Electron Plasma Charging Effects on the Biocompatible Electrospun Dielectric Fibers
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The purpose of this work is to study the dielectric charging of polymer fibers with the electron plasma charging effects accompanied by the emergence of waves propagating along the polymer fiber surface. Monitoring of the charge propagation along the single fiber has been performed using dielectric polyhydroxybutyrate (PHB) fibers obtained by the electrospinning (ESP) method under the electron beam inside the scanning electron microscope chamber. The mechanical effect of the electron beam on the polymer fibers has been detected in a time-lapse mode. The influence of the polymer surface irregularities and mechanical defects on the fiber charging has been demonstrated. Plasma mechanism is typical not only for electrophysical phenomena but also for the control of mechanical movement of the fibers by the electron beam and the charge propagation during electron-beam-induced melting and in the presence of hydrodynamic polymer flows. It is assumed that the mechanical effect in the methods using an electron beam (and plasma on the dielectric surface) as an impact source can be determined by the following factors: pressure of the electron beam and the electric field, contribution of the secondary emission, thermal/thermomechanical factors, and dynamic balance or competition between all the forces affecting the sample (electron-beam pressure, gravity pressure, recoil pressure during evaporation, vapor pressure/surface tension, and so on). In addition to purely scientific interest, the above phenomena are also of significant applied interest since the influence of the polymer fiber charging on the separation procedure of aerosols in nonwoven filters is well known, and hence, charging of such polymer fibers is important for some energy storage devices.A theoretical study was carried out to analyze the impact of composite effect on dielectric constant and tunability in the ferroelectric–dielectric system. Models of Ba 0.5 Sr 0.5 TiO 3 –Mg 2 TiO 4 , Ba 0.45 Sr 0.55 TiO 3 –MgO and Ba 0.5 Sr 0.5 TiO 3 –MgO–Mg 2 SiO 4 system were constructed. The corresponding dielectric constant, tunability, and electric field distribution were obtained from the finite element analysis and the connections between these parameters were analyzed. The effects of the relative relationship between the dielectric constant of ferroelectric and dielectric on the whole dielectric properties were also analyzed by constructing a series of models with different dielectrics.
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Morphology
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In modeling the dielectric properties of inhomogeneous materials, the treatment of the electric field interaction s differentiate the usual modeling formalism and their accuracy. In this paper, we show that the performance of effective medium methods is dependent upon a number of variables - defect concentration, alignment, and the dielectric constant of the material itself. Using our previously developed finite element model of an inhomogeneous dielectric, we have developed models for a number of dielectric films of varying dielectric constant and microstructures. Alignment to of defects parallel to the applied field and the larger defect aspect ratios increase the overall dielectric constant. The extent of these effects is dependent on the dielectric constant of the bulk component.
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The percolative ceramic composites of Ba0.75Sr0.25TiO3∕Ag (BST/Ag) with dense microstructure were sintered at a low temperature of 960°C. Excellent dielectric properties, such as high dielectric constant (εr∼24000), low dielectric loss, and high dielectric tunability, were reported. The dielectric constant is found to be nearly temperature and frequency independent. It is essential to introduce the low-melting-point metal of silver into BST ceramics for significantly enhancing the dielectric properties of the composites. The superproperties make it potential to be used for electronic devices such as high charge-storage capacitors and tunable filters.
High-κ dielectric
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Carbon fiber composites (CFCs) were mechanically refined and classified the scanning electron microscope (SEM) configuration of untreated and heat-treated mechanically recycled carbon fiber epoxy and carbon fiber vinyl ester composite were examined by using scanning electron microscopy (SEM). SEM Results indicate that the main defects in the structure of recycled CFCs are broken fibers, fiber pull-out, fiber-matrix separation. Also Comparing SEM of untreated and heat-treated recycled CFC indicates that there is no significant difference between their micrographs.
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Composites have been extensively studied for dielectric and related applications. This is a review of polymer based 0–3 composites that exhibit a high dielectric constant. These composites are classified into two types: Dielectric–dielectric composite and conductor–dielectric composite. The physical principles and related models are presented with associated assumptions and approximations. In general, a dielectric–dielectric composite needs a higher concentration of the fillers to reach a high dielectric constant than a conductor–dielectric composite. The high dielectric constant observed in the conductor–dielectric composites is usually associated with a high dielectric loss and a low electric breakdown field. The experimental results are summarized to illustrate the principles for, and the achievements in, the development of these composites. The challenges facing the fundamental understanding and the further development of these composites for different applications are discussed.
High-κ dielectric
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A new A site complex lead-free ferroelectric ceramics of(1-x-y)BNT-xBKT-yBiCoO3 was prepared by a conventional ceramic sintering technique.The relation between composition and dielectric properties,dielectric properties and frequency were investigated.It was found that the dielectric constant and dielectric loss of unpoled samples is higher that those of poled samples.The dielectric constant and dielectric loss of unpoled samples decrease with the increase content of BiCoO3.The dielectric constant and dielectric loss of unpoled and poled samples increase with the content of BKT increasing.The dielectric constant decreases with frequency increasing,and the decreasing trend become slowly.The dielectric loss first decrease and then increase with increasing frequency.
Dielectric loss
Ferroelectric ceramics
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Carbon fiber composites (CFCs) were mechanically refined and classified the scanning electron microscope (SEM) configuration of untreated and heat-treated mechanically recycled carbon fiber epoxy and carbon fiber vinyl ester composite was examined by using scanning electron microscopy (SEM). SEM Results indicate that the main defects in the structure of recycled CFCs are broken fibers, fiber pull-out, fiber-matrix separation. Also Comparing SEM of untreated and heat-treated recycled CFC indicates that there is no significant difference between their micrographs.
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Scanning electron microscopy generally requires specimen preparation which includes dehydration or drying and metal coating. This preparation is necessary for beam sensitive specimens or specimens that contain water and/or oil. This has been a necessary requirement for quality imaging with conventional scanning electron microscopes (SEMs). Recently with the development of variable-pressure SEMs (VP-SEMs), scanning electron microscopy of most specimens has become possible without the need of specimen preparation. Water-containing wet specimens can be examined at low temperatures at which water vaporization is suppressed and specimen artifacts due to water evaporation are minimized.
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A novel method of estimating the dielectric constant has been devised based on a theoretical treatment of dielectrics. The expression obtained enables the electronic and ionic components of the dielectric constant to be estimated from data in the literature. The orientational component can be isolated by measuring the temperature dependence of the dielectric constant. The dielectric constants of low-k materials which have not been synthesized can be estimated using this expression.
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