Structure and dynamics of supercooled water in the hydration layer of poly(ethylene glycol)

Yuqing Li; Zehua Han; Changli Ma; Liang Hong; Yanwei Ding; Ye Chen; Junpeng Zhao; Dong Liu; Guangai Sun; Taisen Zuo; He Cheng; Charles C Han

doi:10.1063/4.0000158

Structure and dynamics of supercooled water in the hydration layer of poly(ethylene glycol)

Struct Dyn. 2022 Sep 8;9(5):054901. doi: 10.1063/4.0000158. eCollection 2022 Sep.

Authors

Yuqing Li, Zehua Han, Changli Ma, Liang Hong¹, Yanwei Ding², Ye Chen³, Junpeng Zhao³, Dong Liu⁴, Guangai Sun⁴, Taisen Zuo, He Cheng, Charles C Han⁵

Affiliations

¹ School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
² Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
³ Faculty of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China.
⁴ Key Laboratory of Neutron Physics, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621999, China.
⁵ Institute for Advanced Study, Shenzhen University, Shenzhen 508060, China.

Abstract

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.