High Frequency Spectroscopic Study of the Bound State of Water in PEG-H2O System during Heating from Frozen State

Abstract

The bound state of water in PEG (polyethylene glycol)-H2O systems was studied by using HFS and DSC methods. Samples with the mixing ratios EO:H2O = 1:1 (a) and 1:10 (b), where EO indicates the ethylene oxide units in PEG chain, were heated from frozen state to melt state. Sample (a) gave an HFS peak corresponding to the weakly bound water, while sample (b) gave the peaks of both the bound and free water. DSC measurements gave quite similar patterns to those of HFS measurements, but with additional peaks corresponding to cold crystallization. The difference between the two measurements was reasonably interpreted by considering the origin of the cold crystallization.

Water in Solutions of Chaotropic and Kosmotropic Salts: A Differential Scanning Calorimetry Investigation

“…In another DSC study, which also employed high frequency dielectric spectroscopy, a large exothermic peak at ca. 213 K was also observed reproducibly and attributed to cold crystallization over a wide range of water contents . The authors probed solutions of PEG-10000 using DSC and attributed the observed transitions to free and bound water.…”

“…According to the authors, when bound water molecules of the polymer are cooled down rapidly, they solidify in an amorphous state when the thermal motion of water ceases. An increase in temperature above T g results in a transition from an amorphous state to a crystalline state resulting in the release of heat …”

“…An increase in temperature above T g results in a transition from an amorphous state to a crystalline state resulting in the release of heat. 59 At lower temperatures (259 to 257 K), an endothermic transition is observed representing the melting of the PEG/ water−ice eutectic. At temperatures closer to 273.15 K, endotherms consistent with the melting of pure water were also observed.…”

“…213 K was also observed reproducibly and attributed to cold crystallization over a wide range of water contents. 59 The authors probed solutions of PEG-10000 using DSC and attributed the observed transitions to free and bound water. According to the authors, when bound water molecules of the polymer are cooled down rapidly, they solidify in an amorphous state when the thermal motion of water ceases.…”

Mid-Infrared Spectroscopic Investigation of the Perfect Vitrification of Poly(ethylene glycol) Aqueous Solutions

“…Differential scanning calorimetry (DSC), − on the other hand, has also been frequently used to investigate interactions between PEG and water molecules. Differing from the aforementioned methods, DSC analysis cannot be used to investigate the state of water and PEG in the liquid state but has revealed some unique thermal properties of the PEG–water binary system.…”