Single-particle motions in liquid water. II. The hydrodynamic model

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Abstract
A compilation is made of available data on the self-diffusion coefficient, the dielectric relaxation time, and the NMR orientational time constant for liquid water under 1 atm pressure at temperatures between 273 and 333 K. The data then are examined in a self-consistent manner for their adherence to a simple hydrodynamic model of single-particle motions. In this model, a water molecule is treated as a rigid sphere with the van der Waals radius which carries out diffusive translations and rotations while surrounded by a viscous continuum. Arbitrary boundary conditions on the velocity field in the surrounding liquid are permitted at the sphere–liquid interface. It is found that the measured coefficient of self-diffusion in liquid water is in quantitative agreement with the predictions of the hydrodynamic model under near-slip boundary conditions, whereas the experimental values of the two orientational time constants are described well by the model under stick boundary conditions. Physical arguments are presented to show why the hydrodynamic model should account accurately for single-particle motions in liquid water at low pressures and temperatures.

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