (PMMA) plate (40mm x 40mm x 10mm, Fig. 1, left), using a 100 µm diameter end mill. Each channel has depth 100 µm. The cross section of the channels is rectangular (Fig. 1, right). The width of the narrower channel for the dispersed phase is 100 &micri;m, and that for continuous phase flow is 300-500 µm. A deeper and wider region is made as a reservoir for observing the droplet size (Fig. 2). Adhesive tape is used to enclose these channels.


Fig. 1 A PMMA device (left) and a SEM image of a microchannel (right)

Fig. 2 Top view of the microchannel network (T-junction type)

Experiment

Water is used as the dispersed phase and high oleic sunflower oil (triolein, 80%, 60 mPa s) as the continuous phase. Droplet formation is observed using a microscope and a high-speed video camera (Fig. 3). Regular-sized droplets of water in oil are generated in a microchannel. The droplet size is controlled by changing the continuous phase flow rate and the dispersed phase flow rate. The minimum diameter of droplets was approximately 100 µm and the maximum was greater than 380 µm (Fig. 4). The rate of production increased as the continuous phase flow rate increased (Fig. 5).

Fig. 3 Droplet formation

Fig. 4 Effect of the velocity of a continuous phase flow on droplet size

Fig. 5 Effect of continuous phase flow on droplet production rate

Conclusion

A novel method has been presented for generating water-in-oil droplets in a microchannel network. The droplet size can be controlled; the minimum diameter of the droplets was about 100 µm, and the maximum more than 300 µm, as the flow velocity of the continuous phase is changed from 0.01 m/s to 0.15 m/s. Refinement of this technique will allow the production of oil-in-water droplets and also microcapsules in microfabricated devices. This method is applicable not only to liquid metering but also to emulsification and drug delivery systems (DDS), for example.

References

[1] Takasi Nisisako, Kenta Fukudome, Toru Torii, Toshiro Higchi, "Nanoliter-sized Droplet Formation in a Microchannel Network", Proceedings of ISMM2001, pp. 102-103 (2001)

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