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1
Ding, Ailin. "Particle Assisted Wetting". Doctoral thesis, Universitätsbibliothek Chemnitz, 2007. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200701494.
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Die Benetzbarkeit und Nichtbenetzbarkeit von Oberflächen durch eine Flüssigkeit sind faszinierende und wichtige Phänomene in Wissenschaft und Technologie. Jüngst wurde entdeckt, dass Partikel die Benetzung einer Wasseroberfläche durch ein Öl unterstützen können. Es wurde eine Theorie entwickelt, das Prinzip der zu beschreiben. In der vorliegenden Doktorarbeit wurde diese Theorie im Experiment sowohl qualitativ als auch quantitativ untersucht, wobei zwei Arten von Kieselgelpartikeln Verwendung fanden. Mit Hilfe einer Reihe unregelmäßig geformter Partikel mit variierender Hydrophobie wurde der Einfluss der Oberflächenhydrophobie der Partikel auf die partikel-assistierte Benetzung untersucht. Es wurde herausgefunden, dass die Partikel mit höchster Hydrophilie Linsen aus reinem Öl bilden, während die Partikel in die Wasserphase abtauchen. Die Partikel mit größter Hydrophobie hingegen bewirken die Ausbildung von kleinen Bereichen, in denen Öl und Partikel eine stabile homogene Schicht formen. Für Partikel mit mittlerer Hydrophobie wurden beide Phänomene beobachtet. Diese drei verschiedenen Beobachtungen bestätigen, dass die Oberflächenhydrophobie der Partikel das Benetzungsverhalten des Öls auf der Wasseroberfläche bestimmen. Für die unregelmäßig geformten Partikel war aufgrund des unbekannten Kontaktwinkels ein direkter Vergleich zur Theorie nicht möglich. Um die Theorie quantitativ zu prüfen, wurden sphärische Partikel synthetisiert und ihre Oberflächen mit Hilfe von zehn Silanisierungsmittel modifiziert. Anschließend wurde ein Vergleich der experimentellen Ergebnisse mit dem entsprechenden theoretischen Phasendiagramm durchgeführt. Die Untersuchungen zeigten, dass die theoretischen Vorhersagen zum Großteil mit den experimentellen Ergebnissen übereinstimmen. Es wurden alle Fälle der Benetzung beobachtet, die auch in der theoretischen Beschreibung berücksichtigt wurden. Darüber hinaus wurden auch Abweichungen von der Theorie festgestellt. Haben die Partikel ähnliche Affinitäten zur Luft/Öl- und Öl/Wasser-Grenzfläche, hängt die Beschaffenheit der Benetzungsfilme zusätzlich vom Oberflächendruck ab. Deshalb könnte es notwendig sein, die einfache Theorie zu erweitern um den beschriebenen Beobachtungen Rechnung zu tragenWetting and de-wetting of surfaces by a liquid are fascinating and important phenomena in science and technology. Recently, it was discovered that particles can assist the wetting of a water surface by an oil, and a theory describing the principle behind particle assisted wetting was developed. In this thesis, the theory was experimentally investigated qualitatively and quantitatively by using two series of silica particles. The influence of the surface hydrophobicity of the particles on particle assisted wetting was investigated by a series of irregular shaped particles with varying hydrophobicity. By applying mixtures of particles and oil to a water surface, it was found that for the most hydrophilic particles, only lenses of pure oil formed, with the particles being submerged into the aqueous phase. The most hydrophobic particles helped to form patches of stable homogenous mixed layers composed of oil and particles. For particles with intermediate hydrophobicity, lenses and patches of mixed layers were observed. These three different observations verified that the hydrophobicity of the particle surface determines the wetting behaviour of the oil at the water surface. For the irregular shaped particles with unknown contact angles with liquid interfaces, no direct comparison to the theory was possible. To test the theory quantitatively, a series of spherical particles was synthesized and their surfaces were modified by ten kinds of silane coupling agents; then the experimental results were compared with the corresponding theoretical phase diagram. It indicated that the theory agrees at large with the experimental results. All scenarios of wetting layers taken into account in the theoretical description were observed. In the fine print, deviations from the theory were also observed. If the particles have similar affinities to air/oil and oil/water interfaces, the experimentally observed morphology of the wetting layers depends in addition on the surface pressure. It might therefore be necessary to extend the simple theoretical picture to take these observations into accounts
2
Burgess, Ian Bruce. "Wetting in Color". Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10524.
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Colorimetric litmus tests such as pH paper have enjoyed wide commercial success due to their inexpensive production and exceptional ease of use. However, expansion of colorimetry to new sensing paradigms is challenging because macroscopic color changes are seldom coupled to arbitrary differences in the physical/chemical properties of a system. In this thesis I present in detail the development of Wetting in Color Technology, focusing primarily on its application as an inexpensive and highly selective colorimetric indicator for organic liquids. The technology exploits chemically-encoded inverse-opal photonic crystals to control the infiltration of fluids to liquid-specific spatial patterns, projecting minute differences in liquids’ wettability to macroscopically distinct, easy-to-visualize structural color patterns. It is shown experimentally and corroborated with theoretical modeling using percolation theory that the high selectivity of wetting, upon-which the sensitivity of the indicator relies, is caused by the highly symmetric structure of our large-area, defect-free \(SiO_2\) inverse-opals. The regular structure also produces a bright iridescent color, which disappears when infiltrated with liquid naturally coupling the optical and fluidic responses. Surface modification protocols are developed, requiring only silanization and selective oxidation, to facilitate the deterministic design of an indicator that differentiates a broad range of liquids. The resulting tunable, built-in horizontal and vertical chemistry gradients allow the wettability threshold to be tailored to specific liquids across a continuous range, and make the readout rely only on countable color differences. As wetting is a generic fluidic phenomenon, Wetting in Color technology could be suitable for applications in authentication or identification of unknown liquids across a broad range of industries. However, the generic nature of the response also ensures chemical non-specificity. It is shown that combinatorial measurements from an array of indicators add a degree of chemical specificity to the platform, which can be further improved by monitoring the drying of the inverse-opal films. While colorimetry is the central focus of this thesis, applications of this platform in encryption, fluidics and nanofabrication are also briefly explored.Engineering and Applied Sciences
3
Lee, Khai S. "Kinetics of wetting". Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/33866.
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Wetting and de-wetting processes play an important role in many natural and technological processes. In many cases, wetting is an essential prerequisite for application, for example in paint films, crop sprays, cosmetics, pharmaceutical tablets and in preparation of suspensions. Both equilibrium and dynamic processes of wetting are important in coatings. In many industrial and medical applications, some strategies to control drop-spreading on solid surfaces are being developed. One possibility is that a surfactant, a surface-active polymer, a polyelectrolyte or their mixture are added to a liquid (usually water). Recently discovered trisiloxane and other silicone-based surfactants show very unusual behaviour.
4
Wålinder, Magnus. "Wetting phenomena on wood". Doctoral thesis, KTH, Production Systems, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2908.
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Carlson, Andreas. "Capillarity and dynamic wetting". Doctoral thesis, KTH, Strömningsfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91329.
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In this thesis capillary dominated two–phase flow is studied by means of nu- merical simulations and experiments. The theoretical basis for the simulations consists of a phase field model, which is derived from the system’s thermody- namics, and coupled with the Navier Stokes equations. Two types of interfacial flow are investigated, droplet dynamics in a bifurcating channel and sponta- neous capillary driven spreading of drops. Microfluidic and biomedical applications often rely on a precise control of droplets as they traverse through complicated networks of bifurcating channels. Three–dimensional simulations of droplet dynamics in a bifurcating channel are performed for a set of parameters, to describe their influence on the resulting droplet dynamics. Two distinct flow regimes are identified as the droplet in- teracts with the tip of the channel junction, namely, droplet splitting and non- splitting. A flow map based on droplet size and Capillary number is proposed to predict whether the droplet splits or not in such a geometry. A commonly occurring flow is the dynamic wetting of a dry solid substrate. Both experiments and numerical simulations of the spreading of a drop are presented here. A direct comparison of the two identifies a new parameter in the phase field model that is required to accurately predict the experimental spreading behavior. This parameter μf [P a · s], is interpreted as a friction factor at the moving contact line. Comparison of simulations and experiments for different liquids and surface wetting properties enabled a measurement of the contact line friction factor for a wide parameter space. Values for the contact line friction factor from phase field theory are reported here for the first time. To identify the physical mechanism that governs the droplet spreading, the different contributions to the flow are measured from the simulations. An im- portant part of the dissipation may arise from a friction related to the motion of the contact line itself, and this is found to be dominating both inertia and viscous friction adjacent to the contact line. A scaling law based on the con- tact line friction factor collapses the experimental data, whereas a conventional inertial or viscous scaling fails to rationalize the experimental observation, supporting the numerical finding.QC 20120313
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Modaressi-Esfeh, Hedieh. "Wetting on heterogeneous surfaces". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38084.
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Dynamic wetting and absorption of water droplets on heterogeneous surfaces, including paper, was studied. The objective was to elucidate the role of surface heterogeneities on wetting and absorption properties of paper. To better understand the phenomena, wetting on glass slides with a controlled level of heterogeneity was investigated. Also, partially hydrophobized glass capillaries were used to simulate capillary penetration into the pores on sized paper.Dynamic wetting on paper followed a power law model with a lower rate than wetting on a smooth surface. The chemical composition of the paper surface did not affect the wetting dynamics, which was mainly affected by surface roughness in a micron scale. The super-hydrophobic properties of the sized papers were due to air entrapment in the micron-scale roughness on the surface.
Wetting and absorption of water droplets on sized paper occurred in different time scales. A pseudo-equilibrium contact angle was reached at the end of wetting just before absorption of water droplets. Increasing the surface coverage of the hydrophobic domains on paper by sizing increased the pseudo-equilibrium contact angle and delayed absorption into paper. This delay was related to partial dissolution of the surface sizing polymers in the water droplets on the surface.
The equilibrium contact angle of water droplets on partially hydrophobized glass slides was a linear function of a characteristic dimension of the hydrophobic domains and the length of the three phase contact line.
The dynamic rise of water in partially hydrophobized vertical capillaries followed two mechanisms. First, capillary rise was a function of the dynamic contact angle, changing with the velocity of the contact line. Second, local changes of the advancing contact angle due to the heterogeneities on the capillary walls lowered the capillary rise velocity. The stick (pause) and jump of the contact line was another effect of the hydrophobic domains. Capillary rise dynamics was a function of the advancing contact angle of water droplets measured on a flat glass slide with the same coverage of hydrophobic domains.
7
Aqil, Sanaa. "Wetting of microstructured surfaces". Thesis, Nottingham Trent University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431843.
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Marczewski, Dawid. "Membranes via particle assisted wetting". Doctoral thesis, Universitätsbibliothek Chemnitz, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200901190.
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Spreading of mixtures of oil with suitable silica particles onto a water surface leads to the formation of composite layers in which particles protrude at the top and at the bottom from the oil. Solidification of the oil and removal of the particles give rise to porous membranes. Pore widths and membrane thicknesses depend on particle sizes and usually are in the range of 70 – 80% of their diameters. Often freely suspended porous membranes are too fragile to operate them in pressure filtration without supportive structure. To improve mechanical stability of porous membranes, a mixture of silica particles with an oil is spread onto a nonwoven fibrous support that was drenched with water. Solidification of the oil and removal of particles yields porous membrane attached to the fibers of the support. Due to inhomogeneous surface of the fabric, the membranes that are attached to it are corrugated. To obtain flat supportive structures, glass beads with 75 μm in diameter are spread onto the water surface with the oil. Solidification of the oil and then removal of particles gives rise to porous membranes with pore diameters in micrometer range. Another concept of improvement of mechanical stability is the preparation of asymmetric membranes via spreading of a mixture of two sorts of particles with opposite surface properties with the oil onto the water surface. After solidification of the oil and removal of particles, membranes with pores width in the range from 30 – 50 nm are obtained. Slow removal of silica particles from composite monolayer that floats on the water surface gives rise to silica rings in intermediate stages of removal. Mixed matrix membranes with embedded carbon molecular sieves are prepared in a similar process as detailed above by using carbon particles instead of silica. Carbon molecular sieves protrude at the top and bottom from the polymeric matrix. Theoretical prediction of permeability and selectivity through these membranes are much higher than in membranes where particles are smaller than the membrane thicknessSpreitet man Mischungen eines Öls mit geeigneten Kieselgelpartikeln auf eine Wasseroberfläche, führt dies zur Bildung gemischter Schichten, in denen die Partikel auf der Ober- und Unterseite aus dem Öl herausragen. Härtet man das Öl aus und entfernt die Partikel, erhält man poröse Membranen mit einheitlichen Poren. Dabei hängen die Porenweiten und Membrandicken von der Partikelgröße ab und betragen üblicherweise 70 – 80 % von deren Durchmesser. Oft sind freitragende poröse Membranen zu zerbrechlich um mit ihnen Druckfiltration ohne Stützstruktur durchzuführen. Um die mechanische Stabilität von porösen Membranen zu erhöhen spreitet man eine Mischung aus Kieselgelpartikeln und einem Öl auf einem Vliesstoff, der mit Wasser getränkt ist. Das Aushärten des Öls und die Entfernung der Partikel führt zu einer porösen Membran, die an die Fasern der Stützstruktur angeheftet ist. Durch die inhomogene Oberfläche des Vliesgewebes sind die daran angehefteten Membranen gewellt. Um eine ebene Stützstruktur zu erhalten, werden Mischungen aus dem Öl und Glaskugeln mit einem Durchmesser von 75 μm verwendet. Das Aushärten des Öls und die Entfernung der Partikel führt zu ebenen porösen Membranen mit Porendurchmessern im Mikrometerbereich. Ein weiteres Konzept, um die mechanische Stabilität zu erhöhen, ist die Herstellung asymmetrischer Membranen mit Hilfe des Spreitens einer Mischung zweier Partikelsorten mit unterschiedlichen Oberflächeneigenschaften mit dem Öl auf die Wasseroberfläche. Nach dem Aushärten des Öls und der Entfernung der Partikel erhält man eine asymmetrische Membran mit kleinen Porenweiten an der Oberseite und großen Porenweiten an der Unterseite. Durch langsames Entfernen der Kieselgelpartikel aus der gemischten Schicht, die auf der Wasseroberfläche schwimmt, kann man in einem Zwischenstadium Kieselgelringe erhalten. Kompositmembranen (mixed matrix membranes) mit eingebetteten Kohlenstoffmolekularsieben werden in einem gleichen Prozess wie oben beschrieben hergestellt, indem man Kohlenstoffpartikel anstatt der Kieselgelpartikel verwendet. Die Kohlenstoffmolekularsiebe ragen auf der Ober- und Unterseite aus der Polymermatrix heraus. Die theoretisch vorhersagten Durchlässigkeiten und Selektivitäten solcher Membranen sind wesentlich höher als bei Membranen, in denen die Partikel kleiner als der Membrandicke sind
9
Cowan, Nicola. "Wetting and Spreading of Mucus". Thesis, Heriot-Watt University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490937.
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The wetting and spreading of aqueous solutions of gastric pig mucin has been studied on both high-energy and low-energy surfaces. Static and dynamic contact angles of mucin droplets were measured directly on glass and collagen surfaces of both flat and fibre substrate geometries, using a novel laser-assisted measurement method. The surface tension of the mucin solutions were measured using the du Nouy ring ,.' method, and found to be independent of mucin concentration. // The non-Newtonian properties of mucus was further evidenced by the dynamic wetting on flat glass substrates; the change in contact angle and droplet radius with time could be described by a power law relation with exponents slightly smaller than that observed for Newtonian fluids which obey Tanner's law. The spreading kinetics of mucus on flat collagen substrates were shown to follow a different rule of spreading to that observed on flat glass substrates. Dynamic wetting studies on cylindrical fibre substrates were shown to differ significantly from that observed on flat substrates. Tanner's law was not obeyed for wetting on either glass or collagen fibres. The power law behaviour of the spreading ()(t) t -O.SS±O.06 mucin droplets was characterised by ~ on both glass and collagen fibres. All concentrations of mucus droplets exhibited measurable non-zero contact angles on fibre substrates, regardl~ss 'of the complete wetting nature on a chemically identical flat substrate.
10
Kang, Suk Chae. "Fundamentals of solder interconnect wetting". Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16391.
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Sarkar, Anjishnu. "Wetting robustness on patterned surfaces". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114567.
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Superhydrophobicity of a surface is measured in terms of its wettability. A robust surface exhibits superhydrophobicity when a water droplet is gently deposited or forcibly impinged on it. Governed by the surface chemistry and the surface topology, the surface wettability corresponds to energy minimized equilibrium states, also known as wetting states. The wetting states are characterized by unique geometric configurations assumed by each of the interfaces as a drop-surface-air system is formed. The circumstances governing the formation of a drop-surface-air system hold a key in designing the robustness criteria. Following a two-step computational approach, this thesis analyses the possible wetting states for a surface and consequently comments on the feasibility of these states in context of designing a robust superhydrophobic surface. In the first step, a square pillar surface topology is chosen, and the wetting states are expressed in terms of the penetration depth of water inside the roughness valleys of the surface. Expressions for surface wettability are determined for no penetration (Cassie state), partial penetration (metastable Cassie state) and complete penetration (Wenzel state). The metastable Cassie state is quantified by establishing an implicit relation between the wettability and the penetration depth. In the second step, the thermodynamic feasibility of the metastable Cassie state is understood so as to design the robustness criterion. The metastable Cassie state forms a possible intermediate state between the Cassie and the Wenzel states, and the free energy of the metastable Cassie state determines the robustness condition. Three cases are isolated for the robustness which require either of the Cassie or the metastable Cassie to be the most thermodynamically favorable state. This thermodynamic condition can be attained with an appropriate combination of pillar height and pillar chemistry. It is seen that the metastable Cassie states exists, when a drop is deposited at low velocities (2 mms-1). It is seen that with the choice of an appropriate drop radius and impact velocity, a metastable state can be found. The existence of a metastable state enhances the chances of rendering a surface superhydrophobic.La superhydrophobicité d'une surface se mesure en termes de sa mouillabilité. Une surface robuste manifeste une superhydrophobicité quand une gouttelette d'eau est doucement déposée sur la surface ou introduite de force sur elle. Régie par la chimie de surface et la topologie de surface, la mouillabilité de surface correspond à des états d'équilibre d'énergie minimisée, également appelés des états de mouillage. Les états mouillants sont caractérisés par des configurations géométriques uniques assumées par chacune des interfaces lorsqu'un système de goutte-surface-air se forme. Les circonstances relatives à la formation d'un système de goutte-surface-air est un facteur important dans la conception des critères de robustesse. Suivant une approche computationnelle en deux étapes, cette thèse analyse les états de mouillage possibles pour une surface et, par conséquent, commente sur la faisabilité de ces états dans le contexte de la conception d'une surface robuste et superhydrophobe. Dans la première étape, une topologie de surface de pilier carré est choisie, et les états de mouillage sont exprimés en termes de la profondeur de pénétration de l'eau dans les vallées de rugosité de la surface. La mouillabilité de la surface est determinée pour les cas suivants: sans pénétration (état Cassie), pénétration partielle (état Cassie métastable) et pénétration complète (état Wenzel). L'état Cassie métastable est quantifié en établissant une relation implicite entre la mouillabilité et la profondeur de pénétration. Dans la deuxième étape, la faisabilité thermodynamique de l'état Cassie métastable est entendue de manière à concevoir le critère de robustesse. L'état Cassie métastable constitue un état intermédiaire possible entre les états Cassie et Wenzel, et l'énergie libre du Cassie métastable détermine l'état de robustesse. Trois cas sont isolés pour la robustesse, qui exigent que le Cassie ou Cassie métastable soit l'état le plus favorable en termes thermodynamiques. On peut atteindre la condition thermodynamique par une combinaison appropriée de la hauteur de pilier et de la chimie pilier. On constate les états Cassie métastable lorsqu'une goutte est déposée à des vitesses faibles (2 mms-1), ce qui pourrait se produire par inadvertance lorsqu'on mesure la mouillabilité. Il est constaté qu'en cas d'une collision inélastique entre le bord de l'eau en mouvement et la surface, la probabilité d'une existence d'un état metastable est plus élevée, donc on a plus de chances de produire une surface superhydrophobe.
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Mustonen, Ville. "Wetting, filling and interface dynamics". Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414237.
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Murison, Julie Lynette. "Wetting heterogeneities in porous media". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2014. http://hdl.handle.net/11858/00-1735-0000-0022-5E9C-2.
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Lundgren, Johan Mathias. "Molecular dynamics simulations of wetting". Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397888.
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Williams, K. H. "Dynamic wetting with superspreading surfactants". Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3022625/.
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Vellingiri, Rajagopal. "Complex interfacial and wetting dynamics". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/25998.
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Consider interface evolution in bounded and unbounded settings, namely in the spreading of droplets and stratified gas-liquid flows. A typical prototype consists of the surface-tension-dominated motion of a two-dimensional droplet on a substrate. The case of chemically heterogeneous substrates was examined here. Assuming small slopes, a single evolution equation for the droplet free surface was derived from the Navier-Stokes equations, with the singularity at the contact line being alleviated using the Navier slip condition. The chemical nature of the substrate is incorporated into the system by local variations in the microscopic contact angle. By using the method of matched asymptotic expansions, the flow in the vicinity of the contact lines is matched to that in the bulk of the droplet to obtain a set of coupled ordinary differential equations for the location of the two contact points. The solutions obtained by asymptotic matching are in excellent agreement with the solutions to the full governing evolution equation. The dynamics of the droplet is examined in detail via a phase-plane analysis. A number of interesting features that are not present in homogeneous substrates are observed: multiple droplet equilibria, pinning of contact points on localised heterogeneities, unidirectional motion of droplet and the possibility of stick-slip behaviour of contact points. Unbounded gas-liquid flows are also often encountered in natural phenomena and applications. The prototypical system considered here consists of a liquid film flowing down an inclined planar substrate in the presence of a co-flowing turbulent gas. The gas and liquid problems are solved independently by making certain reasonable assumptions. The influence of gas flow on the liquid problem is analysed by developing a weighted integral-boundary-layer (WIBL) model, which is valid up to moderate Reynolds numbers. We seek solitary-wave solutions of this model using a pseudo-arclength continuation approach. As a general trend, it is found that the wave speed increases with increasing gas shear and the liquid flow rate. Further insight into the problem is provided by time-dependent computations of the WIBL model. Finally, the absolute-convective instability of a falling film that is in contact with a counter-current turbulent gas is analysed. The Orr--Sommerfeld (O-S) problem is formulated from the full governing equations and boundary conditions. The O-S problem along with low-dimensional models, namely, a long-wave and WIBL models are used to explore the linear stability of the gas-liquid system. It is found that for a fixed liquid Reynolds number, at low and high gas flow rates, the system is convectively unstable, and for a range of intermediate gas flow rates we have absolute instability. We supplemented our analysis by doing time-dependent computations of the linearised WIBL model subject to a localised initial condition which showed good agreement. The upper limit of the absolute instability regime predicted by our linear analysis is close to the flooding point obtained from the fully non-linear computations of the WIBL model.
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Pan, Lei. "Hydrophobic Forces in Wetting Films". Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/76918.
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Flotation is an important separation process used in the mining industry. The process is based on hydrophobizing a selected mineral using an appropriate surfactant, so that an air bubble can spontaneously adhere on the mineral surface. The bubble-particle adhesion is possible only when the thin film of water between the bubble and particle ruptures, just like when two colloidal particles or air bubbles adhere with each other. Under most flotation conditions, however, both the double-layer and dispersion forces are repulsive, which makes it difficult to model the rupture of the wetting films using the DLVO theory.
In the present work, we have measured the kinetics of film thinning between air bubble and flat surfaces of gold and silica. The former was hydrophobized by ex-site potassium amyl xanthate, while the latter by in-site Octadecyltrimetylammonium chlroride. The kinetics curves obtained with and without theses hydrophobizing agents were fitted to the Reynolds lubrication theory by assuming that the driving force for film thinning was the sum of capillary pressure and the disjoining pressure in a thin film. It was found that the kinetics curves obtained with hydrophilic surfaces can be fitted to the theory with the disjoining pressure calculated from the DLVO theory. With hydrophobized surfaces, however, the kinetics curves can be fitted only by assuming the presence of a non-DLVO attractive force (or hydrophobic force) in the wetting films. The results obtained in the present work shows that long-range hydrophobic forces is responsible for the faster drainage of wetting film.
It is shown that the changes in hydrophobic forces upon the thin water film between air bubble and hydrophobic surface is dependent on hydrophobizing agent concentration, immersion time and the electrolyte concentration in solution. The obtained hydrophobic forces constant in wetting film K132 is compared with the hydrophobic forces constant between two solid surfaces K131 to verify the combining rule for flotation.Master of Science
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Seyed, Yazdi Jamileh. "WETTING TRANSITIONS AT NANOSTRUCTURED SURFACES". VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/298.
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Shape of a droplet atop a surface heterogeneity at a nanoscale. Small aqueous droplets on homogeneous surfaces, surrounded by a reservoir of vapor are inherently unstable. In contact with supersaturated vapor, the drops will keep growing until they coalesce and form a contiguous aqueous phase. Alternatively, if vapor pressure is below that of the droplets, the droplets gradually evaporate. Departing from this common picture, when nanoscale droplets sit above hydrophilic patches on a heterogeneous surface, at certain conditions they can maintain a stable volume, determined by the pertinent contact angle and the size of the patches. Only the region under the droplet perimeter controls the contact angle, which in turn determines the drops curvature for given volume and the vapor pressure of the liquid in the drop. The drop size may therefore stop changing when its base just covers the hydrophilic patch. The finite range of water-substrate interactions, however, blurs the patch boundaries hence the nanodrop geometry varies with the patch size in a gradual manner. We use molecular simulations to examine this dependence on graphene-like surfaces with topological heterogeneity as complementing studies of chemical heterogeneity (John Ritchie, Master Thesis, VCU, 2010). We measure the microscopic analogue of the contact angle of aqueous nanodrops above circular hydrophilic or hydrophobic patches of varied size. For both the chemically and topographically heterogeneous surfaces, the results confirm the contact angle of a nanodroplet can be predicted by the local Cassie-Baxter mixing relation applied to the area within the interaction range from the drop’s perimeter, which, in turn, enables predictions of condensation and saturated vapor pressure above nanopatterned hydrophilic/hydrophobic surfaces. Switchable nanowetting dynamics. Understanding the dynamic response of contact angle on switchable hydrophobic-hydrophilic surfaces is key to the design of nanofluidic and optical devices. We use molecular dynamics simulation for water droplets with different number of molecules on a molecularly smooth and corrugated substrate. We monitored the relaxation of the droplet geometry in response to a change in surface hydrophobicity. From the time correlation function for the height of the drop’s center of mass we estimate the rates of relaxation for wetting/dewetting processes following the change between hydrophobic and hydrophilic character of the surface. On molecularly smooth surfaces, we find similar forward/backward rates revealing insignificant hysteresis. Calculations on corrugated surfaces, however, reveal quite different relaxation times for forward (Cassie state to Wenzel state) and reverse processes. The observed hysteresis is associated with different friction forces between the droplet and the surface during advancing and receding processes. We calculate the friction coefficient of the corrugated surface for the forward process following the increase in surface hydrophilicity. We compare continuum hydrodynamic (HD) and molecular kinetic theories (MKT) for calculation of the friction coefficient. Although the small size of our system suggests the use of molecular description of the surface, incorporated in MKT, we obtain essentially equal friction coefficients from both theories. This information indicates an overlap between continuum hydrodynamics and molecular dynamics regimes, with both the HD and MKT theories being applicable at the nanoscopic lengthscales we consider. Water dynamics inside nanospheres. Chemical nature of a spherical confinement has significant effect on dynamics of water molecules outside the cage. In a separate study we examined the effect of chemical nature of the cage on the dynamics of water molecules inside the cage. Calculations have been made for variety of time correlation functions of water in four different sizes of spherical hydrophobic/hydrophilic confinements, Cx x=320, 500, 720, 1500 based “hollow buckyballs”, with different spherical pore diameters. Calculated water hydrogen bond lifetimes, diffusion coefficients and rotational relaxation times in these systems reveal a distinctly different water dynamics compared to interfacial water dynamics outside the cage: interestingly we find insignificant changes in time scales for water dynamics in hydrophilic and hydrophobic carbon cages. Even adding partial charges to hydrophilic confinement did not make a big effect on results compared to hydrophobic case. These findings are suggesting that in highly symmetric confinement water molecules do not care about the type of interaction with the wall because of cancellation of forces in different directions.
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Geraldi, N. R. "Wetting of non rigid surfaces". Thesis, Nottingham Trent University, 2015. http://irep.ntu.ac.uk/id/eprint/203/.
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In the world of anti-wetting surfaces, many superhydrophobic substrates comprise rigid structures on rigid substrates. The development of a thin flexible substrate would allow new avenues to be explored to fully take advantage of the non-wetting properties of superhydrophobicity. This thesis presents a novel production method and subsequent analysis of thin, conformable, superhydrophobic films based on the embedding of carbon nano-particles (CNPs) into the surface of polydimethylsiloxane (PDMS) substrates. Firstly experiments were performed to determine the effects of surface roughness on the capillary origami process. It was found that the droplet wrapping process could be controlled with the appropriate choice of liquid. Using a wetting liquid would see an enhanced wrapping state whereas use of a dewetting liquid would see a complete suppression of the wrapping process. The second set of experiments concentrated on determining whether or not it is possible to reduce the drag force experienced on cylinders in a laminar flow situation. By comparing an uncoated cylinder to a CNP PDMS coated cylinder of equivalent diameter, it was determined that it is possible to reduce the drag by a maximum of 28%. The last tests were to determine the potential of the surface as a snail-repellent material. A set of experiments, designed to compare the repellent and adhesive properties of the surface were performed. It was seen that these surfaces show promise as a snail repellent surface. This surface is in keeping with the hypothesis of Shirtcliffe et al. [1] which states an effective snail repellent surface shows anti-adhesive properties and maintains a high receding contact angle in the presence of an anionic surfactant.
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Tsai, Chen-Chih. "Electrospun fibrous materials wetting properties /". Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1263409825/.
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Denesuk, Matthew 1965. "Modelling of dynamic wetting phenomena". Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/291345.
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A general dynamic wetting model is presented in which surface and gravitational driving energies are balanced against energy lost through bulk viscous dissipation. Behavior is described in terms only of independently measurable quantities, with no adjustable parameters. Additionally, the model can be expressed so as to predict liquid viscosity as a function of dynamic wetting behavior. Application of the model to a lead-silicate liquid on a gold substrate demonstrate excellent agreement of the model with experiment. The general framework of the model is especially amenable to the incorporation of other physico-chemical processes which may impact dynamic wetting phenomena. Examples are given which extend the model to specific cases where substrate roughness and/or substrate dissolution are important. Additionally, the dynamic wetting model is extended to porous substrates, accounting for the effects of composite interface formation and depletion of the liquid via capillary flow.
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Trapuzzano, Matthew A. "Controlled Wetting Using Ultrasonic Vibration". Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7974.
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Many industrial processes such as printing and cleaning, as well as products like adhesives, coatings, and biological testing devices, rely on the wetting of liquids on a surfaces. Wetting is commonly controlled through material selection, coatings, and/or surface texture, but these means are sensitive to environmental conditions. Wetting is influenced by variables like surface tension, density, the surface chemistry, local energy barriers like surface roughness, and how the droplet is placed on the surface. Wetting of droplets can also be influenced externally in many ways such as introducing surfactants, applying electrical fields, or by dynamically excitation. Low-frequency, high amplitude vibration can initiate wetting changes prompted by droplet contact line oscillations that exceed the range of stable contact angles inherent of a droplet on a solid surface.
The study of ultrasonic vibration wetting and spreading effects is sparse [1, 2], and is usually only qualitatively analyzed. Therefore, the specific goal of this thesis is somewhat unique, but also has potential as a means to controllably reverse surface adhesion.
High frequency vibration effects and the governing mechanisms are relatively uncharacterized due to difficulties posed by the spatial and temporal scales. To investigate, droplets of 10, 20, and 30 µL are imaged as they vibrate on a hydrophobic surface forced via a piezoelectric transducer over different high frequencies (>10 kHz). Wetting transitions occur abruptly over a range of parameters, but coincide with transducer resonance modes. The magnitude of contact angle change is dependent on droplet volume and surface acceleration, and remains after cessation of vibration, however new droplets wet with the original contact angle.
A more detailed investigation of this phenomenon was necessary to obtain a better understanding. This required repeatable testing conditions, which relies heavily on surface integrity. However, some “hydrophobic” coatings are sensitive to extended water exposure. To determine which hydrophobic coatings may be appropriate for investigating dynamic wetting phenomena, samples of glass slides coated with a series of fluoropolymer coatings were tested by measuring water contact angle before, during, and after extended submersion in deionized water and compared to the same coatings subjected to ultrasonic vibration while covered in deionized water. Both methods caused changes in advancing and receding contact angle, but degradation rates of vibrated coatings, when apparent, were significantly increased. Prolonged soaking caused significant decreases in the contact angle of most coatings, but experienced significant recovery of hydrophobicity when later heat-treated at 160 C. Dissimilar trends apparent in receding contact angles suggests a unique degradation cause in each case. Roughening and smoothing of coatings was noted for coatings that were submerged and heat-treated respectively, but this did not correlate well with the changing water contact angle. Degradation did not correspond to surface acceleration levels, but may be related to how well coatings adhere to the substrate, indicative of a dissolved coating. Most coatings suffered from contact angle degradation between 20-70% when exposed to water over a long period of time, however the hydrophobic fluoropolymer coating FluoroSyl was found to remain unchanged. For this reason it was found to be the most robust coating for providing long term wetting repeatability of vibrated droplets.
Droplets (10 to 70 µL) were imaged on hydrophobic surfaces as they were vibrated with ultrasonic piezoelectric transducers. Droplets were vibrated at a constant frequency with ramped amplitude. Spreading of droplets occurs abruptly when a threshold surface acceleration is exceeded of approximately 20,000 m/s2. Droplet contact area (diameter) can be controlled by varying acceleration levels above the threshold. The threshold acceleration was relatively independent of droplet volume, while initial contact angle impacts the extent of spreading. Wetting changes remain after cessation of vibration as long as the vibrated droplet remained within the equilibrium contact angle range for the surface (> the receding contact angle), however new droplets wet with the original contact angle except for some cases where vibration of liquid can affect the integrity of the coating. Reversible wettability of textured surfaces is a desired effect that has various industry applications where droplet manipulation is used, like biomedical devices, coating technologies, and agriculture [3-5].
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Dobbs, Harvey Thomas. "Studies of non-uniform wetting films". Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334897.
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Blow, Matthew Lewis. "Wetting on flexible and anisotropic surfaces". Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540127.
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Linke, Dorota [Verfasser]. "Wetting of complex liquids / Dorota Linke". Mainz : Universitätsbibliothek Mainz, 2019. http://d-nb.info/1190605988/34.
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Parry, Andrew Owen. "Correlation functions at continuous wetting transitions". Thesis, University of Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330318.
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Chimezie, Ugochi y Gurram Akhila Srinivas. "Wetting properties of stainless steel surfaces". Thesis, Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-32598.
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Systematic pre cleaning, disinfection and sterilization of medical equipment used in examination and treatment of patients are very important for safe care of the patients and the staff handling these instruments. Due to the technical properties of stainless steel, its hygienic experience and the sophisticated look of the stainless steel, it has dominated the medical health care environments for decades. The wetting properties of stainless steel surfaces are presumed to be essential for the process of clean ability and for a wide variety of bio compatibility.In collaboration with the topical company for this thesis, the idea is to find the correlation between the surface properties of various stainless steel in relation to their wetting and spreading ability to enable efficient cleaning of the surface. For a substrate surface to be thoroughly cleaned of any debris or soil, it should be able to allow proper adherence of the liquid across its surface to a certain degree good enough to ensure good wettability of the surface and conversely easy and proper removal of any attached soil on the surface. Higher demand on cleaning, disinfection and sterilization processes became more and more pressing due the development of complex medical equipment.Different stainless steel (316L) surface finishes and some surgical equipment are investigated using the state of the equipment at Halmstad University. Using the imaging interferometer and mapping software, Mountain Map, the results obtained is controlled readings and classification of the various surface parameters. Contact angle measurements were carried out on each surface with three polar (Distilled water, Glycerol and Ethylene glycol) and one non polar (Olive Oil) probe liquids with a drop volume of 3μm using Theta Optical Tensiometer and One Attention Software for the analysis. The impact and correlations of the surface parameters on wettability was later compared from the measurements obtained.
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Abedsoltan, Hossein. "Meso-Scale Wetting of Paper Towels". Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami1501246506048675.
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Stoddard, Ryan Manse. "Experimental Investigations on Non-Wetting Surfaces". Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103477.
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Superhydrophobic (SHS) and lubricant-infused surfaces (LIS) exhibit exceptional non-wetting characteristics that make them attractive for energy production applications including steam condensation and fouling mitigation. The dissertation work focuses on application of non-wetting surfaces to energy production using a systematic approach examining each component of surface fabrication in three functional areas. First, SHS and LIS are fabricated using robust, scalable methods and tested for durability in heated, wet conditions and under high-energy water jet impingement. Clear performance differences are shown based on surface texturing, functionalizing agent, and infused lubricant. Second, SHS and LIS are applied to tube exteriors and evaluated for their ability to produce sustained dropwise condensation in a typical power plant condenser environment. The surfaces are shown to produce heat transfer coefficients up to 7-10 times that of film-wise condensation, with condenser effectiveness of 0.92 or better compared to effectiveness of about 0.6 in conventional condensers. Third, LIS on the interior of tubes are assessed in accelerated mineral fouling conditions. LIS are shown to mitigate calcium sulfate and calcium carbonate fouling under laminar conditions. The results of the study bear profound benefits to reducing the levelized cost of condensers and water uptake in thermoelectric power plants, that currently consume about 50% of the total water use in the U.S.Doctor of Philosophy
Creating durable, hybrid surfaces for improved steam condensation and fouling mitigation would provide substantial impact to power generation worldwide. Bioinspired, non-wetting surfaces, such as superhydrophobic (SHS) and lubricant-infused surfaces (LIS) exhibit exceptional non-wetting characteristics that make them attractive for energy applications. Each of these non-wetting technologies, however, faces durability and scalability challenges that make them unfeasible for widespread, practical adoption. As a result, decades of materials science research have stagnated in the research laboratories with limited demonstrations of dropwise condensation and fouling mitigation in static situations. The dissertation work focuses on application of SHS and LIS to energy production using a systematic approach examining each component of surface fabrication in three functional areas. First, SHS and LIS are fabricated using robust, scalable methods and tested for durability using ASTM standard static and dynamic evaluation methods. Clear performance differences are shown based on surface texturing, functionalizing agent, and infused lubricant. Second, dropwise steam condensation on the surfaces are shown to exhibit heat transfer performance an order of magnitude greater than film-wise condensation in a typical power plant condenser environment. The surfaces are shown to produce heat transfer coefficients up to 7-10 times that of film-wise condensation, with condenser effectiveness of 0.92 or better compared to effectiveness of about 0.6 in conventional condensers. This work presents for the first time, a non-dimensional correlation for a priori prediction of LIS heat transfer performance given known qualities of the LIS. Third, challenges of fouling mitigation in power plants have been studied for over a decade. This work demonstrates for the first time that LIS applied to the interior of tubes mitigate calcium sulfate and calcium carbonate fouling in both static and laminar flow conditions.
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Tuite, Joseph M. "Enhancement of boiling in highly wetting fluids". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA362878.
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Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, March 1999."March 1999". Thesis advisor(s): Matthew D. Kelleher. Includes bibliographical references (p. 95-96). Also available online.
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Ciftja, Arjan. "Solar silicon refining; Inclusions, settling, filtration, wetting". Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5406.
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The main objective of the present work is the removal of inclusions from silicon scrap and metallurgical grade silicon. To reach this goal, two various routes are investigated. First, settling of SiC particles from molten silicon followed by directional solidification is reported in this thesis. Then, removal of SiC and Si3N4 inclusions in silicon scrap by filtration with foam filters and wettabilities of silicon on graphite materials are studied. To supply the increasing needs of the photovoltaic industry it is necessary to produce a low cost silicon feedstock. One of the many routes established from the industry is the Solsilc project. This project aims to produce solar-grade silicon by carbothermal reduction of silicon, based on the use of very pure raw materials. The high carbon content of about 700 mass ppm of the silicon in the form of SiC particles, needs to be removed before the Solsilc silicon could be used as a feedstock to PV industry. Settling of SiC particles in molten silicon was investigated. This part of the work was in cooperation with SINTEF Materials & Chemistry. Two experiments were conducted and the cast silicon ingots were analyzed by light microscopy and LECO carbon analyzer. The results showed that the number of inclusions in the middle of the ingots was less than in the bottom and top. The removal efficiency was above 96% in the middle part of an ingot and the total carbon content measured by LECO was < 25 mass ppm. The difference in density between the particles and the melt gives the SiC particles a relatively high settling velocity leading to a high removal efficiency. Pushing and engulfment of SiC particles by solidification front was also studied. Directional solidification of silicon that followed settling pushes the particles to the top of the ingot. The presence of SiC particles in the middle of the ingot is explained by engulfment. Top-cut silicon scrap represents a considerable loss of the PV silicon. Removal of inclusions from the silicon scrap would make it possible to recycle it to feedstock in the PV cell production. This was carried out by filtration with ceramic foam filters. Carbon and SiC foam filters with various pore sizes were employed in the filtration experiments. They were provided by Eger-Sørensen, a Norwegian company and Foseco AB in Sweden. The top-cut silicon scrap came from REC-Scan Wafer. Characterization of inclusions in silicon scrap before and after filtration experiments took place. Two techniques were developed and used in this work. First, extraction of inclusions by acid dissolution of the silicon was carried out. The SiC and Si3N4 particles collected afterwards were analyzed and counted by automated light microscopy. In the second technique, silicon samples were ground and polished with diamond paste. Microscopic analysis consisted of measuring the surface area of the inclusions found in the silicon samples. Results show that inclusions in top-cut solar cell silicon scrap are needle-like Si3N4 particles and round SiC inclusions. The removal efficiency for a 30 ppi SiC filter is more than 99%. The inclusions remaining after filtration are mainly SiC particles smaller than 10 µm. The experiments show that the filtration efficiency increases with decreasing filter pore size. Some filter cakes that mainly consist of large Si3N4 inclusions are found on the top surface of the filter. Deep bed filtration is the mechanism responsible for the removal of small particles. After taking into consideration various models for the foam filters the main conclusion is that interception seems to be the main removal mechanism of inclusions in silicon. Settling appears to play a minor role for our system. A new model named branch model explains better the experimental results. Due to the low wetting angle between molten metal and the filter material, capillary forces drive the melt through the filter. Therefore, the melt velocity through the filter is high. This justifies the usage of potential flow in the branch model. It is shown that molten silicon may be contaminated in contact with the refractories. Since purity for solar cell silicon is crucial, contamination must be minimized. Graphite crucibles may be a source of relatively high levels of Al, Fe, and P. In the filtration process, wettability of the molten silicon with the filter material is very important. Thus, spreading and infiltration of molten silicon into the graphite substrates were also investigated in this thesis. Five different graphites were provided by Svenska Tanso AB. They are in use as refractories in the PV industry and vary from each other in porosity, density, and average pore size. The sessile drop technique is employed to study the wetting behavior of molten silicon on the graphite materials. The measured contact angles show that molten silicon does not initially wet carbon materials. However, due to the chemical reaction between Si and C, a SiC layer is formed in the interface between molten silicon and the graphite. Formation of this layer lowers the contact angles finally reaching equilibrium wetting angles of molten silicon with SiC materials. Spreading of molten silicon is affected not only by the reaction formed SiC layer, but also by the surface finish. The final contact angles, also called equilibrium contact angles, decrease with increasing surface roughness of the graphites. Infiltration of silicon into graphites is mainly related to the average pore size of graphite materials. Materials with large pores are penetrated deeper by the liquid silicon. Zero contact angles of the silicon with graphites are found in materials with both high surface roughness and large average pore size. These results indicate that graphites for use in the PV industry should have a small average pore size. The surface of the graphite in direct contact with silicon should be smooth (low roughness).
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Bao, Sarina. "Filtration of Aluminium-Experiments, Wetting,and Modelling". Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15147.
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The present work deals with the inclusion removal mechanism in aluminium filtration and the use of alternative filter materials. Four routes are investigated. First, an overview of previous research on filtration knowledge is summarized. The filtration mechanism comprises two parts: transport of inclusions to the filter wall and attachment of inclusions on the wall. We have mainly investigated collision by interception and the wetting (surface tension) of inclusion-Al and Al-filter in this work. Second, the wetting behaviour of inclusion-Al and Al-filter is measured in the laboratory. In filtration it is important that particles to be removed contact, or come close to the filter walls. Therefore the metal carrying the inclusions must come into close contact,i.e. wet the filter material. A systematic and comprehensive investigation of the wetting behaviour in the molten aluminium-filter system is presented. In aluminium filtration,alumina is the most common filter material, even though alumina is not wetted by aluminium. Therefore we have investigated the use of alternative filter materials withimproved wetting. In the laboratory, SiC and graphite demonstrate good wetting bymolten aluminium. Problems with these materials exist, as SiC is easily oxidized to SiO2 and both react with aluminium to give Al4C3. However, SiO2 and SiC react slowly with aluminium, but this does not seem to influence the wetting. The wettability of the inclusion-Al may play a key role in aluminium filtration. Particlesto be removed should ideally have poor wetting with aluminium and filter should hasgood wetting with aluminium. A challenge is that SiC and Al4C3 inclusions show betterwetting with aluminium than alumina. Third, plant scale filtration experiments were carried out with Al2O3 and SiC industrial filters. Metal composition was not changed by the industrial filters. Improved wetting of aluminium on filter materials is an advantage in getting molten metal to infiltrate filtersand thus to improve the filtration efficiency. A SiC filter gives better filtration efficiency. Filtration efficiency increases with particle size. SiC reacts with aluminium so slowly that no carbide inclusions were produced in the industrial SiC filter with approximately 60% of SiC. SiC filters have better wetting than Al2O3 filters with aluminium. Thus SiC could be a good alternative filter material. Fourth, a theoretical model is developed regarding the interceptional and gravitational collision considering the filter as a collection of branches (cylinders). A filtration efficiency equation is derived based on particle diameter, branch diameter, porosity,filter thickness, filter specific surface area, and Reynolds number. The filtration efficiency decreases with the flow rate until it reaches a minimum, and then increases. Gravitational collision must be taken into account at the lower flowrates. The greater the velocity the less time particles have to settle. Thus gravitationalcollision efficiency decays with increasing flow rate. The interceptional collision efficiency increases with the velocity since then more liquid and particles come into contact with the collector. The interceptional collision efficiency that dominates at high velocities is the main topic of the model
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Monast, Patrick. "Wetting behavior of ternary mixtures containing surfactants". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ64410.pdf.
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Fell, Daniela [Verfasser]. "Dynamic wetting of complex liquids / Daniela Fell". Mainz : Universitätsbibliothek Mainz, 2013. http://d-nb.info/1033445487/34.
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Briant, Andrew J. "Lattice Boltzmann simulations of wetting and spreading". Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270243.
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Debacher, Nito Angelo. "Studies on the dynamics of wetting processes". Thesis, University of Bristol, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240354.
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Sipe, Joel E. "A Porous Media Model for Sprinkler Wetting". Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-dissertations/98.
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A one-dimensional porous media model has been developed to investigate water based fire suppression. The model is for heat and mass transfer in porous materials subjected to external water sprays and radiant heating. In the model, heat transfer inside the material occurs by conduction, convection, and phase change. Mass transfer occurs by gas phase diffusion and convection in the liquid and gas phases. Convective mass fluxes are driven by pressure gradients according to Darcy’s Law. Boundary conditions that are appropriate for a range of cases are presented. The model was used, along with experiments, to investigate two scenarios relevant to water based suppression: spray wetting and radiant heating. Ceramic fiberboard samples were used as a test material. For the wetting tests, the model is shown to be able to reasonably predict the rate of water absorption into the samples. Radiant heating tests were conducted in the cone calorimeter with pre-wetted samples. For the heating tests, the model is shown to reasonably predict the drying behavior that would directly precede an ignition event.
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Day, Julia Katherine. "A study of bubble wetting on surfaces". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62747.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 53).
In microfluidics, the formation of bubbles within devices obstructs flow and can damage the microfluidic chip or the samples contained therein. This thesis works toward a better understand of bubble wetting on surfaces, so that future microfluidics devices can be designed to be more robust and free of bubbles. Current wetting theory as applied to bubbles is examined, and two key areas for improvement are identified: disjoining pressure effects and gravitationaleffects. Wetting of textured surfaces is also analyzed for bubble application, leading to a prediction that a model based on a Cassie-Baxter analysis with knowledge of bubble wetting on a flat surface would be most accurate compared to other models. Dynamic and sessile bubble contact angles and droplet contact angles were measured on smooth acrylic, fluorosilanized silicon, glass, nylon, and silicon. These results were compared to the existing model, and the resulting error showed a strong correlation with a Pearson's correlation coefficient of 0.863 to the magnitude of the bubble contact angle hysteresis. Because contact angle hysteresis can be related to the disjoining pressure, these results were a good indicator that disjoining pressure should be considered in developing improved bubble wetting models. Dynamic and sessile bubble contact angles and droplet contact angles were also measured on four silicon samples with different surface textures. These results were compared to three existing wetting models as applied to bubble wetting, and it was found that the Cassie-Baxter model based on the bubble contact angle on a smooth silicon surface was most accurate, with an average percentage error of 0.8%. Finally, recommendations for further research to support developing models of bubble wetting are made.
by Julia Katherine Day.
S.B.
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Wang, Yuli. "Capillarity and wetting of non-Newtonian droplets". Doctoral thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-184146.
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Capillarity and dynamic wetting of non-Newtonian fluids are important in many natural and industrial processes, examples cover from a daily phenomenon as splashing of a cup of yogurt to advanced technologies such as additive manufacturing. The applicable non-Newtonian fluids are usually viscoelastic compounds of polymers and solvents. Previous experiments observed diverse interesting behaviors of a polymeric droplet on a wetted substrate or in a microfluidic device. However, our understanding of how viscoelasticity affects droplet dynamics remains very limited. This work intends to shed light on viscoelastic effect on two small scale processes, i.e., the motion of a wetting contact line and droplet splitting at a bifurcation tip. Numerical simulation is employed to reveal detailed information such as elastic stresses and interfacial flow field. A numerical model is built, combining the phase field method, computational rheology techniques and computational fluid dynamics. The system is capable for calculation of realistic circumstances such as a droplet made of aqueous solution of polymers with moderate relaxation time, impacting a partially wetting surface in ambient air. The work is divided into three flow cases. For the flow case of bifurcation tube, the evolution of the interface and droplet dynamics are compared between viscoelastic fluids and Newtonian fluids. The splitting or non-splitting behavior influenced by elastic stresses is analyzed. For the flow case of dynamic wetting, the flow field and rheological details such as effective viscosity and normal stress difference near a moving contact line are presented. The effects of shear-thinning and elasticity on droplet spreading and receding are analyzed, under inertial and inertialess circumstances. In the last part, droplet impact of both Newtonian and viscoelastic fluids are demonstrated. For Newtonian droplets, a phase diagram is drawn to visualize different impact regions for spreading, splashing and gas entrapment. For viscoelastic droplets, the viscoelastic effects on droplet deformation, spreading radius and contact line motion are revealed and discussed.QC 20160329
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Chang, Boon Fuei. "A non-wetting packed bed gas scrubber". Thesis, University of Sheffield, 2003. http://etheses.whiterose.ac.uk/15160/.
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Present integrated gasification combined cycle (IGCC) systems demonstrate high system efficiency and impressive environmental performance, giving them an edge over conventional pulverised fuel power stations. A key area in the development of IGCCs is hot fuel gas clean-up (HGCU). Fuel gas cleaning at elevated temperatures reduces thermal efficiency losses associated with gas quenching in conventional cold gas cleaning methods. Current hot gas desulphurisation techniques focus on the use of regenerable metal oxide sorbents, however the long-term sorbent performance issues have yet to be fully addressed. A fresh and radical approach may provide the key to overcoming the inherent limitations associated with metal oxide sorbents. A molten tin irrigated packed bed scrubber adopted in this research project is one such innovative way forward in HGCU. The hot scrubber offers the prospect of a multicomponent clean-up device. High-temperature sulphur removal takes place via absorption of H2S (and COS) into molten tin whilst discrete molten tin droplets and rivulets on the packing surface act as solid particulate collectors. The primary aim of this research project was to investigate the workings of a small-scale room temperature packed bed scrubber operating under non-wetting flow conditions analogous to the molten tin irrigated scrubber. Water irrigation of low surface energy packings simulated the nonwetting flow of liquid metals. The air-water analogue of the liquid metal scrubber provided the platform for hydrodynamics (flow visualisation, flooding and liquid holdup), particulate removal and mass transfer studies under non-wetting flow conditions. The performance of a small air lift for water circulation through the column was also investigated. These cold studies offered insight into the operation and performance of the liquid metal hot scrubber. Prior to the cold gas scrubber studies, preliminary small-scale gasification tests on petroleum coke samples were performed to investigate the effect of molten tin on H2S in the product fuel gas. The tests provided actual experimental evidence of the possibility of sulphur removal by molten tin in a gasification environment. It was shown that the maximum possible size of a liquid droplet hanging from a non-wetting spherical solid surface could be predicted from the liquid surface tension and density based on force balance. The mobility of static holdup in a non-wettable packed bed has been demonstrated, this being due to the tendency for the liquid to form discrete droplets rather than spreading films. Existing flooding and liquid holdup correlations that hold for conventional wettable packed beds were shown to be inadequate where non-wetting systems were concerned. Summary hence alternative methods applicable to the latter were sought. The introduction of a non-wetting tendency factor based on the ratio of the solid critical surface tension to the liquid surface tension, enabled the flooding capacities of non-wetting systems including those of this study to be predicted using Sherwood et al. 's graphical flooding correlation. The total volumetric liquid holdup was well correlated against the bed pressure drop, true gas velocity and gas density, offering the prospects of predicting holdup for systems using the same spherical packing. In general, the water-irrigated packed bed showed good hydrodynamic similarities to liquid metal systems, suggesting a dominating influence of liquid-solid contact angle which overrides striking differences in liquid physical properties. The performance of the small air lift pump was unaffected by varying the number of gas ports on the injector without any change to the hole size. The operating curve of the air lift pump could be predicted with good accuracy using momentum balance and two phase flow theory, provided that all major pressure losses in the system were accounted for, including notably the downcomer friction losses and accelerative effects. The non-wetting packed bed scrubber demonstrated impressive dust removal performance. Total separation efficiencies as high as 99.6% and cut sizes approaching submicron were achieved. Dust particles larger than about 6.5 um can be separated to efficiencies greater than 98%. Complete particle separation was achieved in all cases for dust particles larger than 16 J..lm. Particulate removal in a packed bed of spheres under non-wetting flow conditions has also been modelled using computational fluid dynamics (FLUENT). Simulation results showed that particle separation efficiency increases with particle size and density, but is unaffected by particle concentration. The predicted particle size corresponding to 98% efficiency is about 40 J..lm. In mass transfer, the height of the gas film transfer unit of various non-wetting spherical packed bed systems including those of this study was correlated successfully against the gas phase Reynolds number, the liquid superficial velocity and the packing diameter. Results from the cold gas scrubber studies have offered insight and understanding into the workings and development of the liquid metal packed bed gas scrubber. Findings and correlations derived from the water model studies, occasionally complemented by data from other non-wetting systems, have provided the means to predict the hydrodynamics, particulate removal capability and mass transfer performance of the liquid metal based gas scrubber. The pilot unit of the hot gas scrubber has been designed and fully constructed. The high temperature gas cleaning facility is ready for commissioning.
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Pan, Lei. "Surface and Hydrodynamic Forces in Wetting Films". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/51538.
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The process of froth flotation relies on using air bubbles to collect desired mineral particles dispersed in aqueous media on the surface, while leaving undesirous mineral particles behind. For a particle to be collected on the surface of a bubble, the thin liquid films (or wetting films) of water formed in between must rupture. According to the Frumkin-Derjaguin isotherm, it is necessary that wetting films can rupture when the disjoining pressures are negative. However, the negative disjoining pressures are difficult to measure due to the instability and short lifetimes of the films.
In the present work, two new methods of determining negative disjoining pressures have been developed. One is to use the modified thin film pressure balance (TFPB) technique, and the other is to directly determine the interaction forces using the force apparatus for deformable surfaces (FADS) developed in the present work. The former is designed to obtain spatiotemporal profiles of unstable wetting films by recording the optical interference patterns. The kinetic information derived from the spatiotemporal profiles were then used to determine the disjoining pressures using an analytical expression derived in the present work on the basis of the Reynolds lubrication theory. The technique has been used to study the effects of surface hydrophobicity, electrolyte (Al3+ ions) concentration, and bubble size on the stability of wetting films. Further, the geometric mean combining rule has been tested to see if the disjoining pressures of the wetting films can be predicted from the disjoining pressures of the colloid films formed between two hydrophobic surfaces and the disjoining pressures of the foam films formed between two air bubbles.
The FADS is capable of directly measuring the interaction forces between air bubble and solid surface, and simultaneously monitoring the bubble deformation. The results were analyzed using the Reynolds lubrication theory and the extended DLVO theory to determine both the hydrodynamic and disjoining pressures. The FADS was used to study the effects of surface hydrophobicity and approach speeds. The results show that hydrophobic force is the major driving force for the bubble-particle interactions occurring in flotation.Ph. D.
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Zhang, Chi. "Wetting on Lubricant Infused Polyeletrolyte Multilayer Surfaces". University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1435735900.
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Bernardino, Nelson Fernando Rei. "The nonlocal model of short-range wetting". Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/1349.
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Recently, a Nonlocal Model was proposed that seems to overcome difficulties of the fluctuation theory of 3D wetting. In this thesis we explore this model in detail, laying the foundations for its use. We show how the model can be derived from a microscopic Hamiltonian by a careful coarse graining procedure, based on a previous recipe proposed by Fisher and Jin. These authors obtained a model with a position dependent stiffness that has a dramatic effect on the wetting transition, driving the transition first-order. Our improved method does not have an explicit position dependent stiffness, rather the substrate-interface interaction is described by a binding potential functional with an elegant diagrammatic expansion. We then check the robustness of the structure of the Nonlocal Model using perturbation theory to study a more general microscopic Hamiltonian. The model is robust to such generalisations, whose only relevant effect is the change of the values of the coefficients of the Nonlocal Model. The same remarks are valid for the inclusion of a surface field. The generalised model still has the same structure, albeit with different coefficients. Another important extension is a longer-range substrate-fluid interaction. We generalise the model to be able to deal with these and also with a bulk field. The results for the particular case of an exponentially decaying substrate potential reveal interesting consequences for the transition, which can provide a direct test of the Nonlocal Model. We finalise with a chapter proving that the Nonlocal model obeys a sum-rule for complete wetting.
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Liu, Kuang-Yu. "Equilibrium of wetting layers on rough surfaces /". free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9842594.
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Setu, Siti Aminah. "Interfacial instabilities and wetting behaviour in confinement". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:7848f713-437b-4be8-b5f8-8232fcd59667.
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Interfacial instabilities and wetting phenomena of phase separated colloid-polymer mixtures are addressed in this study. Colloidal particles offer certain advantages over molecular systems, due to their larger lengthscales and slower timescales. Moreover, the phenomena can be directly visualised using laser scanning confocal microscopy, and a perfect match with soft-lithography fabrication techniques can be exploited. In particular, we study the viscous fingering instability in three dimensions, focusing on the role of wetting conditions and of thermal fluctuations. Combined with results obtained by lattice Boltzmann simulations, we reveal that the cross-over of the meniscus in the direction across the channel thickness is controlled by the capillary and Peclet numbers, and viscosity contrast of the system. The curvature of the meniscus has a pronounced effect on the onset of the Saffman-Taylor instability, in which the formation of the viscous fingers is suppressed up to a certain threshold. Furthermore, we investigate a related contact line instability, which leads to entrainment and subsequent droplet pinch-off. A theoretical prediction for the onset of the instability is developed, which shows a good agreement with the experimental observations and yields a method to directly measure the slip length of the interface. The large thermal fluctuations of our interface play an important role in pinch-off events, leading to periodic emission of droplets of similar sizes. Finally, we study wetting phenomena at geometrically sculpted walls. We focus on the shape, the thickness and the radius of curvature of the adsorbed liquid film, and find good agreement with theory. Changing the curvature of the wedge from a flat surface to a capil- lary slit furthermore smoothly connects wetting behaviour and capillary condensation, again in qualitative agreement with theory. Non-equilibrium effects may interfere with the data and are difficult to rule out. We end with recommendations for future work.
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Vanzo, Davide <1983>. "Liquid crystal nanodroplets and their surface wetting". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3566/1/vanzo_davide_tesi.pdf.
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Vanzo, Davide <1983>. "Liquid crystal nanodroplets and their surface wetting". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3566/.
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Semprebon, Ciro. "Wetting on Anisotropically Patterned and Rough Surfaces". Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426025.
Texto completoResumen
Since Young in 1805 described in words the trigonometric relations between the contact
angle and the forces acting on a droplet in mechanical equilibrium on a sulid surface, many advances
in the description of several aspects of wetting behavior have been done. Besides the
recent years developements in the field of micropatterning allowed the production surfaces with
chemical and geometrical regular patterns, which make possible a direct test of theoretical models.
Beyond the patterns characterized by a global isotropic disposition if the surface asperities
and heterogeneities, patterns constituted of series of parallel stripes or reliefs have been produced,
introducing an anisotropic element in the substrate. Recently many works focused on the characterization
of the anisotropic behavior of droplets on those surfaces. However there is not a
complete theory describing the anisotropy of droplets in these conditions. Furthermore most part
of previous works study the anisotropy on regular patterns made by micrometric channels.
To give a general description of those aspects of the anisotropic behavior which are independent
by the nature of the micrometric regular pattern, and to focus on the influence of different
wettabilities, in this thesis we studied the anisotropic wetting of droplets sitting on the top of single
posts, characterized by flat surfaces and sharp corners, and made with different materials. The
anisotropy was quantified by measuring the contact angles and base elongations in the two principal
symmetry axis. Measurements were obtained by a homemade apparatus, and the analysis
software has been entirely developed in this thesis. The main finding is that the contact angle
difference and the base eccentricity show the same relation within the experimental errors
regardless of surface wettability. These measurements were complemented by numerical simulations
with the Lattice Boltzmann method, which showed a good agreement with experimental
results. We also developed a simple geometrical model, valid for small eccentricities which reproduces qualitatively
experimental and numerical data.
In addition, during this thesis I characterized the wetting properties of thin (isotropic) films of
nanostructured titania, and related them to the morphological parameters of the substrates.Da quando Young nel 1805 descrisse a parole le relazioni trigonometriche tra l’angolo di contatto e le forze agenti su una goccia in equilibrio meccanico su una superficie solida sono stati ottenuti molti progressi nella descrizione di vari aspetti del wetting. Inoltre i progressi degli ultimi anni nel campo della microlavorazione hanno permesso di ottenere in modo semplice superfici con pattern chimici e geometrici assai regolari, su cui è stato possibile testare sperimentalmente le ipotesi dei vari modelli teorici. Oltre a tutti i pattern caratterizzati da una disposizione globalmente isotropa delle asperità, sono stati prodotti pattern costituiti da una serie di strisce e rilievi paralleli gli uni agli altri, introducendo così un elemento anisotropo nel substrato. Negli ultimi anni molti lavori sono stati rivolti alla caratterizzazione del comportamento anisotropo delle gocce su tali substrati. Tuttavia ad oggi non esiste una teoria completa che descriva l’anisotropia di gocce in queste condizioni. Inoltre la maggior parte dei lavori precedenti riguarda lo studio dell’anisotropia su pattern regolari costituiti da canali micrometrici. Per fornire una descrizione generale di quegli aspetti del comportamento anisotropo che sono indipendenti dai dettagli del pattern regolare su scala micrometrica, e per evidenziare l’influenza di diverse bagnabilità della superficie, in questa tesi abbiamo studiato il wetting anisotropo di gocce depositate su singoli rilievi, caratterizzati da una supervicie piana e spigoli vivi, e costruiti con diversi materiali. L’anisotropia è stata quantificata misurando gli angoli di contatto e le dimensioni della base delle gocce nei due principali assi di simetria. Le misure sono state ottenute con un apparato fatto in casa, e il software di analisi è stato interamente sviluppato durante questa tesi. Il risultato principale consiste nel fatto che la differenza tra gli angoli di contatto nelle due direzioni e l’eccentricità di base mostrano la stessa relazione all’interno degli errori sperimentali, indipendentemente dalla bagnabilità del substrato. Queste misure sono state completate tramite simulazioni numeriche per mezzo del metodo Lattice Boltzmann, e che hanno mostrato un buon accordo con i risultati sperimentali. Inoltre abbiamo formulato un semplice modello geometrico, valido per piccoli, che riproduce qualitativamente sia i risultati sperimentali che quelli numerici. Inoltre in questa tesi ho caratterizzato la bagnabilità di sottili film (isotropici) di titania nanostrutturata, mettendola in relazione con le proprietà morfologiche dei substrati stessi.
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Ataki, Adel. "Wetting of structured packing elements CFD and Experiment /". [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981239463.
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Turk, Ugur. "Boiling of highly wetting liquids in oscillatory flow". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA306226.
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