Mid-infrared Spectroscopic Analysis of Water Structure in Solid Polymers

Abstract

Mid-infrared spectroscopy has an extremely high sensitivity to water, making it a powerful tool for the examination of trace amounts of water in solid polymers. This method does not provide thermodynamic parameters directly unlike calorimetry, which is the most widely used method to examine the state of water in water-polymer systems, but it has the advantage of in-situ measurement and provides information reflecting molecular orientation and hydrogen bonds between water molecules and between water molecules and polymer. This paper outlines various methods for measuring and interpreting the vibrational spectra of water in solid polymers by mid-infrared spectroscopy. In the first part of the paper, the water structure in solid polymers by transmission and attenuated total reflection methods at room temperature will be discussed and we will describe the spectral form reflecting the hydrogen bonding sites in the polymer chain and irremovable water in the polymer matrices. In the second half of the paper, condensation, solidification, deposition, sublimation, melting, and evaporation of water in solid polymers as revealed by variable-temperature mid-infrared spectroscopy will be discussed, as well as deposition during the rewarming process (re-deposition), which was confirmed for the first time by this method.