Structural and Dynamical Properties of H₂O and D₂O under Confinement

CX Liang and A Rayabharam and NR Aluru, JOURNAL OF PHYSICAL CHEMISTRY B, 127, 6532-6542 (2023).

DOI: 10.1021/acs.jpcb.3c02868

Water (H2O) is of greatsocietal importance,and therehas been a significant amount of research on its fundamental propertiesand related physical phenomena. Deuterium dioxide (D2O),known as heavy water, also draws much interest as an important mediumfor medical imaging, nuclear reactors, etc. Although many experimentalstudies on the fundamental properties of H2O and D2O have been conducted, they have been primarily limited tounderstanding the differences between H2O and D2O in the bulk state. In this paper, using path integral moleculardynamics simulations, the structural and dynamical properties of H2O and D2O in bulk and under nanoscale confinementin a (14,0) carbon nanotube are studied. We find that in bulk, structuralproperties such as bond angle and bond length of D2O areslightly smaller than those of H2O while D(2)Ois slightly more structured than H2O. The dipole momentof D2O tends to be 4% higher than that of H2O, and the hydrogen bonding of D2O is also stronger thanthat of H2O. Under nanoscale confinement in a (14,0) carbonnanotube, H2O and D2O exhibit a smaller bondlength and bond angle. The hydrogen bond number decreases, which demonstratesa weakened hydrogen bond interaction. Moreover, confinement resultsin a lower libration frequency and a higher OH(OD) bond stretchingfrequency with an almost unchanged HOH(DOD) bending frequency. TheD(2)O-filled (14,0) carbon nanotube is found to have a smallerradial breathing mode than the H2O-filled (14,0) carbonnanotube.

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