Étude ultrasonore de mélanges de polymères

Ultrasonic experiments have been performed on polyethylene/polystyrene blends of various compositions. Attenuation and velocity measurements were performed on samples made either by injection moulding or by compression. Attenuation varies through the same sample and variations are greater for compressed plates than for moulded plates. Velocities are of the same order of magnitude for both types of samples.     

Étude du mécanisme de polymérisation de l'acide silicique par potentiométre

Ionization and solubility of silicic acid with variation of pH and concentration of silicic acid are studied by potentiometric measurements. Two characteristic points appear on titration plots: the first point occurs at pH = 3 with formation of the ionized silicic acid; the second at pH = 7 is interpreted as revealing monomeric species. Diverse species of ionized silicic acid are in sols between pH = 3 and 7; the sols contain the smallest species of polymer for pH < 6 and show an optimum of polymerization for pH ≥ 6.     

Contribution à l'étude du mécanisme de mûrissement de résines polyesters insaturées en présence de MgO

The thickening process for unsaturated polyester resin in styrene monomer and with magnesium oxide (MgO) has been evaluated by gel permeation chromatography (GPC). The GPC analysis n tetrahydrofuran (THF) shows that with time the distribution shifts towards higher molecular weight. This effect disappears when the products are analysed in a polar solvent. The process of thickening is attributed to the formation of reversible ionic association. The existence of strong ionic bonds in the final products is confirmed by the presence of a rubber-like plateau in dynamic mechanical properties. The effects of water and magnesium oxide concentrations are given.     

Étude thermodynamique du système compatible polyfluorure de vinylidène-polyméthacrylate d'éthyle par chromatographie gaz-liquide

The thermodynamics of interaction between poly(ethyl methacrylate) and poly(vinylidene fluoride) have been studied by gas-liquid chromatography on their homogeneous blends (40 < PVDF < 80% by weight) in the liquid state (t > 140°C) using a variety of probes covering a wide range of polarity and of affinity for the polymers. The average and most representative interaction parameter χ₂₃′ (Flory-Huggins) is estimated as −0.32 ± 0.09, showing only slight sensitivity to temperature between 160 and 200°C and composition of the blend. The purely interactional χ₂₃ parameter (Prigogine-Flory-Patterson) is strongly negative (χ₂₃ = −6.5 J/cm³) as a result of dipolar and hydrogen bond interactions between the polymers.     

Contribution à l'étude des méthodes de dosages électrotitrimétriques

The author establishes a general equation for the polarisation curve of an oxidation-reduction system taking into account the kinetics of reactions and concentration polarisation, and shows how it can be applied to the interpretation of titration curves obtained by the dead-stop end-point method of Foulk and Bawden and by the derivative method of Reilley, Cooke and Furman.     

Étude comparée de quelques méthodes de dosage de l'acide salicylique dans le sérum sanguin

If one deproteinises blood serum by sodium tungstate and sulphuric acid, the excess tungstate impedes the formation of the colourless complex of salicylic acid with the iron. The intervening reactions are not yet well understood. One can use this method if a sufficient concentration of iron is present to eliminate all the tungstate; but the method then becomes slow and delicate. It is shown finally that the most satisfactory method consists of extracting the salicylic acid by dichlorethylene and then bringing it again into aqueous solution by means of a ferric solution.     

Modélisation du comportement mécanique d'un alliage base nickel par une approche thermodynamique de la relaxation des milieux continus

The high-temperature behaviour of a Nickel alloy submitted to uniaxial tension, relaxation and creep, is analysed using a thermodynamics approach to non-linear relaxations. The model is essentially based on a distribution of the dissipation processes obtained by the theory of fluctuations. The agreement between experiment and simulations requires the use of four parameters. These parameters depend on the elastic properties of the alloy and also on the thermal activation necessary for mobility defects. We present a comparison with the classical model of Chaboche including a recovery term in the potential of dissipation.     

Application de la méthode de Melnikov pour l'étude du roulis non linéaire des navires dans la houle

For studying ship rolling within a global analysis more and more mathematical tools from chaos theory are available. For this purpose, however, drastic simplifications must be applied: (i) rolling is the single degree of freedom, (ii) motion is represented by an ordinary differential equation, and (iii) the study is achieved in the vicinity of vanishing stability. Here the Melnikov method is used in this application. The focus is on ships whose restoring moment is represented with an odd polynomial. Above the fifth degree, a harmonically excited system exhibits frequencies which cancel the fluctuating part of the Melnikov function. Hence the heteroclinic orbits still exist whatever the ‘smallness’ of the perturbation as soon as the system is undamped. The existence of such cancellation is otherwise confirmed from an analysis of the erosion of the attraction basin.     

Approche thermodynamique des phénomènes liés à l'usure de contact

This paper proposes a theoretical framework for the study of contact-wear. Wear phenomena due to contact and relative motion between two solids are characterized by a loss of material. The detached particles as well as damaged contact areas of the solids form an interface with complex mechanical properties. Using an analysis of the dissipation in this interface, an energy release rate and then a wear criterion are defined. This dissipation associated with loss of material will be called wear dissipation. An application to steady-state wear processes is then given.     

Spectres d'absorption détectés par effet photoacoustique en infrarouge par transformée de Fourier—applications à quelques médicaments

Photoacoustic detection in Fourier transform i.r. spectrometry has led to spectra obtained without sample preparation. This fact may be a very important advantage in biological applications, but these spectra are not directly in good agreement with transmission spectra. In the present work a simple mathematical correction treatment is presented which is in accord with the theory of the photoacoustic effect. This correction routine is applied to some drugs in view of a possible application to direct identification in pharmaceutical preparations.     

Le spectre d'absorption infrarouge de l'acétate de méthyle perdeutéré

Résumé Les spectres d'absorption infrarouge de l'acétate de méthyle et de l'acétate de méthyle perdeutéré ont été étudiés de 300 à 4000 cm^–1. La comparaison des spectres a permis l'attribution certaine des bandes de l'acétate de méthyle, en particulier de la bande observée vers 1245 cm^–1 qui correspond à une vibration concernant la liaison C-O.

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Summary The infrared absorption spectra of methyl acetate and the perdeuterated methyl acetate have been studied from 300 to 4000 cm^–1. The comparison of the spectra has made it possible to attribute certain of the bands of methyl acetate, in particular the band observed around 1245 cm^–1, which corresponds to a vibration involving the C-O bond.

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Zusammenfassung Die Absorptionsspektren von Methylacetat der Zusammensetzung CH₃COOCH₃ und CD₃COOCD₃ im Infrarot wurden zwischen 300 und 4000 cm^–1 untersucht. Der Vergleich dieser Spektren führte zur sicheren Zuordnung der Banden des Methylacetats, insbesondere der bei 1245 cm^–1 gelegenen Bande, die der C-O-Bindung zugehört.

     

Étude des propriétés viscoélastiques de quelques polyfluorure de vinylidène fondus

The rheological behaviour of molten poly(vinylidene fluoride) was studied in steady flow and dynamic flow. An attempt was made to correlate the experimental results with extrudability.     

Étude des propriétés mécaniques des géomateriaux argileux associant la décoction de Parkia Biglobosa (néré)

Researches for non-energy intensive construction products, that are durable and cheaper is today of global concern because of the limited resources (energy, financial, etc.). To address this issue, the present work presents the combination of the decoction of pods of Parkia Biglobosa (néré) that is rich in tannins compounds including gallic acid, epicatechin gallate and epigallocatechin, with a clay-sand mixture. The clay used is referenced KORO and contains montmorillonite, illite, quartz, albite, orthoclase, kaolinite and goethite. The study of the mechanical properties of geomaterials formulated from the mixture shows that they have values of mechanical resistance higher and that their behavior becomes viscoplastic. This is due to the formation of chemical complexes from carboxylic groups of tannins macromolecules with the iron oxy-hydroxide in the interlayer spacing of clay minerals. This process is enhanced by the sorption of tannins on the surface of clay minerals.     

Application de la fluorimétrie de phase à l'étude des interactions soluté-solvant de quatre amino-9 acridines substituées

The apparent lifetimes of 9-aminoacridine, of atebrin and of two of its derivatives (9-amino-2-methoxy-6-chloroacridine and 9-n-butylamino-2-methoxy-6-chloroacridine) have been measured by phase modulation fluorometry in a glycerol-water mixture (high viscosity) and an ethanol-water mixture (low viscosity). Results are easily interpreted in terms of a relaxation of the first singlet excited state involving a rearrangement of solvent molecules before excitation.In the glycerol-water mixture, the stationary fluorescence spectra of atebrin and its two derivatives can be resolved into fluorescence spectra emitted by the relaxed state and fluorescence spectra emitted by the unrelaxed state. For each compound the lifetimes of these two states have been calculated.In the same solvent mixture the origin of 9-aminoacridine fluorescence is the relaxed state alone. However, the relaxation process is slow enough to be detected by phase modulation fluorometry. The lifetimes of the relaxed and unrelaxed states are still accessible.In the ethanol-water mixture this is no longer true. For each compound under study the origin of the fluorescence is still the relaxed state but the relaxation process is so rapid, compared with the deactivation processes, that it can no longer be detected by phase modulation techniques. In this case, only the lifetime characteristic of the relaxed state is accessible.     

Polymérisation et post-polymérisation de l'acrylate de méthyle en milieu précipitant

The radiation initiated polymerization of methyl acrylate was investigated under precipitating conditions in n-hexane In 10 and 25% monomer solutions, the conversion curves are auto-accelerated and post-polymerization is observed in the dark. The initial rate of this post-polymerization steadily increases with the degree of conversion reached during irradiation, suggesting that trapped growing chains are responsible for the effect. The post-polymerization was followed at 23, 40 and 60°. From the results, it is concluded that chain termination is negligible under such conditions. The addition of methanol to the monomer solutions results in decreased rates and in a reduction of the extent of auto-acceleration. No influence of any “matrix effect” could be detected in these systems.