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| Home > Publications database > The unimpressive origin of the apparent fragile-strong transition. |
| Conference Presentation (Plenary/Keynote) | FZJ-2015-02293 |
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2015
Abstract: Supercooled water is suspected to undergo a fragile-strong transition (FST).Theoretical interest has been fostered by a possible connection with a Widomline emanating from the phase boundary between low and high densityamorphous ice. Experimental support for the FST has mostly come from high-resolution neutron spectroscopy. The FST appears as a kink in the temperaturedependence of a mean relaxation time <τ>. This interpretation depends criticallyon the assumption that the experiment sees one and the same relaxationprocess above and below the kink. Based on new backscattering spectra ofwater in carbon nanohorns we show that the contrary is the case.Formally, our fit function is the same as regularly used in support of a FST: a sumof a delta line, accounting for elastic scattering by the matrix, and a Kohlrauschspectrum. This model suffers from parameter degeneracies. Occam's razor tellsus to maximize constraints under minimal physical assumptions. We useharmonic extrapolations of the T dependent scattering intensity to fix theamplitudes in our delta-plus-Kohlrausch fits. We then identify two q,T regions thatadmit particularly stringent constraints, and a crossover regime in between. Inthis way, we find that quasielastic scattering reveals different physics in differentq,T regimes: At low T, it is dominated by localized motion; at high T by relaxation-coupled diffusion.
Keyword(s): Basic research (1st) ; Others (1st) ; Soft Matter, Macromolecules, Complex fluids, Biophysics (1st) ; Condensed Matter Physics (2nd) ; Soft Condensed Matter (2nd)
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