Insights on Phase Transitions in Submicron Aerosol Particles
- Author:
- Kucinski, Theresa M.
- Published:
- [University Park, Pennsylvania] : Pennsylvania State University, 2020.
- Physical Description:
- 1 electronic document
- Additional Creators:
- Freedman, Miriam Arak
Access Online
- etda.libraries.psu.edu , Connect to this object online.
- Restrictions on Access:
- Open Access.
- Summary:
- Aerosols are suspended liquid or solid particles that are ubiquitous in the atmosphere. These particles can affect the climate directly by absorbing/scattering radiation or indirectly by helping the formation of clouds. Aerosol particles have an overall net cooling effect, however, there is a large uncertainty associated with the magnitude of cooling. A portion of this uncertainty is due to an incomplete understanding of the chemical and physical properties of particles. Aerosol particles also exist over a large range of sizes which can alter these properties due to size effects, that would require parameterization. Properties that need to be further explored include morphology, phase transitions, and their respective size dependence. This dissertation explores size effects associated with liquid-liquid phase separation (LLPS) and the development of a new method to study phase transitions in submicron particles. Previously, we found that LLPS is a size-dependent process in submicron particles consisting of an organic compound and a single salt component. The size-dependence produces large particles that phase separate while small particles remain homogeneous. Particles in the atmosphere are complex and can contain hundreds of organic compounds. To expand the size-dependence study to better mimic ambient aerosol, we studied particles consisting of complex organic mixtures and ammonium sulfate. The organic mixtures included: dicarboxylic acids (DCA), complex organic mixtures (COM), and [alpha]-pinene secondary organic matter (SOM). We imaged the particles with cryogenic- transmission electron microscopy (cryo-TEM) and all systems displayed size-dependent morphology. Additionally, we observed the presence of three-phase particles in addition to 'channel' morphology. Our results provide further evidence that size-dependent LLPS may be relevant for ambient aerosol. Studying phase transitions in individual submicron particles proves to be difficult with currently available techniques. We present a new method that flash freezes particles to create snapshots into the phase transition process for submicron particles. This method uses vitrification, which is a technique which cools the sample rapidly such that crystallization is avoided and the humidified properties are retained. A temperature controlled flow tube is use to vitrify the particles at several relative humidity (RH) points followed by imaging with cryo-TEM. The method was verified using efflorescence of potassium salts. Additionally, we demonstrate the ability to image the process of LLPS in submicron particles consisting of 2-methylglutaric acid (2-MGA) and ammonium sulfate. We applied the flash freeze technique to study the dynamics of LLPS in submicron particles. In particular, we studied separation relative humidity (SRH), which is defined as the RH that separation occurs, for 2-MGA/ammonium sulfate, 1,2,6-hexantriol/ammonium sulfate, and COM/ammonium sulfate. Particles were vitrified and imaged above phase separation, throughout the process of separation, and until LLPS reaches final maturation. We found that the onset of separation is lower for submicron particles than for particles several micrometers in diameter, indicating a potential shift in the phase diagrams. Additionally, the average SRH is significantly lower for submicron particles in the nucleation and growth regime compared to bulk systems. The decrease in SRH indicates a need for new parameterizations to accurately define particles in models. We also found that the dynamics of separation is a random process that is not dependent on size except for the smallest particles which remain homogeneous throughout. The onset of separation occurs over a large range of RH and our results suggest that this is a result of the energy barrier associated with nucleating a new phase.
- Other Subject(s):
- Genre(s):
- Dissertation Note:
- Ph.D. Pennsylvania State University 2020.
- Technical Details:
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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