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| Titel |
Quantifying water diffusion in high-viscosity and glassy aqueous solutions using a Raman isotope tracer method |
| VerfasserIn |
H. C. Price, B. J. Murray, J. Mattsson, D. O'Sullivan, T. W. Wilson, K. J. Baustian, L. G. Benning |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 8 ; Nr. 14, no. 8 (2014-04-16), S.3817-3830 |
| Datensatznummer |
250118618
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| Publikation (Nr.) |
 copernicus.org/acp-14-3817-2014.pdf |
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| Zusammenfassung |
| Recent research suggests that under certain temperature and relative humidity
conditions atmospheric aerosol may be present in the form of a glassy solid.
In order to understand the impacts that this may have on aerosol–cloud
interactions and atmospheric chemistry, knowledge of water diffusion within
such aerosol particles is required. Here, a method is described in which
Raman spectroscopy is used to observe D2O diffusion in high-viscosity
aqueous solutions, enabling a quantitative assessment of water diffusion
coefficients, Dwater, as a function of relative humidity. Results
for sucrose solutions compare well with literature data at
23.5 ± 0.3 °C, and demonstrate that water diffusion is slow
(Dwater ~5 × 10−17 m2 s−1), but
not arrested, just below the glass transition at a water activity of 0.2.
Room temperature water diffusion coefficients are also presented for aqueous
levoglucosan and an aqueous mixture of raffinose, dicarboxylic acids and
ammonium sulphate: at low humidity, diffusion is retarded but still occurs on
millisecond to second timescales in atmospherically relevant-sized particles.
The effect of gel formation on diffusion in magnesium sulfate solutions is
shown to be markedly different from the gradual decrease in diffusion
coefficients of highly viscous liquids. We show that using the
Stokes–Einstein equation to determine diffusion timescales from viscosity
leads to values which are more than 5 orders of magnitude too big, which
emphasises the need to make measurements of diffusion coefficients. In
addition, comparison of bounce fraction data for levoglucosan with measured
diffusion data reveals that even when particles bounce the diffusion
timescales for water are a fraction of a second for a 100 nm particle. This
suggests a high bounce fraction does not necessarily indicate retarded water
diffusion. |
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