Intrusion and extrusion of water in hydrophobic mesopores

We present experimental and theoretical results on intrusion-extrusion cycles of water in hydrophobic mesoporous materials, characterized by independent cylindrical pores. The intrusion, which takes place above the bulk saturation pressure, can be well described using a macroscopic capillary model. Once the material is saturated with water, extrusion takes place upon reduction of the externally applied pressure; Our results for the extrusion pressure can only be understood by assuming that the limiting extrusion mechanism is the nucleation of a vapour bubble inside the pores. A comparison of calculated and experimental nucleation pressures shows that a proper inclusion of line tension effects is necessary to account for the observed values of nucleation barriers. Negative line tensions of order $10^{-11} \mathrm{J.m}^{-1}$ are found for our system, in reasonable agreement with other experimental estimates of this quantity

Influence of fillers on mechanical properties of ATH filled EPDM during ageing by gamma irradiation

International audienceThe presence of a significant content of fillers accelerates the degradation of ATH filled EPDM subjected to gamma irradiation at room temperature. Above the melting temperature of the EPDM, this induces a decrease in the apparent mechanical reinforcement of the fillers. This also promotes de-cohesion mechanisms which leads to an increase in the strain at break with irradiation dose. It is not clear whether the use of a filler treatment attenuates this accelerating effect or not; however, part of this treatment remains efficient at a high dose and seems also to delay but not suppress the occurrence of de-cohesion mechanisms at large strain. Moreover, at room temperature, i.e. below the melting temperature, all the consequences of ageing by gamma irradiation are strongly attenuated by the presence of a semicrystalline microstructure, the morphology of which is not too strongly modified by irradiation. (C) 2010 Elsevier Ltd. All rights reserved

Role of Temperature During Ageing Under Gamma Irradiation of Filled EPDM: Consequences on Mechanical Properties

International audienceFilled EPDM materials have been processed and aged by gamma radiation at ambient temperature and at 80 degrees C to study the influence of the fillers presence in the material degradation. The acceleration of the polymer degradation by the ATH fillers, evidenced when irradiation is performed at 25 degrees C, is also effective at 80 degrees C. In addition, in the case of silica-filled EPDM, the creation of strong filler-matrix bonds, already reported for irradiation at 25 degrees C, is also thermally activated; this enables to this material to keep its integrity at high irradiation dose, whereas the irradiated ATH-filled EPDM is so degraded that it flows. Thus, the introduction of fillers in the polymer has an impact on its resistance to irradiation, whatever the temperature at which the irradiation is performed. Moreover, the consequences of the degradation on the evolution of the mechanical properties of the composite are very dependent on the filler nature

Mechanism of sintering of polyoxymethylene powders investigated by small-ngle X-ray scattering

International audienceThe structural reorganization of polyoxymethylene powders during sintering has been investigated through a detailed analysis of the SAXS data in order to determine the origin of the mechanical property improvement with regard to the compression-moulded counterpart. Two approaches afford a quantitative evaluation of the structural parameter evolutions. On one hand, the correlation and interface distribution functions were calculated for the samples submitted to various thermo-mechanical treatments. On the other hand, the Hosemann's paracrystalline model modified with Reinhold distributions of the crystal and amorphous phase thicknesses was used to evaluate the disorder in the lamella stacking. Both approaches suggest that a more perfect and regular crystalline structure with thicker and wider crystals develops in the sintered samples as compared with the parent powders and the material crystallized from the melt. Theses morphological modifications are discussed in relation to the very high stiffness and brittleness of the sintered materials. Two possible mechanisms of coalescence of the powder grains via the crystalline phase are proposed to account for these specific mechanical properties of the sintered materials

Statistical properties of microcracking in polyurethane foams under tensile and creep tests: influence of temperature and density.

International audienceno abstrac

Assessing crystalline lamellae orientation impact on the properties of semi-crystalline polymer-clay nanocomposites

International audienceSemi-crystalline polymer-clay nanocomposite properties are often considered only by their clay dispersion state. The purpose of this work is to highlight texture effects on semi crystalline polymer-clay properties. Maleic anhydride-grafted polyethylene nanocomposites with two different processing techniques (Blown Extrusion and Compression) were studied. The processing was shown to induce different crystalline lamellae orientation in the films but with no significant changes in the crystalline lamellae long period, degree of crystallinity, clay particle orientation morphology and dispersion. The impact of these specific textures on the nanocomposites barrier and tensile properties were reported

Etude de la stabilite microstructurale des alliages Al-Fe trempes depuis l'etat liquide. Influence du Ni, du Mo et du Zr

SIGLECNRS AR 12383 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc