Generate droplets in microfluidic capillary

Introduction about droplets generation in microfluidic capillary

microfluidic millifluidic t and cross junction - droplets generation in microfluidic capillaryWe describe in details what is digital microfluidic in the tutorial about microfluidic droplets and how to achieve it with a pressure controller in another Elveflow® application note (Digital microfluidics using pressure driven flow).

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Fig.1: Photograph of chromatography tools

(a): a T-junction – (b): a Cross-junction

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DROPLET GENERATION PACK

UP TO 10 000 DROPLETS/SEC

microfluidic-droplet-pack

This fully integrated solution includes all the necessary elements to easily create droplets

DROPLET GENERATION PACK

The droplet generation pack has been designed to fit most common droplet generation needs of researchers. Whatever you need, feel free to contact us to discuss about your exact need and if necessary we will adapt the pack and chips to your particular research application. Moreover for most common additional needs we already propose on the shelf option.

  • Up to 10 000 droplets/sec
  • Flow rate: from 0.1 µL/min to 5 mL/min
  • Droplet size dispersion: 0.3%
  • Change of droplets content : 100 ms

Piezo electric microfluidics flow control

It is possible to make droplets with commercial tools, especially chromatography tools. Here we will focus on how to do it. One can easily make droplets using a cross or a T junction (Fig.1).

These tools are respectively the macroscopic equivalents of flow focusing and cross flowing microfluidic methods. The main difference is the needed setup time. The main drawback is the manufacturing dependence. It means that you cannot choose precisely your channels dimensions. You have to choose between the proposed dimensions  (from 100 µm to 1 mm).

There is a main setup protocol. This protocol describes how to make fluid-fluid dispersion with:

A- Flow focusing method

B- Cross flowing method

The general protocol is the same; you bring two phases in a junction. One phase will be the continuous phase and the other one the dispersed phase (droplets) (Fig.2).

global protocol to make microfluidic droplets with OB1 MK3

Fig.2: Schema of the global protocol to make droplets:

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Microfluidic droplets generation at a T junction:

Microfluidic droplets moving into a capillary:

There are some details however, which differentiate the two methods.
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A- Flow focusing with a cross junction (Fig.3)

1. The main channel is the channel where the droplets will flow

2. It is very important to connect the continuous phase perpendicularly to the main channel

3. The dispersed phase has to be connected to the channel in the continuity of the main channel

4. Control droplets sizes with input pressure driven flow

generate droplets in microfluidic capillary - microfluidic flow focusing cross junction

Fig.3: Scheme of droplets formation at a cross junction (flow focusing):

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B- Cross flowing method (Fig.4)

  1. The main channel is the channel where the droplets will flow
  2. It is very important to connect the dispersed phase perpendicularly to the main channel
  3. The continuous phase has to be connected to the channel in the continuity of the main channel
  4. Control droplets size with input pressure driven flow

generate droplets in microfluidic capillary - microfluidic cross flowing t junction

Fig.4: Schema of droplets’ formation at a T junction (cross flowing):

In conclusion, by connecting submillimeter tubes to submillimeter T and cross junctions, it is possible to generate droplets as in microfluidic devices. It is an easy method to manage the production of droplets. There is no simple alternative to the co-flowing method. But the two main methods used in microfluidics are easily done with chromatographic tools. As described in another Elveflow® application note (Digital microfluidics using pressure driven flow), droplets size are pre-determined by the characteristic dimensions of the tubes and junctions. There are more flexibilities on droplets size with flow focusing method (cross junction). Refer to [1,2] where the control of sizes is well described.

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Piezo electric microfluidics flow control

For more tutorial about microfluidics, please visit our other tutorials here: «Microfluidics tutorials». The photos in this article come from the Elveflow® data bank, Wikipedia or elsewhere if precised. Article written by F. Bertholle, G. Velvé Casquillas, A. Hassan-Zahraee and T. Houssin.

References

[1]: G. F. Christopher and S. L. Anna. Microfluidic methods for generating continuous droplet streams. Journal of Physics D: Applied Physics, 40(19): R319, (2007).

[2]: A. R. Abate, A. Poitzsch, Y. Hwang, J. Lee, J. Czerwinska, and D. A. Weitz. Impact of inlet channel geometry on microfluidic drop formation. Phys. Rev. E, 80(2), (2009).