Theoretical Study on a phase transition between low temperature metastable water phases
| Project/Area Number |
08640646
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
TANAKA Hideki Kyoto University, Polymer Chemistry, Instructor, 工学研究科, 助手 (80197459)
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| Project Period (FY) |
1996 – 1997
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| Project Status |
Completed (Fiscal Year 1997)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1997: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1996: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | Water / Phase transition / percolation / critical point / 準安定相 / アモルファス氷 / 相図 |
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| Research Abstract |
Water exhibits various anomalies in thermodynamic response functions such as heat capacity and isothermal compressibility, which tend to diverge in supercooled state. From molecular dynamics (MD) simulation, this has been accounted for by Stanley and coworkers, introducing a second critical point of the coexistence line above which low and high density amorphous ices (LDA and HDA) are separated on temperature-pressure plane. It is, however, not clear how to reconcile the critical behaviors with the fact that water loses its anomalies around the same pressure range as the critical point was located by them. Speedy conjectured that LDA has no thermodynamically continuous path from normal water at atmospheric pressure. This is in sharp sontrast to MD simulation study, where it is concluded that no phase boundary exists and water changes continuously. We have performed long MD simulations at constant pressure and found abrupt changes in thermodynamic and structural properties around 213 K.This finding enables us to reconcile both ideas, the second critical point and water II.We investigate the fluctuations of coordination numbers and the spatial correlations of imperfectly coordinated water molecules in two phases of supercooled water. It is found, although the average coordination numbers are 4 in local energy minimum structures of both phases, the magnitude of the fluctuation differs significantly between two phases. Connectivity of water molecules whose first and second neighbors are also perfectly (four-) coordinated is examined. It is revealed that such locally ordered water molecules spread over the entire system in the low density liquid phase whereas those molecules form only small size clusters in the high density liquid water phase. The two water phases are different in conncstivity and the phase transition between two liquid states can be recast into the percolation of locally ordered water molecules.
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Report
(3 results)
Research Products
(13 results)
