Estimation of the permittivity of polymeric composite dielectrics from the surface characteristics of the filler using a thermodynamic model

A linear correlation between the permittivity of a composite dielectric based on polyvinyl alcohol cyanate and the content of active surface sites in its filler (dispersed barium titanate) was established. This correlation, in combination with a thermodynamic model of composite dielectrics, allows estimation of their permittivity from the surface characteristics of the filler.     

Interfacial polarization phenomena in organic molecular films

Electrostatic phenomena occurring at the interface between metal/organic and organic/organic materials are discussed from the viewpoint of dielectrics physics. Focusing on two important origins of surface polarization phenomena, orientational ordering of polar molecules and displacement of excess charges at the interface, surface polarization phenomena of organic thin films are discussed. To define the orientational order of polar molecules, orientational order parameters are introduced, and surface polarization due to the alignment of dipoles is expressed. The generation of Maxwell displacement current (MDC) and optical second harmonic generation (SHG) that are specific for surface organic monomolecular films are discussed, and some experimental evidence are shown. As an extension of the concept of surface Fermi level introduced to discuss the electrostatic phenomena due to electron transfer at the interface between metal-organic insulators, the surface Fermi level is extended to the discussion on the electrostatic phenomena of organic semiconductor materials on metals. In this paper, some experimental evidence of surface polarization originating from polar molecules and displacement of excess charges are shown. After that, with consideration of these surface phenomena, single electron tunneling of organic films are briefly discussed in association with surface polarization phenomena.     

Dielectric permittivity profiles of confined polar fluids

The dielectric response of a simple model of a polar fluid near neutral interfaces is examined by a combination of linear response theory and extensive molecular dynamics simulations. Fluctuation expressions for a local permittivity tensor epsilon(r) are derived for planar and spherical geometries, based on the assumption of a purely local relationship between polarization and electric field. While the longitudinal component of epsilon exhibits strong oscillations on the molecular scale near interfaces, the transverse component becomes ill defined and unphysical, indicating nonlocality in the dielectric response. Both components go over to the correct bulk permittivity beyond a few molecular diameters. Upon approaching interfaces from the bulk, the permittivity tends to increase, rather than decrease as commonly assumed, and this behavior is confirmed for a simple model of water near a hydrophobic surface. An unexpected finding of the present analysis is the formation of "electrostatic double layers" signaled by a dramatic overscreening of an externally applied field inside the polar fluid close to an interface. The local electric field is of opposite sign to the external field and of significantly larger amplitude within the first layer of polar molecules.     

Dielectric relaxation measurements on aerosol-OT/water/cyclohexane-solutions at low water content

The complex relative dieletric permittivity of aerosol-OT(AOT)/water/cyclohexane solutions has been measured within the frequency range 5 kHz-10 GHz. The investigated solutions were of oil-rich type with varying AOT- and water content. A marked dielectric relaxation has been found. The dielectric increment as well as the conductivity steeply increase with the water content, while the relaxation time decreases. Theoretical models of heterogeneous dielectrics consisting of polar, highly conductive inclusions in a nonpolar solvent with low conductivity have been applied to the results, allowing conclusions with regard to the inclusions, shape and conductivity.     

Cavity boundary effects within the onsager theory for dielectrics

Means by which the Onsager theory of dielectrics may be modified in a general way to include important structurally nonspecific electrical effects exercised at or near the cavity boundary are developed and discussed. In essence they rely upon extraction of limiting numerical solutions of the Laplace equation potentials for multiple shells approximating regions of smoothly varying permittivity surrounding the dipole-containing cavity. The results of several such modifications, which usefully retain the original reaction and cavity field forms, are applied to evaluate the dielectric constants of polar solvents acting as support media for mean-space-charge attenuation of intracavity electrical interactions, and in correlation of isolated molecule and condensed phase properties of formally nonassociated solvents. For the most part such predictions and correlations are found to be improved by a wide variety of physically reasonable continuity functions. Where they are not, more rational patterns of deviations consistent with possible modes of intramolecular charge transfer and weak intermolecular association in formally nonassociated liquids are detected. Some limited comparisons with particle- and structure-dependent theories, e.g., the mean spherical model and discrete lattice formulations, also suggest that the present permittivity modifications can effectively simulate important short-range nonspecific liquid ordering effects. Various factors relating to possible adaption of the limit procedures developed to other inhomogeneous dielectric medium calculations are also briefly outlined.     

Electrical and dynamooptical properties of Frechet dendron-modified polystyrene molecules in solutions

The electrooptical, dynamic, and dielectric characteristics of polystyrene modified by the Frechet dendrons of 1–4 generations have been studied in benzene, chloroform, and THF solutions. It has been shown that the Kerr constant and the shear optical coefficient for all the studied polymers coincide in sign and their absolute values increase with the dendron generation number. The intrinsic optical anisotropy of the repeating unit of dendronized polystyrene molecules is negative in sign, and its absolute value tends to grow with an increase in the generation number of dendrons. The frequency dispersions of the Kerr constand and of the dielectric polarization have been discovered for solutions of the modified polymer. The ratio between the times of relaxation characterizing the dispersion of dielectric permittivity and of the Kerr constant of solutions and the times of a rise and decay of electric birefringence measured on the onset and termination of the rectangular-pulsed field does not obey the longitudinal relaxation theory for polar macromolecules. The relaxation times of dielectric polarization and of electric birefringence tend to increase with the dendron generation number.     

Ferroelectric polymers and applications

This paper reviews the general features of ferroelectricity in polyvinylidene fluoride and related polymers; ferroelectricity is shown as the origin of piezoelectricity, pyroelectricity and high dielectric permittivity. Preparation technologies are discussed, and applications are presented, with special attention to capacitor dielectrics and piezoelectric transducers.     

Modification of the structure and properties of poly(vinylidene fluoride–trifluoroethylene) 56/44 mol % copolymer by a proton‐irradiation treatment

The effects of high‐energy proton irradiation on the structure and properties of 56/44 mol % poly(vinylidene fluoride–trifluoroethylene) copolymer were studied with differential scanning calorimetry (DSC), X‐ray diffraction (XRD), relative permittivity, and polarization hysteresis measurements. Copolymer films prepared by hot compression molding were irradiated with a broad range of proton dosages (10–107 Mrad) at room temperature. The DSC results showed that the ferroelectric transition was strongly affected by the proton dosages. The XRD data indicated the reduction of polar ordering in the copolymer by the proton‐irradiation treatment. From the relative permittivity and polarization behavior, the copolymer film was found to be converted from a normal ferroelectric material to a relaxor ferroelectric material as the proton dosage was increased to 50 Mrad. The electrostrictive coefficient of the 56/44 mol % copolymer was enhanced after irradiation, and the optimized proton dosage for attaining the highest electrostrictive strain response was determined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2334–2339, 2005     

A method for predicting the polarization of substances

A method for predicting the polarization characteristics of substances from the known permittivity and molar volume of parahydrogen (p-H₂), polarization characteristics of a reference, and the molar volume and internal interaction energy of the substance under study is suggested. The method is based on the assumption that the ratio between the deformation components of molar polarization at the given and critical temperatures is a universal function of reduced temperature.     

Dielectrical and electro-mechanical behavior of NBR at high electric field strength

The aim of this work is to present a new approach to characterize the dielectric properties of elastomers especially at low frequencies and high electric field strength, close to the operating conditions of dielectric elastomer actuators (DEA). By means of an electro-rheological measuring cell, static (DC) and alternating (AC) high electric field strength were applied to different types of acrylonitrile-butadiene rubbers (NBR), with varying content of polar acrylonitrile groups. Based on fundamental theory of electricity complex permittivity and polarization were calculated from Coulomb stress measurements at varying frequencies. During high voltage measurements it was observed, that dielectric loss current increases, if a certain critical field strength is exceeded. It is shown, that polar NBR rubbers exhibit a critical field strength far below of the non-polar polybutadiene rubber (BR), acting as a reference sample. NBR exhibits extraordinary high permittivity at low frequency, which makes this material as a favorite candidate for DEA. Furthermore, mechanical properties of NBR can be easily altered by application of an alternating electric field. This phenomenon opens new opportunities in a great variety of applications.     

Polarization of block textured films of ferroelectric copolymers of vinylidene fluoride with tetrafluoroethylene in an external field

The polarization of oriented films of the ferroelectric copolymer of vinylidene fluoride and tetrafluoroethylene in a sinusoidal electric field is studied. In low fields, the copolymer behaves as a linear dielectric whose permittivity nonlinearly increases with the amplitude of the alternating field. This behavior is related to the preferential orientation of the dipole moment of the chain along the normal to the surface and to the monocrystal-structure formation. In higher fields, the hysteresis behaves formally coincidently with the behavior of an antiferroelectric. The important role of through stressed chains in the amorphous phase in the initiation of domains of a new direction in polar crystals is observed. Increased adsorption of water molecules on the surface of a polarized film is found and is attributed to the formation of the final density of the stable polarization charge on it.     

Occurrence of an Intermediate Relaxation Process in Water-in-Oil Microemulsions below Percolation: The Electrical Modulus Formalism

The dielectric and conductometric spectra of water-in-oil microemulsions below percolation in the frequency range from 1 MHz to 1.8 GHz have been analyzed on the basis of the electrical modulus formalism. In the frequency range investigated, this approach clearly evidences the presence of a particular polarization mechanism, resulting in a well-defined dielectric dispersion, located between that due to the orientational polarization of the bulk aqueous phase and that due to the ionic structure of the interface, usually occurring in heterogeneous systems. This polarization mechanism has been attributed to the "in-phase" correlation displacement of surfactant polar head groups surrounding each water droplet dispersed in the oil phase. This mechanism differs from the usual interfacial Maxwell-Wagner effect. The advantage of the electrical modulus formalism, in comparison with the analysis of the directly measured quantities, the permittivity epsilon'(omega), and the total electrical conductivity sigma(omega), are briefly discussed. Copyright 2001 Academic Press.     

Interactions of polarizable media in water: a molecular dynamics approach

We investigate the interactions of polarizable solutes in water as a function of the solute permittivity. A generic and computationally efficient simulation methodology for the investigation of systems involving dielectric discontinuities is introduced. We report results for interactions between two polarizable cylindrical solutes of nanometer dimensions, which demonstrate that the interactions between the solutes strongly depend on the solute permittivity epsilon. For low permittivity, epsilon approximately 1-2, the interactions are dominated by surface tension forces whose origin lies in the formation of a vapor cavity between the two hydrophobic solutes. This effect leads to a drying transition, where the intersolute force changes discontinuously at a specific solute-solute separation. We find that a moderate permittivity, epsilon approximately 20, enhances the solvation of the polarizable objects inhibiting this drying transition. In the limit of moderately high permittivity, the interactions are dominated by solvation forces. These forces are much larger than those calculated using macroscopic models of dielectrics, which consider water as a continuum dielectric medium. Our results emphasize the importance of including the solvent explicitly to investigate dielectric discontinuities and interactions between polarizable media in water.     

低介电常数介质薄膜的研究进展

用低介电常数介质薄膜作金属线间和层间介质可以降低超大规模集成电路(ULSI) 的互连延迟、串扰和能耗。从介质极化的原理出发,揭示了开发低介电常数介质薄膜的可能途径;综述了低介电常数介质薄膜的制备方法、结构与性能表征、工艺兼容性等领域的最新进展。     

Electric field inside a "Rossky cavity" in uniformly polarized water

Electric field produced inside a solute by a uniformly polarized liquid is strongly affected by dipolar polarization of the liquid at the interface. We show, by numerical simulations, that the electric "cavity" field inside a hydrated non-polar solute does not follow the predictions of standard Maxwell's electrostatics of dielectrics. Instead, the field inside the solute tends, with increasing solute size, to the limit predicted by the Lorentz virtual cavity. The standard paradigm fails because of its reliance on the surface charge density at the dielectric interface determined by the boundary conditions of the Maxwell dielectric. The interface of a polar liquid instead carries a preferential in-plane orientation of the surface dipoles thus producing virtually no surface charge. The resulting boundary conditions for electrostatic problems differ from the traditional recipes, affecting the microscopic and macroscopic fields based on them. We show that relatively small differences in cavity fields propagate into significant differences in the dielectric constant of an ideal mixture. The slope of the dielectric increment of the mixture versus the solute concentration depends strongly on which polarization scenario at the interface is realized. A much steeper slope found in the case of Lorentz interfacial polarization also implies a higher free energy penalty for polarizing such mixtures.     

Effect of dielectric screening on positronium formation in acetone-acetic acid polar solvent blends

The influence of polarization of a medium in the vicinity of the positron-electron pair produced at the end of a fast-positron track on the formation of positronium (Ps) was considered. Weakening interaction between the positron and electron, polarization leads to a decrease in the Ps formation probability. The transience of Ps formation requires that the time delay of medium polarization should be taken into account. In turn, the magnitude of dielectric screening in acetone-acetic acid mixtures strongly depends on the ratio between the amounts of polar monomeric acetic acid and its nonpolar dimer. Sequentially taking account of these effects, it is possible to explain both the complex behavior of the Ps yield and the dependence of dielectric permittivity of the mixture on its composition.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 153–159.Original Russian Text Copyright © 2005 by Stepanov, Byakov, Stepanova.This revised version was published online in April 2005 with a corrected cover date.     

Polarization processes in electrorheological fluids based on conductive polymers

Electrorheological (ER) fluids are composed of dielectric particles dispersed in an inert liquid of low electric permittivity. Upon the application of an electric field ER fluids rapidly solidify, or increase their viscosity. Characteristic increase of the viscosity of ER fluids is due to the formation of particle chains that bridge the electrodes. This process is greatly affected by polarization processes within the solid phase and at the surface of the grains. These phenomena are governed by dopants, functional groups, structure of the solid particles and the solid/liquid interface. To find relations between parameters of the ER effect and material properties of components of ER fluids, two main types of the materials were investigated: conjugated polymers [polyphenylene (PPP), pyrolyzed polyacrylonitrile (PAN) and polythiophene] and solid electrolytes based on polyacrylonitrile complexed with inorganic salts. It was found that the ER activity resulted from surface polarization processes due to the presence of polar species (PAN) or bulk polarization related to mobile ions (PPP). Polythiophene, despite the presence of a conjugated system of multiple bonds, showed only residual ER effect. Solid electrolyte‐based fluids exhibited relatively high activity originated from ionic polarization. Copyright © 2006 John Wiley & Sons, Ltd.     

Apparent Specific Polarization and Dipole Moment of Some Poly(oxyethylene) Glycols in 1,4-Dioxane and Benzene Solutions at 298.15?K

The electrical permittivity of 1,4-dioxane and benzene solutions of some poly(oxyethylene) glycols up to the average molecular weight of 1590 were measured at 298.15 K. From the experimental data the limiting apparent specific polarization and partial molar polarization were calculated. The electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches. The calculated dipole moments increase linearly with the square root of the number of monomeric units. The group dipole moment of the polar monomeric unit was calculated from the corresponding limiting partial molar volume, the refraction and polarization of the solute. The factor g, which takes into account the degree of flexibility of the chain, was estimated and found to be greater than 0.92, which means that the lower members of the poly(oxyethylene) glycols possess almost free rotation within the chain backbone of polymer.