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

O objetivo do presente estudo foi o de avaliar a influência da associação dos tensoativos cetrimida 0,2%, cetrimida 0,1% e cloreto de benzalcônio 0,008% aos hipocloritos de sódio e de cálcio 2,5% nas propriedades de pH, quantidade de cloro livre, tensão superficial, ângulo de contato, dissolução pulpar e atividade antimicrobiana. O pH e a concentração de cloro ativo foram avaliados por pHmetro digital e pela titulação, respectivamente. A tensão superficial foi mensurada através da técnica do anel de platina com um tensiômetro de Du Noüy. O ângulo de contato das soluções em bases de dentina humana foi aferido pelo software Drop Shape Analyzer. Para a análise da dissolução pulpar foram utilizados fragmentos de polpas bovinas e os resultados foram expressos por percentual de perda de massa. A atividade antimicrobiana frente ao Enterococcus faecalis foi realizada pelo método de difusão em Ágar. Os resultados mostraram que a associação de tensoativos aos hipocloritos de sódio e cálcio não alterou as propriedades de pH, cloro livre e dissolução pulpar das soluções. O hipoclorito de cálcio apresentou o maior valor de tensão superficial (72,13 ± 1,82 mN/m). Quando associados aos tensoativos, os hipocloritos de sódio e cálcio tiveram uma redução significativa da tensão superficial. O mesmo foi observado para o ângulo de contato. Os tensoativos apresentam atividade antimicrobiana. A associação dos hipocloritos à cetrimida 0,2% ou 0,1% aumentou o halo de inibição frente ao Enterococcus faecalis. Concluiu-se que a associação de tensoativos não modificaram as propriedades de pH, cloro livre e dissolução pulpar dos hipocloritos de sódio e cálcio 2,5%. Porém, ela foi capaz de diminuir a tensão superficial e o ângulo de contato das soluções. Ainda, a associação da cetrimida 0,2% e 0,1% melhorou a capacidade antimicrobiana dos hipocloritos. / The aim of this study was to evaluate the influence of surfactants 0,2% or 0,1% cetrimide or 0,008% benzalkonium chloride on 2.5% sodium and calcium hypochlorite in the properties of pH, free chlorine content, surface tension, contact angle, pulp dissolution and antimicrobial activity. The pH and free chlorine content were evaluated by digital pHmeter and by titration, respectively. Surface tension was measured by the platinum ring technique with a Du Noüy tensiometer. Solution’s contact angle in human dentin surfaces was checked by Drop Shape Analyzer software. Bovine pulps were used for pulp dissolution analysis and the dissolving capacity was expressed by percentual weight loss. Antimicrobial activity over Enterococcus faecalis was evaluated through the ágar diffusion method. The surfactants association on sodium and calcium hypochlorites did not alter pH, free chlorine content and pulp dissolution properties. Calcium hypochlorite had the higher surface tension (72,13 ± 1,82 mN/m). However, when sodium and calcium hypochlorite were associated to surfactants, a significant reduction of surface tension occured. The same was observed for contact angle analysis. The surfactants used in this study have antimicrobial activity. The association of 0,2% or 0,1% cetrimide enhanced antimicrobial activity of both hypochlorites. It was possible to conclude that surfactants association did not alter pH, free chlorine content and pulp dissolution properties of 2,5% sodium and calcium hypochlorite. It was capable to reduce surface tension and contact angle of the solutions. Moreover, the 0,2% or 0,1% cetrimide association increased antimicrobial activity of hypochlorite.

INTRODUÇÃO: A Síndrome do Desconforto Respiratório (SDR) é uma das principais causas de morbi-mortalidade no período neonatal, acometendo predominantemente os recém-nascidos prematuros, devido a uma está deficiência de surfactante pulmonar. O Instituto Butantan desenvolveu um surfactante de origem porcina com objetivo de torná-lo disponível a todo Sistema Único de Saúde. O objetivo deste estudo foi avaliar, em um modelo experimental de SDR (coelho), a estabilidade do Surfactante Butantan (SB) um ano após sua produção e armazenamento a 2 a 8ºC.. MÉTODOS: 94 coelhos prematuros foram randomizados em dois grupos de tratamento: grupo Butantan e grupo Curosurf (controle), e foram analisados em seis momentos de avaliação: momento zero (imediatamente após a retirada do refrigerador ao final de 1 ano de armazenamento), momento 1 (24 horas após ter sido mantido a 24ºC), momento 2 (após 30 dias de armazenamento a 20º C), momento 3 (após 60 dias de armazenamento a 20º C), momento 4 (após 90 dias de armazenamento a 20º C) e momento 5 (após 180 dias de armazenamento a 20º C). Após receberem o surfactante, os animais foram ventilados por 15 minutos para avaliação da pressão ventilatória e complacência pulmonar dinâmica e curva pressão-volume pulmonar, seguindo-se à avaliação histopatológica dos pulmões. RESULTADOS: A eficácia do SB foi semelhante à do Curosurf, um ano após a sua produção e armazenamento a 2 a 8ºC. Neste momento de avaliação, não houve diferença estatisticamente significante entre os grupos de estudo quanto a: pressão ventilatória, complacência pulmonar dinâmica e curva pressão-volume pulmonar. Ao longo dos seis meses de armazenamento inadequado do SB, demonstrou-se a redução de sua eficácia durante a fase expiratória da curva pressão-volume pulmonar. No entanto, a análise histopatológica, demonstrou não haver diferença significante entre os dois grupos de estudo em nenhum dos momentos de avaliação. CONCLUSÕES: As propriedades bioquímicas do SB foram preservadas após um ano de sua produção e armazenamento em refrigeração de 2 a 8ºC. Condições inadequadas de armazenamento resultam em alterações das propriedades bioquímicas do SB e, conseqüentemente, de sua função, o que foi demonstrado por parâmetros de mecânica ventilatória, mas não pela análise histopatológica dos pulmões / INTRODUCTION: Respiratory Distress Syndrome (RDS) is one of the major causes of death among premature newborns, and its development results from surfactant deficiency. The Butantan Institute has recently produced a porcine-derived surfactant preparation in order to make it available nationwide for RDS treatment in the near future. The aim of this study was to evaluate, in an animal model of surfactant deficiency (premature rabbits), the stability of the Butantan Surfactant (SB) one year after its production and storage in the refrigerator, at 2 to 8ºC. METHODS: 94 premature newborn rabbits were randomized into two treatment groups: SB or Curosurf®(control surfactant), and were assessed in six different time-points: time-point zero (immediately after removal of surfactant from the refrigerator after one year of storage); time-point 1 (after 24h of storage at 24ºC), time-point 2 (after 30 days of storage at 20ºC), time-point 3 (after 60 days of storage at 20ºC), time-point 4 (after 90 days of storage at 20ºC) and time-point 5 (after 180 days of storage at 20ºC). The animals were artificially ventilated for 15 minutes for lung mechanics assessment (ventilatory pressure, dynamic lung compliance and pressure-lung volume curve), followed by removal of the lungs for histopathologic analysis. RESULTS: After one year of its production and storage at 2 to 8ºC, SB was as efficient as Curosurf. At this time-point, The Butantan Surfactant showed no significant differences with Curosurf® regarding the ventilatory pressure, dynamic lung compliance and pressure-lung volume curve. Throughout the six month period of warming, SB showed a decreasing efficiency, as revealed by the expiratory phase of the pressure-lung volume curve. However, the histopathologic analysis revealed no significant differences between the two groups, in any of the study time-points. CONCLUSIONS: The Butantan Surfactant preserved its biochemical properties one year after its production and storage at 2 to 8ºC. On the other hand, adverse storing conditions can lead to alterations in the SB biochemical properties that result in deterioration of its function, which was demonstrated in this study by changes in lung mechanics, but not in the histopathologic analysis

O fenômeno de molhamento, estudo de como um líquido se deposita em um sólido, apresenta problemas ainda em aberto, dos pontos de vista da modelagem física e da simulação numérica. O maior interesse acadêmico neste tipo de escoamento é a linha tríplice (ou linha de contato) formada da interação sólido-líquido-gás. A condição de contorno clássica de não escorregamento na interface líquido-sólido leva a uma singularidade no tensor de tensões nesta linha. Além disso, ainda não está estabelecido qual o melhor modelo para descrever o ângulo de contato formado entre a superfície livre e o substrato (o sólido). Neste trabalho, são discutidos métodos numéricos para a simulação de linhas de contato dinâmicas. Os efeitos da tensão superficial são estudados com a abordagem do princípio do trabalho virtual, o qual leva o problema à equações na formulação variacional, linguagem natural para o tratamento numérico com o método dos elementos finitos (FEM). O domínio é discretizado por uma malha não-estruturada de forma que as interfaces separadoras são explicitamente representadas pela malha. As derivadas temporais são tratadas em uma abordagem Lagrangeana-Euleriana arbitrária (ALE). Finalmente, são apresentados os resultados numéricos obtidos com o método ALE-FEM, discutindo alguns aspectos da sua convergência temporal e espacial. / Wetting phenomena, study of how of a liquid spreads out on a solid substrate, presents challenges both in physical modeling and in numerical simulation. The triple line (or contact line) formed by the solid-liquid-gas interaction has increasingly attracted the attention of the fluid dynamic community. The classical no-slip boundary condition on the liquid-solid interface leads to a singularity in the stress tensor at contact lines. Furthermore, there is no consensus on what the best model to describe the dynamics of the contact angle formed by the solid substrate and free surface. In this work, numerical methods for simulating dynamic contact lines are considered. The capillarity effects are studied in the approach of the virtual-work principle, which describes the problem in the variational formulation, natural language for numerical treatment with the finite element method (FEM). The domain is discretized by a dynamic unstructured mesh, where the separating interfaces are explicit represented by the mesh. Time derivatives present in the governing equations are treated with the arbitrary Lagrangian-Eulerian (ALE) framework. Finally, we discuss some temporal and spatial convergence issues ofthe ALE-FEM method.

Les copolymères à blocs amphiphiles Polyéthylène-b-Polyéthylène glycol comportent un bloc hydrophile et un bloc hydrophobe, tous deux cristallisables. L’intérêt de cette thèse est de mieux comprendre le comportement de ces copolymères aux interfaces solides et liquides, via l’étude de la structure et de l’organisation des couches adsorbées. Des copolymères PE-b-PEG de différentes compositions ont été étudiés à l’état massique, mettant en évidence que le ratio PEG/PE ainsi que la longueur des blocs jouent un rôle significatif sur le taux de cristallinité, la morphologie et la croissance des structures cristallines. La caractérisation en films minces par spectroscopie PM-IRRAS et AFM a permis de déterminer quantitativement l’orientation des chaînes macromoléculaires de chaque bloc sur des substrats modèles hydrophiles et hydrophobes. L’adsorption des copolymères PE-b-PEG a par ailleurs été étudiée aux interfaces eau/air et eau/hexane par les méthodes de la goutte pendante et de la goutte oscillante. Les résultats, appuyés par des mesures de tailles de particules, ont montré que les copolymères sont capables de former des structures sphériques organisées à l’échelle nanométrique. L’influence de la composition du copolymère et de la nature des interfaces sur l’organisation des copolymères a ainsi permis d’élaborer des modèles d’adsorption des blocs aux interfaces. / Polyethylene-b-Polyethylene amphiphilic diblock copolymers are composed of one hydrophilic and one hydrophobic block, both able to crystallize. The aim of this thesis is to better understand the behaviour of PE-b-PEG copolymers at solid and liquid interfaces, via the study of the structure and the organization of adsorbed layers. The crystallinity of bulk PE-b-PEG copolymers with different composition was characterized, revealing that the ratio PEG/PE and the blocks length impact the crystallinity degree, the morphology and the growth of crystalline structures. Thin films characterization by PM-IRRAS spectrocopy and AFM allowed to determine quantitatively the macromolecular chains orientation on hydrophobic and hydrophilic substrates. PE-b-PEG copolymers adsorption at the water/air and water/hexane interfaces was studied thanks to the pendant drop and the oscillating drop techniques. These results, supported by particle size analysis, revealed that copolymers can organize as nanometric spherical structures. The influence of the copolymer composition and the type of interfaces on the organization then lead to the elaboration of adsorption models of PE and PEG blocks at solid and liquid interfaces.

Le présent manuscrit présente le développement méthodologique du calcul de la tension de surface d’interfaces solide-liquide via des simulations de dynamique moléculaire. Après une courte présentation des avancées dans le domaine du calcul de la tension de surface pour les interfaces fluide-fluide et solide-fluide, les principales méthodes de calcul de la tension de surface d’un point de vue théorique sont montrées et généralisées pour le cas des interfaces solide-liquide, puis mises en oeuvre dans le cas de simulations de dynamique moléculaire. Un système école, constitué d’une feuille de graphène pour la phase solide et d’un bain de méthane pour la phase liquide, est ensuite étudié pour observer l’influence des artefacts de simulation sur le calcul de la tension de surface, montrant en particulier des effets de taille bien plus importants que pour le cas des interfaces liquide-liquide. Un autre système constitué d’une tranche de cuivre pour la phase solide, et d’un bain de méthane pour la phase liquide, a permis d’étudier l’effet inédit aux systèmes solide-liquide appelé anisotropie, montrant en particulier l’importance du caractère tensoriel de la tension de surface pour ce type de système. L’influence des paramètres du potentiel croisé entre les atomes de cuivre et de méthane est ensuite étudié. Finalement, deux systèmes applicatifs sont abordés, d’une part le système graphène-eau permettant d’étudier les effets de l’interaction électrostatique, et d’autre part un système constitué d’un solide explosif, le 1,3,5-triamino-2,4,6-trinitrobenzène (TATB) en contact avec un bain polymère pour la phase liquide, représentatif d’un cas réel d’intérêt. / This manuscript presents the methodological development of surface tension calculation of solid-liquidinterfaces via molecular dynamics simulations. After a short presentation of the advances in the field ofsurface tension calculation for fluid-fluid and solid-fluid interfaces, the main methods of surface tensioncalculation from a theoretical point of view are shown and generalized for solid-liquid interfaces, thenimplemented in the case of molecular dynamics simulations. A school system, consisting of a graphenesheet for the solid phase and a methane bath for the liquid phase, is then studied to observe the influenceof simulation artifacts on the surface tension calculation, showing in particular much larger size effectsthan in the case of liquid-liquid interfaces. Another system consisting of a copper slice for the solid phaseand a methane bath for the liquid phase made it possible to study the novel effect of solid-liquid systemscalled anisotropy, showing in particular the importance of the tensor character of the surface tension forthis type of system. The influence of the parameters of the cross potential between copper and methaneatoms is then studied. Finally, two application systems are discussed, on the one hand the graphene-watersystem for studying the effects of electrostatic interaction, and on the other hand a system consisting ofan explosive solid, 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) in contact with a polymer bath for theliquid phase, representing a real case of interest.

An experimental study of phase transitions of long-chain n-alkanes induced by the effect of interfaces is described. ¶ The phase behaviour of long-chain n-alkanes (carbon number 14, 16, 17, 18) adsorbed at isolated mica surfaces and confined between two mica surfaces has been studied in the vicinity of and down to several degrees below the bulk melting points, Tm. Using the Surface Force Apparatus we have measured the thickness of alkane films adsorbed from vapour (0.97 [equal to or greater-than] p/p[subscript o] [equal to or greater-than] 0.997), studied capillary condensation transition, subsequent growth of capillary condensates between two surfaces, and phase transitions in both the adsorbed films and the condensates. By measuring the growth rate of the capillary condensates we have identified a transition in the lateral mobility of molecules in the adsorbed films on isolated mica surfaces. This transition to greater mobility occurs slightly above Tm for n-hexadecane, n-heptadecane and n-octadecane but several degrees below Tm for n-tetradecane, and is accompanied by a change in wetting behaviour and a measurable decrease in adsorbed film thickness for n-heptadecane and n-octadecane. Capillary condensates that form below Tm remain liquid, but may freeze if the degree of confinement is reduced by separation of the mica surfaces. An increase in the area of the liquid-vapour interface relative to that of the liquid-mica interface facilitates freezing in the case of the long-chain alkanes, which show surface freezing at the liquid-vapour interface. ¶ Although thermodynamic properties of the surface freezing transition have been rather well documented, the kinetics involved in formation of such ordered monolayers has so far received very little attention. We studied the surface tension of n-octadecane as a function of temperature in the vicinity of Tm, using the static Wilhelmy plate and the dynamic maximum bubble pressure methods. The two methods give different results on cooling paths, where nucleation of the surface ordered phase is involved, but agree on heating paths, where both methods measure properties of the equilibrium surface phase. On cooling paths, the surface of bubbles may supercool below the equilibrium surface freezing temperature. The onset of surface freezing is marked by a sharp drop in the surface tension. The transition is accompanied by an increased stability of the films resulting in longer bubble lifetimes at the liquid surface, which suggests that the mechanical properties of the surfaces change from liquid-like to solid-like. Our results suggest occurrence of supercooling of the monolayer itself.

<p>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.</p><p>A detailed comparison of various non-ionic model surfactants showed how structural changes affect interfacial properties:</p><p>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. </p><p>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. </p><p>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.</p> / 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.

The main objective of this research was to exploit the interrelations between the rheological behavior and nano-microstructure of complex fluids in solving two state-of-the-art problems, one in the field of biomedical engineering: controlling the amount and characteristics of bioaerosol droplets generated during coughing, and the other in the bitumen-heavy oil industry: characterizing the nano-microstructure of asphaltene particles in bitumen and heavy oil from their rheological behavior. For the first problem, effect of viscoelastic and surface properties of artificial mucus simulant gels on the size distribution and amount of airborne bioaerosol droplets generated during simulated coughing were investigated. The results revealed that suppressing the generation of bioaerosol droplets and/or reducing the number of emitted droplets to a minimum during coughing are practically achievable through modulation of mucus viscoelastic properties. While variation of surface tension did not show any change in the droplet size distribution, an increase in particle size was observed as the samples changed from elastic solid type to viscoelastic type to viscous fluid type samples. This knowledge will help in the development of a new class of drugs being developed at the University of Alberta, aimed at controlling the transmission of airborne epidemic diseases by modifying the viscoelastic properties of mucus. For the second problem, studies of viscoelastic behavior of Athabasca bitumen (Alberta) and Maya crude (Mexico) oil samples, along with their Nano-filtered and chemically separated-plus-reconstituted samples were performed. The results revealed that the rheological behaviors of the bitumen-heavy oil samples are governed by their multiphase nature. The rheological behavior of all feeds, permeates and retentate samples followed a single master curve over the entire temperature interval, consistent with that of a slurry comprising a Newtonian liquid plus a dispersed solid comprising non-interacting hard spheres. The behavior of asphaltenes in the reconstituted samples, however, was found to be significantly different from that in nanofiltered samples. The information about the characteristics and behaviors of asphaltenes obtained in this study will help better understand the asphaltene structures, and support the effort to determine solutions for numerous asphaltene-related industrial problems. In the long run, this knowledge will help to create more efficient extraction and upgrading processes for bitumen and heavy oils. / Thermo Fluids

Micro-assembly processes suffer from some breaches due to the continuing trend towards an increase in the production capabilities as well as in the size reduction of the components manipulated. Usual manipulating schemes have reached their limit and capillary forces constitute a valuable alternative strategy. The goal of this work is to describe the dynamics of liquid bridges in the application of micro-assembly processes. The description is obtained using the Kelvin-Voigt model, with a spring, a damper, and a mass connected in parallel, supported by numerical simulations, analytical approximations and experiments. The works is divided into three parts. First we present important aspects of microfluidics, as well as the constitutive equations and an overview of numerical approaches used to describe fluid flow problems with moving interfaces. The second part is devoted to the capillary rise case, intended to validate and to compare the numerical approaches to analytical laws and experimental results. The implementation of the slipping and the dynamic contact angles is discussed. The last part focuses on the dynamics of the liquid bridge. The liquid bridge is confined between two circular and parallel plates and presents an axial symmetry. The description reveals that the stiffness depends on the surface tension and on the shape of the air/liquid interface, the damping coefficient depends on the viscosity and the volume of liquid and the equivalent mass depends on the density and the volume.