| DATE: |
2004-12-21 11:00 - 12:30 |
| PLACE: |
4-go-kan 2F Rinkoshitsu1 |
| TITLE: |
IMSS Seminar Observation of Fragile-to-Strong Liquid-Liquid Transition in Deeply Supercooled Confined Water by Quasielastic Neutron Scattering |
| SPEAKER: |
Prof. Sow-Hsin Chen (Department of nuclear Engineering, Massachusetts Institute of technology) |
| LANGUAGE: |
English |
| URL: |
http://pfwww.kek.jp/pf-seminar/ |
| ABSTRACT: |
Confining water in lab synthesized nanoporous silica matrices MCM-41-S with pore diameters in the range of 10 to 18 Άς, we have been able to study the molecular dynamics of water in deeply supercooled states, from 350 K down to 200 K, including a range of temperatures inaccessible to bulk water.. Using two high-resolution quasielastic neutron scattering instruments available in NIST CNR and analyzing the data with a new relaxing cage model formulated by us, we determined the temperature variation of the average translational relaxation time and its Q-dependence. We find a clear evidence of an abrupt change of the temperature dependence of the relaxation time from a non-Arrhenius to an Arrhenius behavior at T = 225 K, which we interprete as the predicted fragile-to-strong liquid-liquid transition in supercooled water. Our more recent inelastic neutron scattering measurements of the librational density of states indicate that the transition is related to the structural change of the hydrogen-bond cage around the water molecule.
Collaborators: A. Faraone (MIT), L. Liu (MIT), C.-Y. Mou (NTU), C.-W. Yen (NTU)
A lecture to be given at the Institute for Materials Structure Science,
KEK, Tsukuba, Japan on December 21, 2004. |
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