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Rapid Expansion of Supercritical Fluid Solutions 
The rapid expansion of supercritical fluid solutions through a small
orifice (referred to as the RESS process) produces an abrupt decrease
in dissolving capacity of the solvent as it is transferred from a
supercritical fluid state, having near liquid density, to a very low
density phase after the expansion. This abrupt transition in solvent
characteristics results in the nucleation and growth of any low-vapor-pressure
solute species that were present in the solution prior to expansion.
The solute products which are generated during RESS expansions can
have a number of different forms, depending on specific RESS processing
parameters. RESS-generated products have included submicrometer particles,
thin films, and fine polymer fibers. The RESS process provides a unique
approach to the deposition of supercritical fluid-soluble materials
as either continuous coatings or micorparticulate coatings over relatively
large surfaces. Because the solvent is transformed into the gas phase
during the RESS expansion, RESS products are generated "dry," with
little or no residual solvent.
There is a wide range of different materials that can be processed using RESS technologies including organic and inorganic compounds and pharmaceutical materials.
For information about supercritical fluid capabilities at PNNL, please contact Clement Yonker, at (509) 372-4748, clem.yonker@pnl.gov. |
Pioneering developments in this area in the late 1980's have been
continued with recent discoveries of RESS-hybrid technologies for
high efficient particle collection, for dealing with polar compounds,
and for forming intimate matrixes of two insoluble solids. One of
these technologies know as Aqueous Injection of a Supercritical
Expansion (AISE) is shown in the accompanying photo.
