Effect of the acrylic acid content on the permeability and water uptake of latex films

Acrylic acid (AA) is a monomer commonly employed in emulsion polymerization to provide electrostatic colloidal stability and improve specific film performance. The addition of AA not only modifies the kinetics of the polymerization, but also it takes part in the interaction between colloidal particles, which has a strong influence on their packing and consequent latex film properties. In this contribution a theoretical modeling of the latex film formation is presented and compared to experimental results: water vapor permeability and latex film capacitance are studied as a function of AA content. It has been shown that water uptake is mainly affected by film morphology which in turn is defined by intercolloidal interaction and drying rate.Comment: 16 pages, 7 figure

Thermo-oxidative degradation of additive free polyethylene. Part I. Analysis of chemical modifications at molecular and macromolecular scales

The effects of thermal oxidation on the molecular and macromolecular structures of additive free PE were investigated between 100°C and 140°C in air in order to tentatively establish non-empirical structure/property relationships. In the first part, the changes in POOH concentration were assessed by three different analytical methods: iodometry, modulated differential scanning calorimetry, and Fourier transform infrared (FTIR) spectrophotometry after SO2 treatment. All these methods provided very similar results until the end of the induction period, after which iodometry overestimated strongly POOH concentration because it titrates also other chemical species formed at high conversion ratios, namely double bonds. In parallel, the changes in carbonyl group concentration were determined by FTIR spectrophotometry after NH3 treatment. As the accumulation kinetics of ketones, aldehydes, and carboxylic acids were closely interrelated, the question of their actual formation mechanisms in the current thermal oxidation mechanistic scheme was raised. An alternative reaction pathway was proposed for the bimolecular decomposition of POOH. In the second part, the corresponding changes in weight and number average molecular masses were monitored by high temperature gel permeation chromatography equipped with a triple detection technology. As both quantities decreased dramatically from the beginning of exposure and their ratio Mw/Mn tends toward the asymptotic value of 2 and it was concluded that a "pure" chain scission process operated. Finally, as the number of chain scissions perfectly correlates, the concentration sum of aldehydes and their oxidation products (i.e., carboxylic acids), it was also concluded that these carbonyl groups result exclusively from the β scission of alkoxy radicals

Caractérisation et application de matériaux composites nanostructurés à la réalisation de dispositifs hyperfréquences non réciproques

Anisotropic properties of magnetized ferrites are commonly at the basis of nonreciprocity in microwave devices, e.g., circulators and isolators. However, ferrites are not the best suited materials for such applications, due to their moderate saturation magnetization and high-sintering temperature needed during their manufacturing process. Consequently, research laboratories tend to propose substitute materials. To achieve an optimized performances-nonreciprocal device based on such a magnetized material, the exact knowledge of its tensorial permeability is required over a broad-frequency range. The originality of this work is twofold. At first, a measurement technique enabling the noniterative and broad-band (up to 6-7 GHz) determination of the permeability tensor components (µ, k) of magnetized or demagnetized magnetic materials has been developed. The measurement cell used is composed of a nonreciprocal strip transmission line. The major advantage of this new technique is to permit to study the material behavior in the same environment as microwave devices (« in-situ » characterization method). Then, the measurement capability has been employed to demonstrate the field-induced anisotropy of nanocomposite samples. Based on a comparison with a standard ferrite, this original magnetic anisotropy of magnetized nanophases has been exploited to investigate the design of an optimum an low-cost resonance microwave isolator.Aux fréquences micro-ondes, les ferrites sont caractérisés par une perméabilité tensorielle, représentative de leur anisotropie induite sous champ magnétique. Cette propriété spécifique est à l'origine du comportement non réciproque de dispositifs comme les circulateurs et les isolateurs. Les limitations des milieux ferrites (aimantation à saturation réduite, fortes températures de frittage lors de leur élaboration) conduisent cependant les laboratoires à étudier des matériaux s'y substituant. Pour pouvoir réaliser des fonctions hyperfréquences non réciproques optimisées à partir de tels matériaux, la mesure préalable de leur tenseur de perméabilité est requise sur une large bande de fréquences. L'originalité du travail présenté dans ce mémoire est double : - dans un premier temps, une technique de mesure non itérative des éléments (µ, k) du tenseur de perméabilité des milieux magnétiques, dans un état quelconque d'aimantation, a été développée. Elle est utilisable du continu jusqu'environ 6 à 7 GHz, selon le type de matériau testé. Outre la détermination analytique de (µ, k) en fonction des paramètres S de la cellule de mesure en ligne de transmission élaborée, son principal intérêt est de permettre d'étudier le matériau dans des conditions voisines de celles fixées par l'application en technologie planaire ultérieure (mesure « in-situ »), - à partir de cette technique de caractérisation expérimentale, les propriétés d'anisotropie induite de matériaux composites nanostructurés aimantés ont ensuite été démontrées puis ajustées pour mettre en œuvre un isolateur hyperfréquence à résonance. Les performances de ce dernier sont au moins comparables à celles des isolateurs à ferrites, pour une quantité de matière magnétique moindre