Fabrice Domingues Dos Santos

Ferroelectric fluorinated copolymers with improved adhesion properties

Modified fluorinated electroactive poly(VDF-co-TrFE) copolymers with improved adhesion properties, on glass or metal substrates, are presented. Vinylidene fluoride (VDF) and trifluoroethylene (TrFE) were terpolymerized with 1 to 8 mol% of 2-(trifluoromethyl)acrylic acid (MAF) as an adhesion-promoting monomer. Monitoring the evolution of the reactor pressure and of the 19F NMR spectra of the terpolymer over the course of solution polymerization revealed the very pronounced compositional heterogeneity of the resulting terpolymer. The terpolymerization was scaled-up and implemented under aqueous suspension conditions in a 3 L-autoclave. This aqueous process, more industrially viable, was successful in spite of the undesirable addition reaction of water onto MAF producing 3-hydroxy-2-(trifluoromethyl)propanoic acid. The structure of the resulting polymers was characterized in detail by 1H, 19F NMR and FTIR spectroscopies, and their physical properties (thermal, adhesion and electroactive) were examined. The decarboxylation of MAF, observed by TGA to occur at ca. 250 °C, is not a limitation for the targeted applications. A MAF content of 1 mol% was shown to be sufficient to provide very good adhesion onto glass and metal substrates, and also to decrease the water contact angle from 104° (reference poly(VDF-co-TrFE) copolymer) to 86° (terpolymer containing 1 mol% of MAF). Polarization studies revealed that the terpolymers exhibited identical ferroelectric behavior as unmodified poly(VDF-co-TrFE) copolymers, characterized by a wide hysteresis (Ec = 60 MV m−1) and a high saturation polarization (Psat = 77 mC m−2). This study reports the first electroactive fluorocopolymers with improved adhesion, and paves the way for better incorporation of fluorinated electroactive thin films in multilayer films for flexible electronic devices.

Differences in electroactive terpolymers based on VDF, TrFE and 2,3,3,3-tetrafluoropropene prepared by batch solution and semi-continuous aqueous suspension polymerizations

In the search for new fluorinated electroactive copolymers, 0–8 mol% of 2,3,3,3-tetrafluoropropene (1234yf) was terpolymerized with vinylidene fluoride (VDF) and trifluoroethylene (TrFE). The reactivity in batch solution polymerization of 1234yf was evaluated. First, reactivity ratio measurements showed that homopropagation of 1234yf is favored compared to cross propagation with VDF or TrFE (rVDF-1234yf = 0.079, r1234yf-VDF = 2.6; and rTrFE-1234yf = 0.089, r1234yf-TrFE = 4.9, at 48 °C). Then, the study of a typical batch solution polymerization revealed that the polymerization time was not affected by the initial amount of 1234yf and that polymer chains with strong compositional heterogeneity were obtained. Based on these results, a semi-continuous aqueous suspension polymerization process was used for the synthesis of terpolymers with a more homogeneous composition. Calculation of addition probabilities exemplified the changes in the drift of composition. The monomer sequences in the poly(VDF-ter-TrFE-ter-1234yf) terpolymers, carefully studied by 19F NMR spectroscopy, were not affected by the polymerization process and were dominated by VDF-TrFE and VDF-1234yf dyads. Finally, the thermal and ferroelectric (FE) properties of the homogeneous and heterogeneous terpolymers were characterized and compared. In the case of heterogeneous terpolymers, increasing the 1234yf content from 0 to 6 mol% slightly decreased the crystal size and the overall crystallinity (Tm = 60 °C and ΔHm = 144 J g−1 for a poly(VDF66-ter-TrFE26-ter-1234yf8) terpolymer). On the contrary, for homogeneous terpolymers, 5 mol% of 1234yf strongly affected both the Curie and melting transitions at TCurie = 37 °C and Tm = 107 °C. The reduced coercive field (Ec = 40 MV m−1) and remnant polarization (Pr = 22 mC m−2) for the homogeneous terpolymer compared to a reference poly(VDF65-co-TrFE35) (Ec = 62 MV m−1 and Pr = 45 mC m−2) transcribed modifications of the FE domains.

New water soluble EP additive for environment friendly fluids

Synthetic and semi‐synthetic fluids are known to be less sensitive to bacterial growth than soluble oils. However they often offer poor lubricating properties, especially in the extreme pressure (EP) regime. In this paper, we introduce an innovative sulfur based additive demonstrating outstanding EP performances despite being completely water soluble. In combination with oiliness and anti‐wear agents, such as phosphate esters or alkyl thio acids, it exhibits a wide range of lubricating properties which are requested for multifunctional lubricants. Finally, we show that synthetic and semi‐synthetic fluids containing this type of additive can be considered for severe metalworking operations.

Printed actuators made with electroactive polymers on flexible substrates

This article presents a manufacturing process and the electro-mechanical characterization of actuators made with electroactive polymers based on a PDVF terpolymer. Indeed, the PVDF-TrFE-CFE presents a high electrostrictive strain under electrical field. By introducing it in a metal-insulator-metal structure processed on a thin PEN foil, cantilevers were realized on flexible substrates. The cantilevers fabrication process is described, and their characterization is done by the measurement of the displacement bending and the consequent calculation of the induced strain under electric field. A theoretical model is proposed and validated by the experimental measurements.

All inkjet-printed piezoelectric electronic devices: energy generators, sensors and actuators

Inkjet printing is considered to be a key technology in the field of flexible electronics due to its capability to deposit different types of materials in a controlled and defined manner. However, inkjet printing of functional materials such as the fluorinated piezoelectric copolymer P(VDF–TrFE) still remains a challenge. In this regard, a piezoelectric ink was formulated in a narrow viscosity range compatible with the specific print head used in this work. Characterization of the dielectric, ferroelectric and piezoelectric properties along with the morphology and crystallinity of the film showed excellent agreement with traditional solution processed thin films. Consequently, inkjet printed P(VDF–TrFE) layers were subsequently integrated as a functional layer into entirely inkjet printed flexible electronics devices such as energy harvesters, sensors and actuators contributing to the development of flexible electronic applications.

Fully printed and flexible ferroelectric capacitors based on a ferroelectric polymer for pressure detection

We report on the fabrication and demonstration of fully printed ferroelectric capacitors using poly(vinylidene fluoridetrifluoroethylene) [P(VDF–TrFE)]. The printed ferroelectric capacitors were primarily fabricated by ink-jet printing on a thin plastic film substrate. The annealing process for the P(VDF–TrFE) layer was optimized from the viewpoints of surface morphology and crystallinity. A good ferroelectric polarization–electric field loop and piezoelectricity in the P(VDF–TrFE) were achieved for the printed ferroelectric capacitors. We have succeeded in the detection of a weak pressure of 150 mbar using the printed ferroelectric capacitor, which is an indication of a potential application to health-care biosensors. These results were realized by the optimization of the annealing temperature for the P(VDF–TrFE) layer.

Ultrathin flexible memory devices based on organic ferroelectric transistors

Here, we demonstrate ultrathin, flexible nonvolatile memory devices with excellent durability under compressive strain. Ferroelectric-gate field-effect transistors (FeFETs) employing organic semiconductor and polymer ferroelectric layers are fabricated on a 1-µm-thick plastic film substrate. The FeFETs are characterized by measuring their transfer characteristics, programming time, and data retention time. The data retention time is almost unchanged even when a 50% compressive strain is applied to the devices. To clarify the origin of the excellent durability of the devices against compressive strain, an intermediate plane is calculated. From the calculation result, the intermediate plane is placed close to the channel region of the FeFETs. The high flexibility of the ferroelectric polymer and ultrathin device structure contributes to achieving a bending radius of 0.8 µm without the degradation of memory characteristics.

Fully Printed Wearable Vital Sensor for Human Pulse Rate Monitoring using Ferroelectric Polymer

The ability to monitor subtle changes in vital and arterial signals using flexible devices attached to the human skin can be valuable for the detection of various health conditions such as cardiovascular disease. Conventional Si device technologies are being utilised in traditional clinical systems; however, its fabrication is not easy owing to the difficulties in adapting to conventional processes. Here, we present the development of a fully printed, wearable, ferroelectric-polymer vital sensor for monitoring the human pulse wave/rate on the skin. This vital sensor is compact, thin, sufficiently flexible, and conforms to the skin while providing high pressure sensitivity, fast response time, superior operational stability, and excellent mechanical fatigue properties. Moreover, the vital sensor is connected to a communication amplifier circuit for monitoring the pulse waves with a wireless sensing system. This sensor system can realise the development of new healthcare devices for wearable sensor applications.

Author Correction: Fully Printed Wearable Vital Sensor for Human Pulse Rate Monitoring using Ferroelectric Polymer

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.