Behavior of water during temperature-induced phase separation in poly(vinyl methyl ether) aqueous solutions. NMR and optical microscopy study

摘要

The behavior of water during the temperature-induced phase separation in PVME/D_2O solutions was investigated by ~1H NMR methods and optical microscopy. A fast exchange between water (HDO) bound in mesoglobules and free water was found from ~1H NMR spin-spin relaxation measurements at temperature above the LCST transition for semidilute PVME/D _2O solutions where the exchange time is 1.2 ms for c = 6 wt %. In contrast, there is a slow exchange between bound and free water in highly concentrated PVME solutions and the residence time of the bound water 2 s was found for concentrations c = 20-50 wt % using one-dimensional NOE ~1H NMR experiment. A 3 order of magnitude slower exchange in highly concentrated PVME/D_2O solutions is in accord with our optical microscopy findings that globular-like structures are here approximately 20 times larger than in PVME solution with c = 6 wt %.