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.     

Highly improved dielectric behaviour of ferronematic nanocomposite for display application

We report the investigation of influence of nickel zinc ferrite magnetic nanoparticles (NZFO (Ni_0.5Zn_0.5Fe₂O₄)) on phase transition, optical and dielectric properties in a nematic liquid crystal (NLC). The interaction of NZFO nanoparticles with NLC was confirmed by the formation of ferronematic droplets due to the transfer of magnetic orientational effect onto the underlying NLC matrix. The doping results in shift of nematic to isotropic transition to low-temperature region. An enhancement in the value of refractive index is observed in the nematic region after the addition of NZFO nanoparticles. The dielectric constant of NLC was remarkably enhanced by 10 times after doping, which is found to be maximum at 0.1 wt% concentration of NZFO nanoparticles. The decrease in the value of dissipation factor in low-frequency region shows that the magnetic nanoparticles are able to trap ionic impurities effectively. The obtained results suggest that the optimum amount of doping concentration is 0.1 wt% of NZFO nanoparticles in NLC due to high dielectric constant with low dissipation factor and high refractive index with high dispersive power at room temperature.     

Study of dielectric properties of styrene-acrylonitrile graphite sheets composites in low and high frequency region

Conducting polymer composites should have a high dielectric constant and a high dissipation factor in the low and high frequency regions if they are to be used in charge storing devices, decoupling capacitors and electromagnetic interference shielding applications. Currently, extensive research is being carried out to enhance the dielectric constants of graphite-polymer, ceramic powder-polymer, metal powder-polymer and nanotube-polymer composites in the low frequency region. In this paper, we present the dielectric properties of styrene-acrylonitrile (SAN)-graphite sheets (GS) composites in the low and high frequency ranges. SAN-GS composites were prepared by the mixing process and by the hot compression mold technique. The composites showed a high dielectric constant and a high dissipation factor in the low and radio frequency region. Furthermore, the EMI shielding properties of these composites are evaluated in the radio frequency range. The conductivity and the dielectric constant of the SAN/GS composites increased with the addition of GS composites, and followed the power law model of percolation theory. The dielectric constant and the dissipation factor of the composites were analyzed according to the low and high frequency region.     

Thermal and electrical behaviors of acid functionalized MWCNT/ABC-type triblock copolymer grafted-MWCNT nanocomposites

In this work, ABC-type triblock copolymer grafted onto the surface of the MWCNT/acid functionalized MWCNT (MWCNT-COOH) composites were prepared and the properties of nanocomposites were characterized extensively using differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), thermogravimetric analysis (TGA), ac electrical conductivity and dielectrical measurements.

DSC study showed that the glass transition temperatures of the nanocomposites are a some higher than that of the matrix polymer. The increase in oxidized MWCNT in the nanocomposite improved the thermal stability of the composite, according to initial decomposition temperatures. The ac electrical conductivity has increased moderately with increasing frequency, but has increased slowly with increase in the oxidized MWCNT content in the nanocomposites. The electrical conductivity increases slowly with increasing temperature to about the glass transition temperature, then it increases faster. The dielectric constants for the matrix polymer and all the composites decreases slightly with increasing frequency from 0.1 kHz to 2.0 kHz. The dielectric constant increases slightly with increasing temperature up to about the glass transition temperature region and then the increase in temperature is accelerated the increase in the dielectric constant.     

Evaluation of the (Allyl alcohol 1,2‐butoxylate‐block‐etoxylate)‐b‐PMMA Copolymers Composition by the Dielectric Measurements

Redox initiated free‐radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2‐butoxylate‐block‐etoxylate (AABE) was carried out to yield AABE‐b‐PMMA copolymers at elevated temperatures. The composition of the copolymers depending on the polymerization temperature was qualitatively estimated by the dielectric measurements. It has been seen that AABE segment quantity decreased and PMMA segment quantity increased with increasing the polymerization temperature. The dielectric constant and the dissipation factor of the copolymers were investigated as a function of frequency and temperature. The dielectric constant and the dissipation factor were found to be strongly affected by the polymerization temperature. The highest dielectric constant in all studied temperatures and frequencies was obtained in the case of the copolymer which was prepared at 313 K. The dipolar C‐O and OH groups of the AABE segment have the primary effect on the dielectric constant. The copolymer which was prepared at 323 K, showed the highest dissipation factor near the relaxation temperature of PMMA.     

Dielectric investigation of the effect of ferric chloride on viscose fibres

Measurements of the dielectric constant and the dielectric loss, at frequencies of 0.05-10 kHz over a temperature range of 10–60 °C, were carried out on viscose fibres, viscose with iron adsorbed and with iron removed. The results obtained show that: (i) a relaxation process is observed in the low-frequency region only in the case of the viscose-iron complex, and (ii) the variation of the dielectric constant with temperature showed a transition at about 30 °C with the untreated fibres, and the transition disappeared when the fibres were treated with ferric chloride. These results, together with changes in hydrogen bonding obtained from infrared spectra for these samples are discussed. Oxidation and adsorption of ferric ions can modify the dielectric properties of viscose fibres.     

Thermodynamic properties of liquid Au-Cu-Sn alloys determined from electromotive force measurements

A thermally conductive linear low-density polyethylene (LLDPE) composite with aluminum nitride (AlN) as filler was prepared in a heat press molding. Differential scanning calorimeter results indicated that the AlN filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites display a high thermal conductivity of 1.25 W/m K and improved thermal stability at 70 wt% AlN content as compared to pure LLDPE. The dielectric constant and dissipation factor increased with AlN content, however, they still remained at relatively low levels, i.e., <5 in wider frequency range from 10 to 10⁶ Hz. The surface treatment of AlN particles had a beneficial effect on improving the thermal conductivity and dielectric constant, whereas, the dissipation factor was less affected. Additionally, the obtained AlN/LLDPE composites have possessed rather low dielectric constant and high electrical insulation, which is suitable for substrate and packaging materials.     

Analysis of sample-loss mechanisms in HGA-74 graphite furnace

In this study, a mathematical analysis of atom formation and dissipation mechanisms in HGA-74 graphite furnace is investigated. An equation governing the variation of the amount of analyte atoms in a graphite furnace is developed to calculate the temporal variation of the signal observed with this technique. Good agreement between the observed and calculated signals is observed especially in the rising portion of the signals. The theory presented in this paper, despite a number of simplifications has been shown to agree, at least in part, with experimental results obtained for Ni, Mn, Cr and Pb. Where discrepancies have been observed, reasons for these have been proposed.     

Dielectric study of the liquid crystalline dimer alpha, omega-bis(4'-cyanobiphenyl-4-yloxy)decane

The dielectric properties of a nematogenic dimer alpha,omega-bis(4-cyanobiphenyl-4-yloxy)decane in the nematic and isotropic phases have been investigated in the frequency range between 100 Hz and 13 MHz. It was found that the compound is characterized by a positive dielectric anisotropy. The dielectric constant in the nematic phase is lower than that in the isotropic phase, which suggests variation in the conformational distribution of the dimer after the phase transition. Only one relaxation process, both in the nematic and isotropic phases, has been observed in the frequency range used: the relaxation frequency has been found to take values between 2 and 4 MHz, depending on the temperature.     

Structural,Magnetic, and Electrical Properties of Al3+ Substituted CuZn-ferrites

Nanocrystalline Cu_0.5Zn_0.5Fe_2-xAl_xO₂ (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) ferrite materials were synthesized using standard solid state reaction technique. The effects of Al³⁺ contents on the structural, electrical, and magnetic properties were investigated. Single phase cubic spinel structure was revealed by X-ray diffraction analysis. The crystallite size was evaluated considering the most intense diffraction peak (311) using Scherrer formula. Lattice constant decreased, whereas porosity increased with the increase in Al³⁺ concentration. The value of saturation magnetization decreased with increasing aluminum contents. Temperature dependent value of direct current electrical resistivity has been determined. It is observed that the substitution of Al³⁺ has significant impact on the dielectric constant, tangent of dielectric loss angle and dielectric loss factor. The variation in dielectric properties was attributed to space charge polarization.     

Kinetic study of specific base catalyzed hydrolysis of ethyl acrylate in water-ethanol binary system

Kinetic study of hydroxide anion catalyzed hydrolysis of ethyl acrylate has been carried in ethanol-water (10–50% v/v) binary systems at the temperature range 30 ± 0.1, 35 ± 0.1, 40 ± 0.1, and 45 ± 0.1°C. Calculated specific rate constant values decreases with increasing proportion of ethanol at all temperatures. The observed retardation of a base catalyzed hydrolysis reaction is explained on the basis of fact that the formation of polarized transition state is disfavored with increase in % of ethanol. The relation between the change in dielectric constant due to variation in binary mixtures and change in specific rate constant are explained on the basis of electrostatic and non electrostatic contributions of solvent mixtures. The variation of ΔG*, ΔH*, ΔS* with solvent composition and the specific effect of water on the reaction rate kinetics are also discussed.     

An interlayer model for the complex dielectric constant of composites: An extension to ellipsoidally shaped particles

A theoretical interlayer model (IL) has been developed for the complex dielectric constant of a composite in which the filler particles are enveloped with a layer of interfacial material. The filler particles can be of any ellipsoidal shape. Special cases such as spherical particles, needles, and fabrics are shown to be covered by the model.The analytical formula as derived describes the composite properties as a function of the volume fractions of the filler, the layer and the matrix material, their dielectric properties and the filler particle shape factor.In the case of a two-phase composite the model reduces to the well-known Sillars relation for the complex dielectric constant of composite which contains filler particles of ellipsoidal shape.The effect of an interfacial layer on the static dielectric constant of the composite is discussed using the model. Next, the special case of a conductive interfacial layer in an otherwise non-conductive composite is discussed; it illustrates the effect of interfacially adsorbed water on the electrical properties of composites. Some practical examples are shown.     

Characterization of the electroclinic effect of smectic LCs in terms of the transitional dielectric constant in the SA phase

The electric-field dependence of the dielectric constant of some materials which show a strong electroclinic effect in the S_A phase, has been studied by measurement of the transitional dielectric constant. We suggest that the observed variation of the dielectric constant may originate from the electric field induced dielectric biaxiality; this is inherent in a material that exhibits the electroclinic effect.     

Some aspects of the motion of chain segments in plasticized polyvinyl chloride. I. Dielectric relaxation of plasticized polyvinyl chloride

Analysis of results of experiments on dielectric relaxation of polyvinyl chloride plasticized with tricresyl phosphate and with dioctyl phthalate gives values for heats and entropies of activation for dielectric relaxation rather lower than have been published in the literature for lower frequency ranges. The discrepancy may be due to a variation of heat of activation with temperature. A theoretical relation has been derived for the variation of heat and entropy of activation of dielectric relaxation with plasticizer content. The temperature dependence of the secondary high frequency loss factor maximum in unplasticized PVC has been ascertained, and some aspects of the relation between electrical and mechanical relaxation times and the second-order transition point have been discussed.     

Thermal properties of the graphite/n-docosane composite PCM

Graphite/n-docosane composite phase change materials (PCM) were prepared. 4, 10, and 16% graphite were added into n-docosane in order to study the effect of the amount of graphite to the thermal properties of the composite PCM. The structure of the composite PCM was characterized using scanning electron microscopy. The thermal properties of the composite PCM were determined using thermal constant analysis, heat storage/release curve, differential scanning calorimetry, and thermogravimetry analysis. The results revealed that the heat storage/release rate and the thermal conductivity increased with an increase in the amount of graphite, whereas the latent heat of the composite PCM decreased with the increase in the amount of graphite.     

Concentration dependences of dielectric properties at 105Hz and 106Hz for aqueous solutions of hydroxypropyl cellulose

The concentration dependences of dielectric properties measured at 10⁵ Hz and 10⁶ Hz are reported for aqueous solutions of hydroxypropyl cellulose. Phase behaviour of the solutions was also observed with a polarizing optical microscope. For solutions with concentrations well above 40 wt %, polydomain textures, including the banded texture, were observed after a prehistory of deformation. No significant discontinuous changes in the dielectric constant, ε_r', and loss factor, ε_r', were found at the concentrations around the onset of the isotropic-cholesteric phase transition and in the biphasic region. In contrast, the steeper changes in ε_r' and ε_r' were found at the critical concentration for the fully developed cholesteric phase transition with the polydomain textures.     

Characterization of the electroclinic effect of smectic LCs in terms of the transitional dielectric constant in the SA phase

Abstract

The electric-field dependence of the dielectric constant of some materials which show a strong electroclinic effect in the S_A phase, has been studied by measurement of the transitional dielectric constant. We suggest that the observed variation of the dielectric constant may originate from the electric field induced dielectric biaxiality; this is inherent in a material that exhibits the electroclinic effect.     

Dewetting phenomenon: interfacial water structure at well-organized alkanethiol-modified gold-aqueous interface

The interfacial properties at well-ordered short-chain alkanethiol monolayer-aqueous interfaces are probed to understand the water structure near a hydrophobic surface. Monolayers of hexanethiol on highly oriented gold substrates have been prepared by various methods such as adsorption from alcoholic solution of the thiol, adsorption from neat thiol, and potential-controlled adsorption. The compactness and crystallinity of the monolayer have been probed using reflection-absorption infrared spectroscopy (RAIRS), atomic force microscopy (AFM), quartz crystal microbalance (QCM), and electrochemical techniques. The presence of a thin layer of solvent with reduced density/dielectric constant (termed "drying transition") close to the methyl groups is identified. This is based on reduced interfacial capacitance observed in the presence of an aqueous electrolyte solution as compared to the expected value for a well-ordered monolayer-aqueous interface. Atomic force microscopy allows the determination of the variation in the dielectric constant of the solvent medium as a function of distance from the monolayer head group. The thickness of the transition layer (interphase) is found to be approximately 2 nm. The phenomenon of drying transition is not unique to water; preliminary studies indicate that formamide, which has a two-dimensional hydrogen-bonded network, shows similar characteristics.     

Temperature dependence of photo-charge generation of polymeric photorefractive composite in the glass transition temperature region

For photo-charge generation of polymeric photorefractive (PR) composites, temperature is important factor with electric field, but no study for temperature dependence of photo-charge generation efficiency (φ) at the glass transition temperature (T_g) region has been done yet. In this work, we investigate the temperature dependency of φ of a low T_g PR composite. With increasing temperature the photo-charge generation efficiencies increased below T_g but decreased above T_g. This behavior could be attributed to temperature dependence of heat capacity and the dielectric constant of PR composite. The space charge field was strongly dependent on temperature and increased with increasing φ.     

A study of thermal and dielectric behavior of manganese malonate dihydrate single crystals

Thermal decomposition of manganese malonate dihydrate single crystals grown by gel method has been studied using the TG-DTA and DSC techniques. The presence of water molecules and the dehydration stages are discussed. Dielectric constant, dielectric loss, and AC conductivity have been estimated as a function of temperature in the range of 40–120 °C for four different frequencies. Thermal studies reveal that the material is thermally stable up to123 °C. The dielectric measurements indicate that the dielectric parameters increase with the increase in temperature. Also, the dielectric constant and dielectric loss factor values decrease whereas the electrical conductivities increase with the increase in frequency of the AC applied.