Thermodynamics, Separations, and Materials Processing

The theme of my research is to promote the use of environmentally benign solvents in chemical and materials processing. Our current focus is the application of supercritical fluids (SCFs) to separations and the processing of polymers, foods, and pharmaceuticals. As shown schematically below, these fluids lie somewhere between gases and liquids and have very desirable transport and thermodynamic properties for infusing/ extracting organics into/from complex matrices. The necessary tools in this work include phase equilibrium thermodynamics, mass transport in compressible fluids, physical organic chemistry, and spectroscopic analysis. 

Research opportunities in separations are numerous and provide an excellent area in which to bring together many disciplines, including chemical engineering, civil engineering, and industrial chemistry. Our goal in this area is to develop new technologies for the difficult separations encountered in environmental clean-up and isomer purification. 

SCFs can dissolve into and swell polymeric matrices as efficiently as liquid organic swelling agents with the advantage that they are easier to separate from the polymer after processing. This has the effect of reducing the Tg and melt viscosity of the polymer and allows us to incorporate additives into polymers using a supercritical fluid as a carrier. We can, for example, change the color, wettability, or density of a polymer by swelling and impregnating with an SCF solvent. We can also dramatically alter the polymer blending process in an extruder. This area involves mass transport and thermodynamics of highly asymmetric, complex molecular systems and incorporates both experimental and computational components. 

Finally, SCFs are applied to separating and crystallizing thermally labile compounds, such as foods and pharmaceuticals. In this work, we are interested in all aspects of pharmaceutical crystallization with emphasis on using supercritical fluid solvents as the crystallizing medium. Techniques include rapid expansion of supercritical solutions in which expansion through a capillary sets up a standing shock wave to initiate nucleation from the expanded gas, and gas antisolvent crystallization where the SCF is used as an antisolvent to precipitate particles out of a liquid solution. This work includes projects in nucleation and growth, phase equilibrium, and thermodynamic modeling of pharmaceutical solubility.