Microscale reaction characterization

In droplet-based microfluidics, these reaction vessels are formed by droplets of a dispersed phase, which are embedded into a continuous phase. Both liquid phases are immiscible. A huge amount of such droplet reactors can be generated, transported, controlled, and processed in parallel in a droplet-based lab-on-a-chip device. These devices can be characterized as application specific microfiuidic networks that implement and automate a conventional laboratory workflow in a microfluidic chip device or system. They are built up by appropriately intercoimecting microfluidic operation units, which provide the required laboratory operations at the microscale. Consequently, for each conventional laboratory operation, its microscale counterpart is required. 

However, at the microscale, the performance of the microrocket is limited by viscous losses due to the low Reynolds number of the expanding flow. These losses are characterized by the thrust efficiency which compares the observed momentum flux to the momentum flux predicted for an ideal (zero viscosity) fluid. Computations and experiments (e.g., [1]) cOTifirmed supersonic exit flow and have found efficiencies ranging from 10 % to 80 %, depending on the Reynolds number of the system, which in turn depends directly on the size of the throat and the fluid temperature and pressure as it passes through the nozzle, prior to supersonic expansion. The performance of the system can be improved by raising the temperature of the gas. Examples include using an electrical heater in the plenum upstream of the throat [2] and using a chemical reaction, such as combustion [3]. 

Nielsen et al. described an automated system for the characterization of liquid-phase ethylene polymerizations [10]. The system had control of residence times, concentration of catalysts, temperature and pressure. In real time with in-line sensors, it was possible to determine the heat evolved from the reaction and to determine catalyst performance. Thus, by using a carefully controlled microscale reactor with in-line analysis capabilities, a complex polymerization reaction could be characterized in the laboratory setting. 

The small electrode size not only imposes fabrication challenges and hmits the feasibility of SC-SOFCs with coplanar microscale electrodes, it also limits detailed analyses of these cells. SC-SOFCs with coplanar microscale electrodes yield very low conversion of the reactant gases, so that differences between input and output gases cannot be easily detected by mass spectrometry and information about the reactions that occur cannot be obtained. Similarly, the small electrode size makes impedance analysis difficult. The lack of fundamental studies and appropriate characterization and fabrication techniques leaves the working principles of SC-SOFCs with coplanar electrodes to a great extent unexplored. 

Chapter 9 develops the characterization of organic materials at the microscale level by the use of classical organic reactions to form solid derivatives. Tables of derivative data for use in compound identification by these techniques are discussed and are included on the website as Appendix A. 

Thus, you should appreciate that the chemical industry carries out organic reactions on massive quantities of maferial for use in today s highly technological society. The discovery and characterization of these materials all starts in the research laboratory, with many of them initially prepared in microscale quantities. One of fhe great triumphs of our technology has been the successful scaleup of synthetic organic reactions, but that is a story for anofher day. 

The application of Raman microspectroscopy and synchrotron infrared microspectroscopy to visualize the P-fertilizer-soil reactions on a microscale [90] has the advantage that they have a lateral resolution down to the diffraction limit, allowing for the detection and characterization of small phosphate particles. 

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