Physics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2800
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Item QUANTIFYING PARTICLE PROPERTIES FROM ION-MOBILITY MEASUREMENTS(2012) Li, Mingdong; Zachariah, Michael R.; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoparticles have received considerable interest due to the wide variety of potential applications in biomedical, optical, and electronic fields. However, our capabilities for quantitatively charactering these materials, for example in number concentration or shape are limited. The objective of this work is to develop experimentally verified theories to quantify particle properties from aerosol based ion-mobility measurement. The use of aerosol tools is predicated on the idea that these methods offer the best chance for quantification, due to a better understanding of the physics of ion transport in the gas phase. Nevertheless this does not preclude us from using these techniques to characterize particles in liquids as will be show in the first part of this work which resolves problems associated with generating an aerosol from colloidal suspensions. In this dissertation I resolve the problem of artificial "droplet induced aggregation" during electrospray which can corrupt the eventual determination of particle size. I develop an experimentally verified statistical based model, to determine and correct this undesired artifact. Furthermore, I have found that this nominally undesired artifact can be used in a beneficial way that allows one to determine the absolute number concentration of nanoparticles in solution, without the need for calibration particles. Mobility is one of the most important and fundamental properties of a particle. However most particle characterization approaches interpret the results of mobility measurement in the context of spherical particle transport. I have undertaken to systematically explore the mobility properties of non-spherical particles. In this dissertation I develop a theory to quantify the effect of orientation on the mobility and the dynamic shape factor of charged axially symmetric particles in an electric field. The experimental results of well-defined doublets of NIST traceable size standard 127nm, 150nm, 200nm and 240nm PSL spheres are shown to be in excellent agreement with the expected values based on my theory. More general new theories of the mobility of nonspherical particles are also proposed and compared with current theories. I also propose a new instrument, a pulsed differential mobility analyzer (PDMA), to obtain shape information by measuring the electrical mobility under different electric fields.Item DEVELOPMENT OF ION-MOBILITY AND MASS SPECTROMETRY FOR PROBING THE REACTIVITY OF NANOPARTICLES AND NANOCOMPOSITES(2009) Zhou, Lei; Zachariah, Michael; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols of diameter smaller than 100 nm, usually are referred as nanoparticles or ultrafines, have received considerable interests lately as a source of building blocks to novel materials. However, our capabilities for charactering these materials are greatly limited by lack of appropriate diagnostic tools. The objective of this work is to develop new aerosol-based techniques for the characterization of nanoparticles and nanocomposites. The scope of this dissertation can be categorized in two ways. First, to provide knowledge of just how reactive a material is, we develop particle ion-mobility spectrometry and Single Particle Mass Spectrometry methods to probe the intrinsic size-dependent reactivity of individual metal particles. And second, the development of a new Time-of-Flight mass spectrometer (TOFMS) combined with a temperature jump (T-Jump) technique to study particle-particle reaction, and probe the reactivity of nanocomposite materials under combustion-like condition.