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Supercritical fluids (SCFs) have great technological potential for minimizing the organic wastes associated with polymer manufacturing and processing. However, significant challenges remain for developing the same level of understanding of the behavior of polymers in SCFs as has been reached for polymers in traditional organic solvents. Small-angle neutron scattering was used to study the effect of pressure and temperature on the phase behavior of poly(dimethylsiloxane) (PDMS) in supercritical carbon dioxide (SC CO2). It was demonstrated that PDMS−SC CO2 solutions reproduce all main features of the temperature−concentration phase diagram for polymers in organic solvents. Moreover, because of their continuously adjustable solubility, SCFs exhibit novel effects, such as a pressure-induced transition to the ϑ point and to the good solvent domain, in addition to a polymer−solvent demixing at a lower critical solution pressure.

The volumetric properties of carbon dioxide + ethanol mixtures have been determined at 323, 348, 373, 398, and 423 K at pressures up to 70 MPa using a variable-volume view cell. Densities for pure components and mixtures containing 90, 80, 70, and 50% by mass carbon dioxide are reported as a function of pressure at each temperature. It is shown that this system undergoes a density crossover at high pressures with each composition, a phenomenon previously reported also for mixtures of carbon dioxide + pentane, carbon dioxide + toluene, and carbon dioxide + acetone. In the composition range investigated, the excess volume of the mixtures becomes more positive with increasing pressure but more negative with increasing temperature.

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