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.
Small-angle neutron scattering has been used to study the effect of temperature and pressure on the phase behaviour of semidilute solutions of polymers dissolved in organic and supercritical solvents. Above the theta temperature (T Θ ), these systems exhibit a "good solvent" domain, where the molecules expand beyond the unperturbed dimensions in both organic solvents and in CO 2 . However, this transition can be made to occur at a critical "theta pressure" (P Θ ) in CO 2 and this represents a new concept in the physics of polymer-solvent systems. For T < T Θ , and P < P Θ , the system enters the "poor solvent" domain, where diverging concentration fluctuations prevent the chains from collapsing and allow them to maintain their unperturbed dimensions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.