Behavior of Water during Temperature-Induced Phase Separation in Poly(vinyl methyl ether) Aqueous Solutions. NMR and Optical Microscopy Study
Abstract
The behaviour of water during the temperature-induced phase separation in PVME/D2O 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/D2O 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 three orders of magnitude slower exchange in highly concentrated PVME/D2O solutions is in accord with our optical microscopy findings that globular-like structures are here approx. 20 times larger than in PVME solution with c = 6 wt%.