Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

Fragility index and cooperativity length characterizing the molecular mobility in the amorphous phase are for the first time calculated in drawn polylactide (PLA). The microstructure of the samples is investigated from wide-angle X-ray scattering (WAXS) whereas the amorphous phase dynamics are revealed from broadband dielectric spectroscopy (BDS) and temperature-modulated differential scanning calorimetry (TMDSC). The drawing processes induce the decrease of both cooperativity and fragility with the orientation of the macromolecules. Post-drawing annealing reveals an unusual absence of correlation between the evolutions of cooperativity length and fragility. The cooperativity length remains the same compared to the drawn sample while a huge increase of the fragility index is recorded. By splitting the fragility index in a volume contribution and an energetic contribution, it is revealed that the amorphous phase in annealed samples exhibits a high energetic parameter, even exceeding the amorphous matrix value. It is assumed that the relaxation process is driven in such a way that the volume hindrance caused by the thermomechanical constraint is compensated by the acceleration of segmental motions linked to the increase of degrees of freedom. This result should also contribute to the understanding of the constraint slackening in the amorphous phase during annealing of drawn PLA, which causes among others the decrease of its barrier properties

Semiaromatic polyamides with enhanced charge carrier mobility

The control of local order in polymer semiconductors using non-covalent interactions may be used to engineer materials with interesting combinations of mechanical and optoelectronic properties. To investigate the possibility of preparing n-type polymer semiconductors in which hydrogen bonding plays an important role in structural order and stability, we have used solution-phase polycondensation to incorporate dicyanoperylene bisimide repeat units into an aliphatic polyamide chain backbone. The morphology and thermomechanical characteristics of the resulting polyamides, in which the aliphatic spacer length was varied systematically, were comparable with those of existing semiaromatic engineering polyamides. At the same time, the charge carrier mobility as determined by pulse-radiolysis time-resolved microwave conductivity measurements was found to be about 10-2 cm2 V-1 s-1, which is similar to that reported for low molecular weight perylene bisimides. Our results hence demonstrate that it is possible to use hydrogen bonding interactions as a means to introduce promising optoelectronic properties into high-performance engineering polymers.Peer ReviewedPostprint (author's final draft

Impact of Nanoconfinement on Polylactide Crystallization and Gas Barrier Properties

The barrier properties of poly(l-lactide) (PLLA) were investigated in multinanolayer systems, probing the effect of confinement, the compatibility between the confining and the confined polymer, crystal orientation, and amorphous phase properties. The multilayer coextrusion process was used to confine PLLA between two amorphous polymers (polystyrene, PS; and polycarbonate, PC), which have different chemical affinities with PLLA. Confined PLLA layers of approximately 20 nm thickness were obtained. The multinanolayer materials were annealed at different temperatures to obtain PLLA crystallites with distinct polymorphs. PLLA annealed in PC/PLLA films at 120 °C afforded a crystallinity degree up to 65%, and PLLA annealed in PC/PLLA or PS/PLLA films at 85 °C had a crystallinity degree of 45%. WAXS measurements evidenced that the PLLA lamellas between PS layers had a mixed in-plane and on-edge orientation. PLLA lamellas between PC layers were uniquely oriented in-plane. DMA results evidenced a shift of the PC glass transition toward lower temperature, suggesting the possible presence of an interphase. The development of the rigid amorphous fraction (RAF) in the amorphous phase during annealing was impacted by the confiner polymer. The RAF content of semicrystalline PLLA was about 15% in PC/PLLA, whereas it was neglectable in PS/PLLA. The oxygen barrier properties appeared to be governed by RAF content, and no impact of the PLLA polymorph or the crystalline orientation was observed. This study shows that the confinement of PLLA on itself does not impact barrier properties but that the proper choice of the confiner polymer can lead to decrease the phase coupling which creates the RAF. It is the prevention of RAF that decreases permeability

Thermo-mechanical behaviour and structure characterization at various scale levels of a bio-based polymer : the poly(lactic acid)

Ces travaux de thèse porte sur la caractérisation des propriétés thermomécaniques et sur l’étude à différents niveaux d’échelle de la structuration d’un polymère issu de la biomasse candidat au remplacement des polymères de commodité, à savoir, l’acide poly(lactique) (PLA). Ils ont été motivés par le comportement complexe, encore mal compris à l’heure actuelle, que présente ce polymère notamment en raison de l’existence de stéréoisomères.Le premier but de ce travail a été de caractériser les propriétés thermomécaniques, en fonction du taux de co-monomère, en relation avec les arrangements moléculaires locaux pouvant exister dans la phase amorphe. Le second objectif a été d’étudier la structuration d’un copolymère industriel lorsque celui-ci est déformé uniaxialement à une température supérieure à sa température de transition vitreuse. L’analyse par diffraction-diffusion X in situ sur synchrotron a permis d’établir le lien entre la réponse mécanique du matériau et l’évolution structurale induite par la déformation. Ces essais ont également permis de montrer qu’une phase mésomorphe était induite pour certaines conditions de sollicitation, l’origine de cette phase ayant pu être corrélée avec des aspects de dynamique des chaînes macromoléculaires. Un intérêt particulier a également été porté à l’influence du taux de cristallinité initial du matériau sur ses propriétés mécaniques ainsi que sur la structuration associée en cours de déformation. Finalement, il a été montré que la déformation du PLA en dessous de Tg est gouvernée par une compétition entre plasticité par craquelures et par bandes de cisaillement, le second mécanisme devenant prédominant avec l’augmentation de la température.This PhD work deals with the characterization of the thermomechanical behavior in relation to the structural organization at different scales of a bio-based polymer candidate for the replacement of usual polymers, the Poly(lactic acid). The present study is motivated by the complex behavior exhibited by this polymer, mainly linked to the occurrence of stereo-isomers.The first goal of this work was the characterization as a function of co-monomer content, of the thermomechanical response in relation to the existing local macromolecular arrangements in the amorphous phase The second goal was the study of the structural evolution of an industrial PLA copolymer uniaxially stretched at T>Tg. Combined in situ SAXS and WAXS experiments using a synchrotron radiation have provided clear insights into the structure-property relationships of the material. It has been shown that a mesomorphic phase was induced for some drawing conditions and its origin has been related to some features of the macromolecular chain dynamics.Particular interest has been paid to the study on the one hand, of the influence of initial crystallinity of the material on its mechanical response, and on the other hand, of the structural evolution induced during stretching. Finally it has been shown that PLA deformation at below Tg was governed by a competition between two deformation mechanisms namely crazing and shear banding, the latter becoming predominant as the temperature is increased

Étude de la structuration à différents niveaux d'échelle et du comportement thermomécanique d'un polymère issu de ressources renouvelables (l'acide poly(lactique))

Ces travaux de thèse porte sur la caractérisation des propriétés thermomécaniques et sur l étude à différents niveaux d échelle de la structuration d un polymère issu de la biomasse candidat au remplacement des polymères de commodité, à savoir, l acide poly(lactique) (PLA). Ils ont été motivés par le comportement complexe, encore mal compris à l heure actuelle, que présente ce polymère notamment en raison de l existence de stéréoisomères.Le premier but de ce travail a été de caractériser les propriétés thermomécaniques, en fonction du taux de co-monomère, en relation avec les arrangements moléculaires locaux pouvant exister dans la phase amorphe. Le second objectif a été d étudier la structuration d un copolymère industriel lorsque celui-ci est déformé uniaxialement à une température supérieure à sa température de transition vitreuse. L analyse par diffraction-diffusion X in situ sur synchrotron a permis d établir le lien entre la réponse mécanique du matériau et l évolution structurale induite par la déformation. Ces essais ont également permis de montrer qu une phase mésomorphe était induite pour certaines conditions de sollicitation, l origine de cette phase ayant pu être corrélée avec des aspects de dynamique des chaînes macromoléculaires. Un intérêt particulier a également été porté à l influence du taux de cristallinité initial du matériau sur ses propriétés mécaniques ainsi que sur la structuration associée en cours de déformation. Finalement, il a été montré que la déformation du PLA en dessous de Tg est gouvernée par une compétition entre plasticité par craquelures et par bandes de cisaillement, le second mécanisme devenant prédominant avec l augmentation de la température.This PhD work deals with the characterization of the thermomechanical behavior in relation to the structural organization at different scales of a bio-based polymer candidate for the replacement of usual polymers, the Poly(lactic acid). The present study is motivated by the complex behavior exhibited by this polymer, mainly linked to the occurrence of stereo-isomers.The first goal of this work was the characterization as a function of co-monomer content, of the thermomechanical response in relation to the existing local macromolecular arrangements in the amorphous phase The second goal was the study of the structural evolution of an industrial PLA copolymer uniaxially stretched at T>Tg. Combined in situ SAXS and WAXS experiments using a synchrotron radiation have provided clear insights into the structure-property relationships of the material. It has been shown that a mesomorphic phase was induced for some drawing conditions and its origin has been related to some features of the macromolecular chain dynamics.Particular interest has been paid to the study on the one hand, of the influence of initial crystallinity of the material on its mechanical response, and on the other hand, of the structural evolution induced during stretching. Finally it has been shown that PLA deformation at below Tg was governed by a competition between two deformation mechanisms namely crazing and shear banding, the latter becoming predominant as the temperature is increased.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Organocatalytic synthesis of novel blockcopolymers

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Poly(ethylene oxide)/Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) (PEDOT:PSS) Blends: An Efficient Route to Highly Conductive Thermoplastic Materials for Melt-State Extrusion Processing ?

International audienceBlends of poly(ethylene oxide) (PEO) with poly- (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PE- DOT:PSS) were investigated for the preparation of electrically conductive films using melt-state extrusion processing techniques. High molecular weight PEO is selected as a melting carrier to enable the extrusion processing of PEDOT:PSS. A drop-casting technique from aqueous solutions is first investigated to produce model PEO/PEDOT:PSS blends and identify the influence of relevant parameters on the final electronic conductivity. A low percolation threshold (approximately 9 wt % PEDOT:PSS into PEO) and high electronic conductivities (10−1000 S/cm) are detected. These performances are correlated to homogeneous blend morphologies and miscibility effects arising from strong PEO/PSS interactions detected by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), and differential scanning calorimetry (DSC). Storage time and water ionic content have negative impacts on the electronic conductivity. The procedure was then adapted to prepare PEO-rich blends using twin-screw extrusion at 120 °C. A strong negative impact of the thermomechanical treatment was attested for PEO/PEDOT:PSS blends due to phase segregation phenomena induced by extrusion. However, an acidic post-treatment on extruded and molded thin films efficiently restored high electronic conductivities up to 4 S/cm for PEO-rich blends with 40 wt % PEDOT:PSS due to the removal of insulating phases. Such thermoplastic materials were found to be competitive with traditional thermoplastic solutions and thus represent efficient candidates for the development of thermoplastic electrodes using conventional and advanced processing technologies of the plastic industry

Crystal chemistry and SAXS studies of an octahedral polyoxo-arsenotungstate nanocluster encapsulating four unprecedented thorium arsenate fragments ({Th3As2On} - n=25 or 26).

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Complexation of uranium(IV, VI) cations by polyoxometalate cryptants

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Water Barrier Properties in Biaxially Drawn Poly(lactic acid) Films

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