Factors that Influence Aerosol Particle Liquid-Liquid Phase Separation
Open Access
- Author:
- Ott, Emily Jean
- Graduate Program:
- Chemistry (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 23, 2021
- Committee Members:
- Seong Kim, Outside Unit & Field Member
Christine Keating, Major Field Member
Miriam Freedman, Chair & Dissertation Advisor
Philip Bevilacqua, Program Head/Chair
Michael Hickner, Major Field Member - Keywords:
- Aerosol Particles
Liquid-Liquid Phase Separation
Polymers
Size dependent morphology - Abstract:
- Aerosol particles can have a variety of compositions which determines their origin and their phase transitions. They can exist in the atmosphere where they are emitted from a variety of natural and anthropogenic sources. Aerosol particles can impact the climate directly though interacting with radiation or indirectly by nucleating cloud droplets and the clouds interacting with the sun. Aerosols can also impact health through the respiratory system. Additionally, aerosols can be used for synthetic purposes where they are created purposely for pharmaceutical or material creation along with many other applications. Understanding the factors that influence phase transitions that a particle may undergo is a prerequisite to understanding both atmospheric aerosol and synthetic aerosol. Several of these factors are investigated. First, the impact of the average ratio of oxygen to carbon (O:C) atoms in the organic molecules through the addition of sucrose to aerosol particles is studied using optical microscopy. A variety of organic molecules and salts combinations which are able to undergo phase separation were studied. The organic/inorganic mixtures exhibit a mixture both high and low separation relative humidities. Then sucrose was added until the particles no longer exhibit phase separation. Particles with higher separation relative humidities in the absence of sucrose required larger quantities of sucrose in order to inhibit phase separation. Additionally, phase separation was seen at higher O:C values than published previously, showing that while average O:C is a good indicator of phase separation, the precise composition of the particles is more important. The morphology of polymer/polymer aerosol particles according to their size was determined. In agreement with previous work, large particles undergo liquid-liquid phase separation while small particles remain homogeneous. Polyethylene glycol with dextran was used as well as polystyrene sulfonate with polyvinyl alcohol. Both of these systems inhibited phase separation at small sizes. To understand the size dependent morphology of polymer/polymer systems, different molecular weight mixtures of the polymers were studied. As the molecular weight of the polymers increased, smaller and smaller aerosol particles were able to undergo phase separation. This was further confirmed with a simple model based on the equations of phase separation and Flory-Huggins theory of a binary system which also showed the decrease in the size of the smallest phase separated particle as the molecular weight of the polymers increase in the size regime studied. The project created novel polymer materials and investigated the phase separation of polymer/polymer systems in confinement. The phase separation of submicron aerosol particles with different salts was investigated to determine the influence of different anions on the size dependent morphology of aerosol particles. The ammonium, sodium, chloride and sulfate ions were used. TEM was used to determine that sodium salts transition to homogenous particles at smaller sizes than their comparable ammonium salt. This difference is likely due to the softness of the ammonium ion when compared to the hardness of the sodium ion. This study provides insights into the size dependent morphology of sea spray aerosol may differ from that of continental aerosol in addition to increasing our understanding of how cations and anions impact phase transitions under confinement. These studies combined increase knowledge of confined phase transitions. While the O:C ratio has been studied before, the importance of the actual composition over the average O:C ratio has now been shown which is useful in understanding atmospheric aerosol particles. The presence of a size dependent morphology for polymer-polymer systems has been shown and modeled in addition to the development of novel polymeric materials. The phase separation differences between ammonium containing aerosols and sodium containing aerosols provides key insights into the differences between continental aerosol and sea spray aerosol in addition to contributing new information about the importance of cations in liquid-liquid phase separation of confined systems. Through these studies both atmospheric aerosol and synthetic aerosol are now better understood.