Vaahtoamisen estäminen vesiohenteisissa sisäseinämaaleissa

Maalit ovat hyvin komplekseja seoksia, jotka sisältävät erilaisia pinta-aktiivisia aineita. Erilaisia pinta-aktiivisia apuaineita käytetään varsinkin vesiohenteisissa maaleissa veden korkean pintajännityksen takia. Nämä maalin komponentit saat-tavat kuitenkin aiheuttaa maaliin vaahtoamisongelmia. Maalien vaahtoaminen aiheuttaa esimerkiksi erilaisia pintavikoja maalikalvossa ja epäotpimaalista tuo-tantosäiliöiden ja pakkausten täyttöä. Joissain tapauksissa myös maalin funktio-naalisuus saattaa häiriintyä. Maalien vaahtoamista pyritään vähentämään pääasiassa vaahdonestäjiksi kutsu-tuilla apuaineilla. Tärkeimmät vesipohjaisissa maaleissa käytettävät vaahdonestäjät ovat mineraaliöljyjä sekä silikonipohjaisia vaahdonestäjiä. Tässä työssä tutkitaan kolmen eri vesiohenteisen sisäseinämaalin vaahtoamista ja mahdollisia keinoja vähentää sitä. Laboratoriossa kokeillaan nykyisten vaahdonestäjien tilalle mahdollisia korvaavia apuaineita. Lisäksi kullekin maalille luodaan koesuunni-telma, jonka mukaan toteutetaan tehtaalla sarja koeajoja, joilla pyritään löytämään sopiva vaahdonestäjän annostus sekä lisäystapa kullekin maalille, siten että maalien vaahtoaminen vähenee. Laboratoriokokeiden perusteella korvaavaa vaahdonestäjää nykyisten tilalle ei löydetty. Valmistusprosessin yhteydessä sen sijaan havaittiin, että vaahdonestäjän lisäystapaa muuttamalla voisi olla mahdollista vähentää maalien vaahtoamista merkittävästi lisäämättä käytettävää vaahdonestäjän annostusta.

Development of a Phase Separation Strategy in Macrocyclization Reactions

La réaction de macrocyclisation est une transformation fondamentale en chimie organique de synthèse. Le principal défi associcé à la formation de macrocycles est la compétition inhérente avec la réaction d’oligomérisation qui mène à la formation de sousproduits indésirables. De plus, l’utilisation de conditions de dilutions élevées qui sont nécessaires afin d’obtenir une cyclisation “sélective”, sont souvent décourageantes pour les applications à l’échelle industrielle. Malgré cet intérêt pour les macrocycles, la recherche visant à développer des stratégies environnementalement bénignes, qui permettent d’utiliser des concentrations normales pour leur synthèse, sont encore rares. Cette thèse décrit le développement d’une nouvelle approche générale visant à améliorer l’efficacité des réactions de macrocyclisation en utilisant le contrôle des effets de dilution. Une stratégie de “séparation de phase” qui permet de réaliser des réactions à des concentrations plus élevées a été developpée. Elle se base sur un mélange de solvant aggrégé contrôlé par les propriétés du poly(éthylène glycol) (PEG). Des études de tension de surface, spectroscopie UV et tagging chimique ont été réalisées afin d’élucider le mécanisme de “séparation de phase”. Il est proposé que celui-ci fonctionne par diffusion lente du substrat organique vers la phase ou le catalyseur est actif. La nature du polymère co-solvant joue donc un rôle crutial dans le contrôle de l’aggrégation et de la catalyse La stratégie de “séparation de phase” a initiallement été étudiée en utilisant le couplage oxidatif d’alcynes de type Glaser-Hay co-catalysé par un complexe de cuivre et de nickel puis a été transposée à la chimie en flux continu. Elle fut ensuite appliquée à la cycloaddition d’alcynes et d’azotures catalysée par un complexe de cuivre en “batch” ainsi qu’en flux continu.

The effects of additives and chemical modification on the solution properties of thermo-sensitive polymers

Cette thèse concerne l’étude de phase de séparation de deux polymères thermosensibles connus-poly(N-isopropylacylamide) (PNIPAM) et poly(2-isopropyl-2-oxazoline) (PIPOZ). Parmi des études variées sur ces deux polymères, il y a encore deux parties de leurs propriétés thermiques inexplicites à être étudiées. Une partie concerne l’effet de consolvant de PNIPAM dans l’eau et un autre solvant hydromiscible. L’autre est l’effet de propriétés de groupes terminaux de chaînes sur la séparation de phase de PIPOZ. Pour ce faire, nous avons d’abord étudié l’effet de l’architecture de chaînes sur l’effet de cosolvant de PNIPAMs dans le mélange de méthanol/eau en utilisant un PNIPAM en étoile avec 4 branches et un PNIPAM cyclique comme modèles. Avec PNIPAM en étoile, l’adhérence de branches PNIPAM de à un cœur hydrophobique provoque une réduction de Tc (la température du point de turbidité) et une enthalpie plus faible de la transition de phase. En revanche, la Tc de PNIPAM en étoile dépend de la masse molaire de polymère. La coopérativité de déhydratation diminue pour PNIPAM en étoile et PNIPAM cyclique à cause de la limite topologique. Une étude sur l’influence de concentration en polymère sur l’effet de cosolvant de PNIPAM dans le mélange méthanol/eau a montré qu’une séparation de phase liquide-liquide macroscopique (MLLPS) a lieu pour une solution de PNIPAM dans le mélange méthanol/eau avec la fraction molaire de méthanol entre 0.127 et 0.421 et la concentration en PNIPAM est constante à 10 g.L-1. Après deux jours d’équilibration à température ambiante, la suspension turbide de PNIPAM dans le mélange méthanol/eau se sépare en deux phases dont une phase possède beaucoup plus de PNIPAM que l’autre. Un diagramme de phase qui montre la MLLPS pour le mélange PNIPAM/eau/méthanol a été établi à base de données expérimentales. La taille et la morphologie de gouttelettes dans la phase riche en polymère condensée dépendent de la fraction molaire de méthanol. Parce que la présence de méthanol influence la tension de surface des gouttelettes liquides, un équilibre lent de la séparation de phase pour PNIPAM/eau/méthanol système a été accéléré et une séparation de phase liquide-liquide macroscopique apparait. Afin d’étudier l’effet de groupes terminaux sur les propriétés de solution de PIPOZ, deux PIPOZs téléchéliques avec groupe perfluorodécanyle (FPIPOZ) ou groupe octadécyle (C18PIPOZ) comme extrémités de chaîne ont été synthétisés. Les valeurs de Tc des polymères téléchéliques ont beaucoup diminué par rapport à celle de PIPOZ. Des micelles stables se forment dans des solutions aqueuses de polymères téléchéliques. La micellization et la séparation de phase de ces polymères dans l’eau ont été étudiées. La séparation de phase de PIPOZs téléchéliques suit le mécanisme de MLLPS. Des différences en tailles de gouttelettes formées à l’intérieur de solutions de deux polymères ont été observées. Pour étudier profondément les différences dans le comportement d’association entre deux polymères téléchéliques, les intensités des signaux de polymères correspondants et les temps de relaxation T1, T2 ont été mesurés. Des valeurs de T2 de protons correspondants aux IPOZs sont plus hautes.

Cavitation in 3He-4He liquid mixtures at low temperatures

Bubble formation in solutions of 3He and 4He is studied within a density-functional approach. In particular, the temperature dependence of the cavitation pressure for different 3He concentrations is calculated at low temperatures and compared to that of pure 4He. The presence of Andreev states lowers the surface tension and, consequently, nucleation barriers are drastically reduced. This fact means that even at low 3He concentrations the cavitation process takes place at higher pressures than the spinodal pressure, which is not the case for pure 4He.

Grain boundaries in vortex matter

We explore the statistical properties of grain boundaries in the vortex polycrystalline phase of type-II superconductors. Treating grain boundaries as arrays of dislocations interacting through linear elasticity, we show that self-interaction of a deformed grain boundary is equivalent to a nonlocal long-range surface tension. This affects the pinning properties of grain boundaries, which are found to be less rough than isolated dislocations. The presence of grain boundaries has an important effect on the transport properties of type-II superconductors as we show by numerical simulations: our results indicate that the critical current is higher for a vortex polycrystal than for a regular vortex lattice. Finally, we discuss the possible role of grain boundaries in vortex lattice melting. Through a phenomenological theory we show that melting can be preceded by an intermediate polycrystalline phase.

A New Class of Nonionic Photosensitive Surfactants: Some Insights Concerning Conformations

We report on a new class of nonionic, photosensitive surfactants consisting of a polar di(ethylene oxide) head group attached to an alkyl spacer of between two and eight methylene groups, coupled through an ether linkage to an azobenzene moiety. Structural changes associated with the interconversion of the azobenzene group between its cis and trans forms as mediated by the wavelength of an irradiating light source cause changes in the surface tension and self-assembly properties. Differences in saturated surface tensions (surface tension at concentrations above the CMC) were as high as 14.4 mN/m under radiation of different wavelengths. The qualitative behavior of the surfactants changed as the spacer length changed, attributed to the different orientations adopted by the different surfactants depending on their isomerization states, as revealed by neutron reflection studies. The self-assembly of these photosensitive surfactants has been investigated by light scattering, small angle neutron scattering, and cryo-TEM under different illuminations. The significant change in the self-assembly in response to different illumination conditions was attributed to the sign change in Gaussian rigidity, which originated from the azobenzene photoisomerization.

Corner Flows in Free Liquid Films

A lubrication-flow model for a free film in a corner is presented. The model, written in the hyperbolic coordinate system ξ = x² – y², η = 2xy, applies to films that are thin in the η direction. The lubrication approximation yields two coupled evolution equations for the film thickness and the velocity field which, to lowest order, describes plug flow in the hyperbolic coordinates. A free film in a corner evolving under surface tension and gravity is investigated. The rate of thinning of a free film is compared to that of a film evolving over a solid substrate. Viscous shear and normal stresses are both captured in the model and are computed for the entire flow domain. It is shown that normal stress dominates over shear stress in the far field, while shear stress dominates close to the corner.

The effect of flow field & geometry on the dynamic contact angle

A number of recent experiments suggest that, at a given wetting speed, the dynamic contact angle formed by an advancing liquid-gas interface with a solid substrate depends on the flow field and geometry near the moving contact line. In the present work, this effect is investigated in the framework of an earlier developed theory that was based on the fact that dynamic wetting is, by its very name, a process of formation of a new liquid-solid interface (newly “wetted” solid surface) and hence should be considered not as a singular problem but as a particular case from a general class of flows with forming or/and disappearing interfaces. The results demonstrate that, in the flow configuration of curtain coating, where a liquid sheet (“curtain”) impinges onto a moving solid substrate, the actual dynamic contact angle indeed depends not only on the wetting speed and material constants of the contacting media, as in the so-called slip models, but also on the inlet velocity of the curtain, its height, and the angle between the falling curtain and the solid surface. In other words, for the same wetting speed the dynamic contact angle can be varied by manipulating the flow field and geometry near the moving contact line. The obtained results have important experimental implications: given that the dynamic contact angle is determined by the values of the surface tensions at the contact line and hence depends on the distributions of the surface parameters along the interfaces, which can be influenced by the flow field, one can use the overall flow conditions and the contact angle as a macroscopic multiparametric signal-response pair that probes the dynamics of the liquid-solid interface. This approach would allow one to investigate experimentally such properties of the interface as, for example, its equation of state and the rheological properties involved in the interface’s response to an external torque, and would help to measure its parameters, such as the coefficient of sliding friction, the surface-tension relaxation time, and so on.

Testing the limits of quasi-geostrophic theory: application to observed laboratory flows outside the quasi-geostrophic regime

We compare laboratory observations of equilibrated baroclinic waves in the rotating two-layer annulus, with numerical simulations from a quasi-geostrophic model. The laboratory experiments lie well outside the quasi-geostrophic regime: the Rossby number reaches unity; the depth-to-width aspect ratio is large; and the fluid contains ageostrophic inertia–gravity waves. Despite being formally inapplicable, the quasi-geostrophic model captures the laboratory flows reasonably well. The model displays several systematic biases, which are consequences of its treatment of boundary layers and neglect of interfacial surface tension and which may be explained without invoking the dynamical effects of the moderate Rossby number, large aspect ratio or inertia–gravity waves. We conclude that quasi-geostrophic theory appears to continue to apply well outside its formal bounds.

Modelling metal cutting using modern ductile fracture mechanics: Quantitative explanations for some longstanding problems

The assumption that negligible work is involved in the formation of new surfaces in the machining of ductile metals, is re-examined in the light of both current Finite Element Method (FEM) simulations of cutting and modern ductile fracture mechanics. The work associated with separation criteria in FEM models is shown to be in the kJ/m2 range rather than the few J/m2 of the surface energy (surface tension) employed by Shaw in his pioneering study of 1954 following which consideration of surface work has been omitted from analyses of metal cutting. The much greater values of surface specific work are not surprising in terms of ductile fracture mechanics where kJ/m2 values of fracture toughness are typical of the ductile metals involved in machining studies. This paper shows that when even the simple Ernst–Merchant analysis is generalised to include significant surface work, many of the experimental observations for which traditional ‘plasticity and friction only’ analyses seem to have no quantitative explanation, are now given meaning. In particular, the primary shear plane angle φ becomes material-dependent. The experimental increase of φ up to a saturated level, as the uncut chip thickness is increased, is predicted. The positive intercepts found in plots of cutting force vs. depth of cut, and in plots of force resolved along the primary shear plane vs. area of shear plane, are shown to be measures of the specific surface work. It is demonstrated that neglect of these intercepts in cutting analyses is the reason why anomalously high values of shear yield stress are derived at those very small uncut chip thicknesses at which the so-called size effect becomes evident. The material toughness/strength ratio, combined with the depth of cut to form a non-dimensional parameter, is shown to control ductile cutting mechanics. The toughness/strength ratio of a given material will change with rate, temperature, and thermomechanical treatment and the influence of such changes, together with changes in depth of cut, on the character of machining is discussed. Strength or hardness alone is insufficient to describe machining. The failure of the Ernst–Merchant theory seems less to do with problems of uniqueness and the validity of minimum work, and more to do with the problem not being properly posed. The new analysis compares favourably and consistently with the wide body of experimental results available in the literature. Why considerable progress in the understanding of metal cutting has been achieved without reference to significant surface work is also discussed.

Adsorption of frog foam nest proteins at the air-water interface

The surfactant properties of aqueous protein mixtures ( ranaspumins) from the foam nests of the tropical frog Physalaemus pustulosus have been investigated by surface tension, two-photon excitation. uorescence microscopy, specular neutron reflection, and related biophysical techniques. Ranaspumins lower the surface tension of water more rapidly and more effectively than standard globular proteins under similar conditions. Two- photon excitation. uorescence microscopy of nest foams treated with fluorescent marker ( anilinonaphthalene sulfonic acid) shows partitioning of hydrophobic proteins into the air-water interface and allows imaging of the foam structure. The surface excess of the adsorbed protein layers, determined from measurements of neutron reflection from the surface of water utilizing H2O/D2O mixtures, shows a persistent increase of surface excess and layer thickness with bulk concentration. At the highest concentration studied ( 0.5 mg ml(-1)), the adsorbed layer is characterized by three distinct regions: a protruding top layer of similar to20 Angstrom, a middle layer of similar to30 Angstrom, and a more diffuse submerged layer projecting some 25 Angstrom into bulk solution. This suggests a model involving self-assembly of protein aggregates at the air-water interface in which initial foam formation is facilitated by specific surfactant proteins in the mixture, further stabilized by subsequent aggregation and cross-linking into a multilayer surface complex.

Dynamics of interacting edge defects in copolymer lamellae

It is known that terraces at the air-polymer interface of lamella forming diblock copolymers do not make discontinuous jumps in height. Despite the underlying discretized structure, the height profiles are smoothly varying. The width of a transition region of a terrace edge in isolation is typically several hundreds of nanometres, resulting from a balance between surface tension, chain stretching penalties, and the enthalpy of mixing. What is less well known in these systems is what happens when two transition regions interact with one another. In this study, we investigate the dynamics of the interactions between copolymer lamellar edges. We find that the data can be well described by a model that assumes a repulsion between adjacent edges. While the model is simplistic, and does not include molecular level details, its agreement with the data suggest that some of the the underlying assumptions provide insight into the complex interplay between defects.

Rheology of milk foams produced by steam injection

Rheology of milk foams generated by steam injection was studied during the transient destabilization process using steady flow and dynamic oscillatory techniques: yield stress (τ_y) values were obtained from a stress ramp (0.2 to 25 Pa) and from strain amplitude sweep (0.001 to 3 at 1 Hz of frequency); elastic (G') and viscous (G") moduli were measured by frequency sweep (0.1 to 150 Hz at 0.05 of strain); and the apparent viscosity (η_a) was obtained from the flow curves generated from the stress ramp. The effect of plate roughness and the sweep time on τ_y was also assessed. Yield stress was found to increase with plate roughness whereas it decreased with the sweep time. The values of yield stress and moduli—G' and G"—increased during foam destabilization as a consequence of the changes in foam properties, especially the gas volume fraction, φ, and bubble size, R_32 (Sauter mean bubble radius). Thus, a relationship between τ_y, φ, R_32, and σ (surface tension) was established. The changes in the apparent viscosity, η, showed that the foams behaved like a shear thinning fluid beyond the yield point, fitting the modified Cross model with the relaxation time parameter (λ) also depending on the gas volume fraction. Overall, it was concluded that the viscoelastic behavior of the foam below the yield point and liquid-like behavior thereafter both vary during destabilization due to changes in the foam characteristics.

Development of biomimetic squid-inspired suckers

Biomechanical properties of squid suckers were studied to provide inspiration for the development of sucker artefacts for a robotic octopus. Mechanical support of the rings found inside squid suckers was studied by bending tests. Tensile tests were carried out to study the maximum possible sucking force produced by squid suckers based on the strength of sucker stalks, normalized by the sucking areas. The squid suckers were also directly tested to obtain sucking forces by a special testing arrangement. Inspired by the squid suckers, three types of sucker artefacts were developed for the arm skin of an octopus inspired robot. The first sucker artefact made of knitted nylon sheet reinforced silicone rubber has the same shape as the squid suckers. Like real squid suckers, this type of artefact also has a stalk that is connected to the arm skin and a ring to give radial support.The second design is a straight cylindrical structure with uniform wall thickness made of silicone rubber. One end of the cylinder is directly connected to the arm skin and the other end is open. The final design of the sucker has a cylindrical base and a concave meniscus top. The meniscus was formed naturally using the surface tension of silicone gel, which leads to a higher level of the liquid around the edge of a container. The wall thickness decreases towards the tip of the sucker opening. Sucking forces of all three types of sucker artefacts were measured. Advantages and isadvantages of each sucker type were discussed. The final design of suckers has been implemented to the arm skin prototypes.

Liquid-vapour homogenisation of fluid inclusions in stalagmites: Evaluation of a new thermometer for paleoclimate research

We present a new approach to determine palaeotemperatures (mean annual surface temperatures) based on measurements of the liquid–vapour homogenisation temperature of fluid inclusions in stalagmites. The aim of this study is to explore the potential and the limitations of this new palaeothermometer and to develop a reliable methodology for routine applications in palaeoclimate research. Therefore, we have investigated recent fluid inclusions from the top part of actively growing stalagmites that have formed at temperatures close to the present-day cave air temperature. A precondition for measuring homogenisation temperatures of originally monophase inclusions is the nucleation of a vapour bubble by means of single ultra-short laser pulses. Based on the observed homogenisation temperatures (Th(obs)) and measurements of the vapour bubble diameter at a known temperature, we calculated stalagmite formation temperatures (Tf) by applying a thermodynamic model that takes into account the effect of surface tension on liquid–vapour homogenisation. Results from recent stalagmite samples demonstrate that calculated stalagmite formation temperatures match the present-day cave air temperature within ± 0.2 °C. To avoid artificially induced changes of the fluid density we defined specific demands on the selection, handling and preparation of the stalagmite samples. Application of the method is restricted to stalagmites that formed at cave temperatures greater than ~ 9–11 °C.