Colloid thrusters, and electrospray thrusters as a whole, have been around since the 1960s. When they were first developed, the high efficiency and fine thrust control was overshadowed by the high power requirement for such a low thrust that the system provides. This caused the technology to be put on hold for aerospace applications. Now, as small satellites are becoming more prevalent, there has been a resurgence in interest in electrospray thruster technology. The recent advancements in tech- nology allow electrospray thrusters to use significantly less power and occupy less volume than their predecessors. As electrospray technology continues to advance, these thrusters are meeting the demands of small satellite propulsion. As such, in an effort to keep the spacecraft propulsion curriculum current with today’s technology, a colloid thruster is designed, built, tested, and implemented as a laboratory activity at California Polytechnic State University, San Luis Obispo. Electrospray thrusters work by placing a voltage on an ionic liquid and extracting either beads of propellant or ions to generate thrust. By definition, colloid thrusters are a specific class of electrospray thrusters that use solvents, such as glycerol or formamide, to emit droplets or, in special cases, ions to generate thrust. To keep with the University’s “Learn by Doing” pedagogical philosophy, the thruster for this activity is designed to have a tactile and experiential impact on the students. The final design is a scaled up configuration of an existing electrospray design so that the students can easily see each component with the naked eye and can be correlated to a real world thruster that they might see in industry. As a laboratory experiment, the thruster needs to be able to utilize current equip- ment in the Space Environments and Testing Laboratory. One of the Student Vacuum Chambers (SVC) is utilized as well as two 1 kV power supplies and a 100V power supply. An indirect method of measuring performance metrics needs to be developed as there are no thrust balances sensitive enough in the lab designated for undergrad- uate use. As such, the students will be using the mass of the propellant, the time of operation, and knowledge of the propellant’s properties to estimate the performance of the thruster. To prove success of the thruster, a performance profile of the thruster is produced using an indirect method of measurement as well as visual observations of the thruster moving propellant byway of the electrospray theory. The tests show thrusts produced between 96-311 μN with an Isp ranging from 1270-1684 seconds. The visual evidence demonstrates propellant being collected as well as the operation of the thruster under the electrospray theory. The visual evidence also sheds light on which emission mode the thruster is operating at as well as a self-correcting failure mode that was occurring. The thruster is implemented as a lab for Cal Poly’s AERO 402 Spacecraft Propulsion Lab in Fall 2018, and it receives positive feedback from the students through an anonymous survey. While the colloid thruster demonstrates success in meeting performance and pedagog- ical goals, future work should be continued to improve the thruster. Further design and manufacturing work can be undertaken to improve the efficiency and decrease failure due to propellant impingement. Additionally, the procurement of power sup- plies capable of applying higher voltages can provide a greater range of operation which can enable a more dynamic student discovery of electrospray thrusters.

Electrostatically actuated silicon membranes were designed, modeled, fabricated, and characterized. The intended application was for use in a microspeaker. Fabrication issues necessitated the use of thick diaphragms with a large gap between the electrodes. The devices did not function as speakers but did show actuation with a high DC voltage. Device dimensions were chosen by examining membrane mechanics, testing the processing steps required for device fabrication, and modeling with COMSOL. Several adhesives were researched to fabricate the device sidewalls, including BCB, PMMA, and TRA-Bond F112. A method for patterning PMMA through photolithography was found using a scanning electron microscope. Masks were designed in AutoCAD to create the electrostatically actuated devices and a microfabrication process was developed to produce diaphragms that could be characterized. Twenty micron thick diaphragms were fabricated by etching an SOI wafer in 25% TMAH and the etch depth was measured with a profilometer. Glass slides were coated with gold and patterned with positive photoresist to create counter-electrodes. The diaphragms were bonded to the glass slides using a forty micron thick layer of patterned SU-8 as sidewalls. Bonding was successful in the initial fabrication testing but not successful for the final devices. The final fabrication run resulted in eight devices that were partially bonded. Three devices were chosen to test the membrane actuation and the data analyzed for statistical significance. A DC voltage was applied to the electrodes with a MEMS driver and the change in force measured with a micro-force displacement system. Data analysis showed device actuation at high voltages (300V) for the medium and large devices.

The objectives of this study were to carry out research to better understand of the formation, stability and properties of multilayer emulsions containing nano-laminated biopolymer coatings, and to utilize this information to develop food-grade delivery systems. The effect of various preparation parameters on the formation and stability of multilayer emulsions was investigated: droplet concentration; mean droplet diameter; droplet charge; biopolymer concentration. β-lactoglobulin (β-Lg) stabilized emulsions (0.5 – 10 wt% oil) containing different pectin concentrations (0 to 0.5 wt%) were prepared at pH 7 (where lipid droplets and pectin molecules were both anionic) and pH 3.5 (where lipid droplets were cationic and pectin molecules anionic) and “stability maps” were constructed. At pH 3.5, pectin adsorbed to the droplet surfaces, and the emulsions were unstable to bridging flocculation at intermediate pectin concentrations and unstable to depletion flocculation at high pectin concentrations. At certain droplet and pectin concentrations stable multilayer emulsions could be formed consisting of protein-coated lipid droplets surrounded by a pectin layer. An in situ electro-acoustic (EA) technique was introduced to monitor the adsorption of charged polysaccharides onto oppositely charged protein-coated lipid droplets. The possibility of controlling interfacial and functional characteristics of multilayer emulsions by using mixed polysaccharides (pectin/carrageenan or pectin/gum arabic) was then examined. Emulsions containing different types of polysaccharides had different interfacial characteristics and aggregation stabilities: carrageenan had the highest charge density and affinity for the protein-coated lipid droplets, but gave the poorest emulsion stability. The possibility of assembling protein-rich coatings around lipid droplets was examined using the electrostatic deposition method, with the aim of producing emulsions with novel functionality. Protein-rich biopolymer coatings consisting of β-Lg and pectin were formed around lipid droplets using the electrostatic deposition method. The composite particles formed had relatively small diameters (d < 500 nm) and were stable to gravitational separation. They also remained stable after they were heated above the thermal denaturation temperature of the globular protein and had better stability to aggregation at high salt concentrations (50 – 200 mM NaCl) than conventional emulsions stabilized by only protein. The effect of a polysaccharide coating on the displacement of adsorbed globular proteins by non-ionic surfactants from lipid droplet surfaces was examined to simulate situations where competitive adsorption occurs. Oil-in-water emulsions stabilized by β- Lg were prepared containing either no pectin (1º emulsions) or different amounts of pectin (2º emulsions). At pH 3.5, where pectin forms a coating around the β-Lg stabilized lipid droplets, the amount of desorbed protein was much less for the 2º emulsion (3%) than for the 1º emulsion (39%), which indicated that the pectin coating inhibited protein desorption by surface active agents. Knowledge gained from this research will provide guidelines for rationally designing emulsion-based delivery systems that are resistant to environmental stresses or with controlled release properties. These delivery systems could be used to encapsulate, protect and release functional components in various industrial products, such as foods, pharmaceuticals, cosmetics, and personal care products.

<p> Fine structure in thermal neutron (n, α) reactions has been studied for 149Sm, 147Sm, and 143Nd by means of an instrument called an electrostatic particle guide. This device, which was designed to eliminate the problems of background and low energy tailing in (n,α) spectroscopy, is described in detail. Alpha decay has been observed from thermal neutron capture states to levels in the daughter nucleus to greater than 2 MeV excitation. Cross sections and alpha energies are presented for each transition and as well, the alpha decay schemes for 146Nd, 144Nd, 140Ce. Experimental reduced widths have been calculated and are discussed in terms of Mang's theory of alpha decay. Evidence is presented for the (n, γα) process in the 143Nd (n,α) 140Ce reaction. </p> / Thesis / Doctor of Philosophy (PhD)

A nuclear microprobe, typically consisting of 2 - 4 quadrupole magnetic lenses and apertures serving as objective and a collimating divergence slits, focuses MeV ions to approximately 1 x 1 μm for modification and analysis of materials. Although far less utilized, electrostatic quadrupole fields similarly afford strong focusing of ions and have the added benefit of doing so independent of ion mass. Instead, electrostatic quadrupole focusing exhibits energy dependence on focusing ions. A heavy ion microprobe could extend the spatial resolution of conventional microprobe techniques to masses untenable by quadrupole magnetic fields. An electrostatic quadrupole doublet focusing system has been designed and constructed using several non-conventional methods and materials for a wide range of microprobe applications. The system was modeled using the software package "Propagate Rays and Aberrations by Matrices" which quantifies system specific parameters such as demagnification and intrinsic aberrations. Direct experimental verification was obtained for several of the parameters associated with the system. Details of the project and with specific applications of the system are presented.

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