Fluorinated Electroactive Terpolymers Actuators – FETA

The FETA project concerns fluorinated electroactive terpolymers consisting of VDF, TrFE and CTFE monomers. These P(VDF-ter-TrFE-ter-CTFE) terpolymers are Relaxor-Ferroelectric (RFE) and electrostrictive. They deform under an electric field, respond to a mechanical pressure or a temperature change by generating a current, and have a high dielectric constant. They are synthesized and developed by Arkema and its subsidiary, Piezotech, for applications in the fields of organic electronics (transistors, light-emitting diodes or memories), robotics or medicine (sensors, actuators ...)
The electroactivity of these polymers is related to the existence of a dipole moment in the three monomers. In these semi-crystalline polymers, the dipoles located in the amorphous and crystalline phases are likely to orient under the action of an electric field but do not behave in the same way. The electroactive properties of these polymers are directly related to the crystal phase morphological and structural properties induced by the microstructure of the chains and the processing of the material. In published studies, the RFE properties are explained by the distribution of CTFEs (less mobile and carrying a weaker dipole moment) along the chain in the crystals. They split the large ferroelectric domains into nanodomains which are more mobile under electric fields but unable to maintain a polarization. The microscopic origin of the deformation induced by the electric field is still very much controversial. In contrast, it is unanimously recognized that processing, structure and morphology influence these properties. However the relationship between these parameters and the macroscopic deformation is not established. Now that high-tech applications are emerging, a fundamental understanding of macroscopic behavior of these terpolymers in connection with their microscopic constitution (chemical and structural) is necessary to optimize their properties and thus help to strengthen Arkema's competitiveness.
The FETA consortium, which brings together 2 academic research teams (ICGM and PIMM) and Arkema researchers, builds on solid work and past experience and brings together all the areas of expertise needed in synthesis, advanced characterization, knowledge of the structural and morphological organization of fluoropolymers to achieve the project objectives. The scientific approach relies on:
- An analysis of the synthesis process associated with a study of the chain microstructure by solution NMR to determine the distribution of CTFE units in the terpolymer chains.
- X-ray diffraction at large angles and solid-state NMR studies as a function of temperature of terpolymers having different CTFE contents to specify the distribution of the monomers (and thus the dipoles) in the crystalline and amorphous phases.
- The evolution of macroscopic properties (dielectric constant) and mechanical behavior (deformation) for different terpolymer compositions and processing (heat treatment and confinement) to understand the influence of morphology on properties.
- Microscopic evaluations (in-operando SAXS-WAXS and PFM) and macroscopic observations (deformation measurements) of the electric field behavior of actuators having different compositions and morphologies.
This approach will make it possible to understand the influence of CTFE in the macromolecular chain, its role and its location in the crystal and in the amorphous phase; and to explain how the rotation of the dipoles present in the crystalline, amorphous and interphase phases induces polarization and deformation under the application of an electric field. This crucial knowledge will provide the means to develop more efficient terpolymers better adapted to specific targeted applications.