Microfluidic T-junction

In the first demonstration of formation of monodisperse droplets in a microfluidic T-junction [9], on the basis of the experimental results on scaling of the droplet size with the rate of flow of the continuous fluid, it was hypothesized that the droplets are sheared off from the junction by the flow of the continuous fluid, similarly to the classical models of shear-driven emulsification. However, the fact that the break-up occurs in a confined geometry of the microchannels, and that the droplet growing off the inlet of the fluid-to-be-dispersed usually occupies a significant fraction of the cross-section of the main channel, suggest that the pressure drop along a growing droplet may be an important factor in the process. 

Droplet microfluidics is a science and technology of controlled formation of droplets and bubbles in microfluidic channels. The first demonstration of formation of monodisperse aqueous droplets on chip - in a microfluidic T-junction [1] - was reported in 2001. Since then, a number of studies extended the range of techniques, from the T-junction [2-5], to flow-focusing [6-10] and other geometries [11], and the capabilities in the range of diameters of droplets and their architectures [12-16]. These techniques opened attractive vistas to applications in preparatory techniques [17-19], and - what is the focus of this lecture - analytical techniques based on performing reactions inside micro-droplets. 

The usual way of feeding the microfluidic systems with fluids is to apply either a constant rate of inflow into the chip, or a constant pressirre at the inlet [20]. Formation of droplets or bubbles in systems with such, fixed, boundary conditions for flow is realtively well understood. Two microfluidic geometries are most commonly used a microfluidic T-junction [1] or a microfluidic flow-focusing geometry [6]. 

Garstecki P, Fuerstman M, Stone H, Whitesides G (2006) Formation of droplets and bubbles in a microfluidic T-junction - scaling and mechanism of break-up. Lab Chip 6(3) 437-446... 

Gupta, A., Kumar, R. (2010). Effect of geometry on droplet formation in the squeezing regime in a microfluidic T-junction. Microfiuidics and Nanofiuidics, 8, 799-812. 

V. van Steijn, M. T. Kreutzer, C. R. Kleijn, mu-PlV study of the formation of segmented flow in microfluidic T-junctions, Chemical Engineering Science, 2007, 620, 7505-7514. 

Van Steijn V, Kleijn CR, Kreutzer MT. Predictive model for the size of bubbles and droplets created in microfluidic T-junctions. Lab Chip 2010 10(19) 2513-2518. 

FuTT, Ma YG, FimfechiflingD, etal Squeezing-to-dripping transition for bubble formation in a microfluidic T-junction, Chem Eng Sci 65 3739-3748, 2010. 

Glawdel T, Ren CL Droplet formation in microfluidic T-junction generators operating in the transitional regime. III. Dynamic surfactant effects, Phys Rev E 86 26308, 2012. 

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