Daniel G. Nocera, Moungi G. Bawendi, Klavs F. Jensen (Massachusetts Institute of Technology) and Manoochehr Koochesfahani (Michigan State University) are jointly supported to develop a microfluidic reactor for high throughput materials synthesis. This massively parallel system will allow for rapid mixing and extremely uniform segmentation, required for hydrothermal and solvatothermal synthesis. The microfluidic reactor will be fitted with sensors to provide information on chemical and physical phenomena underlying materials growth as well as allowing feedback optimization of the desired materials properties. New optical diagnostic techniques will allow microflows to be quantitatively measured. These data will allow for the control of reaction kinetics and growth processes for the creation of nanocrystals designed for optical sensing and water-splitting catalysts for solar energy conversion. The new microfluidic reactor system will enable the rapid synthesis and analysis of new materials, allowing many new compositions and combinations to be effectively studied.
This project is funded through the Collaborative Research in Chemistry Program (CRC) and provides collaborative training and research opportunities in chemistry, chemical engineering and mechanical engineering. The investigators also engage the public by discussing the role of basic scientific research in promoting societal sustainability.
Normal 0 false false false EN-US X-NONE AR-SA This collaborative research effort between Chemistry at MIT and Engineering at MSU focused on a general technique for the synthesis of complex materials using a microfluidic reactor. Continuous microfluidic reactors (or microreactors) are of interest in material synthesis due to their small reaction volumes that allow more aggressive reaction conditions with higher yield to be achieved. The new technique is intended for synthesis of complex materials for optical sensing and display, magnetism and solar energy conversion applications. The particular system studied here is the segmented gas-liquid microreactor. The superior performance of this system relies on the uniformity of the gas-liquid segment lengths and the mixing that occurs within the liquid segments confined between gas slugs. One of the important aspects of this flow geometry is that the liquid segments are not completely isolated but interconnected through a thin liquid film. For flow conditions relevant to solid state synthesis, the liquid film often disintegrates and this break-up can cause asymmetries that significantly impact the subsequent mixing and dispersion characteristics. The particular focus of the MSU effort was to use optical imaging techniques to investigate the important parameters that influence the flow characteristics in segmented gas-liquid microreactors, and lead to performance limitation. In a parallel effort, we also investigated the possibility of active mixing enhancement in order to address the slow mixing behavior in microfluidic geometries. Perhaps the most important finding from our study is the critical role of surface roughness in the performance of segmented gas-liquid microreactors, in terms of gas-liquid slug length uniformity, the liquid film break-up process, and the flow stability. Our studies have shown that a rougher surface causes a longer stabilization time of the slug flow for a given flow condition, and may even prevent obtaining a regular pattern altogether at certain flow regimes. Optical imaging results indicate that the process of film break-up is quite different between smooth and rough channels. Typically, the liquid film break-up is accelerated when surface roughness is high. These findings point to criteria for the level of surface roughness that may be acceptable for the high performance of such micoreactors, and the care that must be taken during the fabrication process of these devices and their possible over-usage. Proof-of-concept mixing enhancement studies were carried out in a millimeter scale mixing setup under flow conditions similar to those in microfluidics. We investigated the influence of imposing controlled perturbations onto the flow speed. Results show that significant enhancement of mixing can be achieved with the appropriate selection of perturbation frequency and amplitude. This method of mixing control is active in the sense that it can be turned on and off, if desired. We have subsequently demonstrated the application of this active mixing enhancement approach in a Y-channel microfluidic chip. Findings from this research have so far led to a PhD dissertation, several conference presentations and journal publications. The multi-disciplinary character of this collaborative research program has provided students with an enhanced environment to learn the language of other fields while developing specialized knowledge and skills in chemistry and engineering. Along the way, students have learned how to combine these disparate areas of science and engineering to develop new techniques and materials and then apply them to address important issues in emerging technologies.
