Simultaneous SAXS-WAXS experiments on semi-crystalline polymers: Example of PA11 and its brill transition

This manuscript of the special issue “Microstructural Evolution and Mechanical Behavior of Semi-Crystalline Polymers” aims to show that Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) experiments performed simultaneously constitute a unique tool to obtain valuable information on the hierarchical structure of semi-crystalline polymers. These structural quantitative data are needed tomodel macroscopic properties of polymeric materials, for example their mechanical properties. To illustrate our point, we focus our study on the structure and morphology of polyamide 11. Through a simultaneous SAXS-WAXS experiment, we show that the absence of enthalpic signal in Differential Scanning Calorimetry (DSC) is not synonymous with the absence of structural and morphological evolution with temperature. The case of a thermally activated crystal–crystal transition, the Brill transition, is particularly detailed. Through this SAXS-WAXS study, we show, among other points, and for the first time, that the periodicity of crystalline lamellae (LP) changes at the transition, probably due to a modification of the amorphous phase’s free volume at the Brill transition. We also explain the crucial role of annealing to stabilize polymeric materials that may experience temperature changes over their lifetime. The influence of the annealing on the perfection of crystalline structure, morphology and mechanical behavior is more particularly studied

Evolution of mechanical properties of aged poly(ether ketone ketone) explained by a microstructural approach

In this work, the thermo-oxidative behavior of PEKK films (~50 µm thick) in solid state were investigated. Since the mechanical properties of PEKK samples, especially the strain at break, are clearly affected after long ageing time, the modifications of the PEKK structure have been monitored at the molecular and the macromolecular scales using different techniques such as gel permeation chromatography, X-Ray scattering, differential scanning calorimetry, and dynamic mechanical analysis. If the embrittlement of the PEKK specimens seems to appear due to a predominant branching/cross-linking phenomenon occurring at the macromolecular scale, crystalline morphology is also slightly modified due to a chain scission mechanism occurring simultaneously.The authors acknowledge the financial support of the French National Research Agency (ANR IMPEKKABLE project). The au- thors wish to thank the LEM laboratory (Arkema, Serquigny), es- pecially Sylvie Lebreton and François Bargain for facilitating SAXS- WAXS experiments and Christine Thieulin and Stéphane Bizet for GPC measurements. Stéphane Bizet and Benoît Brulé are warmly thanked for fruitful discussion, reading, and clarifying this article. We would also like to thank Rakhi Sood for some experimental parts in this work. This work was performed within the framework of the Industrial Chair Arkema (Arkema/CNRS-ENSAM-Cnam)

Segmentation of Dynamic PET Images with Kinetic Spectral Clustering

International audienceSegmentation is often required for the analysis of dynamic positron emission tomography (PET) images. However, noise and low spatial resolution make it a difficult task and several supervised and unsupervised methods have been proposed in the literature to perform the segmentation based on semi-automatic clustering of the time activity curves of voxels. In this paper we propose a new method based on spectral clustering that does not require any prior information on the shape of clusters in the space in which they are identified. In our approach, the p-dimensional data, where p is the number of time frames, is first mapped into a high dimensional space and then clustering is performed in a low-dimensional space of the Laplacian matrix. An estimation of the bounds for the scale parameter involved in the spectral clustering is derived. The method is assessed using dynamic brain PET images simulated with GATE and results on real images are presented. We demonstrate the usefulness of the method and its superior performance over three other clustering methods from the literature. The proposed approach appears as a promising pre-processing tool before parametric map calculation or ROI-based quantification tasks

Influence of Field-Induced Phase Transition on Poly(Vinylidene Fluoride-Trifluoroethylene-Chlorotrifluoroethylene) Strain

This work is focused on understanding the reasons behind the large electrostrictive strain of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer. Although a few explanations have been proposed in the literature, it remains largely unclear. Here, the role of an electrically induced phase transition is investigated. The strain in the crystalline part of the polymer is monitored using XRD while an electric field is applied onto the sample. Three regions of interest are clearly evidenced and, of particular interest, we observe a change in crystal symmetry located on the 30-70 V μm-1 range. In that region, the lattice progressively loses its hexagonal symmetry and moves toward the phase usually observed at lower temperature, with a higher polar order. In parallel, we conduct macroscopic strain measurements to compare to the XRD data. Three different regimes are also observed with a sudden increase in electrostrictive coefficient on the 30-70 V μm-1 interval, going from 19 to 33 m4C-1. This corresponds to a 1% strain, i.e., 25% of the total deformation measured at 100 V μm-1. By thoroughly comparing macroscopic strain and x-ray measurements, we are able to single out and quantify the impact of this field-induced phase transition in the polymer overall strain.P.L. and E.D. thank FNR (Fonds National de la Recherche) for partly funding this research through the project CAMELHEAT C17/MS/11703691/Defay. Sylvie Tencé-Girault’s contribution is achieved within the frame-work of the Industrial Chair Arkema (Arkema/CNRS-ENSAM-Cnam)

Unraveling the morphological diversity of P(VDF-ter-TrFE-ter-CTFE) semi-crystalline terpolymers via combined AFM and SAXS experiments

In this article, the diverse morphologies observed after annealing or crystallization from the melt in P(VDF-ter-TrFE-ter-CTFE) terpolymers with varying CTFE amounts were explained through a combination of AFM and SAXS experiments. The very significant and, so far, unexplained evolution of the SAXS spectra after annealing above the Curie transition was interpreted by the formation, during annealing, of semi-crystalline domains without a significant evolution of the crystalline lamellar period. The morphologies obtained after crystallization from the melt were also explained and the coexistence of two periodic stacks (with period around 30–40 nm and 14–18 nm) was shown. Low cooling rates and CTFE amounts create long and thick semi-crystalline domains with a well-defined orientation, while high cooling rates and CTFE amounts create thinner and shorter domains without a predominant orientation. The AFM images showed that the periodic organization of the crystalline lamellae with a period, LP, around 15 nm is maintained, regardless of the crystallization process used (solvent cast, annealed, or melt-crystallized). The combined AFM/SAXS method used in this study can be applied to other semi-crystalline polymers.ANR FETA Chaire Arkema/CNRS-ENSAM-Cna

Quantitative Structural Study of Cold-Crystallized PEKK

Poly(ether ketone ketone) (PEKK) is a semicrystalline polymer investigated for highly demanding applications in aerospace, transportation, electronics, and oil & gas industries. The properties required for these applications, such as thermomechanical and chemical stability, are intimately linked to the crystalline state of the material. PEKK exhibits a polymorphism that depends, among other factors, on its thermal history. The control and quantification of the crystalline state of PEKK is the subject of this study. Amorphous PEKK (T/I = 60/40, where T stands for terephthalic and I for isophthalic units) films were cold-crystallized at various crystallization temperatures, T-C, from 180 to 280 degrees C in a ventilated oven. Based on a quantitative analysis of small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) data, we propose for the first time a methodology to obtain detailed information about the crystalline state of PEKK: total crystallinity, relative amount and stability of crystalline forms, form I and form II, and melting enthalpy of 100% crystallized PEKK. The evolutions of each crystalline form and the total crystallinity with T-C were deduced. The amount of each crystalline form, form I and form II, can be tuned by controlling the heating rate to 280 degrees C. The evolution of the crystalline lamellar thickness and periodicity as well as the crystalline amount and cell parameters with T-C were interpreted and discussed in relation to the published results on PEEK, PEKK (100% T), and PEKK (100% I). Finally, the melting enthalpy of a 100% crystallized PEKK copolymer (T/I = 60/40), Delta H-m(100%) = (202 +/- 20) J/g, was estimated

Structural and Barrier Properties of Compatibilized PE/PA6 Multinanolayer Films

The barrier performance and structural lightening of organic materials are increasingly desired and constitute a major challenge for manufacturers, particularly for transport and packaging. A promising technique which tends to emerge in recent years is that of multinanolayer coextrusion. The advantage is that it can produce multilayers made of thousands of very thin layers, leading to new properties due to crystalline morphology changes induced by confinement. This paper is focusing on the study of multinanolayered films with alternated polyethylene (PE), compatibilizer (PEgMA) and polyamide 6 (PA6) layers and made by a forced assembly coextrusion process equipped with layer multiplying elements (LME). PE/PA6 multilayer films consisting of 5 to 2049 layers (respectively 0 to 9 LME) were successfully obtained with well-organized multilayered structure. The evolution of the morphology and the microstructure of these two semi-crystalline polymers, when the thickness of each polymer layer decreases from micro-scale to nano-scale, was correlated to the water and gas transport properties of the PE/PA multilayers. The expected improvement of barrier properties was limited due to the on-edge orientation of crystals in very thin PE and PA6 layers. Despite this change of crystalline morphology, a slight improvement of the gas barrier properties was shown by comparing experimental results with permeabilities predicted on the basis of a serial model developed by considering a PE/PA6 interphase. This interphase observed by TEM images and the on-edge crystal orientation in multilayers were evidenced from mechanical properties showing an increase of the stiffness and the strength

Enhanced Electrocaloric Response of Vinylidene Fluoride–Based Polymers via One‐Step Molecular Engineering

Electrocaloric refrigeration is one of the most promising environmentally-friendly technologies to replace current cooling platforms—if a notable electrocaloric effect (ECE) is realized around room temperature where the highest need is. Here, a straight-forward, one-pot chemical modification of P(VDF-ter-TrFE-ter-CTFE) is reported through the controlled introduction of small fractions of double bonds within the backbone that, very uniquely, decreases the lamellar crystalline thickness while, simultaneously, enlarging the crystalline coherence along the a-b plane. This increases the polarizability and polarization without affecting the degree of crystallinity or amending the crystal unit cell—undesirable effects observed with other approaches. Specifically, the permittivity increases by >35%, from 52 to 71 at 1 kHz, and ECE improves by >60% at moderate electric fields. At 40 °C, an adiabatic temperature change >2 K is realized at 60 MV m−1 (>5.5 K at 192 MV m−1), compared to ≈1.3 K for pristine P(VDF-ter-TrFE-ter-CTFE), highlighting the promise of a simple, versatile approach that allows direct film deposition without requiring any post-treatment such as mechanical stretching or high-temperature annealing for achieving the desired performance

Hereditary predisposition to malignant myeloid hemopathies: Caution in use of saliva and guideline based on our experience

BackgroundPredisposition to myeloid malignancies is a field at the border of hematology and genetics. Knowledge in this domain has so rapidly increased that WHO defined in 2016 the new “Myeloid Neoplasms with Germline Predisposition” category of tumors. High throughput sequencing is frequently performed in tumors either for diagnosis or prognosis, but this approach may identify potential germline variants that have to be confirmed on non-infiltrated tissues.MethodIn this study, we systematically compared NGS data from genetic analysis performed on all sample types (bone marrow, blood, saliva, skin fibroblasts and hair follicles) in 29 patients, and 44 of their relatives (blood and saliva).ResultsWe showed that saliva was usable for relatives, but only for 24% (7/29) of our patients. Most of patients’ saliva were either “non-contributive” (14/29 i.e., 48% because clearly or probably infiltrated) or “inconclusive” (8/29 corresponding to 28%).ConclusionThe recommendations for the use of saliva we present here focus on the importance of collecting saliva during remission when possible. Moreover, we propose hair follicles as an alternative to skin biopsy, that remains the gold standard especially in case of allogenic hematopoietic stem cells transplantation. Technological progresses have revolutionized the diagnosis of predisposition to solid or hematological malignancies, and it is very likely that new techniques will help to manage the familial predisposition in the future

Spin coating and micro-patterning optimization of composite thin films based on PVDF

We optimize the elaboration of very thin film of poly(vinylidene fluoride) (PVDF) polymer presenting a well-controlled thickness, roughness, and nano-inclusions amount. We focused our effiort on the spin coating elaboration technique which is easy to transfer to an industrial process. We show that it is possible to obtain continuous and smooth thin films with mean thicknesses of 90 nm by properly adjusting the concentration and the viscosity of the PVDF solution as well as the spin rate and the substrate temperature of the elaboration process. The electro-active phase content versus the magnetic and structural properties of the composite films is reported and fully discussed. Last but not least, micro-patterning optical lithography combined with plasma etching has been used to obtain well-defined one-dimensional micro-stripes as well as squared-rings, demonstrating the easy-to-transfer silicon technology to polymer-based devices