Segmented flow microfluidics

A number of elegant studies over the past few years have also addressed the need to minimize particle size distributions through the use of segmented flow microfluidic systems. Such an approach removes the possibility of particle deposition on channels and eliminates the problems of residence time distributions that occur in single phase systems (where drag at the channel walls sets up a velocity distribution inside the channel). For example, Shestopalov et al. reported the two-step synthesis... 

Segmented Flow Microfluidics Definition of segmented flow microfluidics ... 

Segmented flow microfluidics describes the principle of performing an assay within small liquid droplets immersed in a second immiscible continuous phase (gas or liquid). For process automation, the droplets are handled within microchannels, where they form alternating segments of droplets and the ambient continuous phase. 

The segmented flow microfluidic platform relies on a multiphase fluid flow through microchannels. Generally, the applied technologies can be divided into the following categories ... 

In principal, droplets of a dispersed liquid phase are immersed in a second continuous gas (two-phase gas-liquid) or liquid (two-phase liquid-liquid) phase within a microchannel. Thereby, the inner liquid droplets are separated by the continuous carrier liquid along the channel. If the size of the iimer phase exceeds the cross sectional dimensions of the channel, the droplets are squeezed to form non-spherical segments, also called plugs . Following this flow scheme, the platform is called segmented flow microfluidics. 

Synthesis of Nanoparticles via Segmented Flow Microfluidic Devices... 

Cabeza V, Kuhn S, Kiflkami A, Jensen K (2012) Size-controlled flow synthesis of gold nanoparticles using a segmented flow microfluidic platform. Langmuir 28(17) 7007-7013... 

Pressure Drop in Segmented-flow Microfluidic Networks... 

Stanley, C.E., Wootton, R.C.R., deMello, A.J. (2012) Continuous and Segmented Flow Microfluidics Applications in Highthroughput Chemistry and Biology. Chimia 66 ... 

Table 3 gives an overview of the microfluidic unit operations and applications that have been already implemented on the segmented flow platform. They all take advantage of the enclosed reaction confinement within the droplets, either for analytical applications (cell analysis, single organism analysis, DNA assays, drug screening, protein crystallization) or chemical synthesis. 

One of the simple ways to achieve active mixing is to induce a pressure field disturbance. Active micromixers relying on this strategy have been reported from different authors [43, 156-159], Deshmuck et al. [156, 157] proposed a T-junction microfluidic chip with an integrated micropump that alternatively drives and stops the flow within the microdevice to create a segmented flow. 

As a straight microchannel constitutes the basic segment in microfluidic structures, several examples of the combined pressure-driven and electroosmosis-driven flow in straight microchannels are demcmstrated in this entry. Usually a microchannel length dimension is much larger than its lateral dimensions, and the flow in such a channel can be considered as unidirectional this implies that the flow can be modeled as a fully developed flow, namely, du/dx = 0, V = 0, and w = 0, in terms of... 

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. 

The microfluidic format employed in metal nanoparticle synthesis is also critical to the quality and size consistency of the particles produced. The main options are to use a batch-based microreactor format, continuous flow in microfluidic channels, or segmented flow [2]. The microreactor approach allows for the inclusion of mixing architectures such as radial interdigitated mixers, but this approach sometimes produces polydispersity and may be prone... 

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