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 The
theme of my research is to promote the use of environmentally benign solvents
in chemical and materi
als 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
chemistr
y, 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
technol- ogies 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 poly
mer 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 incorpora
tes
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 usi
ng 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. |
