Glass Transition Temperatures of Organic Mixtures from Isoprene Epoxydiol (IEPOX) Derived Secondary Organic Aerosols

BO CHEN, Jessica Mirrielees, Yuzhi Chen, Zhenfa Zhang, Avram Gold, Jason Surratt, Yue Zhang, Sarah Brooks, Texas A&M University

     Abstract Number: 397
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
The phase states and the glass transition temperatures (T_g) of secondary organic aerosols (SOA) are important parameters for understanding their formation, growth, fate, and cloud formation properties. Previous studies have measured the T_g of pure SOA components. However, there is limited understanding of how the T_g changes with the composition of organic aerosol mixtures. Here we measured the T_g of organic binary mixtures of isoprene epoxydiol (IEPOX)-derived SOA components, including 2-methyltetrol (2-MT), 2-methyltetrol-sulfate (2-MTS), and 3-methyltetrol-sulfate (3-MTS) using broadband dielectric spectroscopy. The results demonstrate that the T_g of binary mixtures is a function of their composition and could be affected by molecular interactions between the two components. The commonly used Gordon-Taylor equation cannot accurately predict the S-shaped T_g-composition relationship of 2-MT/2-MTS and 2-MT/3-MTS mixtures. The Kwei equation, which is a modified Gordon-Taylor equation with an added quadratic term and a fitting parameter representing strong intermolecular interactions, provides a better fit in these cases. By combining Raman spectroscopy with geometric optimization simulation using density functional theory, we demonstrate that the non-linear deviation of the T_g of 2-MT/2-MTS and 2-MT/3-MTS mixtures are caused by changes in hydrogen bonding strength and number due to changes in composition.