Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2006.Includes bibliographical references (leaves 146-153).Performing multistep microchemical synthesis requires many techniques from combining micromixers in series to the development of continuous microfluidic separation tools. Safety, high heat and mass transfer rates, and cost savings all continue to motivate microreactor development as a research tool, but many reactions generate a variety of (by)products including solid particles, immiscible fluids (gas and liquid), and miscible components requiring purification. We have endeavored to develop microfluidic systems which compliment existing microreactor technology, using forces that grow stronger with decreasing length scales such as electric fields and interfacial phenomena, and to use straightforward microfluidic mixers for kinetic studies of energetic material synthesis. Dielectrophoresis was used to study the continuous separation of polystyrene particles based on size. Essentially, a microfluidic particle "ratchet" was created using a soft-lithography microchannel and slanted interdigitated electrodes which provide a transverse force component on the particles. Experimental behavior agreed well with the model predictions, and 4 & 6 micron particles were continuously separated. Liquid-liquid extraction is another useful tool for microchemical synthesis and well-suited to small length scales because high mass transfer rates can be attained.(cont.) However, emulsion formation and phase separation can provide significant challenges to continuous processing. To address breaking emulsions, a microfluidic tool was developed that uses AC E-fields to enhance coalescence of emulsified phases even where high surfactant concentrations are present, transforming the flow regime from disperse to slug. Phase separation of immiscible fluids is achieved by interfacial tension using porous membrane films which selectively wet only one fluid phase. An integrated mixer-contactor-separator was fabricated and used to separate fluids with low interfacial tensions due to miscible components. Solvent extraction and solvent switching were demonstrated using the device, which help enable continuous multistep microchemical synthesis. Kinetic studies and optimization of energetic material synthesis were performed with a relatively simple micromixers-in-series setup for diazotization and nucleophilic substitution reactions. Typical batch operation is performed in sub-ambient conditions with copper salts to precipitate the product and avoid degradation, resulting in a slow, hazardous, laborious synthesis. High heat and mass transfer enabled studying reaction temperatures at 300C to obtain kinetic parameters for both reaction steps.(cont.) In addition, an optimum pH range for the substitution reaction was found, which will lead to a streamlined, faster process. Though still early in their development, these new tools will hopefully open the door to a range of new chemical syntheses and applications under conditions unachievable on the macroscale. Full integration of these technologies will enable multistep chemistry in microfluidic systems, which in turn will allow screening of new compounds, synthesis optimization, and reduction in chemical waste in a safe, efficient platform usable by chemists and biologists.by Jason G. Kralj.Ph.D
