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Issue 43, 2011
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Glass transition and phase state of organic compounds: dependency on molecular properties and implications for secondary organic aerosols in the atmosphere

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Abstract

Recently, it has been proposed that organic aerosol particles in the atmosphere can exist in an amorphous semi-solid or solid (i.e. glassy) state. In this perspective, we analyse and discuss the formation and properties of amorphous semi-solids and glasses from organic liquids. Based on a systematic survey of a wide range of organic compounds, we present estimates for the glass forming properties of atmospheric secondary organic aerosol (SOA). In particular we investigate the dependence of the glass transition temperature Tg upon various molecular properties such as the compounds' melting temperature, their molar mass, and their atomic oxygen-to-carbon ratios (O : C ratios). Also the effects of mixing different compounds and the effects of hygroscopic water uptake depending on ambient relative humidity are investigated. In addition to the effects of temperature, we suggest that molar mass and water content are much more important than the O : C ratio for characterizing whether an organic aerosol particle is in a liquid, semi-solid, or glassy state. Moreover, we show how the viscosity in liquid, semi-solid and glassy states affect the diffusivity of those molecules constituting the organic matrix as well as that of guest molecules such as water or oxidants, and we discuss the implications for atmospheric multi-phase processes. Finally, we assess the current state of knowledge and the level of scientific understanding, and we propose avenues for future studies to resolve existing uncertainties.

Graphical abstract: Glass transition and phase state of organic compounds: dependency on molecular properties and implications for secondary organic aerosols in the atmosphere

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Publication details

The article was received on 15 Aug 2011, accepted on 20 Sep 2011 and first published on 12 Oct 2011


Article type: Perspective
DOI: 10.1039/C1CP22617G
Citation: Phys. Chem. Chem. Phys., 2011,13, 19238-19255
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    Glass transition and phase state of organic compounds: dependency on molecular properties and implications for secondary organic aerosols in the atmosphere

    T. Koop, J. Bookhold, M. Shiraiwa and U. Pöschl, Phys. Chem. Chem. Phys., 2011, 13, 19238
    DOI: 10.1039/C1CP22617G

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