Acoustic levitation permits the study of droplet dynamics without the effects of surface interactions present in other techniques such as pendant droplet methods. Despite the complexities of the interactions of the acoustic field with the suspended droplet, acoustic levitation provides distinct advantages of controlling morphology of droplets with nanosuspensions post precipitation. Droplet morphology is controlled by vaporization, deformation and agglomeration of nanoparticles, and therefore their respective timescales are important to control the final shape. The balance of forces acting on the droplet, such as the acoustic pressure and surface tension, determine the geometry of the levitated droplet. Thus, the morphology of the resultant structure can be controlled by manipulating the amplitude of the levitator and the fluid properties of the precursor nanosuspensions. The interface area in colloidal nanosuspensions is very large even at low particle concentrations. The effects of the presence of this interface have large influence in the properties of the solution even at low concentrations. This thesis focuses on the dynamics of particle agglomeration in acoustically levitated evaporating nanofluid droplets leading to shell structure formation. These experiments were performed by suspending 500µm droplets in a pressure node of a standing acoustic wave in a levitator and heating them using a carbon dioxide laser. These radiatively heated functional droplets exhibit three distinct stages, namely, pure evaporation, agglomeration and structure formation. The temporal history of the droplet surface temperature shows two inflection points. Morphology and final precipitation structures of levitated droplets are due to competing mechanisms of particle agglomeration, evaporation and shape deformation. This thesis provides iv a detailed analysis for each process and proposes two important timescales for evaporation and agglomeration that determine the final diameter of the structure formed. It is seen that both agglomeration and evaporation timescales are similar functions of acoustic amplitude (sound pressure level), droplet size, viscosity and density. However it is shown that while the agglomeration timescale decreases with initial particle concentration, the evaporation timescale shows the opposite trend. The final normalized diameter hence can be shown to be dependent solely on the ratio of agglomeration to evaporation timescales for all concentrations and acoustic amplitudes. The experiments were conducted with 10nm silica, 20nm silica, 20nm alumina and 50nm alumina solutions. The structures exhibit various aspect ratios (bowls, rings, spheroids) which depend on the ratio of the deformation timescale (tdef) and the agglomeration timescale (tg). For tdef

Acoustic levitation utilizes general principles of ultrasonics to trap particles in midair without external support. This is done by creating an array of ultrasonic transducers to propagate sound waves to a focused point in space. In order to optimize the particle trap it is necessary to design transducers that can produce enough sound to create pressure pockets. In this work I examine the fundamental principles of acoustics by testing the sound pressure levels (SPL) of a known transducer in both air and water mediums. A comparison between domed and bimorphed transducers are also examined. Experimentation was performed on the feasibility of implementing a domed transducer array. Methods are described to fabricate a piezoelectric thin film made from poly(vinylidene difluoride) (PVDF). These films were analyzed for β-phase concentration, as well as transmission, resolution, and contrast. An additional study into the use of Indium Tin Oxide (ITO) as a conductive dielectric layer of a transducer is also examined. These studies are designed to test if spin coating can provide the necessary conditions to fabricate transparent, piezoelectric PVDF films. Included are the research and experiments that I conducted to determine the transparency of PVDF. I performed analysis on the transmission, absorption, and scatter of fabricated PVDF films. My results show that it is possible to fabricate PVDF films that are both transparent and piezoelectric.

Ultraschalllevitation kombiniert die Vorteile von Mikrofluidik, wie beispielsweise die sehr geringe benötigte Probenmenge, mit einer wandlosen Probenhandhabung. Obwohl die Kopplung zwischen le- vitierten Tröpchen und verschiedenster analytischer Methoden wie optischer Spektroskopie und Röntgenbeugung sehr genau untersucht ist, fehlt es immer noch an einer etablierten Kopplung mit einer massenspektrometrischen Methode für die Analyse auf molekularer Ebene. Die vorliegende Arbeit beschreibt die Prinzipien, auf denen eine kontaktlose massenspektrometrische Analyse von levitierten flüssi- gen Proben beruht. Zuerst wurde der neu entworfene akustische Levitator bezüglich des Einflusses seiner Geometrie auf die Levi- tationseigenschaften experimentell und mittels numerischer Simul- tationen untersucht. Die anschließend durch geführten Experimen- te demonstrieren das Potential von Infrarot-Lasern als kombinierte Desorptions- und Ionisationsquelle für organische Substanzen aus einer Mischung aus Wasser und Glycerin als Cromophor. Um einen tieferen Einblick in die hierbei ablaufenden Ionisationsmechanismen zu erhalten, wurde als Modell ein “Sonic-Spray” Konus räumlich per Massenspektrometrie und Laser-induzierter Fluoreszenz untersucht. Levitator-Geometrie auf die Levitationseigenschaften stimmen sehr gut mit numerischen Simulationen überein. Als komplementäre Ionisationsmethode wurde eine Niedertemperatur-Plasmaquelle ein- gesetzt. Nach einer zeitaufgelösten Untersuchung der grundlegenden Ionisationsmechanismen wurde diese Quelle für die Untersuchung flüchtiger Spezies aus der levitierten Probe in deren direkten Umgebung ohne störende Interferenzen ge- nutzt. / Ultrasonic levitation combines advantages of microfluidics like the required small sample volumes with a wall-less sample handling. While the coupling of analytical methods like optical spectroscopy as well as x-ray scattering are very well elaborated, an established mass spectrometric method to obtain molecular analytical information is still lacking. The herein presented work describes the fundamental processes for a contactless mass spectrometric analysis of levitated droplets. First, the influences of the specially designed levitator geometry on the levitation capabilities is described. During further experiments, the use of infrared lasers has proven useful as a combined desorption and ionization source for organic molecules from a mixture of water and glycerol as chromophore. Subsequently, sonic-spray ionization was used to gain a deeper understanding of the ionization processes occurring within the spray plume. Mass spectrometric mapping as well as laser-induced fluorescence were performed to investigate the ionization during an aerodynamic breakup of the micro droplets in the spray process. As a complementary sampling method, the ionization with a low- temperature plasma source is described. First, a time-resolved mass spectrometric investigation of the ionization process is shown. Sub- sequent to this fundamental study, the application of such a plasma source for the direct analysis of volatile compounds from within the droplets in the surrounding environment without interferences from the droplets bulk phase is described.

The standard technology used in a pick and place machine for lifting and transportingsurface mount electronic components is a vacuum based solution.  This thesis investigates a new acoustic based technology for manipulating surface mountelectronic components.  Using a microelectromechanical systems-based transducers array to create a standing wave, small objects and components were levitated and studied.  It was examined how the distance would affect the levitation ability of different objects with varying density as well as how the stability was affected. It was concluded that the distance variation of approximately 10 mm had no significant affecton the levitation ability. The longer distance did result in a less stable behavior of the levitated object. / Standardtekniken som används i en pick-and-placemaskin för att lyfta och förflytta ytmonterade elektroniska komponenter är baserad på en vakuumbaserad lösning. Detta examensarbete undersöker en ny akustisk baserad teknik för att manipulera ytmonterade elektroniska komponenter.  Med hjälp av en mikroelektromekaniskt system-baserad piezoelektrisk givare skapades en stående våg, för att levitera och studera små föremål och komponenter. Det undersöktes hur avståndet skulle påverka levitationsförmågan hos olika föremål med varierande densitet samt hur stabiliteten påverkades.  Slutsatsen som drogs var att avståndsvariationen på cirka 10 mm inte hade någon signifikant påverkan på levitationsförmågan. Det längre avståndet resulterade dock i ett mindre stabilt beteende hos det svävande föremålet.

Die Kopplung von akustischer Levitation mit optischer Spektroskopie ermöglicht die Untersuchung von Reaktionen und intermolekularen Wechselwirkungen unter besonderen Bedingungen. Mit akustischer Levitation können Proben im µL-Bereich kontaktfrei gehaltert und Verunreinigungen durch Oberflächenkontaminationen ausgeschlossen werden. Durch die Verwendung verschiedener Methoden der optischen Spektroskopie wie Raman-Streuung, UV/Vis-Absorptions- und Fluoreszenz-Spektroskopie konnten die levitierten Proben untersucht werden. Die durchgeführten Untersuchungen zeigen, dass die Ultraschallfalle aufgrund der Wandlosigkeit sowie des Kontakts der levitierten Probe mit der Atmosphäre und der daraus resultierenden möglichen Aufkonzentrierung eine interessante Möglichkeit zur Probenhandhabung in der Mikrofluidik darstellt. Anhand zweier sonochemischer Reaktionen wurde mit Absorptionsspektroskopie gezeigt, dass das Ultraschallfeld des Levitators nur einen sehr geringen Einfluss auf die levitierte Probe ausübt. Mittels Absorptions- und Fluoreszenzspektroskopie wurde die durch die Verdampfung induzierte Aggregation eines Farbstoffes untersucht. Zudem wurde die relative Quantenausbeute des Farbstoffes im levitierten Tropfen bestimmt. Der Kontakt des levitierten Tropfens mit der umgebenden Atmosphäre kann auch zur Aufnahme von Substanzen aus der Atmosphäre führen. Dieser Effekt wurde anhand von levitierten ionischen Flüssigkeiten volumetrisch und schwingungsspektroskopisch bei verschiedenen Luftfeuchten untersucht und die Wechselwirkungen mit dem absorbierten Wasser detailliert charakterisiert. Die Kopplung und simultane Messung von Raman-Streuung und UV/Vis-Spektroskopie ermöglichte die Untersuchung der Bildung und Aggregation von Silber-Nanopartikeln und deren Auswirkungen auf die oberflächenverstärkte Raman-Streuung. Zudem wurde die Stabilisierung von Silber-Nanopartikeln in ionischen Flüssigkeiten und die Wechselwirkungen der Partikel mit den ionischen Flüssigkeiten untersucht. / Acoustic levitation in combination with optical spectroscopy allows for investigations of reactions and intermolecular interactions under specific conditions. Samples with microliter volumes can be handled without contact to solid surfaces resulting in the absence of impurities from surface contamination. Using different optical spectroscopy methods such as Raman, UV/vis, and fluorescence spectroscopy, different levitated samples were characterized in detail within this work. The investigations show that the acoustic levitator is an interesting tool for sample handling due to the wall-less fixture and because of the interaction of the levitated sample with the surrounding atmosphere. This interaction leads to an increase of a solved analyte upon the evaporation of the solvent. The ultrasonic field inside the trap was characterized by investigations of sonochemical reactions, which show a negligible influence of the ultrasonic field on the levitated sample. Absorption as well as fluorescence spectroscopy was used to study the aggregation of a dye due to an increasing concentration upon evaporation of the solvent. Furthermore, the relative quantum efficiency of the dye was determined from levitated droplet experiments. The interaction of the levitated droplet with the surrounding atmosphere can also lead to absorption of airborne substances. This effect was investigated for different levitated ionic liquids. Volumetric and vibrational studies were performed on levitated ionic liquids under different atmospheric humidity conditions to characterize the interaction of ionic liquids with water. Hyphenation of Raman scattering and UV/vis absorption spectroscopy enabled the investigation of the formation and aggregation of silver nanoparticles and the correlation of this information with the recorded surface-enhanced Raman spectra. In addition, the stability of silver nanoparticles in ionic liquids and the interactions of the particles with the ionic liquids were examined.