Droplet Microreactor

Xia B, Lenggoro IW, Okuyama K (2002) Nanoparticle separation in salted droplet microreactors. Chem Mater 14 2623-2627... 

Fig. 5.5 3 Schematic representation of Crieco s reaction in a droplet microreactor. Photographs of droplet displacement during the Crieco s reaction are shown on the right ofthis figure. The droplet containing 1 was allowed to converge towards the droplet containing 2 and TFA. After mixing, the obtained droplet was directed towards the droplet containing 3, thus leading quantitatively to adducts 4 which could be cleaved to the corresponding methyl esters by transesterification.

Cell Adhesion and Detachment Cell Assays in Microfluidics Cell Patterning on Chip Droplet Microreactor... 

A droplet microreactor is a reaction platform that enables chemical reactions to be carried out inside a microdroplet with a volume on the order of a few microliters or less. The droplets are formed and suspended in an immiscible phase such as an oil. Mixing is achieved inside the droplet on the basis of chaotic advection, which is induced by either droplet motion or the channel shape. 

The main advantages of droplet microreactors are the small amount of reagents, the enclosed reaction environment, and rapid mixing. Droplet microreactors are often protected by an immiscible phase such as oil which prevents evaporation of the droplets. Thus, besides fast reactions, long processes such as protein crystallization can also be carried out in droplet microreactors. 

There are two basic platforms for droplet microreactors the planar platform and the in-channel continuous platform. In a planar platform, the droplet can move freely on a planar surface, while the motion of the droplet in an in-channel continuous platform is restricted by microchannels. The actuation of droplets in a planar platform is based on nonmechanical concepts such as electrowettmg, thermocapillary forces, and magnetic forces. Most in-channel... 

Droplet Microreactor, Fig. 1 Droplet microreactor based on actuation by electrowetting, (a) Device concept, (b) The liquid is pulled in by activating the two electrodes on the right. When the middle electrode is turned off, surface tension breaks up the droplet, allowing precise... 

Both platforms for droplet microreactors require the following key functimis for manipulating droplets droplet formation, droplet transport, mixing inside droplets, droplet merging, and droplet splitting. In the following, the basic methods for obtaming these functions are discussed. 

Thermocapillary forces can be used to manipulate a droplet microreactor in the same way as electrowetting does [2]. However, the elevated temperature required may cause evaporation and, in the worst case, boiling of the droplet. ThermocapiUaiy stresses caused by spatial variations of the surface tension at a gas/liquid interface can induce spontaneous flow of a liquid film to a cooler positirai. The surface tension at the... 

Droplet Microreactor, Fig. 2 Droplet microreactor based on thermocapillary actuation, (a) Without a temperature gradient, the droplet is at equilibrium and does not move, (b) If heater 1 is on, the induced temperature gradient propels the droplet owing to the difference in surface stress between the sides of the droplet, (c) If the droplet moves out of the temperature field of heater 1, heater 2 is activated to propel the droplet further... 

Droplet Microreactor, Fig. 4 Droplet formation in an in-channel continuous platform (a) cross-junction and (b) T-junction... 

Droplet Microreactor, Fig. 5 Flow patterns in a droplet microreactor (a) straight channel and (b) curved channel... 

Droplet microreactors find their main applications in analytical chemistry and chemical synthesis. 

An industrial batch reactor has neither an inflow nor an outflow of reactants or products while the reaction is being carried out. Batch reactions can be carried out in droplet microreactors, where nanoliters of fluid are individually manipulated using techniques such as electrowetting on dielectric (EWOD) and surface tension control. Semibatch reactors are used in cases where a by-product needs to be removed continuously and to cany out exothermic batch reactions where a reactant has to be added slowly. Microfluidics allows precise control of concentration and temperature, which allows batch and semibatch reactions to be carried out in a continuous manner. Figure 1 shows the general components of a simple industrial-reactor semp, compared with a laboratory-scale setup to carry out a reaction with microfluidic chips. 

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