Dynamics of bubbles spontaneously entering in a tube

When an open tube of small diameter touches a bubble of a larger diameter, the bubble spontaneously shrinks and pushes a soap film in the tube. We characterize the dynamics for different bubble sizes and number of soap films in the tube. We rationalize this observation from a mechanical force balance involving the Laplace pressure of the bubble and the viscous force from the advancing soap lamellae in the tube. We propose a numerical resolution of this model, and an analytical solution in an asymptotic regime. These predictions are then compared to the experiments. The emptying duration is primarily affected by the initial bubble to tube diameter ratio and by the number of soap films in the tube

Carbon Tetrachloride as Thermoporometry Liquid-probe to Study the Cross linking of Styrene Copolymer Networks

Mesh Size Distributions (MSDs) of swollen cross linked styrene copolymer networks have been measured by thermoporometry using CCl4 as a probe liquid. All numerical relationships required for the calculation of the MSD were established for both the liquid-to-solid and the solid-to-solid thermal transitions of CCl4 and successfully validated on test samples. It was found that the polymer network, for both thermally and photo-cross linked materials, was completely built in about four hours of exposure. A clear correlation was established between the average mesh size of the swollen polymer network on the one hand and the benzoyl peroxide groups content and swelling ratio on the other hand

Melt viscoelastic assessment of Poly(Lactic Acid) composting: Influence of UV Ageing

This study is devoted to the degradation pathway (bio, photo degradation and photo/bio) of Poly(Lactic acid) PLA polymers by means of melt viscoelasticity. A comparison was made between three PLA polymers with different microstructures (L, D stereoisomers). Biodegradability was determined during composting by burying the polymer films in compost at 58 _C. Melt viscoelasticity was used to assess the molecular evolution of the materials during the composting process. Viscoelastic data were plotted in the complex plane. We used this methodology to check the kinetics of the molecular weight decrease during the initial stages of the degradation, through the evolution of Newtonian viscosity. After a few days in compost, the Newtonian viscosity decreased sharply, meaning that macromolecular chain scissions began at the beginning of the experiments. However, a double molar mass distribution was also observed on Cole-Cole plots, indicating that there is also a chain recombination mechanism competing with the chain scission mechanism. PLA hydrolysis was observed by infra-red spectroscopy, where acid characteristic peaks appeared and became more intense during experiments, confirming hydrolytic activity during the first step of biodegradation. During UV ageing, polymer materials undergo a deep molecular evolution. After photo-degradation, lower viscosities were measured during biodegradation, but no significant differences in composting were found. © 2018 by the authors

Influence of Ionic Liquids on the Morphology of Corn Flour/Polyester Mixtures

Polymer mixtures based on native corn flour and synthetic biodegradable polyester are prepared in one processing step. Melt mixing is performed in a laboratory micro-compounder. Starch contained in native corn flour is plasticized either by commonly used glycerol/water mixture or by two types of ionic liquids, 1-allyl-3-methylimidazolium chloride, and 1-butyl-3-methylimidazolium chloride. Efficiency of plasticizers on the compatibility of native corn flour with polyester and starch plasticizing ability is evaluated and compared. The structure of mixtures is examined using scanning electron microscopy and wide-angle X-ray scattering. It is found that the plasticizer applied has a crucial effect on the resulting morphology. Both ionic liquids show a better plasticizing effect on starch compared to the traditional glycerol/water plasticizer. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimMinistry of Education, Youth and Sports of the Czech Republic-Program NPU I [LO1504

[Analyse de la dégradation thermique du Poly(éther imide)]

The thermal degradation of PEI has been studied in wide ranges of temperature (between 180 and 250 °C) and oxygen partial pressure (between 0.21 and 50 bars). First of all, the thermal ageing mechanisms have been analysed and elucidated by FTIR spectroscopy and by differential scanning calorimetry (DSC) on sufficiently thin PEI films (between 10 and 60 μm thickness) to be totally free of the effects of oxygen diffusion. As expected, and by analogy with other aromatic polymers of similar chemical structure, oxidation occurs preferentially on the methyl groups of the isopropylidene unit of the bisphenol A part, leading to the disappearance of their characteristic IR absorption band at 2970 cm -1 and the growth of a new IR absorption band centered at 3350 cm -1 and attributed to alcohol groups. In addition, oxidation leads successively to a relative predominance of chain scissions (decrease in T g ) and crosslinking (increase in T g ). Finally, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on preliminarily polished cross-sections of PEI plates of 3 mm thickness. However, the increase in Young's modulus in the superficial oxidized layer is mainly due to a physical ageing

Le rôle du solvant en cinétique. Hydrochloration du Cyclohexène.

Thèse de doctorat -- Université catholique de Louvain, 196

Dynamique de frottement d'une mousse liquide : superglissement, glissement et accrochage

Our goal is to gain a better understanding of the behaviour of a liquid foam flowing over a surface covered with a network of controlled submillimetre pillars. Firstly, using visualisations, we characterise the footprint of the layer of bubbles in static contact with the surface. This can be deformed or not according to a universal criterion, comparing the size of the network and the radius of curvature of the Plateau borders. In addition, the average number of sides increases as the bubble is shaped. In this case, the length of the sides is a multiple of twice the lattice parameter. We then consider the dynamics of the system by moving the textured surface at an imposed speed. Measurement of the stress at the interface, coupled with visualisations, enables us to characterise the friction. We demonstrate the existence of a super-slip regime, characterised by a reduction in stress relative to smooth surfaces of around 30 % if the height of the pillars is greater than a minimum of thirty microns. The mechanism is based on the presence of liquid between the textures, which modifies the friction conditions. Furthermore, we show that the stresses in the stick-slip regime are no longer described by a dimensionless number similar to previous studies. Above a threshold consistent with the literature, the anchored regime is reached. We measure a yield stress of the foam that is constant with speed, where foam deposition is always observed. More generally, if we see topological rearrangements, it is possible to have a deposit, although no universal criterion has been demonstrated. Finally, we carried out an experiment in which a foam was brought into contact with a capillary tube smaller than the size of a bubble, forcing confinement effects. A model for the spontaneous emptying of bubbles describes the dynamics of both a single bubble and a foam.Nous cherchons à mieux comprendre le comportement d'une mousse liquide mise en écoulement sur une surface couverte d'un réseau de plots submillimétriques contrôlés. Dans un premier temps, grâce à des visualisations, nous caractérisons l'empreinte de la couche de bulles en contact statique avec la paroi. Celle-ci peut être déformée ou non selon un critère universel, comparant la taille du réseau et le rayon de courbure des bords de Plateau. De plus, nous comptons une augmentation du nombre moyen de cotés avec le facetage de la bulle. Dans ce cas, la longueur des côtés est un multiple de deux fois le paramètre du réseau. Ensuite, nous considérons la dynamique du système en déplaçant la surface texturée à vitesse imposée. La mesure de la contrainte à l'interface, couplée à des visualisations, permet de caractériser le frottement. Nous mettons en avance l'existence d'un régime de superglissement qui est caractérisé par une réduction des contraintes par rapport aux surfaces lisses d'environ 30 % si la hauteur des plots est supérieur à un minimum de trente microns. Le mécanisme repose sur la présence de liquide entre les texturations modifiant les conditions de frottement. Par ailleurs, nous montrons que les contraintes dans le régime de collé-glissé ne sont plus décrites par un nombre sans dimension analogue aux études précédentes. Au-delà d'un seuil cohérent avec la littérature, le régime d'ancrage est atteint. Nous mesurons une contrainte seuil de la mousse constante avec la vitesse, où un dépôt de mousse est toujours observé. Plus généralement, si nous voyons des réarrangements topologiques, il est possible d'avoir un dépôt, bien qu'aucun critère universel n'ait été mis en évidence. Enfin, nous avons fait une expérience ou une mousse est mise en contacte avec un capillaire plus petit que la taille d'une bulle, forçant les effets de confinement. Un modèle de la vidange spontanée des bulles décrit la dynamique aussi bien d'une bulle seule que d'une mousse