writer：Yuqing Li, Zehua Han, Changli Ma, Liang Hong, Yanwei Ding, Ye Chen, Junpeng Zhao, Dong Liu, Guang
keywords：hydration water, supercooled, dynamics, qens
source：期刊
specific source：Structural Dynamics 2022, 9, 054901
Issue time：2022年

The statics and dynamics of supercooled water in the hydration layer of poly(ethylene glycol) (PEG) were studied by a combination of

quasi-elastic neutron scattering (QENS) and molecular dynamics (MD) simulations. Two samples, that is, hydrogenated PEG/deuterated

water (h-PEG/D2O) and fully deuterated PEG/hydrogenated water (d-PEG/H2O) with the same molar ratio of ethylene glycol (EG) monomer

to water, 1:1, are compared. The QENS data of h-PEG/D2O show the dynamics of PEG, and that of d-PEG/H2O reveals the motion of

water. The temperature-dependent elastic scattering intensity of both samples has shown transitions at supercooled temperature, and these

transition temperatures depend on the energy resolution of the instruments. Therefore, neither one is a phase transition, but undergoes

dynamic process. The dynamic of water can be described as an Arrhenius to super-Arrhenius transition, and it reveals the hydrogen bonding

network relaxation of hydration water around PEG at supercooled temperature. Since the PEG-water hydrogen bond structural relaxation

time from MD is in good agreement with the average relaxation time from QENS (d-PEG/H2O), MD may further reveal the atomic pictures

of the supercooled hydration water. It shows that hydration water molecules form a series of pools around the hydrophilic oxygen atom of

PEG. At supercooled temperature, they have a more bond ordered structure than bulk water, proceed a trapping sites diffusion on the PEG

surface, and facilitate the structural relaxation of PEG backbone.