A.C. Kumbharkhane

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.

Time domain reflectometric study on toluene + propionitrile binary mixture

ABSTRACT Time domain reflectometry study has been carried out on toluene + propionitrile binary mixture in the frequency range from 10 MHz to 30 GHz at 298 K. The complex permittivity spectrum in the studied frequency range shows only one dispersion region. The dielectric parameters, such as Kirkwood correlation factor , relaxation time , etc., obtained from the complex permittivity spectrum have been analysed in view of the molecular phenomena taking place in the liquid mixtures. Neat propionitrile seems to exist as dimer with antiparallel dipolar alignment.

Temperature-dependent dielectric relaxation study of polyhydric alcohols (propane-1,3 and 1,2-diol) using a TDR technique

The complex dielectric permittivity spectra of 1,2-propanediol, 1,3-propanediol and its binary mixtures with water have been studied as a function of frequency (10 MHz–30 GHz) and temperature. The dielectric relaxation parameters i.e. static dielectric constant and relaxation time were obtained by using non-linear least square fit method. The static dielectric constant of 1,3-propanediol is larger than the corresponding value for 1,2-propanediol. The intermolecular hydrogen bonding of 1,2-propanediol–water and 1,3-propanediol–water has been discussed using Kirkwood correlation factor and thermodynamic parameters. The activation energy decreases with increased water content in the mixture as expected from the Arrhenius behaviour. The dielectric constant for mixture has been fitted to Bruggeman mixture formula in non-linear case.

Dielectric relaxation study of glycine–water mixtures using time domain reflectometry technique

The complex permittivity of glycine in water mixture for various temperatures and concentrations have been measured as a function of frequency between 10 MHz and 30 GHz using time domain reflectometry technique. Dielectric parameters, i.e. static dielectric constant and relaxation time were obtained from the complex permittivity spectra using nonlinear least square fit method. The dielectric relaxation parameter increases with an increase in molar concentration of glycine due to the formation of hydrogen bond groups by glycine molecule in an aqueous solution medium. The activation entropy, activation enthalpy and Kirkwood correlation factor have also been determined for glycine–water mixtures.

Dielectric relaxation study of aniline, N-methylaniline and N,N-dimethylaniline and alcohol in 1, 4-dioxane using picosecond time-domain reflectometry

A time-domain reflectometry technique has been used to measure complex dielectric permittivity ε*(ω) = εʹ(ω) − jε″(ω) of 1-propanol–dioxane, 2-propanol–dioxane, aniline–dioxane, N-methylaniline–dioxane and N,N-dimethylaniline–dioxane mixtures in the frequency range of 10 MHz to 30 GHz. The complex permittivity spectrum has been fitted with a single relaxation time with a small amount of Davidson–Cole behaviour. The least squares fit method has been used to obtain the static dielectric constant (ε0), relaxation time (τ), Bruggeman factor and Kirkwood correlation factor. The Luzar theoretical model is used to compute the binding energies and average number of hydrogen bond between co-solvent–co-solvent and co-solvent–dioxane molecules.

Relaxation dynamics in lens crystallin proteins: a dielectric and thermodynamic approach using TDR

Dielectric relaxation of water in biological systems, such as proteins and DNA, can often be described by two different time constants, one in the picosecond and the other in the nanosecond regime. In the present work, we report the temperature dependence of the relaxation dynamics, dielectric permittivity (e′) and loss (e′′) of aqueous lens proteins (crystalline) in the goat eye lens. The measurements have been carried out in the frequency range from 10 MHz to 20 GHz using TDR and in the temperature region from 298.15 K to 278.15 K. We analyse the three dispersion regions commonly found in protein solutions, usually termed β-, γ- and δ-relaxation. The β-relaxation, occurring in the frequency range between 70 and 100 MHz, and the γ-relaxation between 15 and 18 GHz can be attributed to the rotation of the polar protein molecules in their aqueous medium and the reorientational motion of the free water molecules respectively. The nature of δ-relaxation, which is often ascribed to the motion of bound water molecules, is not yet fully understood. Here, we provide data on the temperature dependence of dielectric and thermodynamic parameters of all three detected processes, β-, γ- and δ-relaxation. We found significant temperature dependence of the dielectric and thermodynamic parameters of the aqueous proteins, indicating conformational changes.

Dielectric relaxation studies of aqueous solution of polyethylene glycol 200 (PEG200), using time-domain reflectometry

Using time-domain reflectometry measurement technique, the dielectric complex permittivity spectra over the frequency range 10 MHz to 30 GHz have been studied for series of various compositions, at various temperatures, for the aqueous solution of polyethylene glycol 200 (PEG200). The relaxation in these mixtures can be described by a single relaxation time using the Cole–Cole model.[1] The values of static dielectric constant, dielectric relaxation time, excess dielectric permittivity, Bruggeman factor and Kirkwood correlation factor are determined for the series of various compositions. Using above parameters, intermolecular interaction of molecules at molecular level are predicated. The negative values of excess dielectric permittivity suggest reduction in dipole moment, and the values of Kirkwood correlation factor, which are found to be greater than unity, show the parallel orientation of electric dipoles. The study confirms that the intermolecular homogeneous and heterogeneous hydrogen bonding varies significantly with the increase in the concentration of PEG200 in water.

Dielectric dispersion and hydrogen bonding interactions study of aqueous D-mannitol using time domain reflectometry

The measurement of complex dielectric permittivity of binary mixtures of D-mannitol and water have been carried out in the frequency range of 10 MHz to 30 GHz using time domain reflectometry (TDR) technique. Measurements were done at different temperatures ranging from 5°C to 25°C for different weight fractions of D-mannitol (0 < WM ≤ 0.18) in water. The dielectric relaxation behaviour of these mixtures is explained using Cole–Davidson model. The dielectric parameters such as static dielectric constant and relaxation time for the mixtures have been evaluated. The activation energy decreases with increased D-mannitol content in the mixture. The molecular interaction between D-mannitol and water molecules is discussed using the Kirkwood correlation factor and Thermodynamic parameters.

Molecular interaction study of ethanol in non-polar solute using hydrogen-bonded model

The dielectric behaviour of binary mixture of ethanol with chlorobenzene and 1,2 dicholoroethane mixtures for various concentrations and temperatures have been studied using hydrogen-bonded model suggested by Luzar. The Luzar theory is applied to determine the molecular parameters and correlation terms for the mixture. The interaction of the chloro group molecules with ethanol hydrogen-bonded liquid is discussed. The calculation of the theoretical dielectric constant using Kirkwood correlation factor provides more precise theoretical model for the mixture.

Temperature-dependent dielectric relaxation study of 1,2,6-hexanetriol using TDR method

The frequency spectra of complex permittivity for 1,2,6-hexanetriol have been determined over the frequency range of 10–30 GHz at various temperatures. The dielectric relaxation for the system can be characterised by the Davidson–Cole behaviour. The static dielectric constant (ε 0), the high-frequency dielectric constant (ε ∞), relaxation time (τ) and the Kirkwood correlation factor are also determined by using least squares fit method. The results have also been compared with results of the glycerol system.