Issue 11, 2020

Transient cavity dynamics and divergence from the Stokes–Einstein equation in organic aerosol

Abstract

The diffusion of small molecules through viscous matrices formed by large organic molecules is important across a range of domains, including pharmaceutical science, materials chemistry, and atmospheric science, impacting on, for example, the formation of amorphous and crystalline phases. Here we report significant breakdowns in the Stokes–Einstein (SE) equation from measurements of the diffusion of water (spanning 5 decades) and viscosity (spanning 12 decades) in saccharide aerosol droplets. Molecular dynamics simulations show water diffusion is not continuous, but proceeds by discrete hops between transient cavities that arise and dissipate as a result of dynamical fluctuations within the saccharide lattice. The ratio of transient cavity volume to solvent volume increases with size of molecules making up the lattice, increasing divergence from SE predictions. This improved mechanistic understanding of diffusion in viscous matrices explains, for example, why organic compounds equilibrate according to SE predictions and water equilibrates more rapidly in aerosols.

Graphical abstract: Transient cavity dynamics and divergence from the Stokes–Einstein equation in organic aerosol

Supplementary files

Article information

Article type
Edge Article
Submitted
09 Dec. 2019
Accepted
15 Febr. 2020
First published
17 Febr. 2020
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2020,11, 2999-3006

Transient cavity dynamics and divergence from the Stokes–Einstein equation in organic aerosol

Y. Song, S. Ingram, R. E. Arbon, D. O. Topping, D. R. Glowacki and J. P. Reid, Chem. Sci., 2020, 11, 2999 DOI: 10.1039/C9SC06228A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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