Pressure- and temperature-induced transitions in solutions of poly(dimethylsiloxane) in supercritical carbon dioxide

Supercritical fluids (SCFs) have great technological potential for minimizi ng the organic wastes associated with polymer manufacturing and processing. However, significant challenges remain for developing the same level of un derstanding of the behavior of polymers in SCFs as has been reached for pol ymers in traditional organic solvents. Small-angle neutron scattering was u sed to study the effect of pressure and temperature on the phase behavior o f poly(dimethylsiloxane) (PDMS) in supercritical carbon dioxide (SC CO2). I t was demonstrated that PDMS-SC CO2 solutions reproduce all main features o f the temperature-concentration phase diagram for polymers in organic solve nts. Moreover, because of their continuously adjustable solubility, SCFs ex hibit novel effects, such as a pressure-induced transition to the Theta poi nt and to the good solvent domain, in addition to a polymer-solvent demixin g at a lower critical solution pressure.