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Polymer‐based pyroelectric thin films are crucial functional materials at the core of flexible and lightweight electronic devices, such as wearable monitoring sensors, energy harvesters, and infrared detectors. Nevertheless, the pyroelectric properties of the polymer films, such as poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)), vanish when the surrounding temperature exceeds the ferroelectric‐to‐paraelectric transition temperature, and thus limits their pyroelectric performance to a low‐temperature range. Herein, to mitigate this issue by employing a new class of P(VDF‐TrFE) copolymer which has a low TrFE molar content is proposed. Fine‐tuning of the structure through thermal annealing in a vacuum environment significantly favors robust and highly polarized polymer films with a large area. Electric poling combined with an optimal annealing temperature (110–120 °C) gives highly ordered ferroelectric crystalline domains in the polymer films. Consequently, this remarkably broadens the temperature range (roughly up to 140 °C) for which the polymer film still presents high pyroelectric properties (pyroelectric coefficient 50 µC (m2K)−1). This study provides an alternative choice for pyroelectric polymer films with enhanced pyroelectricity in applications that require wider temperature ranges. [ABSTRACT FROM AUTHOR]

Self‐assembly of high molecular weight commercially available low χ ABA triblock copolymers with ionic liquids (ILs) was observed after solvent casting without the implementation of an additional annealing step. Here, the addition of an IL to a triblock copolymer poly(methyl methacrylate‐b‐butyl acrylate‐b‐methyl methacrylate) (MAM) with an elastomeric central block and rigid end blocks is proposed to tune the self‐assembled morphology. Two different compositions of this copolymer with different initial microstructures (ill‐defined morphology without long‐range order and a lamellar morphology) were selected. The selectivity of the IL addition in one of the block phases was studied through the evolution of the glass transition of both blocks. The impact of the IL weight concentration on the morphology as well as the domain spacing is presented. Adding IL to the first copolymer detected a lyotropic disorder–order transition towards a gyroid morphology, observed even for a high molecular weight copolymer due to the low χ parameter, and for higher IL content a second transition to a lamellar morphology was observed. For the second copolymer, only an order–order transition (lamellae to cylinders) could be detected at high IL content. IL also enhanced the long‐range ordering of the MAM morphology obtained through solvent casting without additional annealing steps, compared with the same composition without IL. © 2022 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectric polymers exhibit high k at their structural phase transition around room temperature. They are particularly attractive as gate dielectric in organic field effect transistor (OFET). Nevertheless, their applications are limited due to their low thermal stability. A polymer blend system with a high and thermally stable dielectric constant is demonstrated by mixing terpolymer poly(vinylidene fluoride‐trifluoroethylene‐chlorofluorethylene) P(VDF‐ter‐TrFE‐ter‐CFE) with copolymer poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐co‐TrFE). PVDF‐based blends of various compositions are characterized by dielectric spectroscopy, differential scanning calorimetry (DSC), infrared spectroscopy, small and wide angle X‐ray scattering (SAXS and WAXS), and atomic force microscopy (AFM) in order to investigate the relationship between morphology and crystallization of the blend and their dielectric properties. An optimized blend of P(VDF‐ter‐TrFE‐ter‐CFE) [55/37/8] and P(VDF‐co‐TrFE) [46/54] at a ratio of 70/30 is found to exhibit a quasi‐constant dielectric constant of 40 ± 2 over a wide temperature range (20–80 °C). Furthermore, electrical characteristics of the PVDF‐blend‐based gate dielectric OFET show further thermal stability in comparison to OFET based on high‐k terpolymer P(VDF‐ter‐TrFE‐ter‐CFE) [55/37/8]. An improvement of their drain current stability by up to 60% is demonstrated at 60 °C. These findings enable broader applications of fluoropolymers in organic electronics. [ABSTRACT FROM AUTHOR]

Abstract: Transmission electron microscopy (TEM) is a unique tool to visualize polymer morphology: an intimate organization of the matter, encompassing crystalline features in semicrystalline polymers and a kaleidoscopic collection of patterns produced by microseparated phases in polymer blends. This manuscript aims at demonstrating the various opportunities this technique enables, through a miscellany of studies performed in our laboratory. Materials as different as bulk and composite compounds, thin films, hollow fiber membranes, and rubbers are presented, from the viewpoint of the interrelation of TEM with other techniques like scattering, mechanical, and thermomechanical experiments. [ABSTRACT FROM AUTHOR]

Cocontinuous nanostructured blendsof semicrystalline polymers tend to align along a preferential directionwhen subjected to steady flow. We investigate the flow induced changesexperienced by cocontinuous blends using transmission electron microscopyand small-angle X-ray scattering and we demonstrate that shear flowinduces a preferential direction while preserving a cocontinuous structure,which is oriented along the flow direction. In parallel, we studythe viscoelastic properties of the aligned morphology by linear oscillatoryshear above the melting temperature of the blend components and observea liquid-like behavior at short times. Upon annealing at high temperature,the aligned morphology relaxes back to the original isotropic structurewith a solid-like viscoelastic behavior. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 effort 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. [ABSTRACT FROM AUTHOR]

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 to model 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. [ABSTRACT FROM AUTHOR]

Industrial hollow fiber membranes for the purification of wastewater were manufactured by the phase inversion method in a dry-wet spinning process, adding an amphiphilic diblock copolymer to a standard PVDF/Polyvinylpyrrolidone (PVP) formulation. The copolymer designed to provide antifouling properties is composed of a PMMA block and a hydrophilic block bearing pendent hydroxy groups. As PMMA is miscible with PVDF, the copolymer is expected to anchor in the matrix more efficiently than the hydrophilic but water soluble PVP which is washed away overtime during repetitive cleaning procedures. Infrared experiments attest that both antifouling additives are well included in the fibers after the inversion process. Performances of the fibers were checked by permeability, burst pressure and tensile tests. The pore distribution observed by scanning electron microscopy goes from 10 to 30 nm at the outer surface to 0.1–10 µm inside the fiber. Observation of the pore structure by transmission electron microscopy, made possible by embedding the fibers into a resin that filled in the voids, and specific staining of the antifouling additives, shows that both PVP and the amphiphilic copolymer are located all around the pores. This study is the first direct proof at the microscopic scale of pore surface enrichment by antifouling agents. [ABSTRACT FROM AUTHOR]