Dielectric relaxation and hydrogen bonding studies of 1,3-propanediol–dioxane mixtures using time domain reflectometry technique

The complex permittivity, static dielectric constant and relaxation time for 1,3-propanediol, 1,4-dioxane and their mixtures have been studied using time domain reflectometry (TDR). The excess permittivity, excess inverse relaxation time and Kirkwood correlation factor have also been determined at various concentrations of dioxane. Hydrogen bonded theory was applied to compute the correlation terms for the mixtures. The Bruggeman model for the nonlinear case has been fitted to the dielectric data for mixtures.     

Structural study of aqueous solutions of tetrahydrofuran and acetone mixtures using dielectric relaxation technique

The complex permittivity, static dielectric constant and relaxation time for tetrahydrofuran-water and acetone-water mixtures have been determined at 0°, 10°, 25° and 35°C using time domain reflectometry technique (TDR). The behaviour of relaxation time of the mixture shows a maxima for the mixture with 30% of water by volume. This suggests that the tendency to form cluster between water and solute molecule is maximum for this mixture. The excess permittivity for both tetrahydrofuran-water mixture and acetone-water mixtures, are found to be negative. The Kirkwood correlation factor has been determined at various concentrations of water. Static dielectric constant for the mixtures have been fitted well with the modified Bruggeman model. The values of the Bruggeman parametera for tetrahydrofuran is found to be more than the corresponding value for acetone.     

Study of heterogeneous interaction in binary mixtures of 2-methoxyethanol-water using dielectric relaxation spectroscopy

The dielectric relaxation measurements on binary mixtures of 2-methoxyethanol with water have been carried out over entire concentrations and at temperature range of 0 °C to 25 °C using a picosecond time domain reflectometry technique. The complex dielectric permittivity spectra of 2-methoxyethanol/water mixtures were fitted using Havriliak-Negami equation. The static dielectric constant and relaxation time for all concentrations were obtained using least square fit method. The principal relaxation time is small if compared to that of corresponding alcohol/water mixtures this may be due to the hydrogen bonding ether oxygen in the 2-ME-water system. Excess dielectric properties, Kirkwood correlation factor, thermodynamic properties and Bruggeman factor are also determined and the results are interpreted in terms of heterogeneous interactions among the unlike molecules due to hydrogen bonding.     

Dielectric relaxation study of aqueous 2-ethoxyethanol using time domain reflectometry technique

The complex permittivity spectra of 2-ethoxyethanol in water solutions have been studied at different concentrations and temperatures using a picosecond time domain reflectometry technique. The complex dielectric permittivity spectrum of 2-ethoxyethanol shows Cole-Davidson type behavior. Increase in dielectric relaxation time may be due to increase in hetero molecular interaction strength. Minimum in Excess dielectric constant values provides the information about stable complex adduct. The Kirkwood correlation factor, thermodynamic properties and Bruggeman factor have also been determined and the results are interpreted in terms of hydrogen bonding and interactions among the solute — solvent molecules.     

Dielectric absorption in mixtures of anisole with some primary alcohols at microwave frequency

Dielectric properties of binary mixtures of anisole with methanol (MeOH), 1-propanol (1-PrOH), 1-butanol (1-BuOH) and 1-heptanol (1-HeOH) over an entire concentration range have been studied at a fixed temperature 40°C. The dielectric constant (ε′) and dielectric loss (ε″) of the binary mixtures of polar liquids have been determined at a microwave frequency of 9.1?GHz. The static dielectric permittivity (ε ₀) of the liquid samples was also determined using a precision LCR meter. Determined values of static dielectric permittivity (ε ₀) and dielectric permittivity (ε*) at 9.1?GHz frequency were used to evaluate relaxation time (τ) and high frequency limit dielectric permittivity (ε _∞). Dielectric parameters were interpreted in terms of molecular interaction between the anisole and alcohol molecules.     

Pressure and temperature dependence of the static dielectric constant of KBr

The static dielectric constant and the temperature and pressure derivatives of the static dielectric constant of KBr have been measured at several temperatures between 4·3°K and room temperature. The sample was prepared in the form of a three-terminal parallel-plate capacitor and the dielectric constant was determined from measurements of the capacitance with a high precision bridge. The dielectric constant decreases with temperature as does the magnitude of the temperature dependence and the magnitude of the pressure dependence. The data were used to calculate the fixed-volume temperature derivative of the dielectric constant. This quantity, (? ln ε/?T)_v, exhibiting lattice-anharmonicity effects, decreases slightly from its room temperature value as the temperature is lowered, rises to a maximum value at about 33°K and then decreases rapidly at lower temperatures.     

Dielectric relaxation studies of alkanols solubilized by sodium dodecyl sulphate aqueous solutions

Considerable attention has been paid in recent years to the influence of alcohols on ionic micellar structures, alcohol co-surfactants most commonly employed in the preparation of microemulsions. Dielectric relaxation spectroscopy (DRS) is a versatile tool to monitor the dynamic process of such micellar systems. We report here the changes in the dielectric constant of the medium and the relaxation time of micellar solutions of sodium dodecyl sulphate (SDS) in water in the presence and absence of alkanols—hexan-1-ol, octan-l-ol, decan-l-ol and 1,2-ethanediol. The time domain dielectric data were obtained in the reflection mode in the frequency range of 10 MHz to 20 GHz using a HP54750A sampling oscilloscope and HP 54754A TDR plug-in-module. The sample is held at 303 K in a SMA cell with an effective pin length of 1.35 mm. We have determined the relaxation time (τ) using the Cole–Cole method. The relative viscosity ηr on the micellar solutions were also determined. The result shows that the dielectric constant increases linearly with SDS concentration in pure aqueous solutions up to 400 mM and decreases thereafter. The relaxation times are of the order of 15 ps to 25 ps and are far greater than that of Debye rotational relaxation of the monomer species. It is assigned to the dispersion step to water molecules surrounding to hydrophobic particles or the “bound water”. The addition of alcohols results in a linear increase in relaxation time in all the systems. As the concentration of SDS increases τ/ηr attains a near constant value showing that solubilization becomes more difficult at these concentrations. Our results show that the alcohol molecules are solubilized at the surface of the SDS micelle (i.e.) the micelle–water interface.     

Dielectric relaxation studies of aqueous sucrose in ethanol mixtures using time domain reflectometry

Time domain reflectometry method has been used in the frequency range of 10 MHz to 10 GHz to determine dielectric properties of aqueous sucrose in ethanol. The dielectric parameters, i.e., static dielectric constant and relaxation time were obtained from the complex permittivity spectra using the non-linear least squares fit method. The Luzar theory is applied to compute the cross-correlation terms for the mixtures. It adequately reproduces the experimental values of static dielectric constants. The Bruggeman model for the non-linear case has been fitted to the dielectric data for mixtures.     

On the theory of dielectric relaxation

The Kirkwood expression for the static dielectric constant of a polar substance is extended to non-zero frequencies by a means which avoids the introduction of spherical specimens and the connection between the dipoledipole correlation functions of distinct spatial regions. The procedure is based on a previously derived relation between the dynamic dielectric constant and the current-current susceptibility and on the use of the Callen-Welton theorem to relate the susceptibility to fluctuations. Surface effects are eliminated at the outset by consideration of media which are infinite in extent. A general relation between the long-range dipole-dipole correlations (which fall off as the inverse cube of the distance) and short-range correlations in a specimen composed of non-polarizable molecules is found from a consistency relation. It is shown that the two microscopic relaxation times which result from the existence of but one relaxation time in the dielectric constant correspond to the transverse and longitudinal relaxation times with the longitudinal time being screened relative to the transverse time by the static dielectric constant.     

Dielectric relaxation and hydrogen bond interaction study of diol-water mixtures

Complex dielectric permittivity measurements in the frequency range 10MHz-20GHz have been carried out in diol-water mixtures over the entire concentration range using a time domain reflectometry (TDR) method at 25°C. A hydrogen bonded theory is applied to compute the dielectric constant for the mixtures. It adequately reproduces the experimental values of static dielectric constants for the diol-water mixtures. The dielectric parameters confirm that the intermolecular homogeneous and heterogeneous hydrogen bonding vary significantly with the increase in concentration of the constituents of the diol-water mixtures.     

Permittivity of diluted pentanol as a function of temperature

The static dielectric constant of pentanol diluted in decane, cyclohexane and carbon tetrachloride was measured as a function of temperature, at different concentrations. The experimental points were adjusted using the Onsager equation to which a term reducing the molecular interaction was added. Such an empirical equation has already been published for decane solutions. Good agreement between experimental and fitted values of the permittivity was found. The results obtained for the different solvents used are compared and analysed, together with the parameters resulting from the fittings.     

Study of interaction through dielectrics: Behavior of − OH group molecules from 10 MHz to 20 GHz

The complex permittivity spectra for tert-butyl alcohol (TB) with 2-propanol (2P) were determined over the frequency range of 10 MHz to 20 GHz using the time domain reflectometry (TDR) in the temperature range 25 °C to 55 °C for 11 different concentrations of the system. The static dielectric constant (ε₀) and relaxation time (τ) have been determined these spectra using the Debye model. Excess properties and Kirkwood correlation factor of the mixtures have been determined. The excess permittivity is found to be positive in the tert-butyl alcohol rich region and negative in the 2-propanol rich region. However, the excess inverse relaxation time has different trend. The static dielectric constants for the mixtures have also been fitted with the modified Bruggeman model by assuming an additional parameter in the model. It appears that structure of the TB–2P dimer in the TB rich region favors parallel dipole orientation, whereas in the 2P rich region, it favors antiparallel orientation.     

A comparative study of non-polar solvents effect on dielectric relaxation and dipole moment of binary mixtures of mono alkyl ethers of ethylene glycol and of diethylene glycol with ethyl alcohol

Dielectric relaxation and dipole moment of binary mixtures of homologous series of mono alkyl ethers of ethylene glycol and of diethylene glycol, i.e., mono methyl, mono ethyl and mono butyl ethers of ethylene glycol (ROCH₂CH₂OH) and mono methyl, mono ethyl and mono butyl ethers of diethylene glycol (ROCH₂CH₂OCH₂CH₂OH) with ethyl alcohol (C₂H₅OH) of different concentrations were studied in dilute solutions of benzene, dioxane and carbon tetrachloride at 35 °C. Permittivity (ε′) and loss (ε″) at 10.1 GHz, static dielectric constant ε_o at 1 MHz and high frequency limiting dielectric constant ε_∞ = n_D² at optical frequency of these molecules and their binary mixtures at different concentration were measured in dilute solutions of non-polar solvents. The average relaxation time τ_o, relaxation times corresponding to overall molecular reorientation τ₁ and group rotations τ₂ were determined using Higasi's single frequency measurement equations for dilute solutions. The evaluated values of relaxation times and free energy of activation ΔF were used to explore the solvent effect on molecular dynamics of these polar binary systems in non-polar solvents. The excess inverse relaxation time and excess free energy of activation were determined to confirm the existence of hydrogen-bonded heterogeneous cooperative domains of the ethers and alcohol molecules at different concentration their binary mixtures in non-polar solvents. The dipole moment of the binary mixtures was evaluated using Higasi's and Guggenheim's equation for dilute solutions. The evaluated values of dipole moments and computed dipole moment values using a simple mixing equation of the polar molecules binary mixture were used to explore the effect of non-polar solvent environment on heterogeneous molecular interactions between ethers and alcohol molecules. The effect of number of carbon atoms in the molecular structure of these homologous series molecules was also considered for the interpretation of various evaluated dielectric parameters.     

Vibrational and dielectric properties of La2Hf2O7 : Experiment and theory

The physical origin of the static dielectric constant and its relationship with lattice dynamics of La₂Hf₂O₇are studied by combining infrared spectroscopy and density functional perturbation theory (DFPT). Both La and Hf show obvious effective charge anomaly which is attributed to the hybridization between 2p states of the oxygen and 5d states of the cations, indicating a mixed covalent-ionic bonding between the cations and the oxygen. The dielectric response is determined by seven infrared phonon modes and the static dielectric constant extracted from infrared reflection spectrum is in close agreement with DFPT calculation. Both experiment and theory reveal that most of the contributions to the static dielectric constant are dominated by three infrared phonon modes at 137, 172 and 297 cm⁻¹. Two of them (172 and 297 cm⁻¹) are from the displacements of oxygen atoms inside HfO₆ octahedra and the other one (137 cm⁻¹) is from the bending of La₂O′ chain. This result indicates that the origin of the static dielectric constant of La₂Hf₂O₇ is directly connected with the two interpenetrating sub-networks of pyrochlore structure (HfO₆ octahedra and La₂O′ chain).     

Analysis of first and second order strain derivatives of the dielectric constants of alkali halides

Expressions for evaluating the first and second order strain derivatives of the electronic and static dielectric constants of alkali halides are derived. The strain derivatives of the electronic dielectric constant are calculated by taking account of the effect of the crystalline potential on the variation of electronic polarizabilities with volume. The strain derivatives of the static dielectric constant are evaluated adopting the exponential and the inverse power forms for the short range repulsive potential. Two sets of the Born repulsive parameters derived from ultrasonic data and dielectric data are used to evaluate the lattice contribution to the volume dependence of static dielectric constant of alkali halides.     

Dielectric relaxation study of pyridine-alcohol mixtures using time domain reflectometry

Time domain reflectometry is applied to dielectric relaxation measurements on pyridine-alcohol (methanol, ethanol, propan- 1-o1 and butan-1 -o1) mixtures over the entire concentration range and over the frequency range 10MHz-10GHz at 5, 15, 25 and 35°C. From the data, static permittivity and the dielectric relaxation time are extracted using a bilinear calibration method and a nonlinear least-squares fit method. These mixtures exhibit a principal dispersion of the Debye type at microwave frequencies. The Kirkwood correlation factor, which contains information regarding solute-solvent interaction and corresponding structural information, was obtained for these systems, and the excess inverse relaxation time and molar energy of activation for all these systems were determined. The values of the static permittivity, the relaxation time and the Kirkwood correlation factor decrease with increased pyridine concentration in alcohol. The static permittivity of the mixtures fits the modified Brugemann model well.     

Effect of Cu doping on the static dielectric constant of nanocrystalline ZnO

Cu-doped ZnO nanoparticles were synthesized by a simple rheological phase reaction–precursors method using zinc acetate, cupric acetate and oxalic acid for different atomic percentages of Cu doping. X-ray diffraction studies confirmed the correct phase formation and compositions were obtained by energy dispersive X-ray analysis. Particle sizes were recorded from small angle X-ray scattering studies. The static dielectric constant, calculated from the shift in band-gap energy, showed a gradual decrease with Cu doping. A simple theoretical calculation, based on the Penn model, was performed to explain the observed change in dielectric constant with doping. The model could successfully describe the dependence of the static dielectric constant of nanocrystalline ZnO on doping concentration.     

Influence of molecules with chloro group on the associative liquid methanol: A dielectric relaxation approach

The dielectric relaxation parameters, viz., static dielectric constant, ɛ, and relaxation times, τ, have been determined for chlorobenzene-methanol (CB-MET), 1,2 dichloro ethanemethanol (DE-MET) and dimethylene chloride-methanol (DC-MET) mixtures with thirteen different concentrations at three temperatures, viz., 15, 25 and 45°C. The experimental technique used for this work was the time domain reflectometry (TDR) in the frequency range of 10 MHz to 20 GHz using the Hewlett Packard HP 54750 sampling oscilloscope. The information regarding hydrogen bonding structural behavior in MET due to CB, DE and DC are obtained by using the theoretical models based on the excess properties. The data suggest that CB and DE are not influenced by hydrogen bonding in MET whereas DC is influenced by the hydrogen bonding mechanism in MET. It appears that the behavior of DC on MET is different from CB and DE in MET.     

Dielectric study of pharmacologically important drugs in ethanol at different temperatures using time domain technique

The dielectric relaxation study of pharmacologically important drugs in ethanol has been carried out at various temperatures and concentrations in the frequency range of 10 MHz to 10 GHz using Time Domain Reflectometry (TDR) technique. Dielectric properties i.e. dielectric constant and relaxation time were obtained from the complex permittivity spectra using nonlinear least squares fit method. From the values of relaxation time, thermodynamic parameters were determined. The results obtained are used to interpret the nature and kinds of solute-solvent interactions.