This research project investigated the physical aging of glassy polymers in confined environments. Many recent studies of aging in glassy polymers have observed that aging behavior is often strongly affected by confinement. Understanding aging in confined environments (e.g., thin polymer films and nanocomposites) is vital for predicting long-term performance in applications that use confined glassy polymers, such as gas separation membranes and advanced nanocomposite materials. Aging in bulk and layered films produced via layer-multiplying co-extrusion was studied using gas permeability measurement and differential scanning calorimetry (DSC). The layered films consisted of polysulfone (PSF) and a rubbery co-layering material, with PSF layers ranging in thickness from ~185 nm to ~400 nm. Gas permeation aging studies at 35 °C revealed that the PSF layers in layered films aged in a manner that was similar to bulk PSF and independent of layer thickness. This finding differs from what was observed previously in freestanding PSF films, in which aging depended strongly on thickness and was accelerated relative to bulk. Isothermal aging studies at 170 °C and cooling rate studies were performed on both bulk and layered samples using DSC. The aging of the PSF layers was similar to aging in bulk PSF for films having PSF layer thicknesses of ~640 nm and ~260 nm, while the film with 185 nm PSF layers showed a slightly higher aging rate than that of bulk PSF. The results of the DSC studies generally support the conclusions of our gas permeation aging studies. The absence of strong thickness dependence in aging studies of layered films tends to support the idea that the effect of film thickness on physical aging stems from interfacial characteristics and not merely thickness per se. The physical aging of thin polystyrene (PS) films at 35 °C was also investigated using gas permeation techniques. PS films of 400 nm and 800 nm did not exhibit aging behavior that was highly accelerated relative to bulk or strongly dependent on film thickness. At the thicknesses and aging temperature considered, the aging of PS shows much weaker thickness dependence than that seen in polymers like PSF and Matrimid. / text

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Dans le domaine des couches minces (épaisseur~Å) associant un métal magnétique (Fe, Co, Ni) et un élément non magnétique (essentiellement métallique ou isolant), de remarquables propriétés physiques (aimantation, transport) nécessitent des caractérisations structurales fines. En particulier, citons le cas de jonctions tunnel (métal/isolant/métal) à aimantation perpendiculaire qui sont en cours d'étude au laboratoire Spintec (UMR8191 (CEA/CNRS/UJF). Ces nanomatériaux sont déposés par voie physique (pulvérisation cathodique) au sein de ce laboratoire. Ces nanostructures sont également sondées par diffraction aux rayons X au sein de l'Institut Néel (UPR 2940) via une collaboration entre Spintec et une équipe de cet Institut (Surface, interfaces et nanostructures du Département MCMF, Matière Condensée, Matériaux, et Fonctions). Ces mesures de réflectivité X constituent la sonde privilégiée de choix dans la cadre de cette thèse. D'autres voies sont également exploitées: à l'aide des moyens de rayonnement synchrotron tels que la spectroscopie d'absorption de rayons X : EXAFS, XANES et XMCD. La thèse aura pour but d'étudier expérimentalement ces phénomènes en couches continues sur ces empilements à jonction tunnel avec aimantation perpendiculaire. Plus précisément, le travail de thèse permettra de comprendre les mesures magnétiques (effectuées à l'institut Néel notamment par magnétométrie SQUID et HALL à basse température) grâce à une batterie de mesures structurales (diffraction aux rayons X, rasant, figures de pôles, réflectivité, absorption X …). Notamment, l'influence des paramètres de dépôt (types de couches, épaisseurs, recuits) du matériau sont étudiées via la collaboration entre les différents groupes de recherche précédemment cités. Cette thématique s'inscrit d'une part dans le cadre de travaux menés à Spintec et dédiés à la recherche de nouveaux matériaux à forte valeur ajoutée industrielle (sur le stockage d'information à ultrahaute densité sur media discrets par exemple). Elle s'inscrit d'autre part dans le renforcement de liens entre recherches fondamentales (laboratoire propre du CNRS comme l'institut Néel) et appliquées (CEA), avec un recours aux solides compétences en caractérisations structurales et magnétiques de l'Institut Néel. / In the domain of thin film (thickness ~ Å) combining a magnetic metal (Fe, Co, Ni) and a non-magnetic (largely metal or insulator), remarkable physical properties (magnetization, transport) require fine structural characterization. In particular, include the case of tunnel junctions (metal / insulator / metal) with perpendicular magnetization which are being studied in the laboratory Spintec (UMR8191 (CEA / CNRS / UJF). These nanomaterials are deposited by physical (sputtering) in this laboratory. These nanostructures are probed by X-ray diffraction in the Neel Institute (UPR 2940) via collaboration between Spintec and a team of the Institute (Surface, Interfaces and Nanostructures Department MCFP, Condensed Matter Materials and Functions). These reflectivity measurements X are the preferred sensor of choice in the context of this thesis. Other routes are also used: using means such as synchrotron radiation absorption spectroscopy X-ray: EXAFS, XANES and XMCD. The thesis will aim to study these phenomena experimentally in continuous layers on the tunnel junction stacks with perpendicular magnetization. Specifically, the thesis will include the magnetic measurements (performed at the Institut Néel SQUID magnetometry including HALL and low temperature) through a battery of structural. This theme is part of a share in the context of work carried Spintec and dedicated to research of new materials with high added value industries (information storage on ultra-high density of discrete media for example). It registers on the other hand in strengthening links between basic research (CNRS own laboratories as Neel Institute) and applied (ECA), with strong skills in use of structural and magnetic characterization of the Institute Neel.