Dielectric analysis of sheep erythrocyte ghost. Examination of applicability of dielectric mixture equations

The purpose of this study is to confirm the applicability of dielectric mixture equations in dielectric analysis of biological cell suspensions. Two dielectric mixture equations, the Pauly-Schwan (P-S) equation and the Hanai-Asami-Koizumi (H-A-K) equation were tested using sheep erythrocyte ghosts whose internal solution is identical with the external solution. Dielectric measurements were carried out for the ghost suspensions over a frequency range 10 kHz to 100 MHz; a single dielectric relaxation was found between 100 kHz and 10 MHz. From the dielectric relaxation, the conductivity and permittivity of the ghost interior and the capacitance of the cell membrane were calculated following the P-S and H-A-K equations. When the H-A-K equation was employed (and as expected from the property of the ghosts), the estimated internal conductivity was in good agreement with the external conductivity at volume fractions up to about 0.7. With the P-S equation, on the other hand, the same results as above were obtained but only at low volume fractions below about 0.3. In addition, the H-A-K equation provided a better simulation for the observed relaxation curves than did the P-S equation, especially at high volume fractions. It is, therefore, concluded that the H-A-K equation is applicable to a wider range of volume fraction than is the P-S equation.     

Typical superparamagnetism with improved electrical properties of nano modified bismuth ferrite multiferroic composites

Multiferroic composites with the chemical formula, (0.5) BiFeO₃ + (0.5) Ni_0.5Zn_0.5Fe₂O₄, in bulk and nano forms were synthesized by preparing bismuth ferrite (BiFeO₃ or BFO) in bulk (B) and nano (N) forms and nickel zinc ferrite (Ni_0.5Zn_0.5Fe₂O₄or NZFO) in nano form. Single phase BFO was synthesized using conventional solid-state reaction as well as sol-gel autocombustion methods and NZFO powders were prepared by using sol-gel autocombustion method, respectively. X-ray diffraction (XRD) studies reveal the existence of rhombohedrally distorted perovskite structure for BFO and cubic spinel phase for NZFO in single phase as well as composite samples. Microstructural studies and energy dispersive spectroscopy (EDS) data reveal the formation of grains, intergranular porosities and chemical purity of the synthesized samples. Dielectric and AC conductivity measurements confirm the existence of space charge polarization along with the small polaron model in these composites. Ferroelectric and magnetic studies show that there was a considerable enhancement in the ferroelectric and magnetic orders for the nano form of the BFO (N) + NZFO composite. The observed remnant polarization values 2.80388 & 7.75901 μC/cm², saturation magnetization values 37.96072 & 40.47491emu/gm for bulk BFO (B) + NZFO and nano BFO (N) + NZFO composites, respectively. Interestingly, both the samples exhibit superparamagnetic behaviour at room temperature with coercivities close to zero. This typical behaviour is attributed to the corresponding anisotropic contributions originated from the individual constituents. The observed variations in BFO (N) + NZFO sample attributed to the corresponding structural modifications brought about by the variations due to its size effect in the present work.     

Study of dielectric constants of binary composites at microwave frequency by mixture laws derived from three basic particle shapes

Powder mixture rules derived from the filler particles with the shapes of sphere, cylinder or rod, and lamella or disk with random distributions are studied in this paper. Three ceramic powders of fillers with dielectric constants of 10, 20, and 36, respectively, are adopted. The experimental dielectric constants of ceramic dispersions in the polyethylene matrix at microwave frequency are compared to those obtained by using different mixing laws. The mixing rules are also adopted to estimate the dielectric constants of pure ceramics from the measured dielectric constants of composites with various concentrations. The theory for the error of estimation is studied. In contrast to the traditional concept of obtaining the best curve fitting of mixture rule with the experimental data, this study conclude a very important concept on the powder mixture rule, that is, the most adequate mixture law for estimating the dielectric constants of pure ceramics requires both good curve fitting and potential of less error.     

On the definition of the excess permittivity of a fluid mixture. II

In a previous work, an ideal fluid mixture is assumed to be a homogeneous linear and isotropic system that verifies the following conditions: (I) no interaction between molecules, (II) point-like molecules and (III) under fixed temperature and pressure conditions the number of molecules per unit volume is the same for both the individual components and the mixture. It was shown that for such ideal mixture the permittivity is the sum of the individual permittivities weighted with the mole fractions of the components.In this work it is shown that independently of the latter assumption the permittivity of the system can be expressed as the sum of the individual permittivities weighted with the volume fractions of the components.     

Optical and electrical properties of copper alumina nanoparticles reinforced chlorinated polyethylene composites for optoelectronic devices

The incorporation of transition metal oxide fillers into the polymer matrix through solution mixing polymerization imparts enhanced electrical and thermal properties. The present work focused on the optical properties, crystallinity, thermal stability, temperature-dependent conductivity, dielectric constant and modulus of chlorinated polyethylene/copper alumina (CPE/Cu–Al₂O₃) nanocomposites. Optical absorption measured using an ultraviolet–visible (UV–visible) spectrometer shows enhanced intensity and a blue shift for CPE/Cu–Al₂O₃ nanocomposites. The bandgap energy of CPE/Cu–Al₂O₃ nanocomposites was lower than pure CPE and minimum bandgap energy was recorded for a 7 wt% composites. The X-ray diffraction demonstrates that Cu–Al₂O₃ nanoparticles were uniformly introduced into the CPE matrix. Thermogravimetric analysis (TGA) manifests improved thermal stability of nanocomposites. Dielectric properties decrease with frequency, whereas AC conductivity increases with frequency, and both AC conductivity and dielectric properties increase with temperature. The maximum AC conductivity and dielectric constant were obtained for 7 wt % nanofiller loaded sample. For all systems, the activation energy for electrical conductivity decreases with rising temperatures. The experimental dielectric constant values of CPE nanocomposites were correlated with different theoretical models. The Bruggeman model was in good agreement with the experimental permittivity. The impedance experiments showed a decreasing trend with temperature, indicating the semiconducting nature of prepared nanocomposites.     

Dielectric properties of plasma polymerized PVCa and composite PVCa:Au films

Dielectric properties of plasma polymerized PVCa and composite PVCa:Au films had been analyzed in the frequency range from 10 to 10⁵ Hz. In order to explain experimental data obtained the modification of Maxwell-Garnett and Bruggeman self-consistent models for the case of three-component composite has been done. The theoretical analysis performed allows to determine peculiarities of dielectric behavior of a three-component system, as well as to disclose the procedure of evaluation of third-component parameters. Results of this analysis are in agreement with experimental ones.     

The enhancement mechanism of dielectric properties of Pb(Zr,Ti)O3 via (Mg2+,Sb3+) incorporation for supercapacitors

Due to the extraordinary versatility of the perovskite structure in accommodating different dopant ions in its structure, in recent years a huge number of multifunctional perovskite materials have been developed. In this work we aim to obtain high temperature-stable and huge dielectric constant materials for supercapacitors by doping divalent Mg²⁺ and trivalent Sb³⁺ ions into the octahedral sites, and divalent Sr²⁺ ions into the dodecahedral sites of lead zirconate-titanate perovskite. The resulting (Pb_0.95Sr_0.05)(Zr_0.425Ti_0.45Mg_0.042Sb_0.083)O_3-δ is examined by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), dielectric spectroscopy (DS) and resonance dielectric spectroscopy (RDS) in order to correlate composition, local structure, ion valence and chemical environment of the doped material with the dielectric properties. HRTEM evidences that a composite structure, with co-existent ferroelectric domains and relaxor nanodomains, is formed by doping. XPS shows that Sb³⁺ and Mg²⁺ substitute for the Ti⁴⁺/Zr⁴⁺ ions, pointing to these strong defects as the main cause for the appearance of the relaxor phase. DS and RDS found that the ferroelectric lead zirconate-titanate transforms into a re-entrant relaxor-ferroelectric composite with a huge dielectric constant of about 10⁴ which remains stable (within ±10%) in the high temperature range up to 250 °C, pointing to this mechanism of relaxor phase re-entrance below the normal ferroelectric phase transition, as being responsible for the enhancement.     

A 3‐D numerical simulation of AC electrical properties of short fiber composites

The relation between microstructure and electrical properties of polymer reinforced by electrically conducting nanofibers is investigated using a RC type simulation. Real and imaginary parts of the conductivity vs. the frequency and the filler fraction are presented both for two‐ and three‐dimensional systems. In the latter case, resistor and capacitor values are deduced from a random microstructure and the measured macroscopic properties of each component. These results are compared with experimental data obtained on a nanocomposite material composed of electrically conductive fillers dispersed in an insulating matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 805–814, 1999     

The thermal and dielectric properties of high performance cyanate ester resins/microcapsules composites

Novel high performance bisphenol A dicyanate ester (BADCy) resins/poly(urea-formaldehyde) microcapsules filled with epoxy resins (MCEs) composites have been prepared. The effects of different contents of MCEs on the thermal and dielectric properties of cured BADCy were investigated using dynamic mechanical analyzer (DMA), thermalgravimetric analyzer (TGA) and broadband dielectric analyzer. The dielectric properties of BADCy/MCEs treated in hot water and hot air were also discussed. The morphologies of BADCy/MCEs composites were characterized by scanning electron microscopy (SEM). Results indicate that the appropriate content of MCEs can improve or maintain the thermal stability, the low dielectric constant and dielectric loss of cured BADCy mainly owing to higher conversion of cyanate ester (-OCN) groups. After aged in hot water and hot air, respectively, BADCy/MCEs composites with small content of MCEs can retain the low dielectric constant and dielectric loss.     

Study of electrical and dielectric properties of styrene-acrylonitrile/graphite sheets composites

This paper reports the structural, electrical, dielectric and mechanical properties of the Styrene-acrylonitrile (SAN)/graphite sheets (GS) composites. The composites were prepared by in situ polymerization. The variation of electrical conductivity, dielectric constant and ac conductivity as a function of volume fraction of GS was found to follow the power law model. The dielectric constant and dissipation factor of SAN/GS composites increased significantly near the percolation. The frequency dependence of dielectric constant, dissipation factor and ac conductivity was also analyzed. Nearly ohmic behavior of current density with electric field was observed above the percolation threshold. The composite was found to possess the hardness of pure polymer at the threshold value of GS.     

On the dielectric relaxation of biological cell suspensions: the effect of the membrane electrical conductivity

Due to the mismatch of the electrical parameters (the permittivity ?' and the electrical conductivity σ) of the membrane of a biological cell with the ones of the cytosol and the extracellular medium, biological cell suspensions are the site, under the influence of an external electric field, of large dielectric relaxations in the radiowave frequency range. However, a point still remains controversial, i.e., whether or not the value of membrane conductivity σ(s) might be extracted from the de-convolution of the dielectric spectra or otherwise if it would be more reasonable to assign to the membrane conductivity a value equal to zero. This point is not to be considered with superficiality since it concerns an a priori choice which ultimately influences the values of the electrical parameters deduced from this technique. As far as this point is concerned, the opinion of the researchers in this field diverges. We believe that, at least within certain limits, the membrane conductivity can be deduced from the shape of the relaxation spectra. We substantiate this thesis with two different examples concerning the first a suspension of human normal erythrocyte cells and the second a suspension of human lymphocyte cells. In both cases, by means of an accurate fitting procedure based on the Levenberg-Marquardt method for complex functions, we can evaluate the membrane conductivity σ(s) with its associated uncertainty. The knowledge of the membrane electrical conductivity will favor the investigation of different ion transport mechanisms across the cell membrane.     

Spiky nanostructured metal particles as filler of polymeric composites showing tunable electrical conductivity

This work presents a comprehensive investigation of the piezoresistive response of a composite material based on conductive nickel filler in a silicone‐insulating matrix. In the absence of a deformation, the prepared composite shows no electric conductivity, even though the metal particle content is well above the expected percolation threshold. Upon samples deformation (compressive or tensile stress), the composite exploits a variation of electrical resistance up to nine orders of magnitude. This huge variation can be explained with the quantum tunnelling mechanism where the probability of an electron to tunnel from a particle to the next one is exponentially proportional to the thickness of the insulating layer between them and strongly enhanced by the morphology of the nickel particles, showing spiky nanostructured tips. Two different conduction theoretical models are proposed and compared with the experimental results. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

In-situ monitoring of the dielectric and electrostrictive properties of anodised thin films for biochip applications

Further improving the performance of capacitance-based DNA microsensors will depend on the ability to synthesize simply, at a low cost, thin films of high dielectric permittivity with a well-controlled growth morphology. Anodisation of the valve metals Ti, Zr and Ta is a promising route for preparing such films. In this paper, we propose a new method for following the evolution of the dielectric properties of such anodised metallic oxide thin films in-situ during their growth. The technique relies on measuring the evolution of the electrostatic stress developing in the film. Measurements have been carried out on anodic TiO₂ films grown galvanostatically in HNO₃ at 1 and 3 mA/cm² and in H₃PO₄ at 0.5 mA/cm². The dielectric permittivity of the films was observed to decrease during the initial stage of anodisation, characterised by a steady increase of the cell voltage with time. The permittivity then reached a constant value when the oxide entered a second growth regime, characterised by a stabilisation of the cell voltage. The origin of the observed permittivity evolution is interpreted in terms of the evolution of the growth morphology of the films during anodisation.     

Excess properties of the mixture bis(2-dichloroethyl)ether (chlorex) + 2,2,4-trimethylpentane (isooctane)

The excess properties of the mixture bis(2-dichloroethyl)ether (chlorex) + 2,2,4-trimethylpentane (isooctane), i.e. excess volumev ^E, excess enthalpyh ^E, excessGibbs energyg ^E and excess heat capacityc _p ^E are reported. The excess volume is small, negative on the chlorex side and positive on the isooctane side. The excess enthalpy at 293.15 K is 1 913 J mol^–1 for equimolar composition, the excessGibbs energy amounts to 1 367 J mol^–1 under the same conditions. The system undergoes phase separation below 290.47 K. Due to the nearness of the critical point,c _p ^E exhibits a strong maximum at the critical composition (x _isooctane=0.508), though the basic part ofc _p ^E is negative. Discussion focusses on the effects of polarity of chlorex as mixing partner, on near-critical properties, and on mixing rules of avan der Waals-type equation of state.Dedicated to Prof. Dr.K. Komarek on the occasion of his 60th birthday.     

Synthesis,characterization, thermal,electrical and magnetic properties of polyaniline composites with rare earth gadolinium coordination complex

Novel polyaniline/gadolinium (PANI/Gd) composites were successfully synthesized by “in‐situ” polymerization at the presence of rare earth Gd coordination complex and D‐tartaric acid (an a dopant). It is rarely to find the studies on related field to add rare earth Gd coordination complex as fillers. Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD) and scanning electron microscope (SEM) were used to examine the structure and surface appearance characterization of materials. The thermal stability performance of composites was investigated by thermogravimetry and derivative thermogravimetry (TG‐DTG). Electrochemical performance was measured by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge test. The magnetic property was investigated by physical property measurement system (PPMS). The structure and surface appearance characterization and the magnetic properties jointly demonstrate the polymerization of rare earth Gd coordination complex and PANI–D‐tartrate (DTA) not only simple physical mixing but also chemical mixing. TG‐DTG analysis suggests that thermal stability of PANI/Gd composites is higher than that of PANI–DTA. Electrochemical performance tests and SEM indicate that the composite (PANI/Gd = 3.3:1,mass ratio) has the most regular morphology and best specific capacitance. The magnetization of the composite (PANI/Gd = 3.3:1,mass ratio)is evidently smaller compared with PANI–DTA and rare earth Gd coordination complex. Copyright © 2016 John Wiley & Sons, Ltd.     

Enhancement of dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal mixture by dispersing nano-sized copper oxide

ABSTRACT

Here, we present the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal (FLC) mixture, namely W302. The FLC mixture, comprising of pyrimidine compounds, was characterised through dielectric spectroscopy, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and other electro-optical methods. The material parameters such as spontaneous polarisation, rotational viscosity, response time and tilt angle of W302 were found to be 14 nC/cm², 240 mPa.s, 150 µs and 28^?, respectively. The phase transition temperatures of W302 were observed through DSC and further confirmed by the dependence of dielectric loss factor in homogeneously aligned FLC sample with temperature. We also demonstrate the observance of a low-frequency dielectric relaxation mode due to the unwinding of the helix, called as partially unwound helical mode (p-UHM) along with Goldstone mode. The behaviour of p-UHM has been systematically studied with temperature and applied bias field. Further, dispersion of nCuO into host W302 has shown a significant increase in dielectric permittivity. Also, the p-UHM relaxation peak in the dielectric regime has disappeared with the incorporation of nCuO. These studies would be useful to fabricate better electro-optical devices for display, switching and beam steering applications. The formulation and characterization of a ferroelectric liquid crystal (FLC) mixture W302 composed of pyrimidine compounds is presented. Then, we observed the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared and characterized FLC mixture.     

Synthesis,characterization, optical,thermal and electrical properties of polybenzimidazoles

The variation of dielectric constant and dielectric loss of two novel polybenzimidazole (PBI) were studied at constant temperature with variable frequency. The polymers have shown maximum dielectric constant at low applied frequency 50 Hz at 393 K due to the space charge polarization. The AC conductivity and activation energy of polymers were arrived from dielectric constant and dielectric loss values. PBIs were synthesized by the oxidative polycondensation of benzimidazole monomers, 2-(1H-benzo [d] imidazole-2-yl)-4-bromophenol (BIBP), and 2-(1H-benzo [d] imidazole-2-yl)-6-methoxyphenol (BIMP) in an aqueous alkaline medium using NaOCl as oxidant. The monomers and polymers were characterized by various spectroscopic techniques. Fluorescence spectra of monomers and polymers showed their λ _max emission in the region of 472–479 and 463–472 nm respectively. The electrical conductivities of iodine doped polybenzimidazoles were measured by four-point probe technique and it increases with increase in iodine vapour contact time. The electrical conductivity values were correlated with the charge density on imidazole nitrogen obtained from Huckel calculation method. Both the PBI are having reasonably good thermal stability and are shown by high carbines residues of around 40% at 500°C in thermogravimetric analysis.     

Dielectric studies and critical behaviour in the vicinity of nematic–isotropic phase transition of a smectogenic binary mixture showing induced nematic phase

The phase diagram of a binary mixture composed of compounds, one having NCS terminal group (4DBT, showing smectic A₁ phase) and the other with CN terminal group (11OCB, showing smectic A_d phase), exhibiting induced nematic phase in a certain concentration range (0.100 < x_4DBT < 0.951) is reported here. Results of the static dielectric parameters measurement on this binary system within the entire mesomorphic range are presented. Evidence of strong pretransitional behaviour near the nematic–isotropic (N–I) phase transition, indicating the influence of tricritical behaviour, is observed. Precise determination of discontinuity (ΔT) and the critical exponent (α) of N–I phase transition have been carried out. Moreover, the order parameter critical exponent β is correctly predicted by the tricritical hypothesis through the dielectric anisotropy data for all the investigated mixtures.     

A methodology for studying the dependence of electrical resistivity with pressure in conducting composites

This work describes a simple and useful methodology based on electrical-mechanical data taken under dynamic conditions to evaluate the effectiveness of a conducting composite as a pressure sensor. This method utilizes the compression force applied by a universal testing machine and relates this value to the corresponding resistivity value given by an electrometer, using a computer program developed in our laboratory. The proposed methodology was employed on conducting composites constituted of polyaniline as the conducting filler dispersed into styrene-butadiene (SBS) block copolymer as the insulating polymer matrix. The compression sensitivity and the hysteresis of these materials were investigated.