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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2015)

The fundamental properties of 1-n-alkyl-3-methylimidazolium ([CnMIM+], n = number of carbons on the linear alkyl chain)-based ionic liquids (ILs) are not fully characterized, including quantification of the amount of water or carbon dioxide (CO2) absorbed from the atmosphere and the nature of the IL‒water or IL‒CO2 interactions. For example, interactions of bulk ILs and water in previous studies were limited by slow equilibration times of the ILs when exposed to water vapor. This is the first study of the interaction of water or CO2 with aerosolized IL nanoparticles. The particles’ small size ensures IL‒water vapor equilibrium is achieved quickly. Additionally, ILs may have the ability to absorb large amounts of CO2 and can be used for CO2 sequestration in the environment.

The combined experimental and theoretical techniques of tandem nano-differential mobility analysis (TDMA), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and molecular dynamics (MD) simulations were used to provide a comprehensive picture of the behavior of absorbed water or CO2 in IL nanoparticles and thin films. [CnMIM]+ (n = 2, 4, or 6) paired with Cl‒ or BF4‒ were studied to examine the effect of alkyl chain length on IL hygroscopicity and CO2 uptake. Particles' growth from water or CO2 uptake was quantified using TDMA. For the hygroscopicity studies, growth curves show steady uptake of water vapor with increasing relative humidity. Water molar fractions (χw) agreed well with those estimated from ATR-FTIR data. Additionally, the performance of several liquid activity coefficient models were evaluated by fits to the experimental data. MD simulations, used to model IL−water interactions, revealed considerably stronger interactions between Cl− and water compared to BF4− and water. The increase in growth factor after CO2 exposure showed little change for the IL studied. These combined experimental, theoretical, and modeling techniques help provide a more complete picture for these two families of ILs in the presence of water or CO2. The techniques also provide a quantitative parameterization of the amount of water vapor that ILs with different alkyl chain lengths can absorb under equilibrium conditions.

The use of ILs as suitable seed particles for secondary organic formation and growth from α-pinene ozonolysis in an environmental smog chamber was also explored. Additionally, we investigated the sensitivity of the nanoparticles’ chemical composition to varying operation conditions in electrospray aerosol generators.

    Cover page: Uptake of Water and Other Molecules by Aerosolized Nanoparticles
    • Article
    LBL Publications (2014)
    The size and thickness of organic aerosol particles from five field campaigns were compared to those of laboratory generated secondary organic aerosols (SOA) using scanning transmission x-ray microscopy (STXM). Impacted organic particles were identified and the total carbon absorbance (TCA) was analyzed as a function of the area equivalent diameter of the particle on the substrate. Because they flatten less upon impaction, particles with higher viscosity and surface tension can be identified by a steeper slope on a plot of TCA vs. size. The slopes of the ambient data are statistically similar indicating a small range of average viscosities and surface tensions across five field campaigns. Steeper slopes were observed for the plots corresponding to ambient particles, while smaller slopes were indicative of the laboratory generated SOA. This suggests that, on average, ambient organic particles have higher viscosities and surface tensions than the more liquid like laboratory generated SOA particles.
      Cover page: Phase State and Physical Properties of Ambient and Laboratory Generated Secondary Organic Aerosol
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2014)
      The size and thickness of organic aerosol particles collected by impaction in five field campaigns were compared to those of laboratory-generated secondary organic aerosols (SOA). Scanning transmission X-ray microscopy was used to measure the total carbon absorbance (TCA) by individual particles as a function of their projection areas on the substrate. Particles with higher viscosity/surface tension can be identified by a steeper slope on a plot of TCA versus size because they flatten less upon impaction. The slopes of the ambient data are statistically similar indicating a small range of average viscosities/surface tensions across five field campaigns. Steeper slopes were observed for the plots corresponding to ambient particles, while smaller slopes were indicative of the laboratory-generated SOA. This comparison indicates that ambient organic particles have higher viscosities/surface tensions than those typically generated in laboratory SOA studies.
        Cover page: Physical properties of ambient and laboratory‐generated secondary organic aerosolCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2017)
        Secondary organic aerosol (SOA), formed in the photooxidation of diesel fuel, biodiesel fuel, and 20% biodiesel fuel/80% diesel fuel mixture, are prepared under high-NOx conditions in the presence and absence of sulfur dioxide (SO2), ammonia (NH3), and relative humidity (RH). The composition of condensed-phase organic compounds in SOA is measured using several complementary techniques including aerosol mass spectrometry (AMS), high-resolution nanospray desorption electrospray ionization mass spectrometry (nano-DESI/HRMS), and ultrahigh resolution and mass accuracy 21T Fourier transform ion cyclotron resonance mass spectrometry (21T FT-ICR MS). Results demonstrate that sulfuric acid and condensed organosulfur species formed in photooxidation experiments with SO2 are present in the SOA particles. Fewer organosulfur species are formed in the high humidity experiments, performed at RH 90%, in comparison with experiments done under dry conditions. There is a strong overlap of organosulfur species observed in this study with previous field and chamber studies of SOA. Many MS peaks of organosulfates (R-OS(O)2OH) previously designated as biogenic or of unknown origin in field studies might have originated from anthropogenic sources, such as photooxidation of hydrocarbons present in diesel and biodiesel fuel.
          Cover page: Molecular Characterization of Organosulfur Compounds in Biodiesel and Diesel Fuel Secondary Organic AerosolCreative Commons 'BY-NC-ND' version 4.0 license
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