Dielectric mixtures: Importance and theoretical approaches
Physics of dielectric mixtures are presented to stimulate discussion and to provide information on the recent advances in this topic.
cond-mat.other↗
arXiv subjects
Enis Tuncer
Publications and source records attributed to Enis Tuncer.
Numerical modeling of non-woven fiber mats
Numerical simulations on non-woven-fibrous, porous structures were performed to determine material design space for energy storage device (battery and ultracapacitor) separators.
cond-mat.soft↗
High temperature viscosity measurement system and viscosity of a common dielectric liquid
A device to measure viscosity of dielectric oils was developed. The device is an inset to an autoclave system where the temperature and the pressure could be controlled. The device is capable of measuring viscosities up to 400C and 5000psi, which are the limits of our autoclave at the moment.
physics.ins-det↗
Electrical properties of polyetherimide thin films: Nonparametric dielectric reponse analysis with distribution of relaxation times
High temperature polymeric materials for electrical insulation and energy storage are needed for transformational power applications such as pulsed-power and hyrid electrical vehicles. One of the candidate materials has been polyetherimide, an amourphous thermoplastic with a glass transition over 200C. Here dielectric studies on the material are reported by taking into account the polarization and conduction processes in the polyetherimide.
cond-mat.soft↗
Comparison of methods for estimating continuous distributions of relaxation times
The nonparametric estimation of the distribution of relaxation times approach is not as frequently used in the analysis of dispersed response of dielectric or conductive materials as are other immittance data analysis methods based on parametric curve fitting techniques. Nevertheless, such distributions can yield important information about the physical processes present in measured material. In this letter, we apply two quite different numerical inversion methods to estimate the distribution of relaxation times for glassy \lila\ dielectric frequency-response data at $225 \kelvin$. Both methods yield unique distributions that agree very closely with the actual exact one accurately calculated from the corrected bulk-dispersion Kohlrausch model established independently by means of parametric data fit using the corrected modulus formalism method. The obtained distributions are also greatly superior to those estimated using approximate functions equations given in the literature.
cond-mat.mtrl-sci↗
The Landau-Lifshitz/Looyenga dielectric mixture expression and its self-similar fractal nature
In this paper, dielectric permittivity of dielectric mixtures is discussed in view of the spectral density representation method. A distinct representation is derived for predicting the dielectric properties [Tuncer E 2005 J. Phys. Condens. Matter 17 L125]. In order to illustrate the strength of the representation and confirm the proposed hypothesis, Landau-Lifshitz/Looyenga expression is selected, and the structural information of the mixture is extracted. Both a recently developed numerical method to solve inverse integral transforms and the proposed empirical scaled permittivity expression are employed to estimate the spectral density function of the Landau-Lifshitz/Looyenga expression. In the simulations the concentration q of the inclusions phase are varied. The estimated spectral functions for the mixtures with different inclusion concentration compositions show similar spectral density functions, composed of couple of bell-shaped distributions, with coinciding peak locations. We think therefore that the coincidence is an absolute illustration of a self-similar fractal nature of mixture topology (structure) for the considered Landau-Lifshitz/Looyenga expression. Consequently, the spectra are not altered significantly with increased filler concentration level--exhibit a self-similar spectral density functions for different concentration levels. We conclude that the Landau-Lifshitz/Looyenga expression is therefore suitable for complex composite systems that have hierarchical order in their structure, which confirms the finding in the literature.
cond-mat.dis-nn↗
A formula for dielectric mixtures
Dielectric properties of material mixtures are of importance in diagnostics, characterization and design of systems in various engineering fields. In this Letter, we propose a peculiar dielectric mixture expression, which is based on the dielectric relaxation phenomena and the spectral density representation [E. Tuncer J. Phys. Condens. Matter 17(12) L125 (2005)]. The expression is tested on several composite systems. Results illustrate that the proposed expression can be used to obtain valuable structural informations in composites, even for highly filled, bi-percolating, systems. Lastly, the proposed expression is an alternative to other existing homogenization formulas in the literature.
cond-mat.mtrl-sci↗
Analogy between dielectric relaxation and dielectric mixtures: Application of the spectral density representation
The spectral representation is an effecient tool to explore electrical properties of material mixtures. It separates the contributions of geometrical topology and intrinsic properties of the constituents in the system. The aim of this paper is to derive an expression for the spectral density representation, which favors dielectric relaxation phenomenon. This unfamiliar form is distinct in a way that the existing dielectric relaxation models and data analysis tools can be employed for extracting the spectral density function of a given system.
cond-mat.mtrl-sci↗
Elastic properties of highly anisotropic thin poly(propylene) foams
In this letter, elastic properties of highly anisotropic cellular poly(propylene) films are reported. The material shows peculiar elastic properties compared to other foams in the literature. The data is displayed as the relative Young's modulus $E^*/E_s$ versus relative density $ρ^*/ρ_s$. Almost all the data from the literature are located on the region $E^*/E_s=(ρ^*/ρ_s)^n$ with $1\le n\le6$. The introduced material on the other hand have lower relative Young's modulus at high relative densities, $n\ge6$.
cond-mat.mtrl-sci↗
Origin of temperature dependent conductivity of $α$-polyvinylidene fluoride
The conductivity of $α$-polyvinylidene fluoride ($α$-PVDF) is obtained from dielectric measurements performed in the frequency domain at several temperatures. At temperatures above the glass-transition, the conductivity can be interpreted as an ionic conductivity, which confirms earlier results reported in the literature. Our investigation shows that the observed ionic conductivity is closely related to the amorphous phase of the polymer.
cond-mat.mtrl-sci↗
Distribution of relaxation times in $α$-phase polyvinylidene fluoride
In this paper, a recently developed numerical method to analyze dielectric-spectroscopy data is applied to $α$-phase polyvinylidene fluoride (PVDF). The numerical procedure is non-parametric and does not contain any of the extensively used empirical formulas mentioned in the literature. The method basically recovers the unknown distribution of relaxation times of the generalized dielectric function representation by simultaneous application of the Monte Carlo integration method and of the constrained least-squares optimization. The relaxation map constructed after the numerical analysis is compared to $α$-phase PVDF data presented in the literature and results of the parametric analysis with a well-known empirical formula.
cond-mat.dis-nn↗
Numerical Extraction of Distributions of Space-charge and Polarization from Laser Intensity Modulation Method
The Fredholm integral equation of the laser intensity modulation method is solved with the application of the Monte Carlo technique and a least-squares solver. The numerical procedure is tested on simulated data.
cond-mat.other↗
Modeling electromechanical properties of layered electrets: Application of the finite-element method
We present calculations on the deformation of two- and three-layer electret systems. The electrical field is coupled with the stress-strain equations by means of the Maxwell stress tensor. In the simulations, two-phase systems are considered, and intrinsic relative dielectric permittivity and Young's modulus of the phases are altered. The numerically calculated electro-mechanical activity is compared to an analytical expression. Simulations are performed on two- and three-layer systems. Various parameters in the model are systematically varied and their influence on the resulting piezoelectricity is estimated. In three-layer systems with bipolar charge, the piezoelectric coefficients exhibit a strong dependence on the elastic moduli of the phases. However, with mono-polar charge, there is no significant piezoelectric effect. A two-dimensional simulation illustrated that higher piezoelectricity coefficients can be obtained for non-uniform surface charges and low Poisson's ratio of phases. Irregular structures considered exhibit low piezoelectric activity compared to two-layer structures.
cond-mat.mtrl-sci↗
Elastic properties of cellular polypropylene films: Finite element simulations and their comparison with experiments
The Young's modulus of a two-dimensional truss-like structure is simulated by using the finite element method. A power-law expression is proposed for the effective Young's modulus of the system. The obtained numerical results are compared with the experimental data of the {\em anisotropic thin cellular polypropylene films}. At high solid volume fractions ($>0.4$), the average shape of the cells are lateral, and their dimensions have around one-to-five ratio. As the samples are inflated further, volume fraction of the solid is decreased, the average shape approach a diamond-like structure with one-to-two ratio. In addition the effective Young's modulus of the system increases. It is concluded that valuable structural information can be obtained by analyzing the experimental data and the numerical simulations, which take into account the material's micro-structural information, simultaneously.
cond-mat.soft↗
Numerical calculations of effective elastic properties of two cellular structures
Young's moduli of regular two-dimensional truss-like and eye-shape-like structures are simulated by using the finite element method. The structures are the idealizations of soft polymeric materials used in the electret applications. In the simulations size of the representative smallest units are varied, which changes the dimensions of the cell-walls in the structures. A power-law expression with a quadratic as the exponential term is proposed for the effective Young's moduli of the systems as a function of the solid volume fraction. The data is divided into three regions with respect to the volume fraction; low, intermediate and high concentrations. The parameters of the proposed power-law expression in each region are later represented as a function of the structural parameters, unit-cell dimensions. The presented expression can be used to predict structure/property relationship in materials with similar cellular structures. It is observed that the structures with volume fractions of solid higher than 0.15 exhibit the importance of the cell-wall thickness contribution in the elastic properties. The cell-wall thickness is the most significant factor to predict the effective Young's modulus of regular cellular structures at high volume fractions of solid. At lower concentrations of solid, eye-like structure yields lower Young's modulus than the truss-like structure with the similar anisotropy. Comparison of the numerical results with those of experimental data of poly(propylene) show good aggreement regarding the influence of cell-wall thickness on elastic properties of thin cellular films.
cond-mat.soft↗
On micro-structural effects in dielectric mixtures
The paper presents numerical simulations performed on dielectric properties of two-dimensional binary composites on eleven regular space filling tessellations. First, significant contributions of different parameters, which play an important role in the electrical properties of the composite, are introduced both for designing and analyzing material mixtures. Later, influence of structural differences and intrinsic electrical properties of constituents on the composite's over all electrical properties are investigated. The structural differences are resolved by the spectral density representation approach. The numerical technique, without any {\em a-priori} assumptions, for extracting the spectral density function is also presented.
cond-mat.mtrl-sci↗
Resolving distribution of relaxation times in Poly(propylene glycol) on the crossover region
In this paper, a recently developed numerical technique [{\em Tuncer E and Guba{ń}ski S M, IEEE Trans Diel El Insul {\bf 8}(3)(2001) 310-320}] is applied to poly(propylene glycol) complex dielectric data to extract more information about the molecular relaxation processes. The method is based on a constrained-least-squares (\clsq) data fitting procedure together with the Monte Carlo (\mc) method. We preselect the number of relaxation times with no {\em a-priori} physical assumption, and use the Debye single relaxation as ``kernel'', then the obtained weighting factors at each \mc step from the \clsq method builds up a relaxation time spectrum. When the analysis is repeated for data at different temperatures a {\em relaxation-image} is created. The obtained relaxation are analyzed using the Lorentz (Cauchy) distribution, which is a special form of the L{é}vy statistics. In the present report the $β$ and $α$ relaxations are resolved for the \ppg. A comparison of the relaxations to those earlier reported in the literature indicate that the presented method provides additional information compared to methods based on empirical formulas. The distribution of relaxation times analysis is especially useful to probe the crossover region where the $α$- and $β$- relaxations merge and the results show that the relaxation after the crossover region at higher temperatures is Arrhenius-type as the $β$-relaxation. Moreover, this relaxation is more likely to be the continuation of the $β$-relaxation, but with a different activation energy.
cond-mat.soft↗
Signs of low frequency dispersions in disordered binary dielectric mixtures (50-50)
Dielectric relaxation in disordered dielectric mixtures are presented by emphasizing the interfacial polarization. The obtained results coincide with and cause confusion with those of the low frequency dispersion behavior. The considered systems are composed of two phases on two-dimensional square and triangular topological networks. We use the finite element method to calculate the effective dielectric permittivities of randomly generated structures. The dielectric relaxation phenomena together with the dielectric permittivity values at constant frequencies are investigated, and significant differences of the square and triangular topologies are observed. The frequency dependent properties of some of the generated structures are examined. We conclude that the topological disorder may lead to the normal or anomalous low frequency dispersion if the electrical properties of the phases are chosen properly, such that for ``slightly'' {\em reciprocal mixture}--when $σ_1\ggσ_2$, and $ε_1<ε_2$--normal, and while for ``extreme'' {\em reciprocal mixture}--when $σ_1\ggσ_2$, and $ε_1\llε_2$--anomalous low frequency dispersions are obtained. Finally, comparison with experimental data indicates that one can obtain valuable information from simulations when the material properties of the constituents are not available and of importance.
cond-mat.dis-nn↗