Dielectric Relaxation Time Research Articles

Study of the H-bond interaction on binary mixtures of nitromethane with primary alcohols at different temperatures using dielectric parameters

A dielectric spectroscopic study has been carried out on binary mixtures of polar nitromethane (NM) with primary alcohols: ethanol (ETH), 1-propanol (1-PRO) and 1-butanol (1-BUT) at different temperatures. The complex dielectric spectra of pure and binary mixtures were described by Debye model. The dielectric constant (e0), relaxation time (τ), and dielectric constant at an optical frequency (e∞) of binary mixtures were determined at various temperatures. The computed excess dielectric parameters were used to interpret the intermolecular interaction between the unlike dipoles within the binary mixture system. From the experimental analysis, it is confirmed that, the mixture molecules form H-bond complex structure and dipoles are aligned in anti-parallel direction. Among all the binary systems, strong H-bond interaction can be seen in NM + 1-PRO mixture system. Rapid decrement of relaxation time for NM + 1-BUT binary system results higher amount of structural changes symmetry breaking effect. The formation of hydrogen bonding interaction between oxygen atom of nitro groups in NM and hydrogen atom of alcohols in binary mixture systems was confirmed by FTIR analysis.

Structural, optical, dielectric and electrical properties of (PEO–PVP)–ZnO nanocomposites

Polymer nanocomposite (PNC) films of poly (ethylene oxide) (PEO) and poly (vinyl pyrrolidone) (PVP) blend matrix (50/50 wt%) incorporated with zinc oxide (ZnO) nanoparticles (i.e., (PEO–PVP)–x wt% ZnO; x = 0, 1, 3 and 5) were prepared and characterized as potential candidates for applications in the next generation optoelectronic and microelectronic devices. The structural properties of these PNCs were investigated by using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and the X–ray diffraction (XRD) measurement techniques. The porous spherulites morphology, polymer-polymer and polymer-nanoparticle interactions, and the semicrystalline structures of these materials have been significantly influenced by the incorporated amount of ZnO nanoparticles in the polymer blend matrix. The optical behaviour of the PNC films was studied from ultraviolet–visible (UV–vis) spectroscopy, and the optical parameters viz. optical energy band gap (indirect and direct), Urbach tail energy, refractive index and the ZnO surface plasmon resonance energy were determined. Complex permittivity, electric modulus, electrical conductivity and the impedance spectra of these PNC materials as flexible nanodielectrics have been measured in the frequency range from 20 Hz to 1 MHz by employing the dielectric relaxation spectroscopy (DRS). The DRS results reveal that the ambient temperature values of complex permittivity increase with the increase of ZnO contents up to 3 wt% in the PEO–PVP blend matrix and then it slightly decreases at 5 wt%. The dielectric relaxation process confirms that the polymers cooperative chains segmental dynamics in the blend matrix enhances in presence of ZnO nanoparticles in the complex nanocomposite structures. The temperature dependent study of 3 wt% ZnO containing PNC film reveals that the complex permittivity increase linearly with the increase of temperature, whereas the dielectric relaxation time and electrical conductivity values obey the Arrhenius behaviour.

Optical and dielectric dispersion parameters of general purpose furnace (GPF) carbon black reinforced butyl rubber

Optical and dielectric dispersion parameters for butyl rubber–general purpose furnace carbon black (IIR-GPF CB) composites with various carbon black (CB) concentrations were determined using ultraviolet transmittance spectra. X-ray diffraction (XRD) for the composite samples was measured in the 2θ range from 5° to 50°. There was a slight increase in the XRD peak intensity by increasing CB content indicating some significant changes in the composite structure. Some structural parameters were calculated for the XRD fundamental peak. The crystallite size increased significantly with the increase in carbon black concentration. This suggested a tendency of the polymer toward a more crystal state. Analysis of refractive index dispersion was carried out using Wemple–DiDomenico single effective oscillator model. The energy of effective single oscillator ( $$E_{\text{o}}$$ ) and the dispersion energy ( $$E_{\text{d}}$$ ) were estimated for the composites of different CB loadings. Accordingly, the moments of optical spectra, static and high-frequency dielectric constants were calculated. The variation of the real part $$\varepsilon_{1}$$ and imaginary part $$\varepsilon_{2}$$ of the complex dielectric function with the incident photon wavelength was investigated. The recorded values of $$\varepsilon_{1}$$ were greater than the values of $$\varepsilon_{2}$$ . The dielectric energy loss was specified by means of three important parameters: volume energy loss function, surface energy loss function and dielectric loss factor ( $$\tan \delta$$ ). The dielectric relaxation time $$\tau$$ and plasma frequency were studied as a function of incident photon wavelength for different composite samples. There was a great dependence of $$\tau$$ on the wavelength and amount of the carbon black in the composite.

Dielectric Relaxation and Thermodynamic Studies of Binary Mixtures of 2-Nitrotoluene with Primary and Secondary Alcohols at Different Temperatures

The dielectric complex spectra of 2-nitrotoluene with primary or secondary alcohol binary mixtures were studied over the frequency range of 10 MHz to 20 GHz for the whole solute mole fraction range at four different temperatures. An unusual suppression phenomenon was observed in the real and imaginary parts of the mixture complex spectrum, which are smaller than those for the pure alcohols, at low solute concentrations. The dielectric constant and dielectric relaxation time values were obtained by fitting the complex dielectric spectrum data to the single Debye model using a non-linear least squares method. The dielectric constant of mixtures decrease with the increasing mole fraction of 2NT in both the primary alcohols and secondary alcohols; the dielectric relaxation time decreases for all the five binary systems. Using the dielectric data, derived dielectric parameters, namely: the excess dielectric constant, excess inverse relaxation time, effective Kirkwood correlation factor, molar activation enthalpy and molar activation entropy, were calculated. The non-linear variation of permittivity (ɛ0) reveals the change in size and shape of hetero-molecular complex due to intermolecular H-bond interaction. The negative variation of the excess permittivity constant confirms that the dipoles form multimer structures with anti-parallel ordering of unlike dipoles. The molar activation enthalpy was found to be higher at 0.2 mol fraction of 2NT for primary alcohol binary system. To confirm the molecular function group interaction, a FT-IR spectroscopy study was carried out at 298 K. The FT-IR analysis confirmed the formation of hydrogen bonds between the hydrogen atom of hydroxyl groups of the alcohols and the oxygen atom of nitro groups of 2NT in the binary mixtures.

Influence of Grain and Grain Boundary Interfaces on Dielectric Relaxation of Ceria Nanocrystals Using Modulus Formalism Under Biased and Equilibrium Conditions

Dielectric relaxation of ceria nanocrystals under biased condition for different grain sizes was in this study evaluated in modulus formalism using impedance spectroscopy. Prior to the impedance measurements, the ceria sample was calcined at 200 °C for 30 min and pressed into cylindrical pellets with 8 mm diameter and 1 mm thick by applying uniaxial four-ton pressure using a hydraulic press. This was then sintered at 300 °C, 450 °C, 600 °C and 900 °C for 30 min. Systematic analysis of modulus formalism data using commercial Z-view and Z-plot software's permitted, reliable extraction of dielectric relaxation time (τ) of ceria nanocrystals. The observed dielectric relaxation time (τ) at equilibrium condition varied from 10–5 to 10–3 s when the grain size of ceria nanocrystals was increased from 9 nm to 29 nm. But when the DC bias voltage was applied, the same dielectric relaxation time (τ) was tuned to ∼10–4 s for all the grain sizes of ceria nanocrystals, because of Schottky grain boundary potential barrier height (φb) suppression.

Dielectric dispersion, relaxation and molecular interaction of pyrazine binary mixtures

The dielectric depressiveness, absorption and orientation behavior is investigated in relation to solution properties of pyrazine with water, methanol and ethanol for varying temperature and mole fraction. This behavior is discussed in terms of inter molecular bonding. Orientation effects and their dielectric properties are indicated by surface dipole potential charges by displacement of oriented solvent. The charge dependence of polar solvents with organic molecular orientation can be qualitatively evolved and can be calculated in terms of its own dielectric properties, relaxation time, and correlation factor and thermodynamical behavior of solvent mixtures. The macroscopic and optical spectroscopic properties of pyrazine + water and pyrazine + alcohol mixtures are also studied.

Study of H1 spin lattice relaxation and dielectric relaxation in Poly(propylene glycol) system

Proton NMR spin-lattice relaxation time (T1) and dielectric relaxation time (τ0) have been used to correlate the experimental and calculated values of T1 for Poly (propylene glycol) at 300 K. Also, the contributions of dielectric relaxation time (τ0) of each constituent group of PPG-425 to the effective dielectric relaxation time due to the whole chain of the polymer have been calculated using NMR spin–lattice relaxation time. The H1 NMR data and dielectric data of Poly (propylene glycol) HO [CH(CH3)CH2O]nH with number average molecular weight 425 (n = 7) g mol−1have been used to understand the conformation and basic mechanism of relaxation in polymer in its pure liquid state. Conformational analysis using Hartree-Fock formalism was performed for the polymer of n = 7 and the average bond distances obtained from the computation were used to assign NMR relaxation times to specific subgroups. Free energy and enthalpy of activation associated with methyl and other groups in the chain of PPG molecules have been calculated. BPP (Bloembergen Purcell Pound) model gives better correlation for molecular tumbling motion for PPG-425 in pure liquid state than Kubo & Tomita equation.

Nonlinear dielectric features of highly polar glass formers: Derivatives of propylene carbonate.

We have measured the nonlinear dielectric behavior of several highly polar propylene carbonate (PC) derivatives in the vicinity of their glass transition temperatures. Focus is on the effects of a large static electric field on the frequency dependent permittivity and on the cubic susceptibility measured using sinusoidal fields of high amplitude. The case of vinyl-PC shows dielectric saturation as well as an electro-rheological effect, i.e., a field induced increase of dielectric relaxation times, whose magnitude changes linearly with the apparent activation energy. The extent of this shift of the loss profile caused by the field correlates strongly with the peak magnitude of the cubic susceptibility, |χ3|, underlining the notion of a link between the |χ3| "hump" and this electro-rheological behavior. Further support for this picture emerges from the observation that the most polar of these liquids, (S)-(-)-methoxy-PC with εs ≈ 250, lacks both the electro-rheological effect in ε″(ω) and the "hump" typically observed in |χ3(ω)|. The absence of any sensitivity of the dynamics to an electric field is contrary to the expectation that the electro-rheological effect correlates with the field induced entropy change, which is extraordinarily high for this liquid. The results suggest that the dependence of the relaxation time on the electric field is not directly linked to the entropy change.

Dielectric Characteristics of Water and Electric Conductivity of Aqueous Electrolytes

The specific electric conductivities (ECs) of concentrated aqueous solutions of electrolytes were shown to be comparable to the limiting high-frequency (HF) EC of water. The limiting HF EC of water is determined by the ratio of the absolute dielectric constant to the dipole dielectric relaxation time. It was assumed that the specific EC of an aqueous solution cannot exceed the limiting HF EC of water. The specific ECs of the 1.0 М aqueous solutions of lithium, sodium, and potassium chlorides were calculated from the limiting HF EC of water. At elevated temperatures, the specific ECs of aqueous salts were shown to increase in direct proportion to the limiting HF EC of water.

Dielectric relaxation in water-dimethylaminoethanol mixtures as a function of composition and temperature

ABSTRACTUsing Time Domain Reflectometry, the complex dielectric spectra over the frequency range 10 MHz to 20 GHz has been measured in the whole composition range at 288 K, 298 K, 308 K and 318 K for the binary mixtures of water and Dimethylaminoethanol. A systematic variation is observed in dielectric constant (ϵ0) and relaxation time (τ). The excess dielectric constant (ϵE), excess inverse relaxation time (1/τ)E, Kirkwood correlation factor (g), enthalpy of activation (ΔH), entropy of activation (ΔS) and Gibbs free energy of activation (ΔG) have been determined, to confirm the formation of hydrogen bonded homogeneous and heterogeneous cooperative domains, the dynamics of solute-solute interaction and the hindrance to molecular rotation in the hydrogen bonded water-Dimethylaminoethanol system.

Modifying hydrogen-bonded structures by physical vapor deposition: 4-methyl-3-heptanol.

We prepared films of 4-methyl-3-heptanol by vapor depositing onto substrates held at temperatures between Tdep = 0.6Tg and Tg, where Tg is the glass transition temperature. Using deposition rates between 0.9 and 6.0 nm/s, we prepared films about 5 μm thick and measured the dielectric properties via an interdigitated electrode cell onto which films were deposited. Samples prepared at Tdep = Tg display the dielectric behavior of the ordinary supercooled liquid. Films deposited at lower deposition temperatures show a high dielectric loss upon heating toward Tg, which decreases by a factor of about 12 by annealing at Tg = 162 K. This change is consistent with either a drop of the Kirkwood correlation factor, gk, by a factor of about 10, or an increase in the dielectric relaxation times, both being indicative of changes toward ring-like hydrogen-bonded structure characteristic of the ordinary liquid. We rationalize the high dielectric relaxation amplitude in the vapor deposited glass by suggesting that depositions at low temperature provide insufficient time for molecules to form ring-like supramolecular structures for which dipole moments cancel. Surprisingly, above Tg of the ordinary liquid, these vapor deposited films fail to completely recover the dielectric properties of the liquid obtained by supercooling. Instead, the dielectric relaxation remains slower and its amplitude much higher than that of the equilibrium liquid state, indicative of a structure that differs from the equilibrium liquid up to at least Tg + 40 K.

Modeling the dynamic viscosity of associating and polar fluids via the use of density scaling

It is well-known that certain dynamical properties such as the dielectric relaxation times and the viscosity of liquids can be graphically superpositioned onto a single master curve as a function of the thermodynamic potential (ργ/T), where T is the temperature, ρ is the density, and γ is a state-independent scaling exponent. We presently applied the aforementioned thermodynamic scaling to the viscosity of typical hydrogen-bonding formers and polar fluids such as water, hydrogen sulfide, ammonia, methanol and an ionic liquid: [bmim][PF6]. Unlike previous studies on density scaling of transport properties, a more suitable reduction and normalization of the viscosity was introduced here in order to obtain improved correlations of viscosity over much wider temperature and pressure ranges encompassing the zero-density limit, the high-density region, the gas-liquid saturation line and the vicinity of the critical point. A calculation procedure is also described here to optimize the value of the scaling exponent γ that ensures the best super-positioning of all experimental isotherms considered for each substance.

Physical properties of tofu gel probed by water translational/rotational dynamics

The dynamic behavior of water molecules in tofu gels is observed using dielectric spectroscopy (DS) and pulsed field gradient nuclear magnetic resonance (PFG-NMR) methods. The breaking stress of tofu gels are dependent on the heating time, which affects the water structures characterized by the dielectric relaxation time, τ. On the other hand, the inhomogeneity of the gel structures decreases with increasing coagulant concentration was reflected as decreasing of the dielectric broadening parameter, β, that related for a fluctuation of the dynamic water structure. In addition, a decrease in the translational diffusion coefficient of water molecules is obtained with increasing coagulant concentration suggesting a reduction of the free space for the diffusional motion of water molecules. Negative correlations between the broadening parameter, β, and the inverse of diffusion coefficient, 1/D, are found in tofu gels and soymilk with distinct correlation coefficients of −0.95 and −0.87, respectively. These results suggest that water dynamics analysis and complementary analysis using DS and PFG-NMR measuring techniques can be an effective tool to evaluate food gel physical properties. Further these technique could also explain the molecular mechanisms of gel and liquid structures and properties via dynamic water structures.

Conformational and dielectric relaxation studies on hydrogen bonded binary mixture of ethyl acetate in 1-butanol and 1-pentanol

ABSTRACTThe dielectric relaxation study for the hydrogen bonded binary system of polar liquid ethyl acetate in 1-butanol and 1-pentanol, has been carried out at 11 concentrations over the frequency range of 10 MHz to 20 GHz at 30°C using TDR. The least squares fit method has been used to obtain the static dielectric constant (ϵ0) and relaxation time (τ). By using dielectric parameters the excess permittivity (ϵE), excess inverses relaxation time (1/τ)E, Kirkwood Correlation factor (g) are also obtained to explore the hydrogen-bonded hetero-molecular interactions. Conformational analysis of the hydrogen bond between the two systems is supported by the FTIR spectra.

Dielectric and FTIR studies on the hydrogen bonded binary system of ester and alcohol

ABSTRACTConcentration dependent dielectric constant, relaxation time, excess dielectric constant, excess inverse relaxation time and the effective Kirkwood correlation factor of the binary mixture of methyl acetate with butanol and pentanol, over the entire mixing range have been determined at room temperature. The values of these functions emphasize on the hydrogen bond interactions between the unlike molecules in ester-alcohols mixtures, the nature of which depends on the extent of substitution of the alcohols. The concentration depending values of excess dielectric constant and excess inverses relaxation time were used to analyze the hydrogen bonding complexes formed between unlike molecules and the strength of the molecular connectivities in the binary mixtures. Conformational analysis of the formation of hydrogen bond is also supported by the FTIR study.

Investigation of intermolecular interactions between amide-amine binary mixtures through dielectric relaxation study

ABSTRACTDielectric relaxation study on dimethylacetamide with ethanolamine and dimethylaminoethanol binary mixtures has been carried out at eleven concentrations over the frequency range of 10 MHz to 20 GHz at 30°C using TDR technique. The least squares fit method has been used to obtain the static dielectric constant (ϵ0) and relaxation time (τ). By using these dielectric parameters, the excess permittivity (ϵE), excess inverse relaxation time (1/τ)E and Kirkwood correlation factor (geff) are also obtained for investigating the intermolecular interaction. Conformational analysis of the intermolecular interaction between DMA-ETA and DMA-DMAE systems is supported by the FTIR spectra.

Structure and dielectric properties of (Ba0.7Sr0.3)1−x Na x (Ti0.9Sn0.1)1−x Nb x O3 ceramics

(Ba0.7Sr0.3)1−x Na x (Ti0.9Sn0.1)1−x Nb x O3 ceramics with compositions x = 0.6, 0.7, 0.8 and 0.9 were synthesized using the solid-state reaction method. These ceramics were examined by X-ray diffraction and dielectric measurements over a broad temperature and frequency ranges. X-ray diffraction patterns revealed a single-perovskite phase crystallized in a cubic structure, for x < 0.8, and in tetragonal, for x ≥ 0.8, with Pm3m and P4mm spaces groups, respectively. Two types of behaviors, classical ferroelectric or relaxor, were observed depending on the x composition. It is noted that temperatures T C (the Curie temperature) or T m (the temperature of maximum permittivity) rise when x increases and the relaxor character grows more significantly when x composition decreases. To analyze the dielectric relaxation degree of relaxor, various models were considered. It was proven that an exponential function could well describe the temperature dependence of the static dielectric constant and relaxation time.

New Details to Relaxation Dynamics of Dielectric Composite Materials Comprising Longitudinally Opened Carbon Nanotubes

The difference between intact and longitudinally opened multiwalled carbon nanotubes (referred to as CNT and OCNT) has been studied in their application as conductive filler in polymer composite materials. The dielectric properties have been studied in a broad frequency range at the temperatures varying from 293 K through 373 K. Introduction of as little as 0.5% and 1.0% of the conductive filler dramatically increased both parts of the complex permittivity. The percolation threshold is registered at ∼1.5% filling fraction. The main frequency dispersion of the dielectric permittivity lies in the low frequency end of the tested spectrum: from 102 Hz through 104 Hz. At equal filling fractions, the permittivity of the OCNT-based samples exceeds that of the intact CNT-based samples. The relaxation dynamics is largely affected by the nanoscale geometry of the filler: the temperature dependence of such parameters as dielectric strength, activation energy, and relaxation time demonstrated significant difference between the charge transfer mechanism in the CNT-based and OCNT-based samples. The obtained activation energy is 150 and 85 kJ/mol for materials comprising CNTs and OCNTs, respectively. The relaxation mechanism is complex, and the exact factors behind the macroscopic dielectric properties of the tested materials cannot be singled out with certainty. Several experimental data points suggest that the individual nanotubes, not their aggregates, play the major role in the observed electrical properties of the composites. At the low loading fractions, we attained the highest dielectric strength values among all the data reported by the present day for the CNT/polymer host systems.

Modeling the thermal conductivity of n-alkanes via the use of density scaling

It has been well established that certain dynamical quantities such as the dielectric relaxation times and the viscosity of liquids can be graphically represented into a single master curve as a function of the thermodynamic potential (ργ/T), where T is the temperature, ρ is the density, and γ is a state-independent scaling exponent. In this work, we applied the aforementioned thermodynamic scaling to the thermal conductivity of linear alkanes from methane to n-decane. In doing so, a new unreduced yet normalized form of the thermal conductivity was introduced in this work in order to obtain improved correlations of thermal conductivity over much wider temperature and pressure ranges encompassing the zero-density limit, the high-density region, the gas-liquid saturation line and the vicinity of the critical point. A calculation procedure is also described here to optimize the value of the scaling exponent γ that ensures the best super-positioning of all experimental isotherms considered for each hydrocarbon.

Dielectric properties of gadolinium-based liquid crystalline complex

The permittivity components of the liquid crystalline gadolinium complex with Lewis bases and β-diketonates as ligands are measured in the frequency range from 100 Hz to 5 MHz. The magnitude and sign of the dielectric anisotropy of the complex are determined. Two dispersion regions of the permittivities are found in the liquid crystalline phase. The mechanisms responsible for the relaxation phenomena occurring in the sample are established. The dielectric relaxation times, activation energies, and dipole moment of the complex are obtained. The results of the study are compared with the dielectric properties of ytterbium and terbium complexes having the same ligand environment.