Dynamic Properties of Water Molecules within an Au Nanotube with Different Bulk Densities

摘要

Molecular dynamics simulation is used to investigate the dynamic properties of water molecules inside an Au nanotube in different water densities. From the oxygen density profiles, some characteristic peaks appear at specific regions. In order to observe the dynamical behaviors of water molecules in different portions in the Au nanotube, these specific peaks are divided into three regions-I, II, and III-which are 0-4, 4-7, and 7-10 A, respectively, as measured from the center of the tube to the inside wall of the tube. Since the strength of hydrogen bonds between water molecules within regions I and II can overcome the interaction between the Au nanotube and the water molecules within those regions, the major peaks of the region I and II spectra are similar to those of bulk water. However, the strength of hydrogen bonds between water molecules within region III cannot overcome the interaction between the Au nanotube and the water molecules within that region, so the major peak of the region III spectrum shifts to a higher frequency. In addition, the shoulder structure, which can be observed in the spectra of those regions at different densities, exists at high frequency. In the vibration spectra for region I, the shoulders at each different density appears at around 100 cm~(-1), and those of regions II and III at different densities occur around 200 cm~(-1). This is because the shoulder corresponds to O-O stretching intermolecular vibrations of pairs of H-bonded molecules, so the shoulder will gradually appear as the average number of hydrogen bonds increases. Finally, the shoulder in the region I spectrum completely disappears at a bulk density of 0.8 cm~(-1).