S. C. Mehrotra

Dielectric behaviour of propylene glycol-water mixtures studied by time domain reflectometry

Dielectric relaxation measurements on water mixtures of propylene glycol across the entire concentration range were carried out using time domain reflectometry at 25°C over the frequency range from 10 MHz to 4 GHz. For all the mixtures, only one dielectric loss peak was observed in this frequency range. The relaxation in these mixtures can be described by a single relaxation time using the Debye model. A plot of the calculated relaxation time of the mixtures gives a straight line against the mole fraction of water, Xw. It is reasoned that the diameter of the water cluster is nearly the same as the length of propylene glycol. Further, a plot of the dielectric relaxation strength δε against Xw suggests that there is a changing pattern of dielectric behaviour from below Xw = 0.5 to higher values of Xw. The excess permittivity, the excess inverse relaxation time and the activation free energy have been determined, to confirm the formation of hydrogen bonded homogeneous and heterogeneous cooperative domains, the dynamics of solute-solvent interaction and the hindrance to molecular rotation in the hydrogen bonded glass forming propylene glycol-water system.

Temperature-Dependent Dielectric Relaxation of 2-Ethoxyethanol, Ethanol, and 1-Propanol in Dimethylformamide Solution Using the Time-Domain Technique

Complex reflection coefficients for 2-ethoxyethanol–dimethylformamide (DMF), ethanol–DMF, and 1-propanol–DMF mixtures at several temperatures from 20 to 50° and the frequency range 10 MHz to 10 GHz were determined by time-domain spectroscopy in reflection mode. Fourier transforms and least-squares fitting were used to obtain complex permittivity, static dielectric constant, and relaxation time. The excess dielectric parameters, Kirkwood correlation factors, and thermodynamic properties for the binary mixtures were also determined. The static dielectric constant for the mixtures was fitted well with the modified Bruggeman model.

Temperature dependent dielectric relaxation study of tetrahydrofuran in methanol and ethanol at microwave frequency using time domain technique

Abstract Dielectric relaxation study of tetrahydrofuran ( THF ) has been carried out in methanol and ethanol at different temperatures. Time domain Reflectometry (TDR) in reflection mode has been used to measure reflection coefficient in frequency range of 10 MHz to 10 GHz. Further, Fourier transform and least squares fit methods have been used to obtain dielectric parameters such as dielectric constant and relaxation time. The excess dielectric parameters and thermodynamic parameters have also been obtained for the system. The investigation shows the systematic change in dielectric parameters of the system with change in concentration and temperature.

Dielectric relaxation study of chlorobenzene-dimethylformamide mixtures using time domain reflectometry

Abstract The complex permittivity spectra of chlorobenzene-N, N dimethylformamide were determined in the frequency range of 10 MHz to 20 GHz using time domain refractometry (TDR) in the temperature range 15°C to 45°C for 11 different concentrations of the system. The dielectric parameters viz. static dielectric constant ( ϵ 0 ) and relaxation time (τ) have been obtained by the least squares fit method. Excess properties and Kirkwood correlation factor of the mixtures have been determined. In case of chlorobenzene excess permittivity found to be positive, whereas it is negative in N, N dimethylformamide rich region. Activation energy in the mixture are also determined. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model.

Temperature dependent dielectric study of n-nitriles in methanol using time domain reflectometry

Abstract The dielectric properties of N-nitriles in methanol have been studied using Time Domain Reflectometry (TDR) technique, in the frequency range of 10 MHz to 10 GHz. The calibration method based on least squares fit method has been used. The dielectric parameters such as static dielectric constant, relaxation time, Kirkwood correlation factor and thermodynamic parameters for the system have been obtained in the temperature range of 0°C to 45°C. The investigated values of dielectric parameters show systematic change in dielectric values with increase in concentration of nitrile in the solution.

Complex Permittivity Spectra of Binary Pyridine–Amide Mixtures Using Time–Domain Reflectometry

Frequency spectra of the complex permittivity for pyridine–amide binary mixtures have been determined over the frequency range 10 MHz to 10 GHz, at 5, 15, 25, and 40°C, using the time–domain reflectometry method, for 11 compositions of each pyridine–amide system, e.g., formamide, N-methylformamide, and N,N-dimethylformamide. The relaxation in these systems can be described by a single relaxation time using the Debye model. The static dielectric constant, relaxation time, the corresponding excess dielectric properties, Kirkwood correlation factor, and molar activation energy of the mixtures have been determined. The excess permittivity is found to be positive in the amide-rich region and negative in the pyridine-rich region. The excess inverse relaxation time is negative, except in the pyridine-rich region. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model. The temperature-dependent relaxation times show the expected Arrhenius behavior.

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.

Dielectric Relaxation Study of Liquids Having Chloro Group with Associated Liquids. I. Chlorobenzene with Methanol, Ethanol, and 1-Propanol

The complex permittivity for chlorobenzene–alcohol binary mixtures have been determined over the frequency range of 10 MHz to 20 GHz, at 15, 25, 35, and 45°C, using the time-domain reflectometry (TDR) method for 11 concentrations of each chlorobenzene–alcohol system. The alcohols used were methanol, ethanol, and 1-propanol. The values of static dielectric constant, relaxation time, the corresponding excess properties, the Redlich–Kister coefficients up to the third order, the Kirkwood correlation factor, and thermodynamic parameters of the mixtures have been determined. The excess permittivity is found to be negative for chlorobenzene–methanol and chlorobenzene–ethanol, whereas it is positive in the 1-propanol rich region. The excess inverse relaxation time is negative for all the systems studied here. The Kirkwood effective correlation factor increases with an increasing in the molecular size of the alcohol, but decreases with increasing temperature.

Dielectric relaxation study of dimethylene chloride with ethanol using time domain reflectometry

Abstract The complex permittivity spectra of dimethylene chloride with ethanol were determined in the frequency range of 10 MHz to 20 GHz using time domain reflectometry (TDR) in the temperature range 15°C to 45°C for 11 different concentrations of the system. The dielectric parameters viz. static dielectric constant (ϵ0) and relaxation time (τ) have been obtained by the least squares fit method. Excess properties and Kirkwood correlation factor of the mixtures have been determined. In the mixture excess permittivity is found to be positive, and inverse relaxation time is negative. Activation energy in the mixture is also determined. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model.

Dielectric Relaxation Study of Chloro Group with Associative Liquids. II. 1,2-Dichloroethane with Methanol, Ethanol, and 1-Propanol

Frequency spectra of the complex permittivity for 1,2-dichloroethane–alcohol binary mixtures have been determined over the frequency range 10 MHz to 20 GHz at 15, 25, 35, and 45°C, using the time-domain reflectometry (TDR) technique, for 11 compositions of each 1,2 dichloroethane–alcohol system. The alcohols used in the study were methanol, ethanol, and 1-propanol. The relaxation in these systems can be described by a single relaxation time using the Debye model. The static dielectric constant, relaxation time, the corresponding excess dielectric properties, Kirkwood correlation factor, and Bruggeman factor of the mixtures have been determined. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model.