Two kinds of potential surfaces for supercooled water and percolation transition

点击翻译按钮获取中文摘要

The present project covers phase behaviors of water in bulk and confined states.(1) We have reported molecular dynamics (MD) simulations of bulk water in supercooled state and the associated liquid-liquid phase transition. This has been investigated by examining local structure of individual water molecules, the hydrogen bond number distribution etc. Also examined is compression and decompression cycle at temperature 0 K.(2) We have reported MD evidence suggesting a new type of first-order phase transition - a liquid-to-bilayer amorphous transition --- above the freezing temperature of bulk water under atmospheric pressure. This polyamorphic phase transition appears uniquely when a two-layer water is confined in a hydrophobic slit pore at a width of less than one nanometer. Upon cooling, the confined water which has an imperfect random hydrogen-bonded network undergoes the transition to a bilayer amorphous which has a perfect network due to the formation of various hydrogen-bonded polygons yet has no long-range order. This transition was visualized and the associated thermodynamic properties were examined The transition shares some characteristics with those observed in tetrahedrally coordinated substances such as liquid silicon, liquid carbon and liquid phosphorus.(3) We have reported MD simulation evidence of phase behavior of encapsulated water-formation of new phases of quasi-one-dimensional ice and existence of a solid-liquid critical point. We discover that in narrow carbon nanotubes water can freeze into heptagonal, hexagonal, pentagonal, or square ice nanotubes, depending on the diameter of carbon nanotubes (1-1.4 nm) and the applied axial pressure as well. Based on the tree energy calculation, we assessed experimental conditions under which bulk liquid water can be encapsulated into carbon nanotubes and can be transformed into ice nanotubes.