Highly monodisperse droplets are attracting great attention both in many research areas, such as aerosol science, combustion, and Nano-manufacturing. This thesis invents a novel aerosol generator: “Periodic Electro Hydro-dynamic Chopper” termed as “PEHD chopper”, and develops a new method to directly print micro-patterns with monodisperse droplets. The principle of the PEHD chopper is to use the fringe electric field of a capacitor to introduce controlled perturbation on a liquid jet. We first derived the governing equations for a circular inviscid liquid jet under transverse electric fields. The electric fields were obtained through numerical simulation. Then we used a high speed camera (up to one million frames per second) to visualize the jet break-up as well as the droplets’ size and shape. The experiments show that the PEHD chopper can effectively “chop” a neutral micro-jet and generate highly monodisperse micro-droplets, which diameter range from 100 µm to 500 µm. To reduce the droplet size, PEHD chopper with a butterfly design is applied on a typical single electrospray. In this configuration, the jet swings at long wavelengths (>R), where R is the Rayleigh wave length, but breaks up into highly monodisperse droplets near 2R and R without satellite droplets. The butterfly configuration combined with electrified jet expands the diameter range into 20 µm to 100 µm. iv Finally, we demonstrate the electrospray printing of Polymer Derived Ceramics (PDC) for sensor applications in harsh environment. A modified single ES with an additional driving electric field is used to directly print PDC precursor without mask, we achieved 1D feature as narrow as 35 µm and a micro pentagram pattern. Moreover, after pyrolysis of PDC at 1100 °C in nitrogen, amorphous alloys of silicon, carbon and nitrogen (SiCN) are obtained. The samples exhibit excellent good integrity and adhesion to the substrate.

Superhydrophobic (SH) surfaces are characterized by their extraordinary water repellent qualities. When water comes in contact with these surfaces, it beads up and rolls around. This phenomenon is due partially to surface chemistry which promotes weak adhesive forces between liquid and solid. However, micro- and nanoscale surface roughness also plays a crucial role by trapping air beneath the liquid, reducing liquid-solid contact. Many advantages of these surfaces have been identified, including drag reduction and self-cleaning properties, and the body of research regarding them has grown rapidly over the past few decades.This thesis is concerned with water droplets impinging superheated, superhydrophobic surfaces. In these scenarios, boiling is common in the droplet, producing vapor bubbles which burst through the droplet lamella and cause a spray of miniscule water particles known as thermal atomization. The work contained in this thesis uses an image processing technique to quantify trends in thermal atomization intensity during droplet impingement scenarios for a range of surface microstructure configurations, superheat temperatures, and Weber numbers.In one study, droplet impingement on a smooth hydrophobic and three post-patterned SH surfaces of similar solid fraction is considered. In general, as pitch (center-to-center distance between posts) increases, atomization intensity decreases. This is attributed to the enhanced ability for vapor escape beneath the droplet that is present for wider pitch surfaces. Atomization intensity increases with increasing Weber number for each of the surfaces considered. Additionally, the Leidenfrost point is found to increase with increasing Weber number and decreasing pitch.Next, thermal atomization on SH surfaces with two distinct microstructure configurations is considered: square posts (which allow vapor escape between structures) and square holes (which block vapor escape). Tests are done for each configuration with varying microstructure height, and structure spacing and solid fraction are held constant. Comparing the two configurations at each structure height and Weber number, the post-patterned surfaces suppress atomization for a large number of scenarios compared to the hole surfaces, supporting the theory that vapor escape through microstructures suppresses atomization. Microstructure height significantly affects trends in atomization intensity with surface temperature and Weber number. The LFP is seen to decrease with increasing height.

<p> Levitation melting was used to study the oxidation kinetics of free falling iron droplets. Single droplets of Armco iron were deoxidized and allowed to fall through oxidizing columns of known heights and then quenched in Silicone Oil. The rate of oxygen pick up by a droplet was found to be dependent upon its initial temperature, its size, and the composition of the reacting gas. The proposed mechanism is presented with kinetic data.</p> / Thesis / Master of Engineering (MEngr)

Improvements in mass spectrometry (MS)-based strategies for characterizing the plant lipidome through quantitative and qualitative approaches such as shotgun lipidomics have substantially enhanced our understanding of the structural diversity and functional complexity of plant lipids. However, most of these approaches require chemical extractions that result in the loss of the original spatial context and cellular compartmentation for these compounds. To address this current limitation, several technologies were developed to visualize lipids in situ with detailed chemical information. A subcellular visualization approach, direct organelle MS, was developed for directly sampling and analyzing the triacylglycerol contents within purified lipid droplets (LDs) at the level of a single LD. Sampling of single LDs demonstrated seed lipid droplet-to-droplet variability in triacylglycerol (TAG) composition suggesting that there may be substantial variation in the intracellular packaging process for neutral lipids in plant tissues. A cellular and tissue visualization approach, MS imaging, was implemented and enhanced for visualizing the lipid distributions in oilseeds. In mature cotton seed embryos distributions of storage lipids (TAGs) and their phosphatidylcholine (PCs) precursors were distribution heterogeneous between the cotyledons and embryonic axis raising new questions about extent and regulation of oilseed heterogeneity. Extension of this methodology provides an avenue for understanding metabolism in cellular (perhaps even subcellular) context with substantial metabolic engineering implications. To visualize metabolite distributions, a free and customizable application, Metabolite Imager, was developed providing several tools for spatially-based chemical data analysis. These tools collectively enable new forms of visualizing the plant lipidome and should prove valuable toward addressing additional unanswered biological questions.

No description available.

<p><strong> </strong></p> <p><strong> </strong></p> <p>Considerable attention has been paid to the reaction between molten iron oxide containing slag and iron droplets or solid carbon due to the critical roles it plays in various metallurgical processes. However, during the last two decades, most of the studies have been carried out on iron droplets, for which the size remains constant. Another important phenomenon, that the droplet will swell has not been paid the same attention. Knowledge of the extent of droplet swelling is essential in predicting residence times in BOF steelmaking. The objective of this study is to develop the understanding for droplet swelling and produce a predictive model that predicts droplet swelling over the range of oxygen steelmaking conditions.</p> <p>Several workers have observed swelling of high carbon droplets when exposed to oxidizing slags. In the present work, the measurements on swelling rates were made using X-ray fluoroscopy. Comparing the swelling rate with the total volume of gas evolved during the reaction, it is shown that only a small percentage of the gas generated is retained in the droplet to contribute to swelling. The gas generation rate is shown to be controlled by the rate of nucleation of CO bubbles inside the droplet. The critical supersaturation pressure for nucleation is found to be two orders of magnitude less than predicted from theory, which is in keeping with many other studies on nucleation of gases in liquids. However, the effect of surface tension, temperature and saturation pressure shows quantitative agreement with theory.</p> <p>In order to predict the droplet swelling rate, CO bubble escape rate has to be known. In this research, the escape mechanism has been proposed; it is the film rupture around the iron droplet surface. The rupture rate is mainly influenced by viscosity, surface tension and bubble size. For a given experimental condition, the calculated film thickness is 1.5 μm at the maximum drop diameter, assuming the bubble radius is 0.3 mm. The CO escape rate is 2.51 cm³/s, it agrees well with 1 to 12 cm³/s when gas escapes from steelmaking slags considering the differences of surface tensions and viscosities between metal and slag.</p> / Doctor of Philosophy (PhD)

Adipose tissue is a type of connective tissue whose purpose was once thought to be limited to fat storage but is now understood to be a key factor in the pathogenesis of different metabolic diseases, including obesity and type-II diabetes. Adipose tissue consists largely of adipocytes, cells responsible for fat and releasing energy in form of lipids. Different classes of fatty acids, such as saturated and unsaturated have different biological effects on adipocytes. Lipid droplets are the primary organelles in adipocytes that store these fatty acids in form of lipids, and the development of engineered adipose tissues would benefit from improved techniques for analysis of lipid droplet composition, distributions, and dynamics based as a function of fatty acid saturation. Conventional microscopic techniques, such as fluorescence microscopy, provides excellent selectivity of lipid-based structures inside adipose tissue cellular structures based on staining with compound dyes. However, fluorescence staining limits multiplex imaging, and requires time consuming steps in preparing the samples for imaging. Therefore, developing a label-free, high resolution imaging platform with sensitivity to lipid composition could enable analysis of structural and compositional differentiation of lipid droplets within adipocytes during differentiation could give valuable insights into the importance of lipid droplets role in metabolism. As an important step towards achieving this goal, a femtosecond based CARS microscopy imaging platform has been developed to perform in vitro, label-free, imaging of fatty acid composition within engineered adipose tissues. / Bioengineering

The transmission of some infectious diseases requires that pathogens can survive (i.e., remain infectious) in the environment, outside the host. The viability of pathogens that are immersed in aerosols and droplets is affected by factors such as relative humidity (RH) and the chemical composition of the liquid media, but the effects of these stressors on the viability of viruses have not been extensively studied. The overall objective of this work was to investigate the effects of RH and media composition on the viability of viruses in suspended aerosols and stationary droplets. We used a custom rotating drum to study the viability of airborne 2009 pandemic influenza A(H1N1) virus across a wide range of RHs. Viruses in culture medium supplemented with material from the apical surface of differentiated primary human airway epithelial cells remained equally infectious for 1 hour at all RH levels tested. We further investigated the viability of two model viruses, MS2 and Φ6, in suspended aerosols and stationary droplets consisting of culture media. Contrary to the results for influenza virus, we observed a U-shaped viability pattern against RH, where viruses retained their viability at low and extreme high RHs, but decayed significantly at intermediate to high RHs. By characterizing the droplet evaporation kinetics, we demonstrated that RH mediated the evaporation rate of droplets, induced changes in solute concentrations, and modulated the cumulative dose of solutes to which viruses were exposed as droplets evaporated. We proposed that the decay of viruses in droplets follows disinfection kinetics. Lastly, we manipulated the chemical composition of media to explore the stability of viruses as a function of pH and salt, protein, and surfactant concentrations. Results suggested that the effects of salt and surfactant were RH and strain-dependent. Acidic and basic media effectively inactivated enveloped virus. Protein had protective effect on both non-enveloped and enveloped viruses. Results from this work has advanced the understanding of virus viability in the environment and has significant implications for understanding infectious disease transmission. / Doctor of Philosophy / Pathogenic organisms, including bacteria, viruses, fungi, protozoa, and helminths, cause infections that are responsible for substantial morbidity and/or mortality. For example, it is estimated that influenza has caused 9 million to 45 million illnesses and 12,000 to 61,000 deaths annually since 2010 in the United States. The spread of certain diseases relies on people touching the pathogenic organism on surfaces or inhaling it from the air. Successful transmission requires that the pathogen survive, or maintain its infectivity, while it is in the environment. The survival of pathogens can be affected by temperature, humidity, composition of the respiratory fluid carrying them, and other factors. However, there is limited research investigating the effects of these factors on the survival of viruses in the environment. In this work, we studied the effect of relative humidity (RH) on the survival of viruses, including influenza virus and two other types of viruses, in inhalable aerosols and larger droplets. We found that influenza viruses survive well in aerosols across a wide range of RH levels for at least 1 h. Conversely, the two model viruses survived best at both low and very high RHs, such as found indoors in the wintertime or in tropical regions, respectively, but had a pronounced decay at intermediate RHs. By measuring how fast droplets evaporated, we found that RH affected their chemistry and determined the total amount of stress that viruses were exposed to. This explained why a "U-shaped" survival pattern was observed against RH. We also investigated the survival of viruses in droplets containing different components. Results indicated that the effects of salt, surfactant, protein, and droplet pH depended on RH and the type of virus. The outcomes of this work are meaningful in predicting the survival of viruses in aerosols and droplets of various compositions in the environment and could provide insight on developing strategies to minimize the spread of infectious diseases.

Droplet evaporation is ubiquitous to multitude of applications such as microfluidics, surface patterning and ink-jet printing. In many of the process like food processing tiny concentrations of suspended particles may alter the behavior of an evaporating droplet remarkably, leading to partially viscous and partially elastic dynamical characteristics. This, in turn, may lead to some striking mechanical instabilities, such as buckling and rupture. In this thesis, we provide a comprehensive physical description of the vaporization, self-assembly, agglomeration and buckling kinetics of sessile nanofluid droplet pinned on a hydrophobic substrate in various configurations. We have deciphered five distinct regimes of droplet lifecycle. Regime I-III consists of evaporation induced preferential agglomeration that leads to the formation of unique dome shaped inhomogeneous shell with stratified varying density liquid core. Regime IV involves capillary pressure initiated shell buckling and stress induced shell rupture. Regime V marks rupture induced cavity inception and growth. We provide a regime map explaining the droplet morphology and buckling characteristics for droplets evaporating on various substrates. Specifically, we find that final droplet volume and radius of curvature at buckling onset are universal functions of particle concentration. Furthermore, flow characteristics inside the heated and unheated droplets are investigated and found to be driven by the buoyancy effects. Velocity magnitudes are observed to increase by an order at higher temperatures with self-similar flow profiles. With an increase in the surface temperature, droplets exhibit buckling from multiple sites over a larger sector in the top half of the droplet. In addition, irrespective of the initial nanoparticle concentration and substrate temperature, hydrophobicity and roughness, growth of daughter cavity (subsequent to buckling) inside the droplet is found to be controlled by the solvent evaporation rate from the droplet periphery. The results are of great significance to a plethora of applications like DNA deposition and nanofabrication. In the next part of the thesis, we deploy the droplet in a rectangular channel. The rich physics governing the universality in the underlying dynamics remains grossly elusive. Here, we bring out hitherto unexplored universal features of the evaporation dynamics of a sessile droplet entrapped in a 3D confined fluidic environment. Increment in channel length delays the completion of the evaporation process and leads to unique spatio-temporal evaporation flux and internal flow. We show, through extensive set of experiments and theoretical formulations, that the evaporationtimescale for such a droplet can be represented by a unique function of the initial conditions. Moreover, using same theoretical considerations, we are able to trace and universally merge the volume evolution history of the droplets along with evaporation lifetimes, irrespective of the extent of confinement. These results are explained in the light of increase in vapor concentration inside the channel due to greater accumulation of water vapor on account of increased channel length. We have formulated a theoretical framework which introduces two key parameters namely an enhanced concentration of the vapor field in the vicinity of the confined droplet and a corresponding accumulation lengthscale over which the accumulated vapor relaxes to the ambient concentration. Lastly, we report the effect of confinement on particle agglomeration and buckling dynamics. Compared to unconfined scenario, we report non-intuitive suppression of rupturing beyond a critical confinement. We attribute this to confinement-induced dramatic alteration in the evaporating flux, leading to distinctive spatio-temporal characteristics of the internal flow leading to preferential particle transport and subsequent morphological transitions. We present a regime map quantifying buckling & non-buckling pathways. These results may turn out to be of profound importance towards achieving desired morphological features of a colloidal droplet, by aptly tuning the confinement space, initial particle concentration, as well as the initial droplet volume. These findings may have implications in designing functionalized droplet evaporation devices for emerging engineering and biomedical applications.

"The present work is a study of the low inertia spreading dynamics of initially spherical viscous droplets on a planar interface. The droplets are affected by gravity, surface tension and viscous forces and are modeled as two-dimensional axisymmetric bodies. The main focus of this study is the examination of the dependence of droplet stability, equilibrium shape and fluid motion within the drop on the relative magnitude of these forces. The dynamics are modeled using the unsteady, non-linear Navier-Stokes equations for an incompressible fluid. The spreading of a droplet on a solid surface is modeled with both a no-slip and a partial-slip boundary condition. In addition, the spreading of a droplet on another identical drop (two-drop problem) is modeled to study the problem without the contact point singularity. The governing equations are solved numerically using the Mixed Galerkin Finite Element formulation, augmented by the use of the Newton-Raphson iteration scheme to effectively treat the non-linearities of the problem. The Generalized Eulerian Lagrangian formulation is adopted for the treatment of the moving free surface of the droplet. Computations are performed for capillary numbers ranging from 0.01 to 100 and for Reynolds numbers from 0.005 to 50, where the velocity scale is based on the droplet radius and the gravitational acceleration. For the droplet spreading on a solid surface, three distinct behaviors are observed~: for low Reynolds numbers and sufficiently high capillary numbers, droplets deform to a stable, equilibrium shape; for higher Reynolds numbers, an oscillatory droplet behavior occurs; at still higher Reynolds numbers, the droplets shatter. Very often, a recirculation is induced near the contact point just before the droplet shatters, which is also observed for the case of stable oscillating droplets. When a partial-slip boundary condition is applied, it is observed that the stability of the droplet and the rate at which the droplet attains the static contact angle depend strongly on the velocity of slip of the droplet with respect to the solid surface at the contact point. For the two-drop problem, only two distinct behaviors are observed: for low Reynolds numbers and high capillary numbers, the droplet retains a near-spherical shape and remains stable; while for higher Reynolds numbers, the droplet deforms to a high extent and becomes unstable."