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e chemical compatibility, ease and reproducibility of micro reactors, electro osmotic flow (EOF) supporting and detection methods, the materials selection is important for the micro reactorsfabrication. The most popular material is glass, which allows EOF with many solvents to react without any chemical interferences and enables the use of visible light detection3.
For solution-based chemistry, the micro reactors channel networks are connected with reservoirs containing chemical reagents, products or wastes. The chemical reagents can be brought together in a certain sequence, mixed and react in a specified time in a controlled fluidic transport system of micro reactors. The most commonly fluid driving methods for the reagents used are hydraulic pressure andelectrokinetic. The hydraulic pressure is generated by positive displacement pumping1. The advantages of this methods are simply controlling of the reagents flow and knowing the location of a fluid meniscus easily. The disadvantages of this methods are mechanical complexity, low flow rates and hard to find suitable pumps. Thus, the hydraulic pressure method is not good enough for most continuous flow applications. Theelectrokinetic methodfor fluid transportation is known of the electroosmotic flow (EOF)4. EOF occurs in the micro reactors with charged channel walls, and the fluid in the channels will contain a concentration of counter-irons, which resulting a charged fluid. In the electrokinetic method, electrodes are placed in the appropriate reservoirs to apply voltages and charge the channel walls and create the EOF flow, which would cause the fluid pumping through the channel network.This method is controlled by automated computer program. Unlike the hydraulic pressure transportation, the EOF flow velocity is constant in the most channel network. As a results, the electrokinetic method is more simple and effective for fluid transportation.
The common chemical reactions have two or more materials to be mixed as a critical part for achieving reactions. There are two kinds of mixing methods in the continuous flow systems. The first one is called “passive mixing”.In this mixing method, the fluid would flow without any mechanical agitation or forces applied from the continuous flow system. Complete passive mixing can be achieved by increasing the resistant time, which means to design the network with long channels and decline at the flow rates. Another methods is called “active mixing”, which is achieved by applying external forces to the continuous flow system. Complete active mixing can be achieved by changing the flow rate periodically and disrupting the fluid flow for mixing enhancing5.
As a new merging technology, the continuous flow synthesis has several advantages in comparison with traditional batch reactor synthesis. Firstly, the continuous flow synthesis is controlled by automatic computer program. The operations of the continuous flow, such as pumping, mixing, separating products and wastes and chemical analyzing, are easily switch off or on by the computer programs. The automatic continuous flow synthesis enables reactions of various materials and reagents in a time-specific, location-specific and effective way. The entire process of continuous flow synthesis is computer controlled for easy repeatability. And the automatic controlling would reduce the manual manipulation and avoid manual operational errors6.
The continuous flow synthe