Droplet based microfluidics capillary flows

By droplet-based microfluidic techniques, spherical microparticles can be produced. In this process, a polymer solution or a two-component system is separated by an inert nonmiscible fluid to obtain droplets in the 10-200 om range. In most cases, spherical particles are obtained however, also rods or ellipsoids have been realized [108]. For droplet miCTofluidics, either glass capillary devices can be used or devices made by lithography techniques, commonly consisting of PDMS. Figure 3.69 shows a flow scheme for the... 

Chang et al. [5] utilized microtubes to generate micro-segmented flow. Upon surface modification, the prepared nanoparticles were mixed with a monomer and emulsified into uniform droplets in a capillary-based microfluidic device. The microchannel-based reactor offered reliable control over the nanocomposite products by precisely adjusting the interfacial tension. 

Generally, the monoacylation is 3-15 times faster than second acylation and in the batch procedure the diacylated product 54 was obtained as major product (Table 6.5, entries 6, 7, and 13). In contrast, the monoacylated diamine 53 was obtained as major product when the microfluidic droplet and capillary approaches were applied. Here, the droplet-based protocol leads to slightly better yields and selectivities than the capillary procedure (compare entries 3 and 5), which was attributed to the improved mixing efficacy with additional convection effects within the droplets. But the amount of the continuous phase is certainly a major drawback of the droplet protocol. The capillary procedure was therefore improved by the treatment with ultrasound in a commercially available ultrasonic bath (330 W). Sonication of the capillary during the reaction leads to comparable results as in the droplet procedure in a much shorter residence time of 0.5 min (entry 9, overall flow rate 200pl/min, that is, 0.005 mmol/min). Compared to the silent process, the yield was increased by a factor of 4. With an improved ultrasound-supported continuous capillary protocol, a number of symmetric diamines (e.g., piperazine) were successfidly monoacylated. 

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