Littérature scientifique sur le sujet « Inorganic Oxide-Polymer Composites - Dielectric Properties »

Polymer dielectric possess advantages of mechanical flexibility, low temperature processing, and cost. However, for practical applications dielectric constant of polymers is not high enough. To raise the dielectric constant, polymers are often composited with fillers of various morphologies (one-dimensional, two-dimensional, three-dimensional) and types (inorganic, organic, carbon, conductive, non-conductive). Recently discovered two-dimensional (2D) materials including graphene, transition metal dichalcogenides, MXenes, ferroelectric ceramics, etc. have been discovered. These materials have excellent electrical, mechanical, thermal properties and high specific surface area, which makes these ideal materials to reinforce the properties of polymers, especially dielectric properties. Here, in this review we summarize the latest developments regarding the use of 2D fillers to improve the dielectric properties of polymer composites. We have systematically discussed synthesis of 2D materials, processing of their 2D filler/polymer composites, theoretical background of dielectric properties of these composites, and literature summary of the dielectric properties of polymer composites with various type of 2D fillers.

Composite particles associated with graphene oxide (GO) and inorganic materials provide the synergistic properties of an appropriate electrical conductivity of GO with the good dielectric characteristics of inorganic materials, making them attractive candidates for electrorheological (ER) materials. This review paper focuses on the fabrication mechanisms of GO/inorganic composites and their ER response when suspended in a non-conducting medium, including steady shear flow curves, dynamic yield stress, On-Off tests, and dynamic oscillation analysis. Furthermore, the morphologies of these composites, dielectric properties, and sedimentation of the ER fluids are covered.

Polymer blend or composite, which is a combination of two or more polymers and fillers such as semiconductors, metals, metal oxides, salts and ceramics, are a synthesized product facilitating improved, augmented or customized properties, and have widespread applications for the achievement of functional materials. Polymer materials with embedded inorganic fillers are significantly appealing for challenging and outstanding electric, dielectric, optical and mechanical applications involving magnetic features. In particular, a polymer matrix exhibiting large values of dielectric constant (ε′) with suitable thermal stability and low dielectric constant values of polymer blend, having lesser thermal stability, together offer significant advantages in electronic packaging and other such applications in different fields. In this review paper, we focused on the key factors affecting the dielectric properties and its strength in thin film of inorganic materials loaded poly methyl meth acrylate (PMMA) based polymer blend (single phase) or composites (multiple phase), and its consequences at low and high frequencies are explored. A wide range of different types of PMMA based polymer blends or composites, which are doped with different fillers, have been synthesized with specific tailoring of their dielectric behavior and properties. A few of them are discussed in this manuscript, with their different preparation techniques, and exploring new ideas for modified materials.

Fluoropolymer/inorganic nanofiller composites are considered to be ideal polymer dielectrics for energy storage applications because of their high dielectric constant and high breakdown strength. However, these advantages are a trade-off with the unavoidable aggregation of the inorganic nanofillers, which result in a reduced discharge of the energy storage density. To address this problem, we developed polyvinylidene fluoride (PVDF) graft copolymer/cellulose-derivative composites to achieve high-dielectric and energy-storage density properties. An enhanced dielectric constant and improved energy density were achieved with this structure. The optimal composites exhibited a high discharge energy density of 8.40 J/cm3 at 300 MV/m. This work provides new insight into the development of all-organic composites with bio-based nanofillers.

Polymer-ceramic composites have been pursued as the most promising dielectric materials for embedded capacitors in the organic package. In this study, ceramic fillers such as Calcium Copper Titanate (CCTO) was used to produce epoxy thin film composites for the purpose to replace capacitor made of ceramic materials. Spin coating technique was used to produce epoxy thin film composites. The effect of fillers loading on tensile and dielectric properties of the epoxy thin film composites were determined. Results showed that epoxy thin film with 20 vol% filler loading showed good dielectric properties. However, an increase of the fillers content caused reduction in the tensile properties due to filler agglomeration and voids. Dielectric constants and dielectric losses of epoxy/inorganic composite films generally increase with addition of filler.

High discharged energy density and charge–discharge efficiency, in combination with high electric breakdown strength, maximum electric displacement and low residual displacement, are very difficult to simultaneously achieve in single-component polymer dielectrics. Plenty of researches have reported polymer based composite dielectrics filled with inorganic fillers, through complex surface modification of inorganic fillers to improve interface compatibility. In this work, a novel strategy of introducing environmentally-friendly biological polyester into fluoropolymer matrix has been presented to prepare all-organic polymer composites with desirable high energy storage properties by solution cast process (followed by annealing or stretching post-treatment), in order to simplify the preparation steps and lower the cost. Fluoropolymer with substantial ferroelectric domains (contributing to high dielectric response) as matrix and poly (3-hydroxybutyrate-co-3-hydroxyvalerate) with excellent linear polarization property (resulting in high breakdown strength) as filler were employed. By high-temperature annealing, the size of ferroelectric domains could be improved and interfacial air defects could be removed, leading to elevated high energy storage density and efficiency in composite. By mono-directional stretching, the ferroelectric domains and polyester could be regularly oriented along stretching direction, resulting in desired high energy storage performances as well. Besides, linear dielectric components could contribute to high efficiency from their strong rigidity restrain effect on ferroelectric component. This work might open up the way for a facile fabrication of promising all-organic composite dielectric films with high energy storage properties.

Abstract The interface incompatibility between organic polymer and inorganic ceramic filler is a common phenomenon in polymer-based dielectric composites. In this paper, the Ar/CF4 plasma is used to modify the CaTiO3 particles, which improved the dispersion of CaTiO3 and its compatibility with polytetrafluoroethylene (PTFE). The findings demonstrate that growing argon (Ar) flow rate was beneficial to enhance discharge and increase fluorinated graft content. The modified CaTiO3/PTFE is uniformly distributed and has no serious agglomeration phenomenon, which effectively improves its dielectric characteristics. Modified CaTiO3/PTFE composite with 5 wt.% CaTiO3 has a dielectric constant of 2.32 whilst the dielectric loss reaches 2.8 × 10−3 at around 10 GHz.

The dielectric properties of polymer composites with inorganic nanoparticles were investigated. In the demonstration of the dielectric constant expression of the nanocomposite polymer, the dielectric contributions of the displacement polarization, the orientation polarization, and the space polarization in the nanocomposite polymer were all considered. In the demonstration, two dielectric relaxation models were used, that of Debye for inorganic nanoparticles and the Havriliak–Negami function model for polymers. Then the expression of the complex dielectric constant of the nanocomposite polymer was obtained by using Onsager's local field theory. Furthermore, the nanocomposite polymer thin films that consist of PbTiO3 nanoparticles and polyetherketone were prepared. The real parts of the dielectric constants were measured and calculated, respectively. It was found that our calculated results are in good agreement with our measured results. PACS Nos.: 77.20, 77.55, 81.20T

Abstract Dielectric polymer composites containing low content inorganic fillers exhibit superior dielectric properties and endurance for simultaneous enhancement of dielectric constant and breakdown strength. Polyetherimide (PEI) composites incorporated with nanosized BaTiO3 of 0.1vol.% loading fraction was developed in this work and their breakdown strength reached a maximum value along with the highest dielectric constant. The discharged energy density increased to 8.33 J/cm3, which is 2.33 times that of pure PEI. The composite film also maintained an excellent endurance after 104 cycles of fatigue test. The low-level filling for enhanced composite property may reduce the challenge in film scale-up manufacturing.

In recent years the continuous and rapid development of the electronic industry together with the need for more efficient electric energy harvesting have notably increased the demand for: (i) high dielectric constant and breakdown strength materials for high energy density capacitors and (ii) piezoelectric flexible materials, with the ability to bend into diverse shapes, for powering low-power portable devices and self-powered electronic systems. Polymer-based composites and nanocomposites with inclusions of a ceramic active phase are very attractive for these applications because they combine materials with different characteristics, allowing the possibility to tune and optimize the dielectric and piezoelectric properties in the ensuing composite systems. In particular, many parameters can affect the material performance: (i) the nature of the polymer matrix and active component; (ii) the phases connectivity; (iii) the filler concentration, shape and dimensions; (iv) the filler/matrix interactions; (v) the preparation technique and processing. All this variability expands the possible applications of polymer-composites for energy-related purposes but also increases the difficulty in realistically predicting their ultimate properties. The design of polymer composites thus requires a rational selection of components, good interface engineering and proper processing optimization. To achieve this, a thorough comprehension of the process-structure-properties correlations is very important. This is the principal aim of this thesis work, which focus on the preparation of poly(vinylidene fluoride) homopolymer (PVDF) or poly(vinylidene fluoride-co-hexafluoropropylene) copolymer (PVDF-HFP) based composites with 0-3 connectivity containing different perovskite fillers, namely, BaTiO3 (BT), Pb(Zr,Ti)O3 (PZT) and Na0.5Bi0.5TiO3 - BaTiO3 (BNBT). The filler particles were used as prepared or properly surface modified and several techniques were employed for the composites preparation (i.e., solvent casting, melt blending, hot-pressing, compression moulding). Initially, a study of the neat polymer matrices was performed, by using, for the first time in literature, the compression moulding technique to tune the polymorphism of PVDF. A principal component analysis was performed on the infrared spectra of the moulded films to validate the equation usually employed for determining the electroactive phase amount (FEA) then multiple linear regression was applied to better understand how the processing parameters affect the FEA value. A double-step procedure was proven fundamental in inducing the formation of PVDF β phase and improving the dielectric properties of the ensuing polymer films. After this preparatory investigation, the study of the process-structure-properties correlations was extended to PVDF-based composites, addressing three main issues: (i) the influence of processing on the ultimate properties of the prepared samples; (ii) the influence of particles dimensions and surface modification on the dielectric behaviour of the composite materials; (iii) the response of flexible piezoelectric composites. The preparation technique affects the microstructure at different levels, but it was found that not always a flawless particles dispersion necessary leads to the best final performance of the composite. Whereas, a proper moulding method, by affecting the polymorphism of the polymer matrix and the compactness of the film, can improve significantly the dielectric response. The presence of an inorganic shell around BT particles allows a modulation of the effective permittivity of the composites; if intrinsic factors (i.e., the permittivity of the components) prevail on extrinsic ones (i.e., interfacial polarization), the composites response can be predicted by FEM calculations. However, in these conditions, the reduction in the dielectric constant compensates for the increase of the breakdown strength promoted by the shell and, as a whole, the stored energy decreases. It is worth noting that the composites containing core-shell particles are characterized by low tunability, a condition which is important for application as dielectric capacitors. The functionalization of the ceramic particles with the tested coupling agents, despite decreasing to a certain extent the dielectric permittivity of the ensuing composites (due to the intrinsic low permittivity of the silane moieties), increases the maximum electric field, thus leading to an energy recovering capability comparable or slightly higher than that of the composite containing pristine BT particles. The dielectric response of the composites is affected by the particles dimensions even though the films containing pristine BT and those containing TiO2-coated particles exhibit a different trend of dielectric permittivity with filler size; this suggests a not negligible contribution of the interfaces, which varies with the method of particles synthesis. As concerns the piezoelectric composites, the piezoelectric coefficient (d33), in general, increases if the filler dimensions increase significantly. The higher response of the samples containing sintered and crushed PZT or BNBT particles (with respect to simply calcined powders) probably derived from the higher particles connectivity inside the agglomerates, which in turn leads to higher local stresses inside the material. As far as we know, the piezoelectric properties of composites made of fluorinated polymer matrices and BNBT filler had not been studied yet. The obtained d33 are in line with those of many flexible lead-free composites made with particles different from BNBT, suggesting the potentiality of these composites in the field of energy harvesting. As principal achievements, I obtained: (i) an alternative and smart method to tune the polymorphism of PVDF homopolymer and its copolymers, by exploiting a simple and easily-scalable processing technique; (ii) solvent-free fabrication of polymer-based composites with dielectric properties improved by the moulding process; (iii) a better comprehension about the role of the interfaces, useful to tune the final performance of the dielectric composites; (iv) flexible lead-free polymer-based composites with a good piezoelectric response for potential application as safe energy harvesting devices.

This chapter reports the recent advances in the fabrication methods, properties, and microelectronics packaging applications of various inorganic fillers and reinforced-polymer composites. Recently, inorganic particles, including ceramics and carbon-based material reinforced polymeric matrices, have attracted both academic and industrial interest because they exhibit good thermal and mechanical properties. The low dielectric constant and dielectric loss, the low thermal expansion coefficient, and high thermal conductivity make these kinds of composites suitable for microelectronics packaging. The filler ratio, surface modification, and preparation methods of these composites have a marked effect on the final properties of these materials. Herein, the preparation methods, thermal and dielectric properties, shortcomings, and microelectronics applications of polymers/inorganic composites are summarized and discussed along with detailed examples collected from the extensive scientific literature.

During the past decade, the preparation of inorganic/organic hybrid materials with high refractive index has attracted considerable attention. In particular, TiO2 (Titanium dioxide or Titania), as inorganic domains, have been incorporated into a polymer matrix to produce high refractive index hybrid materials [1–3]. Polarization of injection molded liquid crystal polymer/Titania composite parts have been investigated in the broad band millimeter wave frequency range. The measurements have been performed by using two different spectroscopy techniques. First, free space quasi optical millimeter wave spectrometer, equipped with a high power source coherent radiation tunable in the 40–90 GHz frequency range is used. Second, low power dispersive Fourier transform spectrometer has been used for higher frequencies in the range of 100–600 GHz. Dielectric properties of liquid crystal polymer/Titania composites have been determined in the broad band millimeter wave frequency range. A correlation between dielectric properties and dispersed Titania weight percent has been observed using the two spectroscopy techniques. It is found that the absorption coefficient and loss tangent is a strong function of the output power of the sources of the incident radiation. On the other hand, refractive index and real permittivity values measured from both spectroscopy techniques are similar. In addition, it has been found that transmittance level and absorption losses depend on the orientation of the samples with respect to the orientation of electric and magnetic fields in the incident electro-magnetic wave. Finally, the polarization of the parts varies with the direction of flow of the molten plastic into the cavity.

Polymeric materials present certain advantages over inorganic crystals for second-order nonlinear optical (NLO) applications because of their low dielectric constant, large optical nonlinearity, low cost, and ease of processability. Stable NLO polymeric materials are potential candidates for electro-optic (EO) devices such as high bandwidth electro-optic modulators [1], optical interconnects [2], and fiber optic gyros [3]. Second-order NLO properties in polymers are present when the chromophores are aligned in a non-centrosymmetric manner. Chromophores with enhanced NLO susceptibilities can be obtained by increasing electron-donating and/or accepting effects [4], by extending the conjugation length between the donor and acceptor groups [5] and by replacing the phenyl moieties in the chromophores with thiophene moieties [6]. Efforts were made by our group [7] and various other groups [6, 8] to synthesize and optimize the properties of the chromophore functionalized polymers with high optical nonlinearity. Jen and coworkers synthesized a variety of thiophene based chromophores with high optical nonlinearity, 'μβ' [6, 8]. Many of these chromophores, when doped in a polymer matrix exhibited an electro-optic value greater than 20 pm/V. Marder and coworkers studied the effect of strong acceptors in NLO chromophores and have found that an 'r33' value of 55 pm/V at 1.313 μm is realizable with some of these chromophore doped polycarbonate composites. However, most of these systems are of guest-host type, which limit the chromophore solubility as well as temporal stability of the poled order in the NLO chromophore-polymer composites.

Among composites, the polymer matrix ones are the cheapest and the easiest to form but they show major disadvantages such as poor electrical and thermal conductivity, low fire resistance etc. In the case of any composite, some of the properties may be designed, some of them may be obtained by using an appropriate forming technique and, at least, some of them may be improved by special treatments. In the case of polymer matrix composites the first two ways are recommended if we are taking into account the polymers’ properties while the last one will turn the PMC into an expensive material due to the costs of metal or oxide thin film deposition on polymeric surface. Is it possible to solve all the problems by material design and by developing a convenient forming technique? Powders are used as fillers in order to obtain bi-components composites. The most important aim is about the uniform distribution of particles in matrix. If the fillers’ particles are arranged into the polymer volume is possible to change the electro-magnetic behavior of the obtained composite making this one to act as a meta-material. The powders can be dielectric as talc, clay or ferrite can be magnetic active as ferrite, or electric active as CNT or carbon nano-fibers. All these powders have effects on the electromagnetic, thermal and mechanical properties of the composite. This study is about the influence of fillers on the tribological behavior of particulate composites. Epoxy resin was used as matrix and various powders were used to fill the polymer: ferrite, zinc, clay. The materials were thermally treated in order to reach the best polymer properties. Pin on disk fixture on a CETR-UTM had been used to determine the friction coefficient for each filler concentration. The Wear resistance of each material had been evaluated using the same apparatus but with some modifications.

High density polyethylene (HDPE) is known to form banded spherulites when crystallized from the melt. In such spherulites, concentric bands of alternating light and dark colors emanating from the spherulite nucleation center are observable between cross polarizers and appear as a function of the anisotropy of the dielectric susceptibility as crystal orientations continuously rotate about the growth direction. Recently, we identified PE to be a promising compound to induce twisting in conjugated carbonaceous systems, such as triisopropylsilylethynyl anthradithiophene (TIPS ADT). When blended together in ratios between 10 – 70 wt.% PE, TIPS ADT and PE crystals twist in concert with one another to form composite films of intertwined helicoidal fibrils. In this work, we investigate crystal twisting in HDPE-graphene oxide composites. In addition to its unique multifunctionality, graphene has also recently demonstrated peculiar twisting capabilities that strongly alter its physical properties. Here, we first produce graphene sheets through the chemical oxidation of natural graphite, and then investigate the influence of graphene on the twisting of HDPE composites under various processing parameters (graphene concentration, polymer cooling rate, etc). HDPE-graphene composites have been prepared using melt extrusion in the form of microfibers and films. We measured the influence of twisting on the mechanical and electrical properties of the composites, as well as the crystallographic structure using optical and electron microscopy, and X-Ray diffraction spectroscopy.

In this study, we demonstrate the electric and magnetic manipulation of nanoscale M-type Barium Hexaferrite (nBF) in polydimethylsiloxane (PDMS) to engineer a multifunctional nanocomposite with improved dielectric and magnetic properties. First, we synthesized the single crystal nBF via the hydrothermal synthesis route. The hydrothermal temperature, duration, and surfactant conditions were optimized to improve the magnetic properties of the nBFs, with further improvement achieved by post-annealing. The annealed nBFs were aligned dielectrophoretically (DEP) in the polymer matrices by applying an AC electric field. Under the influence of this electric field, nBFs were observed to rotate, align and form chains within the polymer matrix. Optical microscopy (OM) imaging was used to determine the electrical alignment conditions (duration, magnitude, and frequency) and these parameters were used to fabricate the composites. A Teflon setup with Indium Tin Oxide (ITO) coated Polyethylene Terephthalate (PET) was used, where the ITO coatings act as electrodes for the electric field-manipulation. To simultaneously apply the magnetic field, this Teflon setup is placed between two permanent magnets capable of generating a 0.6 T external magnetic field. Along with electric and magnetic fields, concurrent heating was applied to cure the PDMS and freeze the microstructure formed due to electric and magnetic fields. Upon completion of the curing step, parallel chain formation is observed under OM. The X-Ray Diffraction (XRD) results also confirm that the particles are magnetically oriented in the direction of the magnetic field within the chain. Vibrating Sample Magnetometry (VSM) measurements and dielectric spectroscopy are used to characterize the extent of anisotropy and improvement in dielectric and magnetic properties compared to random composites. We find that simultaneous electric and magnetic field alignment improves the dielectric properties by 12% compared to just magnetic alignment. We also observe 19% improved squareness ratio when both fields are applied. The possibility of simultaneous electrical and magnetic alignment of magnetic nanoparticles will open up new doors to manipulate and design particle-modified polymers for various applications.