Dielectric investigation of the low-temperature water dynamics in the poly(vinyl methyl ether)/H2O system

Abstract

Broadband dielectric spectroscopy (10-1−106 Hz) and differential scanning calorimetry measurements have been performed to study the molecular dynamics of water solutions of poly(vinyl methyl ether) (PVME) in the concentration region up to 50 wt % and in the temperature range from 150 to 250 K in order to investigate the low-temperature water dynamics in this system. A symmetric spectrum due to reorientation of water molecules inside the rigid polymer matrix was observed for all hydration levels. However, the dielectric relaxation results evidence that different “water types” can be distinguished depending on the hydration level. For moderate water content (ca. below 30 wt %) the water molecules have both orientational and translational restrictions. For high water contents the excess water is able to fully reorientate at low temperatures and to crystallize above 230 K. Furthermore, our dielectric results support the idea that water molecules are not uniformly distributed among the monomeric units of PVME.