Dissertations / Theses on the topic 'Sessile Drops'

This dissertation reports on the discovery of a new method of patterning bacteria (Pseudomonas aeruginosa PAO1) on a surface using a drying sessile drop. This work identifies bacterial suspension age and the length of time mica is exposed to the laboratory atmosphere as the key parameters which impact the behavior of the sessile drop and the resulting residue. Possible origins of mica aging and bacterial suspension aging are discussed in light of the literature and the experimental conditions. The residue area and the fraction of the residue area on which substantial bacteria and salt deposits remained after the drying of the drop (fill-in fraction) were measured via analysis of optical micrographs. In general, smaller residues are more filled in. For fresh bacterial suspensions, and short mica exposure times, the residue covers the largest area and is characterized by rings formed during discrete depinning events as the solvent evaporates. As the exposure time increases and the mica surface slowly picks up contaminants from the atmosphere, the drop residue shrinks in size and bacteria are deposited in a regular cellular film in the interior of the drop residue. The fraction of the interior area covered by the cellular film is well correlated with the mica exposure time. For sufficiently aged bacterial suspensions, residues are small and more filled-in than residues formed from fresh suspensions on similarly aged mica. In addition, the interior deposition pattern transitions from a cellular film characteristic of fresh suspensions to a cracked carpet pattern for aged suspensions. Suspension aging related changes in the residues are attributed to accumulation of organic materials such as DNA, RNA, proteins, and other bacterial components in the suspension. The suspension aging process is also observed to be at least partially dependent on ventilation of the suspension during aging.

Le processus d'étalement et d'évaporation d'une goutte de suspensions de particules sur une surface solide est très intéressant permettant la formation de motifs. Une étude expérimentale à été effectuée avec du sang total humain et avec des fluides purs dans une chambre sous atmosphère contrôlée en humidité relative. Pour des angles de contact faible, le processus d'étalement/évaporation peut être divisé en deux régimes. Un premier régime rapide gouverné par un équilibre entre les forces visqueuses et les forces capillaires et un deuxième régime plus lent dominé par la cinétique d'évaporation. Nous montrons que les bio-colloïdes jouent un rôle significatif sur la dynamique de la ligne de contact. La vitesse moyenne de la ligne de contact suit la même dynamique d'étalement que le modèle de Tanner, où le temps d'étalement et les paramètres géométriques de la goutte sont fonctions de l'humidité. Dans cette étude, nous montrons que l'humidité relative influence les paramètres géométriques de la goutte et par conséquent le motif a la fin du processus d'évaporation. Un modèle purement diffusif pur a été obtenu dont le diamètre de mouillage et l'angle de contact sont fonction de l'humidité. Pour l'analyse morphologique des motifs de craquelures, une méthode de segmentation manuelle a été utilisée comme une méthode de référence pour la validation de la méthode de segmentation automatique développée dans "iBlood". Par cette méthode, nous montrons que la cinétique d'évaporation influence la distribution structurelle et morphologique des cellules de forme trapézoïdale, et par conséquent, l'espacement des fractures moyenne finale
Spreading/evaporation process of droplets over solid surfaces is a fundamental process and a wide research field because of number of applications in printing, micro-electronics, DNA analysis and even in biomedical. This experimental work aims to investigate the effect of relative humidity on the contact line dynamics, on the evaporation dynamics and on the final pattern of a drop of whole human blood. The spreading of a pure fluid model that has the same physical properties as human blood was studied and compared to the blood. We showed that bio-colloids play significant effect on the dynamics of contact line and the pinning effect of the drop. For low contact angles, we showed that the spreading/evaporation process could be divided into two regimes. A fast first regime determined by a balance between viscous forces and capillary forces and a second slower regime dominated by the evaporation rate. Physical mechanisms that are responsible for the spreading enhancement are proposed and discussed. The average velocity of the contact line was found to follow the same behaviour as Tanner's model, where the spreading dynamics and geometrical parameters of the droplet are function of relative humidity. The experimental measurements are in a good agreement with the purely diffusive model where the equilibrium wetting radius and contact angle are function of relative humidity. For the morphological analysis of crack patterns, a manual segmentation method was used as a reference for the validation of the automatic developed segmentation method. We showed that the evaporation rate influences structural distribution of plaques in the corona region and hence, the mean crack spacing

Coalescence of liquid drops is important in many natural and industrial processes, such as raining, inkjet printing and coating applications. The coalescence for sessile drops is more complicated due to the additional interplay between the drops and solid surface. This work examines the impact of gravity, interfacial tensions and wetting properties on both the static and dynamic aspects of the coalescence of sessile drops. In the presence of gravity, seven dimensionless parameters are identified to describe the axisymmetric configuration of a compound sessile drop after coalescence. A stability criterion is established based on the perturbation of Laplacian shape and the stability criterion is numerically evaluated in the zero Bond number limit. Surface Evolver simulations and experiments are performed for compound sessile drops at small and intermediate Bond numbers. Both simulations and experiments agree closely with the zero Bond number analysis, exhibiting a small discrepancy at intermediate Bond number. For the dynamics of sessile drop coalescence, experiments are performed for miscible fluids with similar surface tensions but different densities and viscosities. The coalescence behavior shows three distinctive stages with well separated timescales: an initial stage of fast bridge healing process, an intermediate stage of advective motion for fluids with different densities, and a final stage of diffusion. A dimensional analysis shows that the flow behavior for the advective motion resembles gravity current. A more detailed analytical model based on the lubrication approximation is conducted and demonstrates good qualitative agreement with the advective motion during the sessile drop coalescence.

L'évaporation d'une goutte reposant sur un support plat semble être un système relativement simple à étudier et a fait l'objet d'études scientifiques depuis plus d'un siècle. Cependant, l'étude de l'évaporation de gouttes sessiles est toujours d'actualité aujourd'hui avec l'essor de nouvelles techniques de visualisation ou de l'apparition de nouveaux types de fluides complexes.Cette étude expérimentale sera focalisée sur deux aspects distincts :- L'étude sur l'évaporation de fluides purs permettra d'étudier la dynamique d'évaporation et les ondes hydrothermales qui apparaissent dans les gouttes de fluides volatils lors du changement de phase. L'influence du type de fluide (différents alcools et alcanes) et du niveau de gravité (terrestre, lunaire et martienne) seront étudiés. De plus, l'utilisation de différents niveaux de gravité permet de développer un modèle empirique afin de prendre en compte dans le modèle quasi-stationnaire limité par diffusion de la vapeur la convection naturelle qui augmente fortement le débit d'évaporation.- Si les fluides complexes présentent une dynamique de séchage similaire à celle des fluides purs, d'autres mécanismes entrent en jeux, comme la gélification, l'organisation des particules et l'apparition de craquelures (voir Figure 2). Le mouillage et les différents groupes fonctionnels graphés sur les particules seront étudiés en regard du motif final de craquelures
Sessile droplets are widely found in day to day life: it might be a coffee spilt, rain onto a waterproof raincoat or again, water falling onto a cooking plate. However, despite the vast number of studies devoted to droplets for almost half a century, the fundamental phenomenon of the evaporation of sessile droplets is still a field that attracts a high level of interest due to its wide applicability and the development of new visualisation techniques or new types of complex fluids. This experimental study is focused two distinct aspects:- The evaporation of pure fluids has allow to study hydrothermal waves that appear in the droplets of volatile fluids during phase change. The influence of the type of fluid ---different alcohols and alkanes--- and the gravity levels ---Terrestrial, Lunar and Martian--- is investigated to have a better understanding of the flow motion inside droplet. Moreover, the use of different gravity levels allows to experimentally evidence the contribution of the atmospheric convective transport to sessile droplet evaporation. This investigation has allowed to develop an empirical model to take account of natural convection which greatly increases the evaporation rate in the quasi-steady diffusion-controlled evaporation model.- If complex fluids exhibit an evaporation dynamic similar to pure fluid, other mechanisms come into play, such as gelation, particles organisation and cracks formation. Wetting and different functional groups on the particles graphs will be studied in relation to the final pattern of cracks

This PhD thesis is focused on the role of interfaces that characterize microfluidic systems, such as the free air/liquid interface of drops or the liquid/solid interface of fluids enclosed in microchannels. This work has a twofold character: on one side, we studied the dynamics of sessile drops subject to oscillations of the substrate; on the other, we investigated the spatial concentration distribution of suspensions of motile bacteria, as a model system for active collids, tuned by geometrical confinement. Dynamics of sessile drops. The first topic is related to the field of wetting phenomena and open microfluidics, which deals with the behaviour of drops, typically in the nano-/microliter range, deposited on open surfaces. At such length scale, these systems are dominated by capillarity and may give rise to unexpected effects, not commonly observed at the larger scale we are used to. Our studies aim to the achievement of an active control on the motion and shape of drops by means of vibration of the substrates, for chemical or biological applications. In particular, the motion of liquid drops on an inclined substrate subject to vertical harmonic oscillations have been considered. Typically, small droplets on inclined surfaces remain pinned because of contact angle hysteresis. When vertical oscillations are applied the droplets unpin and slide down. Surprisingly, for sufficiently large oscillation amplitude the droplets move upward against gravity. The systematical investigation of the response of drops on varying peak acceleration and frequency of oscillations, for fluids with different surface tensions and viscosity, allowed the control of the unidimensional motion along the substrate. Then, we have studied the interfacial morphologies of water drops confined on the hydrophilic top face of rectangular posts of width 0.5 mm and various length. For small volumes, the liquid film adopts the shape of a homogeneous filament with a uniform cross section close to a circular segment. For larger volumes, the water interface forms a central bulge, which grows with the volume. In the case of posts longer than a characteristic length, the transition between the two film shapes on varying the volume is discontinuous and exhibits the bistability of the two morphologic states associated with a hysteresis phenomenon. Vertically oscillating the post, with fixed water volume corresponding to the bistability, at certain frequencies induces an irreversible transition from the filament to the bulge state. Self-propelled particles under geometrical confinement. The second topic deals with the behaviour of active fluids, i.e. self-propelled colloid suspensions which are intrinsically out of equilibrium systems (Active Matter). In particular, in the presence of geometrical structures, such systems behave in a very different way with respect to equilibrium Browinan colloids. We have analyzed the role of different swimming patterns on the concentration distribution of bacterial suspensions confined between two flat walls, by considering wild-type E. coli and P. aeruginosa, which perform Run and Tumble and Run and Reverse patterns, respectively. The concentration profiles have been obtained by counting motile bacteria at different distances from the bottom wall. In agreement with previous studies, an accumulation of motile bacteria close to the walls was observed. Different fraction of motile bacteria and different wall separations, ranging from 100 μm to 250 μm, have been tested. The concentration profiles resulted to be independent on the walls separation and on the different kind of motility and to scale with the motile fraction. These results are confirmed by numerical simulations, based on a collection of self-propelled rod-like particles interacting only through steric interactions.
Questa tesi di dottorato prende in esame il ruolo delle interfacce che caratterizzano i sistemi microfluidici, come ad esempio l’interfaccia libera aria/acqua delle gocce o l’interfaccia liquido/solido di fluidi racchiusi in microcanali. Questo lavoro ha un duplice carattere: da una parte, abbiamo studiato la dinamica di gocce sessili soggette ad oscillazioni del substrato; dall’altra, abbiamo investigato come la distribuzione spaziale della concentrazione in sospensioni batteriche, prese come sistema modello per colloidi attivi, venga alterata da un confinamento geometrico. Dinamica di gocce sessili. Il primo argomento rientra nel campo dei fenomeni di bagnabilità e della microfluidica aperta, che tratta il comportamento di gocce, tipicamente nel range dei nano- /microlitri, depositate su superfici aperte. A tali scale di lunghezza, questi sistemi sono dominati dalla capillarità a possono produrre effetti inaspettati che non vengono comunemente osservati alle scale macroscopiche a cui siamo abituati. I nostri studi sono volti al raggiungimento del controllo attivo del moto e della forma delle gocce per mezzo di vibrazioni del substrato, con applicazioni dalla Chimica alla Biologia. In particolare, è stato considerato il moto di gocce su in substrato inclinato sottoposto ad oscillazioni armoniche verticali. Normalmente, su superfici inclinate le goccioline rimangono ferme a causa dell’isteresi dell’angolo di contatto. Quando vengono applicate oscillazioni verticali le goccioline si sbloccano e scivolano giù. Sorprendentemente, per ampiezze di oscillazioni sufficientemente grandi le goccioline si muovono verso l’atro contro la forza di gravità. Un’analisi della risposta delle gocce al variare dell’accelerazione di picco e della frequenza di oscillazione, prendendo in esame fluidi con diverse tensioni superficiali e viscosità, ha permesso il controllo del moto unidimensionale lungo il pianoinclinato. Inoltre, abbiamo studiato le morfologie interfacciali di gocce d’acqua confinate sulla faccia superiore idrofilica di post rettangolari con larghezza 0.5 mm e varie lunghezze. Per piccoli volumi, il film liquido prende la forma di un filamento omogeneo con una cross-section uniforme simile ad un segmento circolare. Per volumi più grandi, l’interfaccia acqua/aria forma un rigonfiamento centrale, che cresce con il volume. Nel caso di post più lunghi di una lunghezza caratteristica, la transizione tra le due forme al variare del volume discontinua e mostra la bistabilità dei due stati morfologici associata ad un fenomeno di isteresi. Applicando al post, con volume d’acqua fissato corrispondente alla bistabilità, vibrazioni verticali con determinate frequenze si più indurre una transizione irreversibile dallo stato di filamento omogeneo a quello rigonfiato. Particelle auto-propulse sotto confinamento geometrico. Il secondo argomento riguarda il comportamento di fluidi attivi, cioè sospensioni di colloidi auto-propulsi che costituiscono sistemi intrinsecamente fuori equilibrio (Materia Attiva). In particolare, in presenza di strutture geometriche, tali sistemi si comportano in modo molto differente rispetto a colloidi Browniani all’equilibrio. Abbiamo analizzato il ruolo di diversi schemi di motilità sulla distribuzione di concentrazione di sospensioni batteriche confinate tra due pareti solide. considerando E. coli a P. aeruginosa wild-type, che si muovono secondo gli schemi Run and Tumble e Run and Reverse, rispettivamente. I profili di concentrazione sono tati ottenuti contando i batteri motili a diverse distanze dalle pareti. In accordo con studi precedenti, si osservato un accumulo di batteri motili in prossimit delle pareti. Sono state testate diverse frazioni di batteri motili e diverse distanze di separazione tra le pareti, nel range tra 100μm e 250 μm. I profili di concentrazione risultano indipendenti dalla distanza tra le pareti e dai differenti schemi di motilità e scalano con la frazione di batteri motili. Questi risultati sono confermati da simulazioni numeriche, basate su una collezione di particelle allungate auto-propulse che interagiscono solo tramite interazioni steriche.

In this Study, the surface energy was investigated for six penetration grade 70/100 bitumen binders. Wilhelmy Plate and the Sessile Drop were used to determine the contact angles. The purpose of this study was to compare the Wilhelmy Plate method with the Sessile Drop method, and to compare the significance of Owens-Wendt model with the significance of Acid Base model by correlating surface energy components. Better R2 –values were found for surface energy components by using the Owens-Wendt model than by using the Acid Base model. It was concluded here that Owens-Wendt model is a better model for determining surface energy components of bituminous binders than the Acid Base model since bituminous binders have low energy surfaces. For both instruments: When using Diiodomethane as a probe liquid the biggest variations among the binders were observed. When using water as a probe liquid the least variations among the binders were observed. The advancing contact angles for water determined for these six bitumen binders using the Wilhelmy plate method do not exceed the 90 degree by much, suggesting that bitumen is not extremely hydrophobic. The Sessile Drop method offers a faster and more convenient way to measure the surface energy components of bitumen binders than the Wilhelmy Plate method.

La maîtrise de la fabrication de films de suspension colloïdale par évaporation constitueencore à ce jour, un véritable verrou scientifique pour l’élaboration des matériaux. Le séchage desuspensions colloïdales entraine souvent des défauts de surface et de volume dans le film. Lorsque lesparticules sont molles, les films sont continus mais présentent des défauts de plissement de surface.Lorsque les particules sont dures (latex vitreux, silice..), le film se fissure et se délamine. Ces défautssont souvent liés aux contraintes résiduelles dans le gel à la fin du séchage qui sont dues à la pressioncapillaire causée par la déformation des ménisques d’eau à la surface des films. Par contre on neconnait pas encore l’échelle de taille où agit la contrainte ni la relation entre la contrainte et la périodedes craquelures.Dans ce travail de thèse, nous étudions la morphologie des craquelures dans des films dedivers mélanges de suspensions colloïdales, élaborés par séchage. Ces mélanges sont composés departicules dures (polystyrène et PBMA réticulés) et molles (PBA et PBMA). La structurenanométrique de ces mélanges est caractérisée par diffusion de neutron et par turbidité. Nousdisposons de mélanges avec diverses structures et divers états de dispersion. Certains mélangescontiennent des particules dispersées à l’échelle nanométrique (l’ordre de grandeur est celle de la tailledes particules - 50 nm) alors que d’autres contiennent des particules agrégées. L’étude de lamorphologie des craquelures est réalisée sur des gouttes sessiles avec séchage à la surface libre. Descraquelures radiales périodiques sont observées lors du séchage. Nous observons que la période descraquelures augmente avec l’augmentation de la fraction en particules molles et de la température maistoute en conservent la périodicité. Nous avons mis en évidence que le rapport : période des craqueluressur l’épaisseur des films λ/h est le seul paramètre qui décrit parfaitement la morphologie descraquelures pour un séchage au niveau d’une surface libre. Nous avons aussi démontré que ce rapportλ/h ne peut pas descendre au-dessous de 2 même dans le cas de particules vitreuses. Le séchage induitde fortes contraintes résiduelles dans le gel qui permettent à certaines fibres situées entre deuxcraquelures de délaminer radialement. Ce phénomène de délamination s’estompe avec la dissipationdes contraintes. Nous avons démontré que le modèle mécanique de Russel ne permet pas de décrire lapériode de craquelures loin de la contrainte critique. Nous proposons ainsi dans le cadre de notretravail, un autre modèle plus à même à caractériser la périodicité de ces craquelures. Nous avonsremarqué que les propriétés du substrat n'ont aucune incidence sur la morphologie des craquelures. Letaux d'évaporation modifie la morphologie des craquelures, où dans le cas d’un séchage rapide, onobtient des fibres décollées longues unidirectionnelles tandis que pour le cas d’un séchage lent, onassiste à la formation de craquelures non décollées avec apparition de craquelures secondairestransverses
Controlling the production of colloidal suspension films by evaporation is still, nowadays, atruly scientific obstacle for materials development. The drying of colloidal suspensions leads often tosurface and volume defects in the film. When the particles are soft, films are continuous but haveseveral folding surface defects. However, when the particles are hard (glassy latex, silica,...), the filmtends to crack and to be delaminated. These defects are often associated with residual stresses in thegel at the end of drying, due to the capillary pressure caused by the water menisci deformation at thefilm surface. Nevertheless, neither the size scale where constraint acts nor the relation between stressand cracking time were known.In this thesis we present the study of cracks morphology observed in films of differentcolloidal suspension mixtures obtained by a drying process. These mixtures are composed of hard(polystyrene crosslinked PBMA) and soft (PBA and PBMA) particles. The nanometric structure ofthese mixtures is obtained through neutron scattering and turbidity studies. We have mixtures withdifferent structures and different states of dispersion. While some mixtures contain dispersed particlesat a nanoscale, with an order of magnitude same as the particles size - 50 nm, some others containaggregated particles. The study of cracks morphology is performed on sessile drops by drying at thefree surface. Periodic radial cracks are observed during drying. We also observe that cracks periodincrease with the increment of soft particles fraction and temperature, but keeping constant itsperiodicity. We have demonstrated that the ratio: crack period between film thickness, i.e. λ/h, is theonly parameter that describes perfectly cracks morphology for a drying process at a free surface. Wealso demonstrated that this relation (λ/h) couldn’t decrease below 2 even in the case of glassy particles.Drying process induces high residual stresses in the gel, allowing to some fibers located between twocracks to delaminate radially. This delamination phenomenon fades with dissipation constraints. Wehave also established that the Russel’s mechanical model does not describe the period of cracks nearthe critical stress. Therefore, in this work we propose another model able to characterize theperiodicity of the cracks. We noticed that the properties of the substrate did not affect cracksmorphology. The evaporation rate changes the morphology of cracks, which in the case of a quickdrying it is possible to obtain unidirectional long loose fibers. However, for a slow drying, we arewitnessing the formation of not protruding cracks with the apparition of secondary transverse cracks

Povrchy inorganických materiálov, zvlášť kovov alebo kovových oxidov, ktoré sú často charakteristické vysokou povrchovou energiou, sú zvyčajne kontaminované adsorbovanými organickými molekulami. Tieto molekuly majú na povrchy zväčša nepriaznivý vplyv, do značnej miery napríklad ovplyvňujú funkcionalitu a výkonnosť polovodičov a znemožňujú, prípadne sťažujú prevedenie povrchových úprav na povrchoch kovov aj keramík. Taktiež majú nepriaznivý vplyv na priľnavosť. Adsorbované častice spôsobujú znižovanie hydrofilicity povrchu. Hydrofilicita, adhezivita a zmáčavosť povrchu sa veľmi dobre posudzujú prostredníctvom merania kontaktného uhlu. V tejto práci je značná pozornosť venovaná práve meraniu statického kontaktného uhlu. [10] Samotné meranie kontaktného uhlu je možné vykonať rôznymi spôsobmi, v tejto práci bol však použitý najvhodnejší prístup, a to metódou „sessile-drop“, teda pokladanej alebo depozitovanej kvapky na meraný povrch. K meraniu bol využitý klasický „sessile-drop goniometer“, teda aparatúra, ktorá pozostávala z nastaviteľného stojanu na vzorky, nad ktorým bol umiestnený zdroj svetla, a objektívu fotoaparátu, ktorý bol prepojený s kamerou zabudovaného smartfónu. Meranie prebiehalo tak, že kvapka s objemom 3L destilovanej superčistej vody bola depozitovaná na povrch substrátu pomocou mikroinjekčnej striekačky. Cieľom tejto práce bolo nielen stanoviť kontaktné uhly a porovnať ich hodnoty medzi rôznymi typmi materiálov navzájom a po upravách tepelného a/lebo chemického charakteru. Vyhodnotené údaje zachycovali zmeny, ku ktorým došlo na povrchoch daných keramických materiálov pri adsorpcii organických molekúl. Proces tepelnej úpravy (kalcinácia na teplote 800°C, následne pokles na teplotu 600°C, po celkovú dobu 16 hodín) bol aplikovaný na všetkých typoch vzoriek, kde niektoré sa medzi sebou líšili teplotou slinovania. Ihneď po kalcinácii boli vzorky podrobené meraniu kontaktných uhlov, z ktorého jasne vyplynulo, že hydrofilicita a zmáčavosť povrchu sa zvýšila. Tento jav bol pozorovaný na všetkých vzorkách, a na všetkých vzorkách sa hodnoty kontaktného uhlu líšili veľmi významne od hodnoty, ktorá bola získaná v tzv. primárnom meraní. Všetky detailné hodnoty a vyhodnotené výsledky sú posudzované v časti diskusia. Ďalšou úpravou povrchu, ktorá bola vykonaná na vybraných vzorkách, bolo čistenie povrchu etanolom. Proces bol opäť realizovaný na všetkých vzorkách. Potom, ako boli zrealizované všetky merania na kalcinovaných vzorkách, boli všetky tieto vzorky ponorené do etanolu na približne 2 hodiny. Po vybratí vzoriek a ich osušení na vzduchu boli uskutočnené ďalšie merania kontaktných uhlov. Výsledky priniesli opäť rozdielne hodnoty v porovnaní s predchádzajúcimi meraniami a sú rozvinuté v časti diskusia.

L’objectif de ce travail, qui s'inscrit dans le cadre d'une équipe de modélisation mathématique, consiste à caractériser les paramètres susceptibles de définir les propriétés de mouillabilité d'un liquide (environné d'un autre fluide) sur la surface d'un solide. Cette étude, essentiellement expérimentale, s'est concentrée sur le cas d'une goutte sessile posée. Elle s'est attachée à déterminer une relation entre l'aire de base d'une telle goutte et de son volume, lorsque l'on fait évoluer ce dernier dans une situation quasi-statique, engendrant ainsi un hystérésis. Pour cela, nous décrivons dans un premier temps la mise au point d'un banc de mesure sophistiqué. Après avoir testé différentes conjectures et corrélations, nous mettons à jour une loi mixte très prometteuse, et en étudions l'intérêt théorique, permettant l'établissement d'une liaison phénoménologique entre trois paramètres. Enfin, nous abordons une interprétation énergétique de la loi obtenue.

Cette thèse présente une étude expérimentale sur l'évaporation de gouttes reposant sur un substrat solide. Dans une première partie, nous nous sommes intéressés à la description de l'évaporation d'une goutte liquide en regardant notamment l'influence du substrat. Le problème est approché sous un angle nouveau : en contrôlant avec précision les différentes propriétés du substrat que sont sa rugosité, son énergie de surface et ses propriétés thermiques. Cette méthode a permis de découpler les différentes influences du substrat et d'étudier l'évaporation pour différentes dynamiques de ligne triple et une large gamme d'angles de contact, de conductivités thermiques et de températures de substrat. Les résultats expérimentaux sont comparés au modèle classique d'évaporation. Ce modèle considère l'évaporation comme un processus contrôlé par la diffusion de la vapeur dans l'atmosphère. L'étude révèle les domaines de validité de ce modèle et met en évidence les différents mécanismes additionnels pouvant se développer ainsi que leur contribution. L'utilisation d'une caméra infrarouge dévoile le développement d'un motif hydrodynamique complexe non-axisymétrique. L'origine de cette instabilité, ces dynamiques spatiales et temporelles sont également explorées. Dans une seconde partie, l'étude a été étendue à l'évaporation d'une goutte de suspension biologique : le sang. Le séchage de ce fluide conduit à la formation d'un motif complexe dépendant de la mouillabilité du substrat. Alors qu'une situation mouillante met en évidence un dépôt de type annulaire accompagné de fractures radiales, une situation non-mouillante révèle une forme complexe composée de fractures et de plis
This thesis presents an experimental study on the evaporation of droplets on a solid substrate. In the first part we describe the evaporation of a liquid droplet, taking a particular interest in the influence of the substrate. The problem is approached from a new angle by ensuring that the various properties of the substrate, such as its roughness, surface energy and thermal properties, are controlled precisely. Thanks to this method it is possible to decouple the different influences of the substrate and to study evaporation in relation to various dynamics of triple lines and a wide range of contact angles, thermal conductivities and temperatures of the substrate. Experimental results are compared with the classic evaporation model, which considers evaporation as a process determined by the diffusion of vapor into the atmosphere. The study reveals the range of validity of this model and highlights the different additional mechanisms which may develop as well as their contribution. The use of an infrared camera reveals the development of a complex hydrodynamic non-axisymmetric pattern. The origin of this instability and its spatial and temporal dynamics are also explored. In the second part, the study is extended to the evaporation of a dropl of a biological suspension: human blood. As this fluid dries a complex pattern is formed which is dependent on the wettability of the substrate. Whereas a wetting situation leads to a ring-like deposit with radial cracks, a non-wetting situation reveals a complex shape composed of cracks and folds. The study focuses on the understanding of the physical mechanisms leading to these patterns and of the role of biology

Breathable water-repellent garments are common products on the outdoor market. There are many recommendations on how to wash and waterproof your garment in order to make sure that its water-repellence is cared for, but the advice given by different sources is inconsistent. Are expensive products really necessarily or are regular laundry products just as good? What waterproofing agents should one use in order to insure that the water-repellent layer is restored? Four different water-repellent wash-in products were tested on polyester and polyamide fabrics. Seven laundry products and two water-repellent wash-in products were tested on jackets with dendrimer based finishes and untreated polyamide fabrics. The results were evaluated by spray testing according to ISO EN 24920 and sessile drop tests. Not all wash-in products offer good water-repellence on polyamide and polyester fabrics. Two laundry detergents decreased the water-repellence of the jackets. The laundry detergents did not affect the function of wash-in waterproofing agents on the jackets. The water-repellence of one wash-in product was affected by the use of two different detergents on untreated fabric
Program: Textilingenjörsutbildningen

The surface response of a polymer substrate to external stimuli such as initial wetting is controlled by the outermost molecular layer. Thus, changes on the nanoscale may be engaged to control macroscale wetting behavior. Our work has predominantly focused on surface modification of conventional polyurethane coatings (HMDI-BD-PTMO). Studies on network constrained phase separation and facile polydimethylsiloxane surface functionalization led to the discovery of a simpler one-step and more general approach to functional polymer surfaces that we have designated as “Bottle-Brush Nanoglass” (BB-NG) after the two principle components: (a) a polyoxetane soft block “spine” with side chain “A” bristles and triethoxysilyl chain ends and (b) an alkoxysilane that together with BB chain ends comprise precursors to a “nanoglass”, NG phase. This paper focuses on the extent of modification for a conventional aliphatic polyurethane using a range of fluoropolyoxetane (poly(trifluoroethoxymethyl-methyl oxetane) diol) or 3F diol based modifier concentrations. Upon generating a blend of the polyurethane with the modifier, the BB-NG which is a minor constituent of the blend, phase separates to provide the topmost layer of the coating. Initial results demonstrate that the modified polymer coatings exhibit an expected increase in contact angles with water. Wetting behavior was characterized using the sessile drop technique as well as Dynamic Contact Analysis (DCA, Wilhelmy Plate). Surface composition as well as near surface topology and morphology are characterized by X-ray Photoelectron Spectroscopy (XPS) and Tapping Mode Atomic Force Microscopy (TM-AFM) respectively. Contrast in phase images reflect the surface modulus and viscoelasticity, from which physical form or compositional differences may be deduced. These characteristics have also been explored in our study by hardness tests via nanoindentation.

La interacció entre metalls fosos i les superfícies de materials ceràmics o metàl·lics és protagonista en diversos processos de fabricació, com ara la injecció d'aliatges lleugers, la foneria de ferro o la síntesi de materials compostos metall-ceràmics (MMC, Metall Matrix Composites). Aquesta interacció es tradueix en un fenomen de mullat en major o menor mesura de la superfície, fet que es pot modular mitjançant l'aplicació de tractaments superficials. El procés d'injecció d'aliatges d'alumini és probablement un dels processos amb metalls fosos amb més impacte industrial. En el present treball s'han estudiat experimentalment el procés de mullat per Al9Si3Cu i alumini pur fosos sobre mostres d'acer recobertes utilitzant el mètode de la gota jacent en buit en un equip d'angle de contacte dissenyat i construït expressament per a aquest projecte. D'una banda s'han assajat recobriments de capa prima dipositats per la tècnica MS-PVD (Magnetron Sputtering Physical Vapor Deposition) o HiPIMS-PVD (High Power Impulse Magnetron Sputtering) de TaN, TiB2, TiN, (Ti,Al)N, MoN i DLC (CrN) . D'altra banda, s'han utilitzat recobriments gruixuts dipositats per HVOF (High Velocity Oxyfuel) de Cr3C2-NiCr i WC-CoCr. L'evolució de l'angle i el radi de contacte s'han estudiat mitjançant el registre de seqüències d'imatges i s'han determinat les corbes de mullabilitat mitjançant el posterior tractament i anàlisi d'imatges. El mecanisme de mullat s'ha determinat a partir de les corbes de mullabilitat i de la caracterització metal·logràfica de la superfície i de les seccions transversals que mostren l'evolució de la interfase líquid-sòlid i la formació de compostos intermetàl·lics. Es discuteixen l'efecte de l'aliatge, de la composició i morfologia del recobriment en la mullabilitat de el sistema i es comparen els resultats obtinguts amb la mullabilitat en sistemes no recoberts. Els resultats mostren que els recobriments retarden la reacció entre el substrat metàl·lic i l'alumini fos.
La interacción entre metales fundidos y las superficies de materiales cerámicos o metálicos es protagonista en diversos procesos de fabricación, tales como la inyección de aleaciones ligeras, la fundición de hierro o la síntesis de materiales compuestos metal-cerámicos (MMC, Metal Matrix Composites). Esta interacción se traduce en un fenómeno de mojado en mayor o menor medida de la superficie, hecho que puede modularse mediante la aplicación de tratamientos superficiales. El proceso de inyección de aleaciones de aluminio es probablemente uno de los procesos con metales fundidos con más impacto industrial. En el presente trabajo se han estudiado experimentalmente el proceso de mojado por Al9Si3Cu y aluminio puro fundidos de muestras de acero recubiertas utilizando el método de la gota yaciente en vacío en un equipo de ángulo de contacto diseñado y construido ex profeso para este proyecto. Por un lado se han ensayado recubrimientos de capa delgada depositados por la técnica MS-PVD (Magnetron Sputtering Physical Vapor Deposition) o HIPIMS-PVD (High Power Impulse Magnetron Sputtering) de TaN, TiB2, TiN, TiAlN, MoN y DLC(CrN). Por otro lado, se han utilizado recubrimientos gruesos depositados por HVOF (High Velocity Oxyfuel) de Cr3C2-NiCr y WC-CoCr. La evolución del ángulo y el radio de contacto se han estudiado mediante el registro de secuencias de imágenes y se han determinado las curvas de mojabilidad mediante el posterior tratamiento y análisis de imágenes. El mecanismo de mojado se ha determinado a partir de las curvas de mojabilidad y de la caracterización metalográfica de la superficie y de las secciones transversales que muestran la evolución de la interfase líquido-sólido y la formación de compuestos intermetálicos. Se discuten el efecto de la aleación, de la composición y morfología del recubrimiento y en la mojabilidad del sistema y se comparan los resultados obtenidos con la mojabilidad en sistemas no recubiertos. Los resultados muestran que los recubrimientos retardan la reacción entre el sustrato metálico y el aluminio fundido.
The interaction between molten metals and the surfaces of ceramic or metallic materials is the key in various manufacturing processes, such as the injection of light alloys, iron foundry or the synthesis of metal-ceramic composite materials (MMC, Metal Matrix Composites). This interaction translates into a phenomenon of wettability to a greater or lesser extent of the surface, which can be modulated by the application of surface treatments. The process of injection of aluminum alloys is probably one of the processes with molten metals with more industrial impact. In the present work, the wetting process for Al9Si3Cu and pure aluminum were analyzed experimentally with coated steel samples using the sessile drop method in vacuum in a contact angle device designed and constructed specifically for this project. On one hand, thin coating deposits deposited by the MS-PVD (Magnetron Sputtering Physical Vapor Deposition) or HiPIMS-PVD (High Power Impulse Magnetron Sputtering) of TaN, TiB2, TiN, (Ti,Al)N , MoN and DLC (CrN). On the other hand, thick coatings deposited by HVOF (High Velocity Oxyfuel) of Cr3C2-NiCr and WC-CoCr have been used. The evolution of the angle and the contact radius have been studied by recording sequences of images and the wettability curves have been determined through the subsequent treatment and image analysis. The wetting mechanism has been determined from the wettability curves and the metallographic characterization of the surface and the cross sections that show the evolution of the liquid-solid interface and the formation of intermetallic compounds. The effect of the alloy, the composition and morphology of the coating in the wetting behavior are discussed, and the results are compared to those obtained with uncoated system. The results show that coatings delay the reaction between the metal substrate and the molten aluminum.

The objective of this research work was to develop a methodology for experimentally estimating the interfacial properties at slag-metal interfaces. From previous experiments carried out in the division, it was decided to use surface active elements like sulfur or oxygen to trace any motion at the interface. For this purpose the following experimental investigations were carried out. Firstly the density of slag was estimated using the Archimedes Principle and the Sessile Drop technique. The density of the slag would give the molten slag height required for the surface active element to travel before reaching the slag-metal interface. Diffusivity measurements were uniquely designed in order to estimate the sulfur diffusion through slag media. It was for the first time that the chemical diffusivity was estimated from the concentration in the metal phase. Experiments carried out validated the models developed earlier. The density and diffusivity value of sulfur in the slag was used to accurately capture the time for sulfur to reach the slag-metal interface. The oscillations were identified by calculating the contact angle variations and the interfacial velocity was estimated from the change in the surface area of the liquid iron drop. The interfacial tension was estimated from the contact angles and the interfacial dilatational modulus was calculated. Based on cold model experiments using water as well as mercury, an equation of the dependence of the interfacial shear viscosity on the interfacial velocity and interfacial tension was established. This paved way for the estimation of the interfacial shear viscosity at the slag-metal interface. The present study is expected to have a strong impact on refining reactions in pyometallurgical industries where slag/metal interfaces play an important role. From a fundamental view point, this provides a deeper insight into interfacial phenomena and presents an experimental technique to quantify the same.
QC 20101130

Дисертація присвячена дослідженню і розробці методик вимірювання поверхневого натягу рідин та їхніх розчинів на межі контакту рідина-оточуюче повітря. Проаналізовано відомі методики і прилади для вимірювання поверхневого натягу рідин та їхніх розчинів методом лежачої краплі. Визначено їхні недоліки, проведено оцінку умов проведення вимірювання поверхневого натягу методом лежачої краплі.
Диссертация посвящена разработке методик измерения поверхностного натяжения жидкостей и растворов на границе раздела жидкость - окружающий газ воздух, разработке математического описания формирования лежащей капли жидкости в процессе измерения поверхностного натяжения, исследованиюю телевизионной системы измерения размеров лежащей капли, разработке прибора, реализующего предложенные методики -измерение поверхностного натяжения и разработке требований к нему, а также к методике использования результатов измерения поверхностного натяжения растворов поверхностно-активных веществ для технологических процессов интенсификации добычи нефти.
Dissertation is dedicated to research and development of surface tension measurement procedures at the boundary of contact of fluid and gas and the device, that realizes corresponding developed procedures. The known procedures of surface tension of fluids and solutions measurement by method of sessile drop are analyzed, their merits and demerits are determined. Surface tension measurement procedures of application are suggested. The process of sessile drop’s forming is analyzed and its mathematical description is given. The method of sessile drop parameters calculation is developed. These results are used for the development of surface tension measurement procedures. One of the developed procedures is based on calculation of two radiuses of curvature of a capillary surface for a point that belongs to the profile of a drop. Another assumes the measuring of the equatorial radius of a sessile drop and its square, limited by this radius and its top. The device for surface tension of fluids and solutions measurement has been developed, metrological analyses of famous and developed surface tension measurement procedures by method of sessile drop are conducted.

Nous etudions les phenomenes de mouillage, d'infiltration capillaire et de penetration intergranulaire de depots de tungstene projetes plasma par l'alliage eutectique u-fe sous vide secondaire. Les principaux parametres explores sont la microstructure du tungstene, la chimie de surface du tungstene et la duree des essais. Des essais de goutte posee realises dans les systemes cu/w et cu-ag/w nous ont permis de qualifier, in situ, la chimie de surface des substrats. Nous montrons que l'infiltration du w projete plasma par le cuivre liquide depend de facon critique de la chimie de surface des parois capillaires (oxyde w#3o herite de l'elaboration) l'alliage u-fe mouille bien le tungstene (=30) et peut de ce fait infiltrer differents types de defauts : les defauts de planeite preexistant sur la surface du tungstene, la porosite ouverte presente dans le tungstene projete plasma et les joints de grains. Des traitements thermiques prealables de grossissement des grains permettent de limiter la penetration intergranulaire du liquide. Ces traitements se sont cependant reveles insuffisants pour proteger le w plasma de la corrosion par l'alliage u-fe qui se traduit par une destruction du squelette solide. Des traitements d'oxydation conduisant a un recouvrement des parois capillaires par des couches d'oxydes wo#n ne nous ont pas permis de proteger le w plasma de la corrosion par l'alliage u-fe car l'oxyde uo#2, forme par reduction de l'oxyde de tungstene, s'est avere non adherent et par consequent non protecteur.

The present work was initiated to investigate the surface- and interfacial phenomena for iron and slag/iron systems. The aim was to understand the mechanism of the effect of surface active elements on surface and interfacial properties. In the present work, the adsorption of oxygen and sulfur on iron surface as well as adatom surface movements were studied based on the ab initio method. BCC iron melting phenomena and sulfur diffusion in molten iron were investigated by Monte Carlo simulations. The impact of oxygen potential on interfacial mass transfer was carried out by X-ray sessile drop method. Firstly, the structural, electronic and magnetic properties as well as thermodynamic stability were studied by Density functional theory (DFT). The hollow site was found to be the most stable adsorption site both for oxygen and sulfur adsorbed on iron (100) surface, which is in agreement with the experiment. The relaxation geometries and difference charge density of the different adsorption systems were calculated to analyze the interaction and bonding properties between Fe and O/S. It can be found that the charge redistribution was related to the geometry relaxation. In addition, the sulfur coverage is considered from a quarter of one monolayer (1ML) to a full monolayer. It was found that the work function and its change Δφ increased with S coverage, in very good agreement with experiment. Due to a recent discussion regarding the influence of charge transfer on Δφ, it is shown in the present work that the increase in Δφ can be explained by the increasing surface dipole moment as a function of S coverage. S strongly interacts with the surface Fe layer and decreases the surface magnetic moment as the S coverage increases. Secondly, a two dimensional (2D) gas model based on density functional calculations combined with thermodynamics and statistical physics, was proposed to simulate the movement of the surface active elements, viz. oxygen and sulfur atoms on the Fe(100) surface. The average velocity of oxygen and sulfur atoms was found to be related to the vibration frequencies and energy barrier in the final expression developed. The calculated results were based on the density function and thermodynamics & statistical physics theories. In addition, this 2D gas model can be used to simulate and give an atomic view of the complex interfacial phenomena in the steelmaking refining process. A distance dependent atomistic Monte Carlo model was developed for studying the iron melting phenomenon as well as effect of sulfur on molten iron surface. The effect of boundary conditions on the melting process of an ensemble of bcc iron atoms has been investigated using a Lennard-Jones distance dependent pair potential. The stability of melting process was energetically and spatially analyzed under fixed wall and free surface conditions and the effects of short and long-range interactions were discussed. The role of boundary conditions was significantly reduced when long-range interactions were used in the simulation. This model was further developed for investigating the effect of sulfur on molten iron surface. A combination of fixed wall and free surface boundary condition was found to well-represent the molten bath configuration while considering the second nearest neighbor interactions. Calculations concerning the diffusion of sulfur on molten surface were carried out as a function of temperature and sulfur concentration. Our results show that sulfur atoms tended to diffuse away from the surface into the liquid bulk and the diffusion rate increased by increasing temperature. Finally, impact of oxygen potential on sulfur mass transfer at slag/metal interface, was carried out by X-ray sessile drop method. The movement of sulfur at the slag/metal interface was monitored in dynamic mode at temperature 1873 K under non-equilibrium conditions. The experiments were carried out with pure iron and CaO-SiO2-Al2O3-FeO slag (alumina saturated at the experimental temperature) contained in alumina crucibles with well-controlled partial pressures of oxygen and sulfur. As the partial pressure of oxygen increased, it was found that interfacial velocity as well as the oscillation amplitude increased. The thermo-physical and thermo-chemical properties of slag were also found to influence interfacial velocity.
QC 20101123

La cinetique de mouillage et sa relation avec la reactivite interfaciale ont ete etudiees pour le systeme aluminium liquide/carbone en fonction des parametres suivants: temperature (entre 1000 et 1250 k), ordre microstructural des substrats de carbone et concentration en elements carburogenes (silicium, titane) dans l'aluminium. Le mouillage a ete etudie par la technique de la goutte posee. Le controle de l'etat de surface des substrats et la caracterisation des produits des reactions interfaciales ont ete realises par les techniques suivantes: microscopie electronique a balayage, microsonde electronique, diffraction des rayons x, profilometrie haute resolution, spectroscopie d'electrons auger et de photoelectrons x. Les conditions experimentales utilisees pour l'etude de la mouillabilite (preparation des echantillons, type du four et nature de l'atmosphere de travail) ont permis d'acceder a l'angle de contact et a l'energie d'adhesion intrinseques du systeme aluminium/carbone. Pour des temps de contact tres courts (interface non-reactive), l'aluminium ne mouille pas le carbone vitreux (l'interface est energetiquement faible). Puis, le mouillage s'ameliore consecutivement a la formation a l'interface d'une couche de carbure d'aluminium. La diminution de la temperature, l'augmentation de l'ordre microstructural du carbone et la presence de silicium dans l'aluminium modifient peu les angles de contact mais conduisent a un net ralentissement des cinetiques d'etalement et des vitesses des reactions interfaciales. De facon plus generale, l'analyse des resultats obtenus pour le systeme aluminium/carbone mais aussi pour un systeme modele (cuivre-silicium et cuivre-titane/carbone), nous a permis d'elucider les questions de la force motrice du mouillage et de la cinetique d'etalement dans les systemes reactifs

L'imbibition est d'une importance fondamentale dans de nombreuses applications technologiques et intervient par ailleurs dans de nombreux phénomènes naturels (industrie textile, industrie pharmaceutique, érosion des sols ....). Malgré l'importance de ce phénomène, la description et la modélisation des mécanismes d'imbibition sont encore sujettes à discussion dans la littérature, en particulier, la prédiction des cinétiques d'imbibition à partir de la connaissance de la topographie du milieu poreux. L'objectif de ce travail de thèse a été de relier les cinétiques d'imbibition à la structure du milieu poreux imbibé. Pour cela, nous avons étudié l'imbibition capillaire (ou spontanée) en suivant une démarche expérimentale dans laquelle nous avons utilisé des substrats poreux modèles dont nous contrôlons le volume et la structure de pores. La configuration d'imbibition choisie dans ce travail est celle d'une goutte sessile (ou posée).Ces travaux ont permis de mettre en œuvre une technique de construction de pastilles macroscopiques, autosupportées et cohésives, par assemblage de microbilles de polymère. Ces systèmes modèles ont été utilisés pour étudier les cinétiques d'imbibition capillaire de liquides dans des supports tridimensionnels à structure de pores complexe en fonction de la taille des microbilles constituant la pastille poreuse, de la reconstruction thermique, de la perméabilité pour une structure poreuse bicouches et de la force capillaire. Ces études ont permis entre autres de mettre en évidence des régimes cinétiques et des transitions d'imbibition inattendues dans ces systèmes (régimes visqueux et inertiel).

Friction stir welding (FSW) of steel is often performed with an insert made of polycrystalline cubic boron nitride (PCBN). Specifically, MS80 is a grade of PCBN made by Smith MegaDiamond that has been optimized for the FSW process. The PCBN insert is attached to a tungsten carbide (WC) shank by a compression fitting. However, FSW tools manufactured by this method inevitably fail by fracture in the PCBN. Permanently bonding PCBN to WC would likely solve the fracturing problem and increase the life of PCBN FSW tools to be economically viable. Partial transient liquid phase (PTLP) bonding, a process used to join ceramics with thin metallic interlayers, was proposed as a method to permanently bond PCBN to WC. PTLP bonding is often performed using three layers of pure elements. On heating, the two thin outer interlayers melt and bond to the ceramics. Concurrently, these liquid layers diffuse into the thicker refractory core until solidification has occurred isothermally. A procedure was developed to reduce the number of possible three-layer PTLP bonding setups to a small set of ideal setups using logical filters. Steps in this filtering method include a database of all existing binary systems, sessile drop testing of 20 elements, and a routine that calculates maximum interlayer thicknesses. Results of sessile drop testing showed that the PCBN grade required for this research could only be bonded with an alloy of Ti, Cu, Mg, and Sb. Two PTLP bond setups were tested using this special coating on the PCBN, but a successful bond could not be achieved. However, a PTLP bond of WC to WC was successful and proved the usefulness of the filtering procedure for determining PTLP bond setups. This filtering procedure is then set forth in generalized terms that can be used to PTLP bond any material. Also, recommendations for future research to bond this grade of PCBN, or some other grade, to WC are presented.

The present thesis deals with two-phase electrohydrodynamic simulations of bubble and droplet dynamics under externally applied electric fields. We used the Coupled Level-Set and Volume-of-fluid method (CLSVOF) and two different electrohydrody-namic formulations to study the process of bubble and drop formation from orifices and needles, the interactions of two conducting drops immersed in a dielectric medium, and the oscillations of sessile drops under two different ways of applying external elec-tric field. For the process of bubble formation in dielectric liquids due to the injection of air from submerged orifices and needles, we show that a non-uniform electric field pro-duces smaller bubbles while a uniform electric field changes only the bubble shape. We further explain the reason behind the bubble volume reduction under a non-uniform electric field. We show that the distribution of the electric stresses on the bubble inter-face is such that very high electric stresses act on the bubble base due to a non-uniform electric field. This causes a premature neck formation and bubble detachment lead-ing to the formation of smaller bubbles. We also observe that the non-uniform elec-tric stresses pull the bubble interface contact line inside the needle. With oscillatory electric fields, we show that a further reduction in bubble sizes is possible, but only at certain electric field oscillation frequencies. At other frequencies, bubbles bigger than those under a constant electric field of strength equal to the amplitude of the AC electric field, are produced. We further study the bubble oscillation modes under an oscillatory electric field. We implemented a Volume-of-fluid method based charge advection scheme which is charge conservative and non-diffusive. With the help of this scheme, we were able to simulate the electrohydrodynamic interactions of conducting-dielectric fluid pairs. For two conducting drops inside a dielectric fluid, we observe that they fail to coalesce when the strength of the applied electric field is beyond a critical value. We observe that the non-coalescence between the two drops occur due to the charge transfer upon drop-drop contact. The electric forces which initially bring the two drops closer, switch direction upon charge transfer and pull the drops away from each other. The factors governing the non-coalescence are the electric conductivity of the drop’s liquid which governs the time scale of charge transfer relative to the capillary time scale and the magnitude of the electric forces relative to the capillary and the viscous forces. Similar observations are recorded for the interactions of a charged conducting drop with an interface between a dielectric fluid and a conducting fluid which is the same as the drop’s liquid. For the case of a pendant conducting drop attached to a capillary and without any influx of liquid from the capillary, we observed that the drop undergoes oscillations at lower values of electric potential when subjected to a step change in the applied electric potential. At higher values of electric potential, we observed the phenomenon of cone-jet formation which results due to the accumulation of the electric charges and thus the electric forces at the drop tip. For the formation of a pendant conducting drops from a charged capillary due to liquid injection, we observed that the drops are elongated in presence of an electric field. This happens because the free charge which appears at the drop tip is attracted towards the grounded electrode. This also leads to the formation of elongated liquid threads which connect the drop to the capillary during drop detachment. We plotted the variation of total electric charge inside the drops with respect to time and found the charge increases steeply as the drop becomes elongated and moves towards the grounded electrode. For sessile drop oscillations under an alternating electric field, two different modes of operations are studied. In the so called ‘Contact mode’ case, the droplet is placed on a dielectric coated grounded electrode and the charged needle electrode remains in direct contact with the drop as it oscillates. In the ‘Non-contact mode’ case, the drop is placed directly on the grounded electrode and electric potential is applied to a needle electrode which now remains far from the drop. We show that the drop oscillations in the contact mode are caused by concentration of electric forces near the three phase contact line where the electric charge accumulates because of the repulsion from the needle. For the non-contact mode, we observe that the electric charge is attracted by the needle towards the drop apex resulting in a concentration of the electric forces in that region. So the drop oscillates due to the electric forces acting on a region near the drop tip. We also present the variation of the total electric charge inside the drop with respect to time for the two cases studied.

碩士
國立臺灣大學
機械工程學研究所
107
This research is trying to find out the influence of the acceleration and the frequency of a sessile resonating drop. Also, this research is trying to maintain the resonance shape of the drop by using cold fluid to freeze it. The experimental fluid is gallium. We used aLED halo as the lighting method. From the reflection of the halo on the surface of the drop, we could tell the shape of the resonating drop. In this research, we found 16 modes which had been found before, including 7 sectoral modes, 4 zonal modes and 5 tesseral modes. In addition to these 16 modes, we also found several unstable sectoral modes which don’t have the same amplitude in every crest, and 3 jumping modes with different polygon shapes. We found the relation between the frequency and the amplitude. The experiment result shows that the force thresholds of sectoral modes are independent of the volume of the drop. In other words, if the volume of the resonating drop increases, the minimum force to trigger the specific sectoral mode will still be the same. We found that the shape of the solidification drop depends on fluid and the wave amplitude, not the resonance mode. Additionally, the experiment and the calculation results show that it’s impossible to maintain the resonance shape by using solidification.

The word piezo in greek means \to compress". Piezoelectric sensors work on the principle of direct piezoelectric effect, where a mechanical input generates a corresponding electric charge. The advantages of these sensors are wide fre-quency range of operation, high stiffness and small size. The main limitation of a piezoelectric sensor is that it cannot be used in measurements that are truly static. When a piezoelectric sensor is subjected to a static force, a fixed amount of charge is developed which would eventually decay at a rate dependent on the external impedance of the sensor circuitry. Operating sensors at resonance have been one of the methods to overcome the limitation of using piezoelectric sensors for static measurements. However, since both actuation and sensing are done by the same piezoelectric element, this results in a cross-talk of input and output signals. The drawback of using single piezoelectric element for actuation and sensing is overcome in this work by using two identical elements|one for actuation and one for sensing. The operating frequency is about 10 % of the natural frequency of the sensor, thus enabling to operate the sensor in non resonant mode. Since the actuation and sensing mechanisms are separated, static measurement can be carried out. The output signal from the sensing element is monitored by a Lock-in amplifier which works on the principle of phase sensitive detection. The advantage of this sensor design is high sensitivity along with narrow band detection. It can be shown that the voltage output of the sensor Vout / a1 + m(b1 + b2F + b3K) + c1F + d1K, where m and K are the external mass and interaction stiffness, respectively, F is the force acting on it. By maintaining any two of these three quantities constant, the remaining one can be measured without any difficulty. The non resonant mode of operation makes it possible to explore the potential of this sensor in investigating mechanics of solid-liquid (viscous), solid-solid (inelastic) and solid-tissue(viscoelastic) interactions. High sensitivity, wide range of measurement (1 g{1 g) and high resolutio(0.1 g) of the non resonant mass sensor makes it possible to use it in measure-ment of very small masses of the order 1 g. Typically, resonant sensors such as quartz crystal microbalance (QCM) are used for mass measurements at that range. However, since the performance of resonant sensors is controlled by damp-ing, a phenomenon known as `missing mass effect' arises. Operating a sensor in non resonant mode (stiffness controlled mode) is a way to overcome this problem, especially when the mass is viscous and/or viscoelastic in nature. Drosophila fly, egg and larvae are the viscoelastic masses that are measured using this non res-onant sensor. Evaporating sessile drops of water and Cetyl trimethylammonium bromide (CTAB) surfactant solution from nominally flat surfaces are monitored to characterize the sensor for viscous mass measurement. Evaporation rate per unit surface area remains more or less constant, during the initial stages of evap-oration. When the surfactant concentration is varied, evaporation rate per unit surface area is highest for solutions around critical miscelle concentration (CMC). A study is carried out to understand the effect of concentrations on spreading of ink over inkjet printing paper. It is found that the spreading is least around CMC, since spreading is dependent on the rate of evaporation. The non resonant piezoelectric sensor which has high stiffness and quick re-sponse is also capable of measuring very small frictional forces. This sensor is configured to work as an inertial slider. Friction measurement at micro scales is important for designing microsystems such as stick-slip actuators. At such length scales, experiments have to performed at low loads and high excitation frequencies. The support stiffness of such systems should be high and the force of friction generated during slipping, when displacements are smaller than the contact radius, are of the order of few N. The displacement during slipping (S) is dependent on the amplitude of the input voltage to the actuation element. The frictional force measured during slipping by the sensor element indicates that the co-efficient of friction ( ) is independent of the sliding velocity. The developed non resonant sensor in this work under small amplitude exci-tation, can measure force gradient (i.e. stiffness). The total force generated when a needle is inserted into a viscoelastic material is a sum of force due to stiffness of the material, friction and the cutting force at the tip. The force due to stiffness is dominant when the needle is bending the tissue before the puncture occurs. Use of the non resonant sensor in tandem with strain gauge force sensor enables distinguishing the three components of the total force. The slope of the force-displacement (F -d) curve during the initial stages of needle penetration into the viscoelastic material, before puncture, is indicative of the stiffness of the mate-rial. The peak force measured during penetration is higher for needles with larger diameters and lower insertion velocities. The viscoelastic response (relaxation) of the material remains independent of the insertion velocity, for a given thickness of the material and a constant needle diameter. In summary, the sensor designed and developed in this work operates in stiffness controlled mode to eliminate the `missing mass effect' encountered dur-ing resonant mode of operation, has been clearly highlighted. Mass, force and stiffness measurements are possible over a wide range just by varying the ampli-tude of the input signal to the actuator element. The advantages such as high stiffness, small size and high response makes it advantageous to carry out in-situ micro scale studies in scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

碩士
國立臺灣大學
化學工程學研究所
101
There are two topics discussed in this study: water evaporation on soft patterned surfaces and the observation of the Cassie impregnating wetting state. First, we demonstrate the evaporation mechanism of water sessile drop on different softness of fixed patterned PDMS (polydimethylsiloxane) substrate and also compare the results from the viewing angle of 0° with that from the viewing angle of 45°. The evaporation mechanism generally starts from the constant contact radius mode and turns into constant contact angle mode when the receding contact angle is reached. The softer the substrate is, the smaller the receding contact angle is. The wetting transition from the Cassie to the Wenzel state is also observed after the constant contact angle mode and the softer substrate will induce an earlier wetting transition due to the softer texture. By comparing the theoretical calculation of evaporation rate in different modes, we can examine whether the expected evaporation mechanism is suitable or not. Second, the Cassie impregnating wetting state is investigated by placing the ethanol drop on different patterned PDMS surfaces. Due to the lack of the knowledge of the Cassie impregnating state, our main purpose is to find out the relationship between the structure of the surfaces and the impregnating region. It is observed that the rougher the substrate is, the larger the impregnating region is. However, so far we cannot specify this phenomenon and its impregnating region. Our preliminary inference is that the Cassie impregnating wetting state is only the metastable state passing to complete wetting and the metastable state is the result of the equilibrium of the imbibition rate and the evaporation rate of ethanol. Besides, the contact angle in the Cassie impregnating wetting state is also examined to see if the Cassie equation can describe and the study of the ethanol drop evaporation on patterned surface is discussed to further understand the Cassie impregnating wetting state.

碩士
國立中正大學
化學工程所
95
In contact angle measurement from analysis of sessile drop shapes, the quality of drop images and the analysis of drop shapes determine accuracy of the contact angle. High quality drop images should have large contrast in brightness at the edges. We improved the image quality by adjusting the elements of the homemade contact angle goniometer, and found a better technique for contact angle measurement. Then we determined the drop edges consistant with the real image by gradient method and analyzed the drop shape by circle fitting. Contact angle can be obtained from the slope at the solid-liquid-vapor contact point. The adsorption mechanism of aliphatic dithiocarboxylic acid (ADTCA), CH3(CH2)nCS2H (n=13,14) self-assembled monolayers(SAMs) onto the gold surfaces can be studied by advancing contact angle. The trend of advancing contact angle of these SAMs with two different chain length during the formation process are opposite. This can be attributed to the odd-even effect.

In enhanced oil recovery the displacement of oil is most effective at low interfacial tensions, usuall below 10$\sp{-2}$ dyne/cm. This condition can be achieved by surfactant or chemical flooding but requires accurate modeling of reservoir conditions and determination of interfacial tensions, IFTs. The spinning drop technique is very popular but the sessile drop method offers the advantage that it is a static system. Most previous systems required a photograph to be taken and analysis was limited to key coordinates along the profile. A sessile drop system has been designed which allows drops or bubbles to be formed by injection through the base, uses a digital image processor for recording of the profile coordinates and partial analysis, and performs an optimization on the shape of the drops based on an accurate objective function using the entire profile. Measurements have been made for IFTs from 7 dyne/cm. to as low as 0.005 dyne/cm.

碩士
國立臺灣科技大學
化學工程系
104
This experiment shows the influence of triple line retraction velocity on receding contact angle by using sessile drop method. The experiment was performed by dropping the liquid drops on polymer PMMA (polymethyl methacrylate) and PC (poly carbonate) substrates. The suction process was then performed to reduce the droplet volume by pumping out the liquid drop using syringe pump and needle. It was found that the contact angle change when the de-wetting velocity increase. From the experimental results, we can observe there are three stages: constant contact radius (CCR mode), constant contact angle, (CCA mode) and the mixing stage (mixed mode). In CCR stage the wetting diameter is constant but contact angle continue to decline, when the CCA stage the contact angle is nearly constant but wetting diameter decrease. Finally, both contact angle and wetting diameter are continue to decline and retreat constantly, we call this stage is mix stage. From this experiment, we observe that in CCA stage, the greater retraction velocity will resulting smaller contact angle. The comparison between the experimental data and the theoretical models obtained from literatures was performed to verified our conclusion that the receding contact angle is caused by the interaction between liquid molecules and substrates or viscous dissipation.

碩士
國立臺灣科技大學
化學工程系
102
The dynamic and equilibrium surface tensions for the adsorption of anionic surfactant AOT and cationic surfactant DDA in aqueous solutions onto a clean air-water interface was measured by using a video-enhanced pendant bubble tensionmeter. A comparison between the nonionic and ionic models (Langmuir, Frumkin and generalized Frumkin models) and the equilibrium and dynamic surface tensions of AOT and DDA were performed in order to study the adsorption mechanism and to determine the diffusivity of surfactant molecules. The adsoprion kinetics for AOT in aqueous 500 mM NaCl solution was found to be diffusion controlled with a diffusivity of (1.55±0.3)×10-6 cm2/s. A plateau region was observed at dynamic surface tension profile of DDA aqueous solution at γ = 43.7 mN/m at 25oC. The existence of a plateau implied the existence of a liquid expanded and liquid condensed phase transition for the DDA molecules adsorbed at air-water interface. In the second part of this study, polycarbonate (PC) substrates with various surface roughness were used on the investigation of the evaporation process in a circumstance of fixed humidity. Relaxation of contact angle was monitored and the pinning phenomenon was studied. The definition of receding contact angle was also discussed at the end of this work.

碩士
國立交通大學
奈米科技研究所
97
EWOD (Electrowetting-on-dielectric) is a method to change the surface wettability on top of an electrode. This phenomenon is reversible and consumes very low power. MEWOD (Mirror-EWOD) is occurred when we replace solid electrode with liquid electrode, and the size of the liquid electrode is shrunk to a comparable volume of the upper droplet. Electrowetting was found on both sides of the dielectric film and the mirror-EWOD force would bring the overlapped droplets to each other. In this thesis, we analyze the phenomenon of MEWOD and put the device into silicone oil to reduce the problem of vibration and evaporation. Finally, we integrate EWOD and MEWOD to manipulate parallel droplets. When applying a voltage, two stacked droplets can be actuated concurrently. By increasing the number of the dielectric sheet, the concept would be expanded to manipulate more than two droplets without increasing the complicity of the device fabrication and the electric circuit.

博士
國立臺灣大學
材料科學與工程學研究所
102
The purpose of this study is to investigate the high temperature contact angle and surface tension under various components of the refractories for Fe-Si-B alloys and Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels. The high temperature contact angle and surface tension are measured by Sessile Drop Method in this study. According to Bashforth and Adams equation, the accurate measurement of the contour droplet size and density will affect the measurement results of its surface tension. The surface tension of pure silver is measured and compare with literatures, the measured result is based for measurement calibration. This research can be discussed and divided into three parts: (1) The surface tension results under various refractories and surface roughness condition for Fe-Si-B alloys. (2) Thermodynamics data and Butler equation is calculated the surface tension of Fe-Si-B ternary alloys. (3) The surface tension of Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels on single high alumina contents refractory. The experimental results are shown the surface tension and contact angle of Fe-Si-B alloys and Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels decreases as temperature increases. The surface tension of Fe-Si-B alloys is not different with various refractories compositions and roughness. Only contact angle and wetting behavior variable and depends on various refractories compositions and roughness. The contact angle measurement results are shown that the refractories with the silicon-nitrogen-containing components have the highest contact angles, the refractories with single alumina or silica containing components have the lowest contact angles. The refractories with composite alumina - silica contacting have middle contact angles in between silicon-nitrogen-containing refractories and single alumina or silica containing refractories. The experimental results also showed that the contact angle increases as roughness increases. The thermodynamics data and Butler equation calculation surface tension results is close to measurement values when the metal is melted fully near liquid temperature. However, as the temperature increases, the thermodynamic surface tension calculation result is not close to experimental measured value, the reason might be interfacial chemical reaction and blurred solid-liquid-vapor triple interface line caused volume measured error at high temperature. Furthermore, increasing boron and carbon contents will decrease the surface tension of Fe-Si-B alloys. Increasing manganese and nitrogen contents will decrease the surface tension and contact angle of the Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels. The contact angle and surface tension measurement results are shown that the Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels with the lowest manganese and nitrogen containing components have the highest contact angle and surface tension.