Vinylidene fluoride- and trifluoroethylene-containing fluorinated electroactive copolymers. How does chemistry impact properties?

International audienceFluoropolymers are attractive niche polymers used in high added value materials for high-tech appli-cations in aerospace, electronics, coatings, membranes, cables, and the automotive industries. Amongthem, VDF- and TrFE-based copolymers exhibit remarkable electroactive properties allowing their incor-poration into a wide range of devices such as printed memories, sensors, actuators, artificial muscles,and energy storage devices. In a first section, a detailed overview of semi-crystalline poly(VDF-co-TrFE)copolymers and of their ferroelectric (FE) properties from the point of view of polymer chemists is sup-plied. In addition to the polymer microstructure that may sometimes be controlled or influenced by thesynthesis strategies, physical properties such as the phase transitions, and electroactivity are also affectedby processing, such as annealing for example, and film thickness for example. Building on the conclusionsand understanding obtained from the first section, the effect of the introduction of a termonomer (leadingto poly(VDF-ter-TrFE-ter-M) terpolymers) is detailed in a second section of this review. Modifying theterpolymer chain microstructure has a major impact on the crystalline phase of the terpolymers that mayresult in a relaxor-ferroelectric behavior (RFE). The distribution of the termonomer along the polymerchain, the capacity of the termonomer units to enter the crystal lattice, as well as its dipole momentgovern in large part the terpolymer electroactive properties. Poly(VDF-ter-TrFE-ter-CFE) and poly(VDF-ter-TrFE-ter-CTFE) terpolymers appeared to be the best candidates for RFE properties and were thus themost studied. In two following sections, the block or graft architectures of VDF- and TrFE- based copoly-mers, and the various crosslinking strategies used so far for such copolymers are described. Chemicalmodification is indeed a very powerful tool to tune electroactive properties of copolymers or to impartadditional properties. Finally, in the last section, a few examples of emerging applications for these fluo-rinated electroactive polymers (EAPs) are briefly discussed. This review aims to provide a comprehensivereport on the use of polymer chemistry as a tool to produce better electroactive fluorinated polymers, andhighlights possible opportunities and perspectives for future progress in this field. Research in this inter-disciplinary field requires different kinds of expertise, ranging from organic and polymer chemistries,polymer films engineering, physics of semi-crystalline polymers and electroactivity, to the design andfabrication of electronic devices

From solvent-cast to annealed and poled poly(VDF-co-TrFE) films: New insights on the defective ferroelectric phase

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Phase diagram of poly(VDF-ter-TrFE-ter-CTFE) copolymers: Relationship between crystalline structure and material properties

Depending on their CTFE content (from 0 to 10 mol %), poly(VDF-ter-TrFE-ter-CTFE), poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) copolymers, exhibit ferroelectric (FE) or relaxor ferroelectric (RFE) properties at room temperature. Solvent cast films of these terpolymers can crystallize in three orthorhombic phases: FE, DFE (Defective Ferroelectric) or RFE according to their amount of CTFE. The relative amount of each crystalline phase depends on the amount of CTFE and evolves after annealing. We study the dependence of the electric displacement−electric field (D−E) loop with the amount of CTFE and with annealing step. We observed a closely link between the remnant polarization, PR, and the fraction of (FE + DFE) crystalline phase. Macroscopic properties, studied using thermo-mechanical experiments (DSC and DMA) and dielectric spectroscopy, evolve continuously with the CTFE amount and are well correlated with the structural properties. Finally, a temperature versus mol% CTFE phase diagram is established and discussed in relation-ship with material properties.“Plate-forme de l’Université de Bordeaux pour l’organique électronique imprimable : de la molécule aux dispositifs et systèmes intégrés - valorisation et commercialisation

Semicrystalline Organization of VDF- and TrFE-Based ElectroactiveTerpolymers: Impact of the trans-1,3,3,3-TetrafluoropropeneTermonomer

International audienceIn the search for fluorinated polymers with newelectroactive properties, the radical polymerization of vinylidenefluoride (VDF), trifluoroethylene (TrFE), and trans-1,3,3,3-tetrafluoropropene (1234ze) was achieved. The crystallineorganization and the electroactive properties of semicrystallinepoly(VDF-ter-TrFE-ter-1234ze) terpolymer films with 1234zemolar contents ranging from 0 to 6%, obtained by solventcasting,were investigated using a combination of structural,dielectric, and electromechanical techniques. For 0 mol %1234ze, poly(VDF-co-TrFE) copolymers exhibited a Curietransition from the ferroelectric (FE) phase to the paraelectric (PE) phase at the Curie temperature (TC ∼ 95 °C). DSC,dielectric spectroscopy, and FTIR experiments revealed the preservation of this Curie transition (TC ∼ 75 °C) while increasingthe termonomer content. WAXS measurements confirmed the persistence of the FE phase as the main phase at roomtemperature but also showed the appearance of a secondary ZFE phase (expanded FE phase incorporating 1234ze units) in lowerproportion. The WAXS crystallinity was halved (42 to 23%) from 0 to 6 mol % 1234ze terpolymer annealed films. Furthermore,SAXS and WAXS experiments highlighted a decrease of the crystalline lamellae thickness and a significant modification of theelectronic density distribution upon increase of 1234ze units. A new model for this particular arrangement of crystalline lamellaewas thus proposed with the location of the ZFE phase at the interface between the FE crystalline lamellae and the amorphousphase. Finally, reduced remnant polarization (Pr ∼ 15 mC/m2) and transverse piezoelectric coefficient (d33 ∼ −5 pC/N),compared to those of the reference poly(VDF-co-TrFE) copolymer (Pr ∼ 50 mC/m2 and d33 ∼ −20 pC/N), were mainlyassigned to the decrease of the FE phase content in terpolymer poled films

Crystal-Crystal transitions in poly(VDF-ter-TrFE-ter-CTFE): Influence of CTFE termonomers

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Crystal-Crystal transitions in poly(VDF-ter-TrFE-ter-CTFE): Influence of CTFE termonomers

The increasing industrial interest for printed organic electronics these last years has led to the development of VDF-based electroactive polymers for numerous energy-related applications (sensors, actuators, capacitors) [1]. Depending on their CTFE content (from 0 to 10 mol %), poly (VDF-ter-TrFE-ter-CTFE), poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) copolymers exhibit ferroelectric (FE) or relaxor ferroelectric (RFE) properties at low temperature whereas they all present paraelectric (PE) behavior at high temperature. This thermal evolution of their electro-active properties is related to reversible crystal-crystal transitions. Using simultaneous SAXS-WAXS experiments along thermal cycles, we studied these structural transitions for three different copolymers with various amount of CTFE (0, 5 and 10 mol %). We identified two types of crystalline phase at low temperature with their proper crystal-crystal transition: the first one containing all-trans conformations (orthorhombic FE phase) presents a discontinuous transition towards the hexagonal PE phase, the second one which incorporates gauche disordered conformations (orthorhombic DFE (Defective Ferroelectric) or RFE) transits continuously towards the same hexagonal PE phase. The discontinuous FE to PE transition is the predominant transition observed in the copolymer without CTFE, it is the well-known Curie transition. The unique transition observed in the terpolymer with 10 mol % of CTFE is the continuous RFE to PE transition. For the intermediate composition, we observe the coexistence of these two simultaneous phase transitions, FE to PE and RFE to PE. These observations are well correlated with the ferroelectric and relaxor-ferroelectric behaviors of each terpolymer. All the conclusions and discussion of this study were recently published in Polymer [2]. At the epf2019 congress, we will focus on the SAXS-WAXS structural study

Static and Dynamic Studies of Electro-Active Polymer Actuators and Integration in a Demonstrator

Nowadays, the haptic effect is used and developed for many applications—particularly in the automotive industry, where the mechanical feedback induced by a haptic system enables the user to receive information while their attention is kept on the road and on driving. This article presents the development of a vibrotactile button based on printed piezoelectric polymer actuation. Firstly, the characterization of the electro-active polymer used as the actuator and the development of a model able to predict the electromechanical behavior of this device are summarized. Then, the design of circular membranes and their dynamic characterization are presented. Finally, this work is concluded with the construction of a fully functional demonstrator, integrating haptic buttons leading to a clear haptic sensation for the user