The elastic properties of oil/water/surfactant interfaces play an important role in the phase behaviour of microemulsions and for the stability of macroemulsions. The aim of this thesis is to obtain an understanding of the relationship between the structure of the surfactant molecules, the structure of the interface, and macroscopic interfacial properties. To achieve this aim, we performed molecular simulations of oil/water/surfactant systems. We made a quantitative comparison of various model surfactants to determine how structural changes affect interfacial properties and film rupture. The model consists of water, oil, head, and tail beads, and surfactants are constructed by coupling head and tail beads with harmonic springs. We used a hybrid dissipative particle dynamics-Monte Carlo scheme. The former was used to simulate particle trajectories and the Monte Carlo scheme was used to mimic experimental conditions: bulk-interface phase equilibrium, tensionless interfaces in microemulsions, and the surface force apparatus. A detailed comparison of various non-ionic model surfactants showed how structural changes affect interfacial properties: Comparison between linear and branched surfactants showed that the efficiency of adsorption is higher for linear surfactants, although branched surfactants are more efficient at a given surface density. Linear surfactants can be more efficient also at the same surface density if the head group is sufficiently soluble in oil, because low head-oil repulsion makes the branched isomers stagger at the interface. The bending rigidity is higher for linear surfactants. Furthermore, branched surfactants make oil droplets coalesce more easily than linear surfactants do, but linear and branched surfactants have roughly the same effect on water droplet coalescence. Comparison of linear surfactants with varying chain lengths showed that longer surfactants have a lower surface tension and higher bending rigidity. The increase in rigidity with chain length follows a power law, but the exponent is higher for surfactant monolayers at a fixed density than at a fixed tension. Longer tails and/or denser monolayers influence the stability of water droplets in a positive direction, and the stability of oil droplets in a negative direction. Addition of cosurfactant showed that mixed monolayers have a lower bending rigidity than pure monolayers at the same average chain length and tension. Cosurfactants have a negative effect on the stability of water droplets, and a positive effect on the stability of oil droplets. / Paper I reprinted with kind permission of EDP Sciences. Paper III reprinted with kind permission of the American Institute of Physics. Paper IV reprinted with kind permission of the American Physics Society.

Within the general context of solid-state sintering process, this work presents a numerical modeling approach, at the particle scale, of ceramic particle packing consolidation. Typically, the sintering process triggers several mass transport paths that are thermally activated. Among those diffusion paths, the most important ones are: surface diffusion, grain boundary diffusion and volume diffusion. Including this physics into a high-performance computing framework would permit to gain precious insights about the driving mechanisms. The aim of the present work is to develop a model and a numerical strategy able to integrate the different diffusion mechanisms into continuum mechanics framework. In the cases of surface diffusion and volume diffusion, the mass flux is calculated as a function of the surface curvature Laplacian and the hydrostatic pressure gradient, respectively. The physical model describing these two transport mechanisms is first presented within the framework of continuum mechanics. Then the numerical strategy developed for the simulation of the sintering of many particles is detailed. This strategy is based on a discretization of the problem by using a finite element approach coupled with a Level-Set method used to describe the particles free surface. This versatile strategy allows us to perform simulations involving a relatively large number of particles. Furthermore, a mesh adaptation technique allows the particles surface description to be improved, while the number of mesh elements is kept reasonable. Several 3D simulations, performed in a parallel computing framework, show the changes occurring in the structure of 3D granular stacks.

Amphiphiles that possess a dual character, hydrophobic and hydrophilic, are employed in many chemical, pharmaceutical and biological applications. Amphiphile molecules that include a hydrophilic head and a hydrophobic tail can easily adsorb at a liquid/vapour interface, to reach to a minimum free energy and hence a most thermodynamically stable state. Surface tension is a key parameter for understanding such behavior of an amphiphile, or a surfactant. This thesis represents a comprehensive study on adsorption and surface tension of slightly volatile, organic amphiphiles in aqueous solution. Although for a vapor-liquid interface, adsorption from both liquid and vapor phases should be considered, they have been almost always considered exclusive of one another. When a volatile surfactant is dissolved in the liquid phase, it also applies a finite partial pressure in the vapor phase. Recently, dynamic surface tension experiments showed that adsorption from both sides of a vapor/liquid interface must be studied simultaneously. It is noted that surface tension phenomena are often dynamic, in particular when the surface under consideration is perturbed. With the newly discovered importance of adsorption from both sides of a vapor/liquid interface, one may have to ask the question: how dynamic surface tension is influenced and responding to the surface perturbation and environment changes, and whether both sides of the interface play a role in surface tension responses. In this research, axisymmetric drop shape analysis-profile (ADSA-P) is used for surface tension measurement. The experiments are performed in a closed chamber where the effects of surfactant concentrations of both liquid and vapor phases on the surface tension can be studied. The partial vapor pressure of surfactant is controlled with an environment solution containing the same surfactant as the sample solution. The environment solution is to facilitate adsorption from the vapor side of the interface by creating a surfactant vapor phase. The effects of surface perturbation, environment condition (i.e., temperature and pressure) and carbon chain length on the surface tension and adsorption kinetics are studied in detail. The surface tension response of 1-octanol aqueous solution to surface area perturbation is investigated. Upon surface compression, the surface tension decreases followed by a gradual increase back to the value prior to compression. On surface expansion, two categories of surface tension response are observed: First, when the change in surface area is smaller than 5%, the behavior similar to that of conventional surfactants is observed. The surface tension increases followed by a gradual decrease back to the value prior to expansion. Second, when the change in surface area is greater than 5%, and the drop concentration is sufficiently larger than the environment concentration, the surface tension initially slightly increases, but after a time delay, it sharply decreases, followed by a gradual increase back to the value prior to expansion. Previous studies showed that at steady-state condition a network of hydrogen bonding between surfactant and water molecules near the surface is created. The unique surface tension response after large expansion might be related to the momentarily destruction of this hydrogen bonding network and gradually making a new one. The effect of temperature on the surface tension and adsorption kinetics of 1-octanol, 1-hexanol and 1-butanol aqueous solutions is studied. The steady-state surface tension is found to decrease upon an increase in temperature, and a linear relationship is observed between them. The modified Langmuir equation of state and the modified kinetic transfer equation are used to model the experimental data of the steady-state and dynamic (time-dependent) surface tension, respectively. The equilibrium constants and adsorption rate constants are evaluated through a minimization procedure for temperatures ranging from 10°C to 35°C. From the steady-state modelling, the equilibrium constants for adsorption from vapor phase and liquid phase are found to increase with temperature. From the dynamic modelling, the adsorption rate constants for adsorption from vapor phase and liquid phase are found to increase with temperature too. The influence of carbon dioxide pressure on the surface tension and adsorption kinetics of the aforementioned surfactant aqueous solutions is investigated. To consider the effect of adsorption/desorption of the two species (surfactant and carbon dioxide) from both sides of a vapor/liquid interface on the surface tension, the modified Langmuir equation of state and the modified kinetic transfer equation are derived. The steady-state and dynamic surface tension data are modelled using the modified Langmuir equation of state and the modified kinetic transfer equation, respectively. The equilibrium constants and adsorption rate constants of surfactant and carbon dioxide are evaluated through a minimization procedure for CO2 pressures ranging from 0 to 690 KPa. From the steady-state modelling, the equilibrium parameters for surfactant and carbon dioxide adsorption from vapor phase and liquid phase are found unchanged for different pressures of carbon dioxide. From the dynamic modelling, the adsorption rate constants for surfactant and carbon dioxide are found to decrease with carbon dioxide pressure. The role of carbon chain length of amphiphiles in aqueous solution is also studied. It is illustrated that the equilibrium constants for adsorption from both sides of a vapor/liquid interface increase from 1-butanol to 1-octanol. The modelling results show that the ratio of the equilibrium constant for adsorption from vapor phase to the equilibrium constant for adsorption from liquid phase declines from 260 to 26 as the chain length is increased from 1-butanol to 1-octanol. Therefore, the contribution to adsorption from liquid phase augments as the chain length is increased. The adsorption kinetics for this group of short carbon chain surfactants is modelled using a kinetic transfer equation. The modelling results show that the adsorption rate constants from vapor phase and liquid phase (kag and kal) increase from 1-butanol to 1-octanol. Steady-state and dynamic modelling also reveals that the maximum surface concentration increases with carbon chain length. These results may be due to the higher hydrophobicity character of a surfactant molecule at longer carbon chain length.

Generating natural phenomena in a virtual world has a number of practical applications. Thanks to the rich and complicated details in the real world, the goal of realistically and efficiently reproducing natural phenomena is well known as an open problem for graphics researchers. In this dissertation, three different issues in modeling liquid animations have been addressed. First, a virtual surface method is proposed to account for surface tension effects and their interactions with solid surfaces in physically based fluid simulation. This allows us to generate various surface tension behaviors in small scale liquid. The second issue that is addressed is how to make small scale fluid simulation more efficient. The proposed solution is a general shallow wave equation model, extended from the original shallow wave equations. By simplifying 3D incompressible fluid dynamics into 2D, small scale liquid can be stably and efficiently simulated over arbitrarily curved surfaces using implicit numerical schemes. The third contribution is a novel hybrid framework that combines image based reconstruction techniques with physically based fluid simulation. While image based methods cannot correctly generate fluid animations alone frame by frame, physics is used as a refinement tool to enforce physical soundness by propagating shape information back and forth in space and time. In this way, water animations can be realistically and faithfully generated from images without error accumulation or stability issues.

<p>In industrial use of paint systems a swift processing is crucial. Another very important issue is to improve the quality of the final coating. This report investigates the film formation process of powder coatings, specially the spreading of individual powder particles. The obtained results can be used to understand and control the film formation process. In this way the desired levelling can be achieved and thus the desired gloss or other surface characteristics that may be required. This means that the method could be used when evaluating different polymer and additive combinations that could be used to change film formation behaviour or curing time for powder coating systems to suit various substrates. It makes it possible to avoid and minimize different surface defects as orange peel or cratering in the powder coated film.</p><p>We used a reflection optical microscope to better understand the film formation process and especially the spreading of a powder melt on surfaces with various surface energies. The obtained data were: the particle diameter, the area, area ratio and the contact angle of the powder particle as a function of time and temperature. This information can be used to derive the surface tension of any powder melt.</p><p>In this report we evaluate the dependencies of temperature, heat rate and surface energy for powder coatings on different substrates. The method provides information that can be used to optimize the film formation of a specific powder coating/substrate combination. This method can be used to evaluate the powder spreading and levelling on different substrates from a surface tension point of view.</p><p>We found, as expected, that the powder flows out on a hydrophilic surface and is inhibited by a hydrophobic. The increase of the area ratio on a hydrophilic surface was about five times as the initial area coverage and on a hydrophobic surface only two times the initial area coverage. The contact angle between the melted powder particle on the different surface types could be calculated. The melt surface tension could be calculated since three substrates surfaces with various surface energies were used. The melt surface tension was found to be about 18.5 mN/m.</p> / <p>Sammanfattning</p><p>Vid industriell användning av ett färgsystem är det viktigt med en snabb och smidig målningsprocess. En viktig del är att förbättra kvaliteten på den färdiga ytan. Denna rapport undersöker filmbildningsprocessen för pulverfärg, närmare bestämt spridningen av individuella pulverpartiklar. Resultaten från utvärderingen av denna metod kan användas för att bättre förstå och få kontroll över filmbildningsprocessen. Med denna undersökningsmetod kan den önskade utslätningen uppnås och därmed den önskade glansen eller annan yteffekt som kan vara önskvärd.</p><p>Metoden kan användas för att utvärdera olika polymer- och additivkombinationer som kan användas för att ändra filmbildningens uppförande eller bestämma härdningstiden för en pulverfärg att passa ett visst substrat. Metoden gör det möjligt att förhindra och minska olika ytdefekter såsom apelsinskals- eller kratereffekter i pulverfärgens yta.</p><p>Ett optiskt reflectionsmikroskop användes för att bättre kunna förstå filmbildningsprocessen och särskilt spridningen av smält pulver på substrat med olika ytenergier. De mätdata vi fick var partikeldiameter, area, areaförändring och kontaktvinkeln för pulverpartiklar som funktion av tid och temperatur. Ur denna information kunde pulversmältans ytenergier härledas.</p><p>I denna rapport utvärderas pulvrets beroende av temperatur, uppvärmning och ytenergi på olika substrat. Denna metod ger information som kan användas för att optimera filmbildningen av en specifik kombination av pulverfärg och substrat. Denna metod kan också användas för att utvärdera pulverspridning och utjämning av färgfilmen på olika substrat med avseende på ytenergierna.</p><p>Som förväntat flyter pulvret ut på hydrofila ytor och utflytningen ändras på en hydrofob yta. På en hydrofil yta sprider sig partikeln till fem gånger den ursprungliga arean över substratet och motsvarande två gånger för en hydrofob yta. Kontaktvinkeln mellan en smält pulverpartikel på olika sorters substrat från utförda mätningar beräknas utifrån utförda mätningar. Kontaktvinklar mellan pulver och olika substrat kan användas för att beräkna smältans ytspänning. Smältans ytspänning kan beräknas då experiment gjorts på tre sorters ytor med olika kända ytenergier. Smältans ytspänning var 18,5 mN/m.</p><p>Slutsatsen är att det går att observera och utvärdera resultaten av utsmältningsförloppet för pulverfärg med denna metod.</p>

No description available.

Amphiphiles that possess a dual character, hydrophobic and hydrophilic, are employed in many chemical, pharmaceutical and biological applications. Amphiphile molecules that include a hydrophilic head and a hydrophobic tail can easily adsorb at a liquid/vapour interface, to reach to a minimum free energy and hence a most thermodynamically stable state. Surface tension is a key parameter for understanding such behavior of an amphiphile, or a surfactant. This thesis represents a comprehensive study on adsorption and surface tension of slightly volatile, organic amphiphiles in aqueous solution. Although for a vapor-liquid interface, adsorption from both liquid and vapor phases should be considered, they have been almost always considered exclusive of one another. When a volatile surfactant is dissolved in the liquid phase, it also applies a finite partial pressure in the vapor phase. Recently, dynamic surface tension experiments showed that adsorption from both sides of a vapor/liquid interface must be studied simultaneously. It is noted that surface tension phenomena are often dynamic, in particular when the surface under consideration is perturbed. With the newly discovered importance of adsorption from both sides of a vapor/liquid interface, one may have to ask the question: how dynamic surface tension is influenced and responding to the surface perturbation and environment changes, and whether both sides of the interface play a role in surface tension responses. In this research, axisymmetric drop shape analysis-profile (ADSA-P) is used for surface tension measurement. The experiments are performed in a closed chamber where the effects of surfactant concentrations of both liquid and vapor phases on the surface tension can be studied. The partial vapor pressure of surfactant is controlled with an environment solution containing the same surfactant as the sample solution. The environment solution is to facilitate adsorption from the vapor side of the interface by creating a surfactant vapor phase. The effects of surface perturbation, environment condition (i.e., temperature and pressure) and carbon chain length on the surface tension and adsorption kinetics are studied in detail. The surface tension response of 1-octanol aqueous solution to surface area perturbation is investigated. Upon surface compression, the surface tension decreases followed by a gradual increase back to the value prior to compression. On surface expansion, two categories of surface tension response are observed: First, when the change in surface area is smaller than 5%, the behavior similar to that of conventional surfactants is observed. The surface tension increases followed by a gradual decrease back to the value prior to expansion. Second, when the change in surface area is greater than 5%, and the drop concentration is sufficiently larger than the environment concentration, the surface tension initially slightly increases, but after a time delay, it sharply decreases, followed by a gradual increase back to the value prior to expansion. Previous studies showed that at steady-state condition a network of hydrogen bonding between surfactant and water molecules near the surface is created. The unique surface tension response after large expansion might be related to the momentarily destruction of this hydrogen bonding network and gradually making a new one. The effect of temperature on the surface tension and adsorption kinetics of 1-octanol, 1-hexanol and 1-butanol aqueous solutions is studied. The steady-state surface tension is found to decrease upon an increase in temperature, and a linear relationship is observed between them. The modified Langmuir equation of state and the modified kinetic transfer equation are used to model the experimental data of the steady-state and dynamic (time-dependent) surface tension, respectively. The equilibrium constants and adsorption rate constants are evaluated through a minimization procedure for temperatures ranging from 10°C to 35°C. From the steady-state modelling, the equilibrium constants for adsorption from vapor phase and liquid phase are found to increase with temperature. From the dynamic modelling, the adsorption rate constants for adsorption from vapor phase and liquid phase are found to increase with temperature too. The influence of carbon dioxide pressure on the surface tension and adsorption kinetics of the aforementioned surfactant aqueous solutions is investigated. To consider the effect of adsorption/desorption of the two species (surfactant and carbon dioxide) from both sides of a vapor/liquid interface on the surface tension, the modified Langmuir equation of state and the modified kinetic transfer equation are derived. The steady-state and dynamic surface tension data are modelled using the modified Langmuir equation of state and the modified kinetic transfer equation, respectively. The equilibrium constants and adsorption rate constants of surfactant and carbon dioxide are evaluated through a minimization procedure for CO2 pressures ranging from 0 to 690 KPa. From the steady-state modelling, the equilibrium parameters for surfactant and carbon dioxide adsorption from vapor phase and liquid phase are found unchanged for different pressures of carbon dioxide. From the dynamic modelling, the adsorption rate constants for surfactant and carbon dioxide are found to decrease with carbon dioxide pressure. The role of carbon chain length of amphiphiles in aqueous solution is also studied. It is illustrated that the equilibrium constants for adsorption from both sides of a vapor/liquid interface increase from 1-butanol to 1-octanol. The modelling results show that the ratio of the equilibrium constant for adsorption from vapor phase to the equilibrium constant for adsorption from liquid phase declines from 260 to 26 as the chain length is increased from 1-butanol to 1-octanol. Therefore, the contribution to adsorption from liquid phase augments as the chain length is increased. The adsorption kinetics for this group of short carbon chain surfactants is modelled using a kinetic transfer equation. The modelling results show that the adsorption rate constants from vapor phase and liquid phase (kag and kal) increase from 1-butanol to 1-octanol. Steady-state and dynamic modelling also reveals that the maximum surface concentration increases with carbon chain length. These results may be due to the higher hydrophobicity character of a surfactant molecule at longer carbon chain length.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2097" Chuanping Li. 12/19/2004. Report is also available in paper and microfiche from NTIS.

L'effet Leidenfrost répresente un cas particulier de caléfaction : lorsqu'une goutte de liquide est déposée sur une surface dont la température est très supérieure à la température d'ébullition du liquide, ce dernier s'évapore avant de toucher la surface et la vapeur ainsi créée forme un coussin sous la goutte qui la maintient en sustentation et l'isole de la plaque chauffante.Ce travail de thèse concerne la modélisation et la simulation de ce phénomène complexe. Dans une première partie, nous étudions un modèle avec interface raide basée sur les équations de Navier-Stokes enrichies avec des termes interfaciaux prenant en compte le changement de phase et la tension de surface. La simulation d'une couche uniforme de liquide sur un film de vapeur nous ramène à un cas unidimensionnel pour lequel on utilise la méthode ALE (Arbitrary Lagrangian Eulerian) afin de gérer la hauteur variable de chaque phase. La discrétisation du modèle est validée sur un cas test.Dans une seconde partie, on utilise la méthode de capture d'interface Level-Set dans laquelle la frontière liquide/gaz est représentée par la ligne de niveau zéro d'une fonction. Cette interface est artificiellement épaissie et les quantités thermodynamiques y sont régularisées. La tension de surface et le changement de phase sont alors introduits sous forme de termes volumiques dans nos équations. L'hypothèse d'incompressibilité de chaque phase pure nous amène alors à un fluide généralisé dont la compressibilité se manifeste uniquement dans la zone interfaciale, là où se produit le changement de phase.La troisième partie est consacrée à la discrétisation de ce modèle pour l'étude tridimensionnelle d'une goutte d'eau, immobile et symétrique par rotation, se ramenant ainsi à un problème bi-dimensionnel axisymétrique. La méthode Level-Set nécessite des choix numériques particuliers qui sont alors explicités : schéma d'advection peu diffusif, redistanciation par résolution d'une équation de Hamilton-Jacobi et correction globale du volume de la goutte, prenant en compte le changement de phase. Un algorithme de projection de type Chorin est également utilisé afin de satisfaire la contrainte sur la compressibilité de notre fluide. On présentera également un nouveau schéma aux différences finies à stencil compact pour l'approximation du gradient.La dernière partie présente et compare nos résultats numériques avec plusieurs courbes théoriques, décrivant chacune l'évolution de certains paramètres de la goutte de liquide : son volume, son rayon et la hauteur de la couche de vapeur. / The Leidenfrost effect is a special case of calefaction: when a liquid is dropped on a surface which temperature is far hotter than the liquid's boiling point, he evaporates before touching the hot plate and the produced gas forms a thin layer, under the liquid droplet, that makes it hovering and isolates it from the heat source.This thesis deals with the modeling and the numerical simulation of this complex phenomenon. In the first part, we study a sharp interface model that supplement the Navier-Stokes equations with interfacial conditions taking into account the phase change and the surface tension. Simulating an uniform liquid layer over a vaporous film reduces the problem to one dimension. The ALE method (Arbitrary Lagrangian Eulerian) is then used to deal with the variable height of each phase. The numerical code is finally validated on a test case.In the second part, the gas/liquid interface is captured by a Level-Set method. The interface is artificially thickened and inner regularization is applied to the thermodynamic quantities. Therefore, surface tension and phase change are approximated by volume terms. Each pure phase is supposed to be incompressible but, due to the phase change, the velocity field is not divergence-free in the interfacial zone.The third part focusses on the discretization of this three-dimensional model, for the simulation of a motionless and rotational symmetric droplet. The problem reduces to an axisymmetric two-dimensional setting. The use of the Level-Set method requires devoted numerical algorithms which are developed: non-diffusive efficient advection scheme, reinitialization by Hamilton-Jacobi equation with global volume correction taking into account the phase change. An adapted Chorin projection algorithm is used to ensure the prescribed compressibility constraint that holds on the interfacial fluid. In addition, we introduce a new finite difference scheme for the gradient approximation that uses a compact stencil.The last part describes and compares our simulation results with several theoretical curves based on different droplet shape simplifications, plotting the evolution of indicators like the volume and radius of the droplet, or the height of the vapor layer.

Depuis le début du millénaire, la simulation numérique directe est apparue comme un outil précieux capable d'étudier l’atomisation d’une goutte isolée par un écoulement à grande vitesse. L’atomisation peut être divisée en deux phases distinctes : l'éclatement se produit d'abord sous la forme d'aplatissement de la goutte, formant également des filaments, puis il se poursuit via l'obtention d'une multitude de gouttes de tailles réduites ce qui complète le processus d’atomisation. Les principaux objectifs pour le présent travail étaient donc d’établir un modèle et une méthode numérique capables d’étudier au mieux ces phénomènes. L'atomisation d’une goutte isolée est présentée et est accompagnée d’une comparaison avec l’expérience qui confirme les capacités du modèle et de la méthode à simuler numériquement les différents processus physiques mis en jeu. Des informations essentielles quant aux mécanismes d’atomisation, non exploitables avec l’expérience, sont décrites et l’objectif d’obtenir des gouttes de tailles réduites est atteint. / Only at the beginning of the millennium, direct numerical simulation has emerged as a valuable tool capable of studying the atomization of an isolated droplet by a high-speed flow. The atomization can be divided into two distinct phases: the aerobreakup occurs first in the form of flattening of the droplet, also forming filaments, and then it continues via the obtaining of a multitude of reduced sizes droplets what completes the process of atomization. The main objectives of this work were therefore to establish a model and a numerical method able to study these phenomena as well as possible. The atomization of an isolated droplet is presented and is accompanied by a comparison with the experiment which confirms the capacities of the model and the method to numerically simulate the different physical processes involved. Essential information on atomization mechanisms, which cannot be exploited with experiments, is described and the objective of obtaining droplets of reduced sizes is achieved.