Electrostrictive Energy Conversion of Polyurethane with Different Hard Segment Aggregations

This work reported the electrostriction of polyurethane (PU) with different aggregations of hard segments (HS) controlled by dissimilar solvents: N,N-dimethylformamide (DMF) and a mixture of dimethyl sulfoxide and acetone denoted as DMSOA. By using atomic force microscopy and differential scanning calorimetry, the PU/DMSOA was observed to have larger HS domains and smoother surface when compared to those of the PU/DMF. The increase of HS domain formation led to the increase of transition temperature, enthalpy of transition, and dielectric constant (0.1 Hz). For the applied electric field below 4 MV/m, the PU/DMSOA had higher electric-field-induced strain and it was opposite otherwise. Dielectric constant and Young’s modulus for all the samples were measured. It was found that PU/DMF had less dielectric constant, leading to its lower electrostrictive coefficient at low frequency. At higher frequencies the electrostrictive coefficient was independent of the solvent type. Consequently, their figure of merit and power harvesting density were similar. However, the energy conversion was well exhibited for low frequency range and low electric field. The PU/DMSOA should, therefore, be promoted because of high vaporizing temperature of the DMSOA, good electrostriction for low frequency, and high induced strain for low applied electric field

Récupération d’énergie à partir de matériaux électroactif. Modélisation du comportement de ces derniers

He need of self-powered and wireless systems is at the origin of intense research activity on the electrical energy harvesting from surrounding sources of thermal or mechanical origin. This energy harvesting can be made only if adapted materials of conversion, object of this thesis and efficient methods of extraction of energy are available. Among different types of materials, electro-active polymers occupy a place of choice because they are easy of implementation and can be deposited on of very large surfaces. Firstly, an analytical model was proposed to model the expression of electric current and available power that can be harvested by using a polymeric film glued together on a metallic beam mechanically excited on its first flexural mode. This model showed for instance that the permittivity of the polymeric film is one of the key parameters to improve the conversion. This model was experimentally validated by using polymers of trade and also allowed to assess the effect of the thickness of the film and working frequency. Secondly, polymers filled in volume by nanometric or micrometric conductive powders have been synthesized. It was shown that the use of such fillers allows increasing the permittivity thanks to a mechanism of interfacial polarization and, in accordance with the results predicted by the model, also allows enhancing the performances of energy harvesting.Le besoin de systèmes auto-alimentés et sans fils est à l’origine d’une activité intense de recherches sur la récupération d’énergie électrique à partir de sources ambiantes d’origine thermique ou mécanique. Cette récupération ne peut se faire que si l’on dispose de matériaux de conversion adaptés, objet de cette thèse et de méthodes efficaces d’extraction d’énergie. Parmi les différents types de matériaux, les polymères électro-actifs occupent une place de choix car ils sont faciles de mise en œuvre et peuvent être déposés sur de très grandes surfaces quelles soient planes ou non. Dans un premier temps, un modèle analytique a été réalisé pour obtenir l’expression du courant électrique et de la puissance disponible lorsqu’on récupère l’énergie électrique avec un film polymère collé sur une poutre métallique excitée mécaniquement sur son premier mode de flexion. Ce modèle a par exemple montré que la permittivité du film polymère est un des paramètres clefs pour augmenter la conversion. Ce modèle a été validé expérimentalement en utilisant des polymères du commerce et a permis aussi d’évaluer l’effet de l’épaisseur du film et de la fréquence de travail. Dans un deuxième temps, des composites utilisant des charges conductrices de taille nanométriques ou micrométriques dispersées en volume dans le polymère ont été synthétisés. Il a été montré que l’emploi de charges conductrices permet d’augmenter la permittivité grâce à un mécanisme de polarisation interfaciale et, conformément à ce que le modèle prédit, d’accroitre les performances en récupération d’énergie

High Electromechanical Deformation Based on Structural Beta-Phase Content and Electrostrictive Properties of Electrospun Poly(vinylidene fluoride- hexafluoropropylene) Nanofibers

The poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) polymer based on electrostrictive polymers is essential in smart materials applications such as actuators, transducers, microelectromechanical systems, storage memory devices, energy harvesting, and biomedical sensors. The key factors for increasing the capability of electrostrictive materials are stronger dielectric properties and an increased electroactive β-phase and crystallinity of the material. In this work, the dielectric properties and microstructural β-phase in the P(VDF-HFP) polymer were improved by electrospinning conditions and thermal compression. The P(VDF-HFP) fibers from the single-step electrospinning process had a self-induced orientation and electrical poling which increased both the electroactive β-crystal phase and the spontaneous dipolar orientation simultaneously. Moreover, the P(VDF-HFP) fibers from the combined electrospinning and thermal compression achieved significantly enhanced dielectric properties and microstructural β-phase. Thermal compression clearly induced interfacial polarization by the accumulation of interfacial surface charges among two β-phase regions in the P(VDF-HFP) fibers. The grain boundaries of nanofibers frequently have high interfacial polarization, as they can trap charges migrating in an applied field. This work showed that the combination of electrospinning and thermal compression for electrostrictive P(VDF-HFP) polymers can potentially offer improved electrostriction behavior based on the dielectric permittivity and interfacial surface charge distributions for application in actuator devices, textile sensors, and nanogenerators

Récupération d énergie à partir de matériaux électroactif. Modélisation du comportement de ces derniers

Le besoin de systèmes auto-alimentés et sans fils est à l origine d une activité intense de recherches sur la récupération d énergie électrique à partir de sources ambiantes d origine thermique ou mécanique. Cette récupération ne peut se faire que si l on dispose de matériaux de conversion adaptés, objet de cette thèse et de méthodes efficaces d extraction d énergie. Parmi les différents types de matériaux, les polymères électro-actifs occupent une place de choix car ils sont faciles de mise en œuvre et peuvent être déposés sur de très grandes surfaces quelles soient planes ou non. Dans un premier temps, un modèle analytique a été réalisé pour obtenir l expression du courant électrique et de la puissance disponible lorsqu on récupère l énergie électrique avec un film polymère collé sur une poutre métallique excitée mécaniquement sur son premier mode de flexion. Ce modèle a par exemple montré que la permittivité du film polymère est un des paramètres clefs pour augmenter la conversion. Ce modèle a été validé expérimentalement en utilisant des polymères du commerce et a permis aussi d évaluer l effet de l épaisseur du film et de la fréquence de travail. Dans un deuxième temps, des composites utilisant des charges conductrices de taille nanométriques ou micrométriques dispersées en volume dans le polymère ont été synthétisés. Il a été montré que l emploi de charges conductrices permet d augmenter la permittivité grâce à un mécanisme de polarisation interfaciale et, conformément à ce que le modèle prédit, d accroitre les performances en récupération d énergie.he need of self-powered and wireless systems is at the origin of intense research activity on the electrical energy harvesting from surrounding sources of thermal or mechanical origin. This energy harvesting can be made only if adapted materials of conversion, object of this thesis and efficient methods of extraction of energy are available. Among different types of materials, electro-active polymers occupy a place of choice because they are easy of implementation and can be deposited on of very large surfaces. Firstly, an analytical model was proposed to model the expression of electric current and available power that can be harvested by using a polymeric film glued together on a metallic beam mechanically excited on its first flexural mode. This model showed for instance that the permittivity of the polymeric film is one of the key parameters to improve the conversion. This model was experimentally validated by using polymers of trade and also allowed to assess the effect of the thickness of the film and working frequency. Secondly, polymers filled in volume by nanometric or micrometric conductive powders have been synthesized. It was shown that the use of such fillers allows increasing the permittivity thanks to a mechanism of interfacial polarization and, in accordance with the results predicted by the model, also allows enhancing the performances of energy harvesting.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Electrostrictive and Structural Properties of Poly(Vinylidene Fluoride-Hexafluoropropylene) Composite Nanofibers Filled with Polyaniline (Emeraldine Base)

Previous studies have reported that poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymers can exhibit large electrostrictive strains depending on the filler. This work examines the electrostrictive and structural properties of P(VDF-HFP) nanofibers modified with conductive polymer polyaniline (PANI). The P(VDF-HFP)/PANI composite nanofibers were prepared by an electrospinning method with different PANI concentrations (0, 0.5, 1, 1.5, 3 and 5 wt.%). The average diameter, water contact angle and element were analyzed by SEM, WCA and EDX, respectively. The crystalline, phase structure and mechanical properties were investigated by XRD, FTIR and DMA, respectively. The dielectric properties and electrostrictive behavior were also studied. The results demonstrated that the composite nanofibers exhibited uniform fibers without any bead formation, and the WCA decreased with increasing amount of PANI. However, a high dielectric constant and electromechanical response were obtained. The electrostrictive coefficient, crystalline, phase structure, dielectric properties and interfacial charge distributions increased in relation to the PANI content. Moreover, this study indicates that P(VDF-HFP)/PANI composite nanofibers may represent a promising route for obtaining electrostrictive composite nanofibers for actuation applications, microelectromechanical systems and sensors based on electrostrictive phenomena