Pierre-Jean Cottinet

Evaluation of energy harvesting performance of electrostrictive polymer and carbon-filled terpolymer composites

Recent trends in energy conversion mechanisms have demonstrated the abilities of electrostrictive polymers for converting mechanical vibrations into electricity. In particular, such materials present advantageous features such as high productivity, high flexibility, and processability. Hence, the application of these materials for energy harvesting purposes has been of significant interest over the last few years. The purpose of this paper consists in evaluating the energy scavenging abilities of electrostrictive terpolymer composite filled with 1 vol % carbon black poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene). For fair comparison, a new figure of merit taking into account the intrinsic parameters of the material is introduced. This figure of merit equals the squared product of the electric field-related electrostrictive coefficient by the Young modulus, divided by the permittivity, relating the electric energy density per cycle per squared strain magnitude and squared bias electric fi...

Modeling and experimentation on an electrostrictive polymer composite for energy harvesting

The harvesting of energy from ambient environments is an emerging technology with potential for numerous applications, including portable electronic devices for renewable energy. Most of the current research activities refer to classical piezoelectric ceramic materials, but more recently the development of electrostrictive polymers has generated novel opportunities for high-strain actuators. At present, the investigation of using electrostrictive polymers for energy harvesting (a conversion of mechanical to electrical energy) is beginning to show potential for this application. This paper discusses the development of a model that is able to predict the energy harvesting capabilities of an electrostrictive polymer composite (EPC). An equivalent electrical scheme has been developed by using the model of current that was recently developed by our group. After the validation of the model on a macroscopic level, an empirical relationship was established to predict the value of power from the electrostriction coefficient, the dielectric permittivity, and the compliance of the material. Finally, results indicated that the dielectric permittivity was the crucial parameter for energy harvesting.

Electrostrictive energy conversion in polyurethane nanocomposites

Electrostrictive polymers have demonstrated an ability to convert mechanical energy into electrical energy and vice versa. This energy conversion has been exploited in an extensive range of applications, including sensors and actuators. Recently, electrostrictive polymers have been investigated as electroactive materials for energy harvesting. The present work aims at establishing an analytical modeling based on electrostrictive equations for predicting a current that can be obtained from the first flexural mode of a beam which was attached by the electrostrictive polymers. The study was carried out on polyurethane films, either without filler or filled with nanosized SiC or a carbon nanopowder. Experimental measurements of the harvested current have been compared to the theoretical behavior predicted by the proposed model. A good agreement was observed between the two sets of data, which consequently validated that the modeling can be used to optimize the choice of materials. It was also shown that the i...

Effects of copper filler sizes on the dielectric properties and the energy harvesting capability of nonpercolated polyurethane composites

Nonpercolated composites based on polyurethane (PU) filled with low concentrations copper (Cu) powders of varying sizes were studied as electrostrictive materials for mechanical energy harvesting. The dispersion of the fillers within the polymeric matrix was investigated by scanning electron microscopy, and results showed a relatively homogeneous dispersion for the microsized fillers and the existence of agglomerates for their nanosized counterparts. Differential scanning calorimetry measurements displayed that there occurred no interaction between the polymeric matrix and the microsized fillers whereas the nanosized fillers slightly enhanced the glass transition of the soft segments of PU and significantly affected the recrystallization temperature. The dependence of the dielectric properties of the composites as a function of the filler volume fraction and filler size was investigated over a broad range of frequencies, showing an increase in the permittivity when fillers were used. This increase was more pronounced for the composites containing nanosized fillers. The measurement of the harvested current and of the harvested power also demonstrated an enhancement of the energy harvesting capability when nanofillers were employed. From the experimental data, it appeared that the electrostrictive coefficient Q was not proportional to the inverse ratio of the permittivity and the Young modulus for the studied composites. Finally, analytical modeling of the harvested current and of the harvested energy offered an accurate description of the experimental data.

Analysis of AC-DC conversion for energy harvesting using an electrostrictive polymer P(VDF-TrFE-CFE)

Harvesting systems capable of transforming unused environmental energy into useful electrical energy have been extensively studied for the last two decades. The recent development of electrostrictive polymers has generated new opportunities for harvesting energy. The contribution of this study lies in the design and validation of electrostrictive polymer- based harvesters able to deliver dc output voltage to the load terminal, making the practical application of such material for self-powered devices much more realistic. Theoretical analysis supported by experimental investigations showed that an energy harvesting module with ac-to-dc conversion allows scavenging power up to 7 μW using a bias electric field of 10 V/μm and a transverse strain of 0.2%. This represents a power density of 280 μW/cm3 at 100 Hz, which is much higher than the corresponding values of most piezo-based harvesters.

Focus on the electrical field-induced strain of electroactive polymers and the observed saturation

Thanks to their large electrical field-induced strains, electroactive polymers can be used in various applications; as electroactive materials for artificial muscles or as active materials of membranes, due to their flexibility. One drawback concerning their use involves the saturation of the electrical field-induced strain which occurs at around 20% for a polymer film with a thickness of 80 μm. Few studies have been devoted to the understanding of this saturation. To this end, the present paper describes mechanical measurements of the extensive strain versus stress and the determination of the current flowing through an electroactive polymer driven by an electrical field. These experiments have clearly demonstrated that the observed saturation of the electrical induced strain was not due to a mechanical saturation within the sample but to the saturation of the electrically induced polarization. By carrying out a suitable modeling of the polarization versus electrical field, it was possible to calculate t...

Differential scanning calorimeter and infrared imaging for electrocaloric characterization of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

Electrocaloric properties of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer were determined by two methods. A modified differential scanning calorimeter measures the entropy variation when applying an electric field under isothermal conditions. Alternative technique consists of an infrared imaging camera that gives direct information on temperature variation in pseudo-adiabatic condition. Both techniques give similar results with a heat capacity of 1500 J/(kg K). For an electric field of 80 V/μm, entropy variation was measured at 15.1 J/(kg K) and a temperature variation of 2.75 K. High frequency measurement is possible using infrared imaging, and a strong frequency dependence of the electrocaloric effect was observed.

Evaluation of macroscopic polarization and actuation abilities of electrostrictive dipolar polymers using the microscopic Debye/Langevin formalism

Electrostrictive polymers, as an important category of electroactive polymers, are known to have non-linear response in terms of actuation that strongly affects their dynamic performance and limits their applications. Very few models exist in the literature, and even fewer are capable of making reliable predictions under an electric field. In this paper, electrostrictive strain of dipolar polymeric systems is discussed through constitutive equations derived from the Boltzmann statistics and Debye/Langevin formalism. Macroscopic polarization is expressed as a function of the inherent microscopic parameters of the dielectric material. Electrostrictive strain, polarization and dielectric permittivity are described well by the model in terms of dipole moment and saturation of dipole orientation, allowing the physical definition of the electrostrictive coefficient Q. Maxwell forces generated by dipolar orientation inducing surface charges are also used to explain the electrostrictive strain of polymers. The assessment of this analysis through a comparison with experimental data shows good agreement between reported values and theoretical predictions. These materials are generally used in low-frequency applications, thus the interfacial phenomena that are responsible for low saturation electric field should not be omitted so as not to underestimate or overestimate the low electric field response of the electrostrictive strain.

Electrostrictive polymer composite for energy harvesters and actuators

Abstract Polymers have attractive properties when compared with inorganic materials: they are lightweight, inexpensive, pliable, and easily processed and manufactured. They can be configured into complex shapes and their properties can be tailored according to demand. With the rapid advances in materials used in science and technology, various substances embedded with intelligence at the molecular level are being developed. A type of electroactive polymer known as electrostrictive has shown considerable promise for a variety of applications, such as actuation with a strain thickness of 15% for an electric field of 10 V/μm. Polyurethane-based nanocomposite films were prepared by incorporating a carbon black nanopowder (C) into the polymer matrix. Electric field-induced strain measurements revealed that a loading of 1 vt% C (volume percentage of carbon black nanopowder) increased the strain level by a factor of 2.5 at a moderate field strength (10 V/μm). Moreover, another application for this material concerned the harvesting of mechanical energy, which constitutes an attractive alternative to the strict reliance on traditional batteries with limited lifetimes. For instance, an effective conversion from the mechanical-to-electric domains of 2.3 μW/cm3, under a transverse vibration level of 0.25% at 100 Hz, has been demonstrated for nylon. The final results indicated that the dielectric constant was a crucial parameter for energy harvesting.

Energy harvesting by nonlinear capacitance variation for a relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

The present letter describes the investigation of the electrostatic energy harvesting through nonlinear capacitance variation caused by changes in temperature for a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer. Owing to the electric tunability of the terpolymer, the harvested energy can-using an Ericsson cycle-be simulated from permittivity under a dc electric field. When going from 25 to 0 °C, it was found, from simulation, that the harvested energy increased up to 240 mJ/cm3 when raising the electric field at 80 kV/mm. Experimental measurement was also carried out, thus confirming the feasibility of electrostatic energy harvesting through low temperature Ericsson cycle.