Different Insights of Water Structure in Polymer–Water Systems Observed by Vibrational Spectroscopic and Calorimetric Methods

Abstract

The objective of the present report is to review literature concerning the different insights of the water structure obtained by vibrational spectroscopic and calorimetric methods. Water sorbed into the solid polymers is categorized into "free", "intermediate", and "non-freezing" waters based on its freezing/melting behaviors observing by differential scanning calorimetry (DSC). Crystallization behavior of water sorbed into various non-water soluble polymers was examined by DSC and temperature-variable infrared spectroscopy (TV-IR). In general understanding of the sorbed water at low water content on the basis of DSC, all of the sorbed water has been considered to be non-freezing water. However, their TV-IR spectra clearly demonstrated the existence of the change in state (condensation, crystallization, vapor-deposition, sublimation, fusion, and vaporization) including recrystallization of water by revapor deposition, which was vapor-deposition (sublimation) during heating. Recrystallization water being categorized into intermediate water has been proposed to be devitrification of amorphous ice. These results require to reconsider the definition of water structure based on DSC.