期刊
NATURE PHYSICS
卷 5, 期 8, 页码 565-569出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/NPHYS1328
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资金
- World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan
- NSF [DMR-0427239]
- Bernard W. Gamson Computational Science Center at Yeshiva College
The Stokes-Einstein relation has long been regarded as one of the hallmarks of transport in liquids. It predicts that the self-diffusion constant D is proportional to (tau/T)(-1), where tau is the structural relaxation time and T is the temperature. Here, we present experimental data on water confirming that, below a crossover temperature T-x approximate to 290 K, the Stokes-Einstein relation is replaced by a 'fractional' Stokes-Einstein relation D similar to (tau/T)(-zeta) with zeta approximate to 3/5 (refs 1-6). We interpret the microscopic origin of this crossover by analysing the OH-stretch region of the Fourier transform infrared spectrum over a temperature range from 350 down to 200 K. Simultaneous with the onset of fractional Stokes-Einstein behaviour, we find that water begins to develop a local structure similar to that of low-density amorphous solid H2O. These data lead to an interpretation that the fractional Stokes-Einstein relation in water arises from a specific change in the local water structure. Computer simulations of two molecular models further support this interpretation.
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