Fong Wai-Yin Karen. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001 / Includes bibliographical references (p. 173-181). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

This study explores an innovative approach to control the droplet size distribution produced by an electrospray with the intention of eventually being able to deliver precisely controlled quantities of precursor materials for nanofabrication. The technique uses a thermionic cathode to charge the droplets in excess of the Rayleigh limit, leading to droplet breakup or fission. The objective of these experiments was to assess whether the proposed technique could be used to produce a new droplet size distribution with a smaller mean droplet diameter without excessively broadening the distribution. An electrospray was produced in a vacuum chamber using a dilute mixture of ionic liquid. During their transit from the capillary source to a diagnostic instrument, the resulting droplets were exposed to an electron stream with controlled flux and kinetic energy. The droplets were sampled in an inductive charge detector to characterize changes in the size distribution. A positively biased anode electrode was used to collect electron current during droplet exposure. This collected current was used as the primary control variable and used as a measure of the electron flux. The anode bias voltage was a secondary control variable and used as a measure of the electron energy. In a series of seven tests, two sets showed evidence of fission having occurred resulting in the formation of two droplet populations after electron bombardment. Three sets of results showed evidence of a single droplet population after electron bombardment, but shifted to a smaller mean diameter, and one set of results was inconclusive. Because of the large standard deviation in the droplet diameter distributions, the two cases in which a second population was evident were the strongest indication that droplet fission had occurred.

"Orbital flight of CubeSats in extremely Low Earth Orbit, defined here as an altitude between 150 – 250 km, has the potential to enable a wide range of missions in support of atmospheric measurements, national security, and natural resource monitoring. In this work, a mission study is presented to demonstrate the feasibility of using commercially available sensor and electric thruster technology to extend the orbital lifetime of a 3U CubeSat flying at an altitude of 210 km. The CubeSat consists of a 3U configuration and assumes the use of commercially available sensors, GPS, and electric power systems. The thruster is a de-rated version of a commercially available electrospray thruster operating at 2 W, 0.175 mN thrust, and an Isp of 500 s. The mission consists of two phases. In Phase I the CubeSat is deployed from the International Space Station orbit (414 km) and uses the thruster to de-orbit to the target altitude of 210 km. Phase II then begins during which the propulsion system is used to extend the mission lifetime until propellant is fully expended. A control algorithm based on maintaining a target orbital energy is presented in which simulated GPS updates are corrupted with measurement noise to simulate state data which would be available to the spacecraft computer. An Extended Kalman Filter is used to generate estimates of the orbital dynamic state between the 1 Hz GPS updates, allowing thruster control commands at a frequency of 10 Hz. For Phase I, operating at full thrust, the spacecraft requires 25.21 days to descend from 414 to 210 km, corresponding to a ΔV = 96.25 m/s and a propellant consumption of 77.8 g. Phase II, the primary mission phase, lasts for 57.83 days, corresponding to a ΔV = 119.15 m/s during which the remaining 94.2 g of propellant are consumed. "

Ever since its accidental discovery in the 70s, methylaluminoxane, MAO, has been a popular and widely used activator in olefin polymerization. Hydrolysis of primethylaluminum, Me3Al, produces MAO, an aluminum-, oxygen-, and methyl-containing oligomer. Polyolefins have become one of the most produced polymers, where MAO-activated single-site catalysts are responsible for the synthesis of polymers with highly defined structures. The detailed structure of MAO however, remains a mystery. In order to thoroughly understand the reactivity of MAO, knowing more about it is essential. Electrospray ionization mass spectrometry (ESI-MS) has proven to be a useful technique for studying catalysts and their activation chemistry. It has been shown that MAO is best thought of as a source for the highly reactive and Lewis acidic dimethylaluminum cation, [Me2Al]+. Synthetically, this ion is accessible via the reaction between trityl tetrakis(pentafluorophenyl)borate, [Ph3C]+[B(C6F5)4]- and trimethylaluminum, and this reaction was investigated in detail. A new reaction, substitution of H for CH3 onto the phenyl ring of the trityl carbocation, [Ph3C]+, was detected and found to be general for all trialkylaluminums studied. All instruments with detectors are prone to signal saturation at high concentration and mass spectrometers are no exception. Despite the advantages that ESI-MS offers, saturation can be one of the main obstacles in terms of the accurate quantification of species. This thesis tackles saturation issues in ESI-MS explicitly, because relatively high concentrations were necessary in order to keep unwanted decomposition reactions to a minimum. By detuning various parameters that allows troubleshooting this issue, data that better reflects the reality and the corresponding quantification of species is obtained. With the optimal settings of parameters, quantitative studies and the reactivity regarding the addition of trimethylaluminum, Me3Al, to the trityl carbocation [Ph3C]+ can be better understood. / Graduate

No description available.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2006. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010. / Committee Chair: Fernandez, Facundo M.; Committee Member: Bottonley, Lawrence A.; Committee Member: Kelly, Wendy L.; Committee Member: Merrill, Alfred; Committee Member: Orlando, Thomas; Committee Member: Sullards, Cameron. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Not available / text

Electrospray Ionization (ESI) is a technique that permits the soft ionization of large proteins and biomolecules without fragmenting them, which allows them to be characterized via Mass Spectrometry (MS). It has the potential of permitting the identification of transient intermediate products in biological processes in situ, which would provide great insight to researchers in the growing fields of proteomics and metabolomics. However, this application presents a technical challenge in that most relevant biochemistry occurs in aqueous solutions with high salt content, which makes successful identification of analytes by ESI-MS difficult. This thesis presents the design, fabrication, and characterization of a microfabricated dialysis module that could alleviate this issue by desalting samples inline between sampling and electrospraying interfaces. Its small volume (~10 nL) minimizes sample transit time and, thus, optimizes ESI-MS analysis temporal resolution. A preliminary analytical model of dialysis elucidates the key performance parameters and sets the guidelines for consideration in its design. The device is then microfabricated in a cleanroom environment using techniques that have been well established by the microelectronics industry such as E-beam evaporation and Reactive Ion Etching. The system efficiency is demonstrated experimentally by assessing its salt removal effectiveness as a function of sample residence time. Mass spectrometry analyses of proteins in solutions with high salt content further corroborate its performance.