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    COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS
        Institute for Computational Sciences and Informatics
                              CSI 898-Sec 001  
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        Supercritical Fluids: Their Properties and Applications

                        Johanna M.H. Levelt Sengers
                            NIST Fellow Emeritus
 Physical and Chemical Properties Division, NIST, Gaithersburg, MD 20899

A supercritical fluid is loosely defined as a fluid above, but not very far
away from its critical point. Properties such as density or viscosity are
intermediate between those of gas and liquid. Others, such as
compressibility or thermal conductivity, may be very different from those
of either gas or liquid.  The structure of a supercritical fluid is unlike
that of a gas or liquid. Near a critical point, long-range correlations
extend far beyond the range of intermolecular forces.  Snapshots produced
by molecular simulation reveal a sponge-like structure. The properties of a
supercritical fluid may be gradually modified or "tuned" by varying
pressure or temperature, without occurrence of a phase transition.  Solvent
properties of supercritical fluids are contrary to those of liquid
solvents; they can be understood on the basis of the underlying
binary-mixture phase diagrams. 

Widely used supercritical fluids are carbon dioxide and water, which are
nontoxic, nonflammable and friendly to the environment. Tunable solvent
properties and environmental compatibility make supercritical fluids
desirable agents for extraction of food products and fragrances. They are
used as carriers in chromatography, and as media for chemical and materials
processing. Virtually all aspects of polymer processing may involve the use
of supercritical fluids.

                         Monday , October 26 1998
                                  4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served.
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(http://www.csi.gmu.edu/lcdm/seminar/schedule.html)