Thermophysical study of crosslinked polymers based on Isobornyl Acrylate : Experimental approach and modeling

Les technologies en perpétuelle évolution exigent des matériaux nouveaux, performants et plus spécialisés avec des fonctions hautement spécialisées. De tels matériaux ne sont plus des systèmes a un seul composant. Les systèmes qui font l’objet de l’investigation, les copolymères chimiquement réticulés de type "isobornyl acrylate-co-isobutyl acrylate" (IBOA-co-IsoBA), ont été préparés par photopolymérisation/réticulation sous rayonnement UV-visible des deux monomères IBOA et IsoBA en présence d'un agent de réticulation di-fonctionnel et d'un photoamorceur. Dans ce travail les propriétés thermiques et mécaniques ont été étudiées par calorimétrie différentielle à balayage (DSC), analyse mécanique dynamique (DMA) et analyse thermogravimétrique (ATG). Nous avons constaté par l’analyse calorimétrique (DSC) que la modification de la concentration d’agent réticulant, la quantité des monomères, et la vitesse de la rampe de chauffage influent notamment sur la température de transition vitreuse Tg : Une augmentation de ces paramètres provoque une augmentation de la température de transition vitreuse du copolymère. L’analyse thermogravimétrique par ATG montre que la dégradation du copolymère se fait en deux étapes, et que l’augmentation de la quantité de l’IsoBA diminue la température de dégradation du copolymère. L’étude des copolymères de type (IBA-co-IsoBA) par DMA a été entreprise en fonction de la fréquence et de la température, afin d’évaluer les modules d’élasticité (E’) et de perte (E’’). Une courbe maitresse (master curve) a été obtenue à l’aide du principe de superposition temps-température. Des modélisations des relaxations mécaniques ont été effectuées en appliquant les modèles d’Arrhenius, Cole-Cole, WLF et de VFT (Vogel Fulcher Tamman).Ever-changing technologies require new, high-performance and more specialized materials with highly specialized functions. Such materials are no longer one-component systems. The systems which are the subject of the investigation, the chemically crosslinked copolymers of the "isobornyl acrylate-co-isobutyl acrylate" type (IBOA-co-IsoBA), were prepared by photopolymerization / crosslinking under UV-visible radiation of the two monomers. IBOA and IsoBA in the presence of a di-functional crosslinking agent and a photoinitiator. In this work the thermal and mechanical properties were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).We have found by calorimetric analysis (DSC) that the modification of the concentration of crosslinking agent, the amount of monomers, and the speed of the heating ramp affect, in particular, the glass transition temperature Tg: an increase of these parameters causes an increase in the glass transition temperature of the copolymer. Thermogravimetric analysis by (TGA) shows that the degradation of the copolymer occurs in two stages, and that the increase of the amount of IsoBA decreases the degradation temperature of the copolymer. The study of copolymers of type (IBA-co-IsoBA) by DMA was undertaken according to the frequency and the temperature, in order to evaluate the modulus of elasticity (E') and of loss (E''). A master curve has been obtained using the time-temperature superposition principle. Modeling of the mechanical relaxations was carried out by applying the models of Arrhenius, Cole-Cole, WLF and VFT (Vogel Fulcher Tamman)

Heat management and losses of electrocaloric cooling devices based on electrostatic thermal switches

International audienceElectrocaloric cooling is a promising technology that could replace existing vapor-compression technology with lighter and more efficient solid state based devices. Among those, electrocaloric coolers using electrostatic actuation are rising; therefore harnessing their advantages and understanding their shortcomings is still a work in progress.In this paper, we pin down two limitations that stem from a commonly used device design, and we propose a model that takes them into account. The first is due to the displacement of the film, which moves the air around and causes losses. We estimate the air losses through a Poiseuille flow model. The second is related to the non-ideal Brayton cycle the device performs and which results in generating a heat flow opposite to cooling. We estimated the effect of this back-flow on the cold flux using a 2D thermal diffusion model. Ultimately, our results point at several possible improvements for further designs. Among them, a slight reduction of the air pressure in the device looks as a promising solution to reduce air losses

ELECTROCOOLING DEVICE BASED ON MULTILAYERS PVDF BASED POLYMER

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Relationship between process and electrocaloric effect in relaxor ferroelectric materials

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Relationship between process and electrocaloric effect in relaxor ferroelectric materials

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ELECTROCOOLING DEVICE BASED ON MULTILAYERS PVDF BASED POLYMER

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Temperature measurement for the characterization of the electrocaloric effect in PVDF-based polymer

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