Molecular dynamics simulation on the structure and properties of water near platinum and study on various water using liquid structure theory

Abstract

In spite of the fact that water is involved in many systems of engineering and plays a crucial role in them, the need of research on the water itself is often neglected unconsciously. In this thesis, several researches are performed on the structures of various water not only for the scientific purpose but also for the eventual engineering application with a mind that a practical improvement in many systems can be achieved if we have sufficient knowledge about the relationship between the structure and the properties of water and we can control the structure of water properly. In Chapter 2, the structures and properties of liquid water near (111) and (100) planes of platinum with those of bulk liquid water are studied using molecular dynamics simulation. First, three regions, i.e., bound water region (Z), semi-bound region (Y), and bulk-like region (X) are determined according to density profile analysis. This criterion is confirmed by investigating the diffusivities of water molecules in these regions. Ring size analysis in Y regions near (111) and (100) planes shows the ratio(R6/R5) of hexameric ring structure(R6) and penameric ring structure(R5) is higher than that of bulk water in both of them. Previous works showed hydrophilicity resulted in such a behavior, and it is supposed that other adsorbent materials in addition to Pt which can attract water strongly give such a result generally. The reason for the use of adsorbent ceramics as photocatalyst, support material, and bio ceramics is discussed in terms of the change of water structure near them: Proton transfer is facilitated and beneficial biological effect is observed in hexameric ring structure of water. Thicker hydration layer is also expected in this structure. In Chapter 3, based on the model that water is composed of two main structures and at equilibrium of them, the partition function of water which represents two liquid structures explicitly is induced using significant liquid structure theory....