Formation of Monodisperse Bubbles in a Microfluidic Flow-Focusing Device

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G. Whitesides, H. Stone et al., Applied Physics Letters Vol.85 No.13 (2004) [1]

Brief Summary

This paper reports one of the first devices to produce monodisperse bubbles for microfluidic applications. Droplet-based microfluidics have huge potential in medical diagnostics, chemistry, drug discovery and beyond. The physical understanding of the process by which bubbles or droplets are created in various microfluidic geometries is critical to the development of such methods. The authors of this paper demonstrate the creation of gaseous bubbles surrounded by a liquid phase, with a polydispersity of less than 2% and at rates of <math>10^5</math> per second. Some scaling relations are presented in an attempt to develop an intuition of the factors affecting the volume of the bubbles produced and the frequency behaviour of the bubble formation.

Capillarity Phenomena

Device Operation

The basic idea behind the formation of bubbles in the geometry investigated is simple enough. A gaseous phase is set to flow through a central channel and comes to a first orifice of width <math> W_g</math>. This orifice is met by two perpendicularly flowing channels of a liquid phase. Downstream of this, there is a second, smaller orifice of width <math>W_{or}</math>. A pressure is applied to the central channel so that a thread of gas reaches out of the second smaller orifice. The elongated liquid-gas interface carries an increasingly large energy which leads to a Rayleigh-Plateau-like instability [2]. At a critical and well defined surface energy, the gaseous thread breaks into a bubble which is then carried downstream. The geometry is depicted in figure 1
Schematic description of the flow focusing device.