Microchannels cross-junction

Abraham et al. [48] fabricated spherical polymeric microcapsules by flow focusing of an organic phase consisting of amphiphilic block copolymer solution in DCM vhth a continuous aqueous phase in a cross-junction microchannel of 100 x 100 pm channel cross-section. The ratio of the flows of the two immiscible solutions... 

Figure 1 Varied flow patterns in microchannels. (A) Liquid plug flow. (B) Droplet flow. (C) Liquid/liquid parallel flow. (D) Bubble droplet alternate flow. (E) Parallel water/oil flow containing gas slugs. (F) Bubbles embedded in liquid/liquid annular flow. (G) Multiemulsions. (H) Janus fluid particles generated in a cross-junction microchannel. All scale bars are 0.5 mm. Panel (D) Adapted from Wang et al (2015a) with permission of Wiley, panel (E) adapted from Yue et al (2014) with permission of The Royal Society of Chemistry, panel (G) adapted from Deng eta (2013 a) with permission of The Royal Society of Chemistry, and panel (H) adapted from Nisisako and Hatsuzawa (2010) with kind permission from Springer Science and Business Media.

Figure 2 Flow maps of T-junction microchannels. (A) Liquid/liquid two-phase flow in a T-junction microchannel, whose cross-section is 0.52 x 0.2 mm for the main channel and 0.27 x 0.2 mm in for the side channel. The solid dots are from the experiment with water/2 wt% spanSO-dodecane and the hollow dots are from the experiment with octane/3 wt% SDS (sodium dodecyl sulfonate)—water. (B and D) Gas/liquid two-phase and gas/liquid/liquid three-phase flows in a cross-junction microchannel. (C) Liquid/ liquid/liquid three-phase flows in a cross-junction microchannel in a flow-focusing microfluidic device. Panels (B and D) These figures are adapted from Wang et al (2013b) with permission of Wiley. Panel (C) Reprinted from Nieetal (2005) with permission of American Chemical Society.

The varied interfacial tensions in the microflow processes we discussed above have to be measured online using fluid dynamic models. In recent years, a series of methods have been developed to determine the dynamic interfacial tension, basing on the measurements of droplet size, droplet deformation, and the pressure drop across the droplet. Using the average diameters of droplets generated from joint channels, such as T-junction and cross-junction microchannels, the interfacial tension at the droplet pinch-off moment was obtained. This method should be based on a reliable droplet size model, which contains interfacial tension. In the previous study, the dynamic interfacial tension between Hquids at the droplet pinch-off... 

Wang K, Lu YC, Qin K, et al Generating g3s-Hquid-liquid three-phase microflows in a cross-junction microchannel device, Chem Eng Technol 36 1047—1060, 2013b. 

The temperature gradient can also be achieved at the junction of two microchannels of two different cross-sectional areas in the presence of an electric field. Since there is a higher current density in the narrower channel than in the wider channel, it is hotter in the narrower channel [597]. 

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. 

Emulsion Preparation with Microstructured Systems, Fig. 1 Outline of some microfluidic emulsification geometries, (a) Cross section of a microchannel with a depth difference at the junction. The dispersed phase is pushed onto the terrace (indicated by the arrow) and an emulsion droplet is formed when the dispersed phase falls from the terrace into the deeper well (see also Fig. 2). (b) Top view of a T-Junction with a uniform... 

Essentially there exist two sources of electric field nonuniformities at the reservoir-microchannel junction One is due to the reduction in cross-sectional area from reservoir to microchannel which gives rise to electric field gradients primarily parallel to the streamlines. 

Crossflow Cross-flow breakup of the droplet phase is achieved by using a T-junction [51] (Figure 8.6b) or in terrace-like microchannels [52]. The two modes of operation include droplet formation in unconfined and confined geometries, as shown in Figure 8.6f and g, respectively. Design of MF reactors that use an unconfined breakup typically utilizes the width of channels supplying a... 

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