Evolution de morphologie pendant le processus de mélanges des polymères incompatibles

3 p.Sous l'action d'un écoulement, la structure d'un mélange de polymères incompatibles évolue. Les inclusions (constituées par la phase minoritaire) peuvent se déformer (si leur taille est suffisamment grande), se rompre et éventuellement coalescer. Cette évolution de la morphologie sous l'action de l'écoulement contrôle le comportement rhéologique du mélange. Lors d'une opération de mise en forme, un mélange de polymères voit sa structure passer d'un mélange grossier (de la taille d'un granulé) à un mélange fin (inclusions dans le produit fini de l'ordre du micron). La morphologie finale étant à l'origine des propriétés d'emploi de la pièce finie, il est important de savoir la contrôler. Or, le contrôle de cette structure implique de comprendre les mécanismes régissant l'évolution de la structure sous l'action d'un écoulement. Dans cette étude, nous nous intéressons d'une part, au comportement rhéologique particulier de certaines structures aux limites de la co-continuité et d'autre part, à l'influence du temps et de la vitesse de mélangeage sur la morphologie des mélanges. Cette étude a été réalisée sur des mélanges polystyrène / polyoxyéthylène, Polyoxyéthylène / PolyFluorure de vinylidène pour lesquels plusieurs rapports de viscosité et d'élasticité ont été testés. Les conditions de mélangeage ont été modifiées afin de comprendre le processus de formation des morphologies au cours du temps

Fine control of carbon nanotubes-polyelectrolyte sensors sensitivity by electrostatic layer by layer assembly (eLbL) for the detection of volatile organic compounds (VOC)

International audienceVolatile organic compounds (VOC) sensors have recently extended their field of application to medical area as they are considered as biomarkers in anticipated diagnosis of diseases such as lung cancer by breath analysis. Conductive polymer nanocomposites (CPC) have already proved their interest to fabricate sensors for the design of electronic noses (e-noses) but, for the first time to our knowledge, the present study is showing that electrostatic layer by layer assembly (eLbL) is bringing an interesting input to tailor the sensitivity of carbon nanotubes (CNT)-polyelectrolyte sensors. By this technique transducers are progressively built in 3D alternating dipping into sodium deoxycholate (DOC)-stabilized SWNT and poly(diallyldimethyl-ammonium chloride) [PDDA] solutions, respectively anionic and cationic. The precise control of transducers thicknesses (between 5 and 40 nm) resulting from this process allows a fine tuning of multilayer films resistance (between 50 and 2 kΩ) and thus of their sensitivity to VOC. Interestingly the surfactant used to disperse CNT into water, DOC is also found to enhance CNT sensitivity to vapors so is it for the polyelectrolyte PDDA. Finally it is found that transducers with 16 bilayers of PDDA/DOC-CNT provide optimum chemo-resistive properties for the detection and discrimination of the eight vapors studied (chloroform, acetone, ethanol, water, toluene, dichloromethane, tetrahydrofuran and methanol)

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial.

Importance: Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited. Objective: To determine whether hydrocortisone improves outcome for patients with severe COVID-19. Design, Setting, and Participants: An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020. Interventions: The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108). Main Outcomes and Measures: The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%). Results: After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively. Conclusions and Relevance: Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions. Trial Registration: ClinicalTrials.gov Identifier: NCT02735707

Etude et mise au point de films par extrusion pour une application de batterie lithium-polymère

Séminaire au Laboratoire Polymères et Matériaux Avancés CRNS-Rhodia, Lyo

Contrôle de la morphologie d'un mélange de polymères lors de l'extrusion de films (application aux batteries lithium-polymère)

L'objet de ce travail est d'étudier et de mettre au point par extrusion deux films polymères entrant dans la fabrication d'une batterie lithium-polymère. Ces films sont basés sur un mélange de deux polymères incompatibles. Les propriétés opposées de ces polymères sont mises à profit conjointement lorsque le mélange adopte une morphologie co-continue. En préambule de l'étude de faisabilité des films par extrusion, ce travail propose l'étude du mélange binaire des polymères d'un point de vue morphologique et rhéologique. L'extraction sélective et la microscopie sont utilisées et les observations effectuées sont mises en parallèle avec les données rhéologiques du système. Le rapprochement entre la morphologie et la rhéologie du système a donné lieu à l'élaboration d'un modèle prédictif de l'évolution du module élastique G' aux basses fréquences. Le comportement particulier de ce mélange a également été comparé à celui des systèmes chimiques (gels). La seconde partie de ce travail décrit l'étude de faisabilité des films par extrusion. Des mesures de conductivité, résistivité et de tenue mécanique ont permis d'aboutir à une formulation adaptée au process. Le procédé de transformation développé au laboratoire a été transféré à l'échelle industrielle. Ce transfert s'est concrétisé par la fabrication des films d'électrolyte et de cathode entrant dans la confection d'une batterie lithium-polymère. L'extraction sélective, la microcopie, la calorimétrie différentielle, la spectrométrie mécanique et la thermogravimétrie ont été utilisées pour caractériser ces systèmes complexes. Suite à ce travail, les composants ont été testés avec succès dans une batterie lithium-polymèreThis work deals with the design engineering and the characterization of two polymer films made by extrusion. These films are the components of a lithium-polymer battery. They are based on a blend of two immiscible polymers. To take advantage of the opposite properties of the two components, the morphology of the blend must be cocontinuous. Before studying the process ability of such polymer films, morphological and rheological properties are investigated. The observations made by selective extraction and microscopy are compared with the rheological behaviour. Since no model has achieved a good prediction of the behaviour of the storage modulus, a new model has been developed to predict the evolution of G' at low frequencies. In a wider range of frequencies, this particular behaviour of the continuous structure has been assimilated with the chemical gelation of crosslinked networks. The second part of this work described the study of the process. Conductivity, resistivity measurements and mechanical characterization have been used to determine the composition of films. The process has been developed in the laboratory and transferred to the industrial site. It allows us to produce large amount of electrolyte and cathode films to build a lithium-polymer battery. Selective extraction, microscopy, differential calorimetry, mechanical spectrometry and thermogravimetry have been used to characterize these complex systems. Finally, batteries have been made to test successfully the different components, electrolyte and cathodeST ETIENNE-BU Sciences (422182103) / SudocSudocFranceF

Quantum resistive CPC vapour sensors for environmental monitoring

International audienc

Thermal degradation during melt processing of poly(ethylene oxide), poly(vinylidenefluoride-co-hexafluoropropylene) and their blends in the presence of additives, for conducting applications

In this paper, the thermal degradation during compounding of poly(ethylenc oxide) and poly(vinylidenefluoride-co-hexafluoropropylene) and their immiscible blends was investigated. Infrared spectroscopy, size exclusion chromatography, dynamic theology, thermogravimetric analysis, and coupled gas chromatography-mass spectroscopy were used. Most of the identified degradation products or substances are glycols, formates, lactones, ethers or even acids for long processing times. The mechanisms for the production of these chemical compounds were already reported in previous publications. Additionally, the influence of carbon black and LiV3O8 additives, currently used for enhancing the conductive properties, was studied. Addition of carbon black causes an increase in the PEO stability, whereas addition of LiV3O8 has an opposite and dramatic effect. PVDF-HFP is found to be less susceptible to degradation because of the inherent stability of fluorine-containing polymers. However, melt processing provides additional contributions to degradation because of the high viscosities. (c) 2005 Elsevier Ltd. All rights reserved

Cocontinuity in immiscible polymer blends: A gel approach

Rheological properties of poly(ethylene oxide)/poly(vinylidenefluoride)-(hexafluoropropylene) immiscible polymer blends were studied in the low frequency domain. According to the blend composition, two critical compositions were determined by rheology. These compositions exhibit a power law relaxation spectrum with a critical exponent A. This observation leads us to compare the evolution of the morphology in a binary blend with the process of gelation. The supermolecular structure at the limit of the cocontinuity zone is comparable to the chemical or physical incipient network obtained during the gelation. This point is discussed in term of self-similar superstructure and fractal dimension