Comparison of the Behavior of Polymers in Supercritical Fluids and Organic211 Solvents Via Small Angle Neutron Scattering

摘要

Small-angle neutron scattering has been used to study the effect of temperature211u001eand pressure on the phase behavior of semidilute solutions of polymers dissolved 211u001ein organic and supercritical solvents. Above the theta temperature (To), these 211u001esystems exhibit a good solvent domain, where the molecules expand beyond the 211u001eunperturbed dimensions in both organic solvents and in COZ. However, this 211u001etransition can be made to occur at a critical theta pressure (PO) in CO2 and this 211u001erepresents a new concept in the physics of polymer-solvent systems. For T, To, 211u001eand PPo, the system enters the poor solvent domain where diverging concentration 211u001efluctuations prevent the chains from collapsing and allow them to maintain their 211u001eunperturbed dimensions.