Microchannels droplet formation

S. Sugiura, M. Nakajima, N. Kumazawa, S. Iwamoto, and M. Seki Characterization of Spontaneous Transformation-Based Droplet Formation During MicroChannel Emulsification. J. Phys. Chem. B 106, 9405 (2002). 

T. Kawakatsu, G. Tragardh, C. Tragardh, M. Nakajima, N. Oda, and T. Yonemoto The Effect of Hydrophobicity of Microchannels and Components in Water and Oil Phases on Droplet Formation in MicroChannel Water-in-Oil Emulsification. Colloid and Surfaces A Physicochem. Eng. Aspects 179, 29 (2001). 

Kawakatsu, T., Trhgardh, G., Tragardh, C., Nakajima, M., Oda, N., and Yonemoto, T. (2001b). The effect of the hydrophobicity of microchannels and components in water and oil phases on droplet formation in microchannel water-in-oil emulsification. Coll Sutf. A 179(1), 29-37. 

Microfluidic generation of droplets is a method of droplet formation in microfluidic channels. It works by combining two or more streams of immiscible fluids and generating a shear force on the discontinuous phase causing it to break up into discrete droplets. In contrast to piezoelectric, pneumatic and acoustic forms of droplet generation, in this method, there is no need for an actuator to impose instabilities on the liquid jet. In the absence of an actuator, the size and polydisper-sity of the droplets are determined by the dimensions of microchannels, the flow rates of liquids, wetting properties of microchannels, etc. 

Kuksenok O, Jasnow D, Yeomans J, Balazs AC (2003) Periodic droplet formation in chemically patterned microchannels. Phys Rev Lett 91 108303-1-108303-4... 

For spontaneous droplet formation, a difference in dimensions is needed (e.g., a depth difference as shown in Fig. la). In these (straight-through) microchannels, the incipient oil droplet spontaneously changes from a flat disk shape to a spherical droplet that is released (see also Fig. 2). 

Spontaneous Droplet Formation in Microchannels This phenomenon was originally demonstrated by Kawakatsu and coworkers [7], and the droplet formation mechanism was first proposed by... 

Sugiura and his team [8]. When taking a detailed look at spontaneous droplet formation in microchannels, see Fig. 2, it is clear that the droplet formation process consists of various phases. First the to-be-dispersed phase is pushed through the feed channel toward a wider shallow area called the terrace where it takes a disklike shape (Fig. 2a). This disk will keep growing through the supplied dispersed phase and eventually reach the end of the terrace, after which (part of) the disk can leap into the deeper channel to which the terrace is connected as shown in Fig. 2b. The droplet may still be connected to the feed, but after reaching a specific size, the neck keeping the droplet connected will break and a droplet will be released (Fig. 2c). This process was captured by Van Dijke and coworkers in CFD calculations, from which a relatively simple flux criterion was derived [5]. 

Schroen, C.G.P.H. Sman, R.G.M. van Act Boom, R.M. (2006) Lattice Boltzmann simnlatirais of droplet formation in a T-shaped microchannel. Langmuir 22 (9), p. 4144-4152. Copyright 2006 American Chemical Society)... 

Nisisako T, Torii T, Higuchi T (2002) Droplet formation in a microchannel network. Lab Chip 2 19... 

Sugiura, S., Nakajima, M., Kumazawa, N., Iwamoto, S., and Seki, M., Characterization of spontaneous transformation-based droplet formation during microchannel emulsification, J. Phys. Chem. B, 106, 9405-9409, 2002. 

The modeling of electrohydrodynamic droplet generation from a microchannel within a microchip via an applied electric field has been studied by Kim et al. [96]. They modeled the droplet formation using a Level Set method coupled with a Poisson solver for the electric field. The model was used to determine the role of the surface properties of the microtube. They demonstrated that the system could generate mono-sized droplets at a regular frequency with no satellite droplets. The... 

Kobayashi, S. Mukataka, M. Nakajima, CFD simulations and analysis of emulsion droplet formation from straight-through microchannels, Langmuir, 2004, 20, 9868-9877. 

Figure 18.4 Top design and dimensions of the T-junction microchannel device used forthe synthesis of poly(l,6-hexanediol diaciylate) beads. Bottom images of droplet formation for different continuous phase flow rates at a flxed flow rate of the...

Optimizing the efficiency of droplet formation, disintegration and stabilization is the domain of microengineered devices. Here, micromixers, optimized high-pressure homogenizer nozzles and specific microfluidic devices such as microchannels are under investigation. 

Figure 20.8 Conventional and innovative membrane emulsification principles spontaneous droplet formation at microchannels (left), droplet formation and detachment at conventional membranes (middle) and jet formation at microengineered microsieves (right) as a function of dispersed phase pore velocity...

By microchanneling (Figure 20.8, left), monodisperse emulsions may be produced in the absence of shear forces [63]. A strongly non-cylindrical geometry at the microchannel exit followed by a terrace is responsible for this effect [64, 65]. The droplet formation mechanism is limited to a critical velocity of the dispersed phase, above which the droplet sizes are widely distributed [51]. 

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