Origin of cononsolvency, based on the structure of tetrahydrofuran--water mixture

Poly ($N$-isopropylacrylamide) (PNIPAM) is soluble in (cold) water and THF, but insoluble in mixtures of the two in certain conditions. The origin of this cononsolvency phenomenon was studied from the point of view of mixed solvent structures. Dynamic light scattering, small angle neutron scattering, and viscometry were used to study this phenomenon. From this study, the dynamic equilibrium of THF-water compositional fluctuations in the mixed solvent system was found to be the main cause for this cononsolvency effect.