Date of Degree
PhD (Doctor of Philosophy)
Alexei V. Tivanski
The contribution of atmospheric aerosols towards radiative forcing has a very high uncertainty due to their short atmospheric lifetime. The aerosol effects are largely controlled by the density, elemental composition, and hygroscopic properties of the aerosol particles. Therefore, we have performed designed new methodology using Scanning Transmission X-ray Microscopy (STXM), Atomic force spectroscopy (AFM), micro-FTIR spectroscopy and Scanning Electron Microscopy (SEM) to quantify these important aerosol properties. Hygroscopic properties are quantified by plotting the mass of water on a single particle basis, calculated from STXM, as a function of relative humidity. Alternatively, micro-FTIR spectra have been used to study the effect of composition of aerosol particles on the hygroscopic properties of NaCl. Moreover, a unique combination of STXM and AFM has been utilized to quantify density and elemental composition of micrometer dimensional particles. This method has also been extended towards exploring mixing state of particles, consisting of heterogeneously mixed inorganic and organic compounds. In addition to these above mentioned properties, the fate of an atmospheric particle is often altered by chemical transformation and that in turn is influenced by the atmospheric RH. Therefore, we have studied an unusual keto-enol tautomerism in malonic acid particles at high RH, which is not observed in bulk. This observation could potentially be utilized to significantly improve the models to estimate Secondary Organic Aerosols (SOA). Using STXM and micro-FTIR technique, RH dependent equilibrium constant of the tautomerism reaction has been quantified as well.
Organic nanocrystals capable of undergoing solid state photochemical changes in a single-crystal-to-single-crystal (SCSC) manner have been particularly important in fabricating molecular switches, data storage devices etc. Mechanical properties of these nanomaterials may control its SCSC reactivity. In addition, investigation of mechanical stiffness is important to define allowable limit of stiffness towards device application. Therefore, we studied mechanical properties of series organic nano cocrystals primarily consisting of trans-1,2-bis(4-pyridyl)ethylene and substituted resorcinol using AFM nanoindentation technique. Dependence of mechanical properties and SCSC reactivity on the resorcinol structure is also investigated as well. Moreover, photolithography on the thin film of these organic cocrystals has been performed to demonstrate its applicability as a photoresist.
AFM, Atmospheric aerosol, Hygroscopic properties, mechanical properties, STXM, thin film
Copyright 2013 Suman Ghorai