Rozprawy doktorskie na temat „Compound droplets”

The development of a novel method of droplet levitation to be employed in lab-on-a-chip (LOC) applications relies upon the mechanism of thermocapillary convection (due to the temperature dependence of surface tension) to drive a layer of lubricating gas between droplet and substrate. The fact that most droplets of interest in LOC applications are aqueous in nature, coupled with the fact that success in effecting thermocapillary transport in aqueous solutions has been limited, has led to the development of a technique for the controlled encapsulation of water droplets within a shell of inert silicone oil. These droplets can then be transported, virtually frictionlessly, resulting in ease of transport due to the lack of friction as well as improvements in sample cross-contamination prevention for multiple-use chips. Previous reports suggest that levitation of spherical O(nL)-volume droplets requires squeezing to increase the apparent contact area over which the pressure in the lubricating layer can act allowing sufficient opposition to gravity. This research explores thermocapillary levitation and translation of O(nL)-volume single-phase oil droplets; generation, capture, levitation, and translation of O(nL)-volume oil-encapsulated water droplets to demonstrate the benefits and applicability to LOC operations.

Compound droplets raise great interests due to their applications in the pharmaceutical, cosmetic, and food industry. In spite of the growing demand of theoretical investigation of dynamics of compound droplets from those applications, very limited effort has been contributed in the analytical and/or numerical study of them. In this work, a 3D spectral boundary element method is employed to investigate the dynamics of compound droplets for both concentric and eccentric configurations. A comprehensive investigation has been carried out on the influences of the relative droplet size, relative surface tensions on the two interfaces, relative viscosities of the fluids, and the initial location of the inner droplet, on the deformation, migration, and stability of compound droplets. Two mechanisms of droplet breakup have been observed: (a) the contact of the outer and inner interface and (b) the instability of the inner droplet.
Department of Energy
National Science Foundation
ND EPSCoR

Abstract Multiphase Droplet Interactions with a Single Fiber By: Noor M. Farhan A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University. Virginia Commonwealth University, 2019 Director: Hooman V. Tafreshi, Professor, Department of Mechanical and Nuclear Engineering Formulating the physics of droplet adhesion to a fiber is interesting intellectually and important industrially. A typical example of a droplet–fiber system in nature is the dew droplets on spider webs, where droplets first precipitate and grow on the fibers, but they eventually fall when they become too heavy. Obviously, quantifying the force of adhesion between a droplet and a fiber is crucial in designing fog harvesting devices or manufacturing filtration media for liquid–gas or liquid–liquid separation, among many other industrial applications. This study is aimed at developing a mathematical framework for the mechanical forces between a droplet and a fiber in terms of their physical and wetting properties. To this end, a series of experiments were conducted to detach ferrofluid droplets of varying volumes from fibers with different diameters and Young–Laplace contact angles (YLCAs) in a controlled magnetic field. The force of detachment was measured using a sensitive scale and used along with the results of numerical simulations to develop a semi-analytical expression for the force required to detach a droplet from a fiber. This universally-applicable expression allows one to predict the force detachment without the need to run an experiment or a computer simulation. This work also reports on the use of magnetic force to measure the force of detachment for nonmagnetic droplets for the first time. This is accomplished by adding a small amount of a ferrofluid to the original nonmagnetic droplet to create a compound droplet with the ferrofluid nesting inside or cloaking the nonmagnetic droplet. The ferrofluid is then used to induce a body force to the resulting compound droplet and thereby detach it from the fiber. The recorded detachment force is used directly (the case of nesting ferrofluid) or after scaling (the case of cloaking ferrofluid) to obtain the force of detachment for the original nonmagnetic droplet. The accuracy of these measurements was examined through comparison with numerical simulations as well as available experimental data in the literature. In addition, a simple method is developed to directly measure the intrinsic contact angle of a fiber (i.e., Young–Laplace Contact angle of the fiber material) with any arbitrary liquid. It is shown that the intrinsic contact angle of a fiber can be obtained by simply measuring the angle between the tangent to the fiber surface and the tangent to the droplet at the contact line, if the droplet possesses a clamshell conformation and is viewed from the longitudinal direction. The novelty of the proposed method is that its predictions are not affected by the volume of the droplet used for the experiment, the wettability of the fiber, the surface tension of the liquid, or the magnitude of the body force acting on the droplet during the experiment. Also, a liquid droplet interaction with granular coatings is simulated and the droplet apparent contact angle (ACA) and the transition from Cassie (fully dry) to Wenzel (fully wet) state as a function to the roughness wavelength have been studied. For a fixed droplet volume, two different granular coatings have been used, spherical and hemispherical bumps. It is demonstrated that the chemistry (YLCA) and geometrical parameters for the granular microtexture play an important effect on the droplet ACA and its transition from Cassie to Wenzel state.

Les composés organiques volatils (COV), les hydrocarbures saturés, insaturés et autres hydrocarbures substitués, jouent un rôle majeur dans la chimie atmosphérique. Ils sont principalement émis par des sources anthropiques et biogéniques dans l'atmosphère; ils sont également transformés in situ par des réactions chimiques, et plus spécifiquement par photo-oxydation conduisant à la formation d'ozone (O3) et d'aérosol organique secondaire (SOA). En modifiant la fraction organique des particules d'aérosol, les COV modifient l'équilibre radiatif de la Terre par un effet direct (absorption et diffusion du rayonnement solaire) ou par un effet indirect en altérant les propriétés microphysiques des nuages. Ils présentent également un effet direct sur la santé humaine et l'environnement. Au cours de leur transport atmosphérique, les COV et leurs produits d'oxydation, les composés organiques volatils oxygénés (OVOC), peuvent se répartir entre les phases gazeuses et aqueuses en fonction de leur solubilité. Les nuages ​​ont un effet significatif sur la chimie troposphérique en redistribuant les traces de constituants entre les phases et en fournissant de l'eau liquide dans laquelle la chimie de la phase aqueuse peut avoir lieu. En effet, pendant la durée de vie des nuages, les composés chimiques et notamment les COV se transforment efficacement car les nuages ​​favorisent le développement d'une «chimie multiphasique». Cette dernière présente plusieurs particularités. Premièrement, les processus photochimiques à l'intérieur des gouttelettes sont importants dans la transformation des composés chimiques. Deuxièmement, les réactions chimiques aqueuses sont efficaces et peuvent être plus rapides que les réactions équivalentes en phase gazeuse. Cela peut être lié à la présence d'oxydants puissants tels que le peroxyde d'hydrogène H2O2 ou les ions métalliques de transition (TMI), qui participent à la formation de radicaux tels que les radicaux hydroxyles (HO •) qui favorisent les processus d'oxydation. De plus, la présence de micro-organismes viables a été mise en évidence et a montré sa participation aux transformations des espèces chimiques. Enfin, ces transformations dans les nuages ​​sont également fortement perturbées par des processus microphysiques qui contrôlent la formation, la durée de vie et dissipation des nuages. Ces processus redistribueront les espèces chimiques entre les différents réservoirs (eau de nuages, pluie, phase particulaire, phase gazeuse et phase de glace solide). Dans ce cadre, la transformation des COV dans le milieu nuageux peut conduire à la production de composés secondaires contribuant à la formation de SOA, appelés «nuage aqSOA». Cette masse d'aérosol organique secondaire produite pendant la durée de vie du nuage pourrait expliquer en partie l'ubiquité des petits acides dicarboxyliques et céto et des composés de haut poids moléculaire mesurés dans les particules d'aérosol, l'eau de brouillard, l'eau de nuage ou l'eau de pluie à de nombreux endroits, car ils n'ont ni sources d'émission directe ni aucune source importante identifiée en phase gazeuse. Cette masse d'aqSOA reste en phase particulaire après évaporation des nuages ​​impliquant une modification des propriétés (micro) physiques et chimiques des particules d'aérosol (taille des particules, composition chimique, morphologie). Ceci conduit à des modifications de leurs impacts sur les cycles consécutifs de nuages ​​ou de brouillard (effets indirects des aérosols) et de leurs interactions avec les rayonnements entrants par diffusion / absorption (effet direct des aérosols). (...)
Volatile Organic Compounds (VOC), including saturated, unsaturated, and other substituted hydrocarbons, play a major role in atmospheric chemistry. They are primarily emitted by anthropogenic and biogenic sources into the atmosphere; they are also transformed in situ by chemical reactions, and more specifically, by photo-oxidation leading to the formation of ozone (O3) and Secondary Organic Aerosol (SOA). By altering the organic fraction of aerosol particles, VOC modify the Earth’s radiative balance through a direct effect (absorption and scattering of solar radiation) or through indirect effect by altering cloud microphysical properties. They also present a direct effect on human health and on the environment.During their atmospheric transport, VOC and their oxidation products, Oxygenated Volatile Organic Compounds (OVOC), may partition between the gaseous and aqueous phases depending on their solubility. Clouds have a significant effect on tropospheric chemistry by redistributing trace constituents between phases and by providing liquid water in which aqueous phase chemistry can take place. Indeed, during the cloud lifetime, chemical compounds and particularly VOC are efficiently transformed since clouds favor the development of complex “multiphase chemistry”. The latter presents several particularities. First, photochemical processes inside the droplets are important in the transformation of chemical compounds. Second, aqueous chemical reactions are efficient and can be faster than the equivalent reactions in the gas phase. This can be related to the presence of strong oxidants such as hydrogen peroxide H2O2 or Transition Metal Ions (TMI), which participate in the formation of radicals such as hydroxyl radicals (HO•) that favor oxidation processes. Furthermore, the presence of viable microorganisms has been highlighted and shown to participate in transformations of the chemical species. Finally, these transformations in clouds are also strongly perturbed by microphysical processes that control formation, lifetime and dissipation of clouds. These processes will redistribute the chemical species between the different reservoirs (cloud water, rain, particle phase, gaseous phase, and solid ice phase). In this frame, the transformation of VOC in the cloud medium can lead to the production of secondary compounds contributing to SOA formation, reported as “cloud aqSOA”. This secondary organic aerosol mass produced during the cloud lifetime could explain in part the ubiquity of small dicarboxylic and keto acids and high molecular-weight compounds measured in aerosol particles, fog water, cloud water, or rainwater at many locations, as they have neither substantial direct emission sources nor any identified important source in the gas phase. This aqSOA mass stays in the particle phase after cloud evaporation implying a modification of the (micro)physical and chemical properties of aerosol particles (particle size, chemical composition, morphology). This leads to modifications of their impacts on consecutive cloud or fog cycles (aerosol indirect effects) and of their interactions with incoming radiation by scattering/absorbing (aerosol direct effect). (...)

While lipid droplets have traditionally been considered as inert sites for the storage of triacylglycerols and sterol esters, they are now recognized as dynamic and functionally diverse organelles involved in energy homeostasis, lipid signaling, and stress responses. Unlike most other organelles, lipid droplets are delineated by a half-unit membrane whose protein constituents are poorly understood, except in the specialized case of oleosins, which are associated with seed lipid droplets. Recently, we identified a new class of lipid-droplet associated proteins called LDAPs that localize specifically to the lipid droplet surface within plant cells and share extensive sequence similarity with the small rubber particle proteins (SRPPs) found in rubber-accumulating plants. Here, we provide additional evidence for a role of LDAPs in lipid accumulation in oil-rich fruit tissues, and further explore the functional relationships between LDAPs and SRPPs. In addition, we propose that the larger LDAP/SRPP protein family plays important roles in the compartmentalization of lipophilic compounds, including triacylglycerols and polyisoprenoids, into lipid droplets within plant cells. Potential roles in lipid droplet biogenesis and function of these proteins also are discussed.

Aerosols have significant impacts on earth's climate and hydrological cycle. They can directly reflect the amount of incoming solar radiation into space; by acting as cloud condensation nuclei (CCN), they can indirectly impact climate by affecting cloud albedo. Our current assessment of the interactions of aerosols and clouds is uncertain and parameters used to estimate cloud droplet formation in global climate models are not well constrained. Organic aerosols attribute much of the uncertainty in these estimates and are known to affect the ability of aerosol to form cloud droplets (CCN Activity) by i) providing solute, thus reducing the equilibrium water vapor pressure of the droplet and ii) acting as surfactants capable of depressing surface tension, and potentially, growth kinetics. My thesis dissertation investigates various organic aerosol species (e.g., marine, urban, biomass burning, Humic-like Substances). An emphasis is placed on the water soluble components and secondary organic aerosols (SOA). In addition the sampled organic aerosols are acquired via different media; directly from in-situ ambient studies (TEXAQS 2006) environmental chamber experiments, regenerated from filters, and cloud water samples. Novel experimental methods and analyses to determine surface tension, molar volumes, and droplet growth rates are presented from nominal volumes of sample. These key parameters for cloud droplet formation incorporated into climate models will constrain aerosol-cloud interactions and provide a more accurate assessment for climate prediction.

碩士
國立成功大學
機械工程學系碩博士班
93
A compound drop, composed of a fuel shell and a water core, was suspended and heated to micro-explosion. Three ambient temperatures, namely, 300 oC, 400 oC, and 500 oC and two fuels, namely diesel and n-hexadecane, were tested. The heating process was recorded by a high-speed video system, and the time at temperature of the micro-explosion were measured. The experimental results on compound drops were also compared with the micro-explosion of a heated emulsified W/O diesel-water drop. The micro-explosion of a heated compound drop was classified as either a indirect micro-explosion, if there were quite a few bubbles generated at the shell-core interface before the explosion, or a direct micro-explosion, if few or no bubble could be seen before the explosion. At an ambient temperature of 400 oC or 500 oC, the micro-explosion time was observed to increase with the micro-explosion temperature; but this trend was not as obvious at 300 oC ambient temperature. The intensity of the micro-explosion rose as the micro-explosion time lengthened, because the accumulation of thermal energy within the over-saturated water core drop grew to a higher extent. However, the size of the core water drop was not seen to influence either the micro-explosion time or micro-explosion temperature. Compared with pure n-hexadecane and pure water, the impurities or microscopic air bubbles in diesel and dyed water enhanced nonhomogenous nucleation and thus more steam bubbles were produced before micro-explosion. Furthermore, contrary to the intense micro-explosion of a compound drop, a heated emulsified diesel-water drop generally expanded, and followed by squirting of steam to relieve the pressure within the expanded drop. The distributed microscopic water drops in an emulsified drop acted as nonhomogeneous nucleation sites and made an overall micro-explosion improbable.

Compound droplets are utilized in applications ranging from the preparation of emulsion to biological cell printing and additive manufacturing. Here, we report on the impact dynamics of a compound hollow droplet on a solid substrate. Contrary to the impact of simple droplets and compound droplets with liquids of similar densities, the compound droplet with an encapsulated air bubble demonstrates the formation of a counterjet in addition to the lamella. Here, we experimentally investigate the influence of the size of the air bubble, liquid viscosity, and height of impact on the evolution of counterjet and the spreading characteristics of the lamella. For a given hollow droplet, the volume of the counterjet is observed to depend on the volume of air and liquid in the droplet and is independent of the viscosity of the liquid and impact velocity of the droplet. We observe that the spread characteristics, counterintuitively, do not vary significantly compared to that of a simple droplet having an identical liquid volume as the hollow droplet. We propose a model to predict the maximum spread during the impact of a hollow droplet on a substrate based on the energy interaction between the spreading liquid and the liquid in the counterjet during the impact process. Furthermore, the maximum spread diameter during the impact of a HD obtained using the model developed is in excellent agreement with that observed in experiments.

博士
國立臺灣大學
環境工程研究所
84
In this study, effusion process and solubilization process were conducted to investigate the enriched solubility of n-octane, a surrogate of the hydrophobic organic compounds in atmospheric fog. In effusion process, we presented a dynamically corrected double-layer diffusion model with a new parameter, the effusion factor (.alpha.) to quantify the change of the effusion rate across the air/fog interface. The .alpha. values were in the range of 0.798 to 0.421 for the effect of SDS. Thus, SDS could decrease the mass transfer of n-octane effusing from the fog droplet by about 20 to 60%. However, the .alpha. values varied from 1.17 to 1.57 and 1.42 to 4.23 for the effects of sulfuric acid and NaCl, respectively. Therefore, the ionic strength contributed by sulfuric acid and NaCl could enhance the effusion rate of n-octane by about 17 to 57% for the effect of sulfuric acid and 42 to 323% for the effect of NaCl. NaCl resulted in stronger effusion rate of n-octane from the fog droplets than sulfuric did because of the stronger ionic hydration provided by NaCl. As for solubilization process, the surfactant film on the fog droplets was identified to elevate the solubility of n-octane. The enrichment factor (EF) of n- octane in the fog droplets (diameter: 35 to 75 .mu.m) were between 27.2 to 1.87, depending on the SDS concentration (0.00285M to 0.0000515M). In addition, the larger fog droplets provided n-octane with higher EF value than the smaller fog droplets while below the specific SDS concentration, 0.000103M, The enrichment model was used to describe the micro-states of the n-octane molecules partitioning in the SDS film at the air/ fog interface and the SDS monomers inside the fog water. Above enriching effect could be easily expounded and discussed by use of this model.

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Earth and Space Science.
Typescript. Includes bibliographical references (leaves 188-201). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19810

碩士
國立臺灣大學
環境工程學研究所
86
ABSTRACT Non-ionic surfactants , Tween 20 , Tween 60 and Tween 80 were used to investigate the effect of non-ionic surface active substance on the effusion of hydrophobic organic compounds from fog droplet . N-decane was chosen as a surrogate of hydrophobic organic compounds (HOCs) . N-decane in aqueous samples was by SPME(solid phase microextration) and relative standard deviation of analysis (RSD%) are between 2.2%~7.5% . The collection bottle was ice bathed to prevent the vaporization of n-decane . Double layer d The results show that Tween 20 , Tween 60 and Tween 80 can decrease the mass transfer of n-decane from 107.8μm droplet to gas phase . At Tween 20 concentration 1.0~12.0×10-2g/L , theα values are decreased 11.9~55.2% . At Tween 60 concentration 1.0~9.7×10-2g/L , the reduction percentage of α values are between 1.8~58.1% . At Tween 80 concentration 5×10-3~12.0×10-2 g/L , the reduction percentage of α values are between 6.2~65.3% . The effect of non-ionic surfactants on effusion can categorized into two Below the concentration of 1.0×10-3M NaCl , salt effect can be ignored whether Tween 20 concentration is below the cmc or above . But , at high concentration of NaCl(1.0×10-2M) , salt effect reduce n-decane effusion (α reduction by 43.4%) when Tween 20 concentration is below the cmc and enhance the effusion (α increase by 48.6%) when Tween 20 concentration is above cmc . Low pH can enhance n-decane effusion whether Tween 20 concentration is below the cmc or not .

Multiphase flows abound in nature and enterprises. Our daily interactions with fluids - washing, drinking, and cooking, for example - occur at a free surface and within the realm of multiphase flows. The applications of multiphase flows within the context of emulsions, which are caused by mixing two immiscible fluids, have been of interest since the nineteenth century: compartmentalizing one fluid in another is particularly of interest in applications in pharmaceutical, materials, microfluidics, chemical, and biological engineering. Even more control in compartmentalization and delivery can be obtained through the usage of double emulsions, which are emulsions of smaller drops (i.e., inner drop) within larger drops (i.e., outer drop). The goal of this work is to understand the dynamic behavior of compound drops in confined flow at low Reynolds numbers. These behaviors include the migration patterns, limit cycles, and equilibrium locations in confined flows such as channel flows.

Firstly, we look at non-concentric compound drops that are subject to simple shear flows. The eccentricity in the inner drop is either within the place of shear, normal to the plane of shear, or mixed. We show unreported motions that persist throughout time regardless of the initial eccentricity, given that the deformations of the inner and outer drops are small. Understanding the temporal dynamics of compound drops within the simple shear flow, one of the simplest background flows that may be imposed, allows us to probe at the dynamics of more complicated background flows.

Secondly, we look at the lateral migration of compound drops in a Poiseuille flow. Depending on the initial condition, we show that there are multiple equilibria. We also show that the majority of initial configurations results in the compound drop with symmetry about the short wall direction. We then show the time it takes for the interfaces to merge if a given initial configuration does not reach the aforementioned symmetry.

Thirdly, while the different equilibria of compound drops offer some positional differences at different radii ratio, we show that the lift force profiles at non-equilibrium locations offer distinctly different results for compound drops with different radii ratio. We then look at how this effect is greater than changes that arise due to viscosity ratio changes, and offer insights on what may create such a change in the lift force profile.

Les protéines de type prion, contenant des Séquences en acides aminés de Faible Complexité (SFC), ont tendance à s’agréger et à former des compartiments non-membranaires dans la cellule. Ces derniers ont des propriétés physiques communes à celles des liquides, telles que la capacité de mouiller les surfaces, de s’écouler et de fusionner avec d’autres corps liquides. Dans cette étude, nous avons démontré que la protéine Hrp1 forme, in vitro, des gouttes de différentes tailles via une transition de phase liquide à liquide, et ce, uniquement lorsqu’elle est exposée à un milieu chargé négativement. Exclusivement dans ce même milieu, nous avons aussi observé que le domaine SFC de Hrp1 s’assemble et forme une matière de type gel. Sur la base de ces observations, nous avons émis l’hypothèse que la tendance des systèmes moléculaires à former des compartiments liquides in vivo peut être influencée par la présence, dans le cytosol, de polyélectrolytes chargés négativement tels que l'ADN, l'ARN et les polyphosphates (PolyP). En utilisant la levure comme modèle cellulaire et des techniques de microscopie à fluorescence, nous nous sommes focalisés sur l’étude du rôle des PolyP dans l'assemblage des P-bodies. Les P-bodies ont été choisis comme système moléculaire de référence in vivo, étant des corps qui, après une transition de phase, se trouvent dans le cytosol sous forme de gouttes. Nous avons démontré que la déplétion du phosphate et la délétion du gène vtc4, responsable de la synthèse des PolyP dans la levure, n’ont pas d’influence dans la formation des P-bodies. Nous avons aussi remarqué que les PolyP et la protéine Edc3, une des composantes principales des P-bodies, ne sont pas co-localisés dans la cellule. Cette étude préliminaire nous suggère un manque de corrélation entre la formation des P-bodies et la présence de PolyP dans la cellule. Cependant, pour confirmer nos observations, des expériences complémentaires doivent être envisagées, en considérant d’autres composantes des P-bodies, tel que Lsm4, ou en analysant, in vivo, les effets des PolyP sur d’autres systèmes moléculaires de nature liquide.
Prion-like proteins containing Low Complexity Sequences (LCSs) have the propensity to aggregate and form membrane-less compartments in the cell. These proteins form droplets that have liquid features such as wetting, dripping and fusion. In this study, we demonstrated that the prion domain-containing protein Hrp1 forms droplets of different sizes in the presence of negatively charged polymers via liquid-liquid phase separation, whereas under the same conditions, the prion-like domain PolyQ/N of Hrp1 forms a gel-like material. Based on these findings, we hypothesize that droplets in vivo could be modulated by negatively charged polyelectrolytes found in the cell such as DNA, RNA and polyphosphate (PolyP). My goal was to examine the role of the polyanionic nature of PolyP on the assembly of P-bodies using Saccharomyces cerevisiae as a cellular model and fluorescence microscopy. We chose to study processing (P)- bodies, based on previous findings that these cellular subcompartments are formed by liquid-liquid phase separation of component proteins in the cytoplasm. We found that depleting phosphate from the media and deleting vtc4 gene, which is responsible for PolyP synthesis, did not have any effect on P-body formation. In addition, we demonstrated that PolyP and the protein Edc3, a core component of P-bodies, do not colocalize. Our data suggest that PolyP does not affect P-body formation. However, further and complementary studies have to be performed to confirm that PolyP have no effects on other membrane-less organelles.