title: Glass transition and phase state of organic compounds: dependency on molecular properties and implications for secondary organic aerosols in the atmosphere.
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 T(g) 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.
authors: Bielefeld University, Faculty of Chemistry, D-33615 Bielefeld, Germany. thomas.koop@uni-bielefeld.de
authors: Thomas
authors: T
authors: Koop
authors: Johannes
authors: J
authors: Bookhold
authors: Manabu
authors: M
authors: Shiraiwa
authors: Ulrich
authors: U
authors: Pöschl
mesh_terms: D000336:Aerosols / Q000737:chemistry*; D001272:Atmosphere / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry*; D010084:Oxidation-Reduction; D010316:Particle Size; D044367:Phase Transition; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D000336:Aerosols; D009930:Organic Chemicals; D014867:Water