Suresh C. Mehrotra

Dielectric relaxation studies of aqueous N,N-dimethylformamide using a picosecond time domain technique

The dielectric relaxation studies of N,N-dimethylformamide at thirteen concentration in aqueous solutions have been carried out using a time domain reflectometry technique in the frequency range 10 MHz to 10 GHz. The dielectric parameters and excess dielectric properties have also been determined from 5 to 40°C. The Luzar theory was applied to compute the cross correlation terms for the mixture. It adequately reproduces the experimental values of the static dielectric constants. The Bruggeman model for the nonlinear case has been fitted to the dielectric data for mixtures.

The static permittivity of binary mixtures using an improved bruggeman model

Abstract The Bruggeman mixture formula of static permittivity has been modified for binary mixtures of polar liquids by considering nonlinear behaviour of volume fraction of one polar liquid in another polar liquid. The modified equation describes well the experimental dielectric data.

Dielectric relaxation of tert-butyl alcohol–water mixtures using a time-domain technique

Dielectric relaxation measurements in the frequency range 10 MHz–10 GHz have been carried out in tert-butyl alcohol–water mixtures with various concentrations over the temperature range 273–313 K using a time-domain reflectometry (TDR) method. The bilinear calibration method as suggested by Cole has been used to correct the permittivity spectra. The corrected spectra could be fitted with a single relaxation time with a small amount of Cole–Davidson behaviour. Deviations from ideal mixing behaviour in the permittivity parameter (Iµo–Iµ∞) and relaxation time (τ) suggested the formation of a polymeric structure in tert-butyl alcohol–water mixtures. The dielectric relaxation behaviour showed the same structural changes as observed in ultrasonic relaxation. However, the maxima in excess permittivity and excess relaxation time occurred at different positions. This could not be explained by a simple model of the polymeric structure.

Structural study of amide-water mixtures using dielectric relaxation technique

Abstract Dielectric constants and relaxation times for aqueous solutions of formamide (FMD) and N-methylformamide (NMF) have been determined in the temparature range 5°C to 40°C and frequency range of 10 MHz to 10 GHz using a time domain reflection method. The relaxation behaviour far these system can be described by the Debye model in the temperature range. For temperature range, considered here, the relaxation time of both amide—water systems decreases monotonously towards water relaxation time, whereas, static dielectric constants behave differently in the aqueous solutions of FMD. In case of aqueous FMD solutions, the excess permittivity found to be positive, whereas, in case of aqueous NMF, it is found to be negative. This behaviour can be understood by hydrogen bond with the asymmetry group in NMF ( --- indicates hydrogen bond).

Dielectric relaxation study of hexamethylphosphoramide-water mixtures using time domain reflectometry

The dielectric relaxation studies of hexamethylphosphoramide‐water mixtures have been carried out at different temperatures using time domain reflectometry technique in the frequency range of 10 MHz to 10 GHz. A calibration method based on the least squares fit has been suggested to determine the complex permittivity at the high frequency region for the aqueous solutions. The excess dielectric, Kirkwood correlation factor and thermodynamic properties in the mixture have been determined. These properties suggest a Cage‐type structure of hexamethylphosphoramide molecules around water molecules. The structure has a tendency to break down in the presence of water.

Temperature Dependent Dielectric Relaxation Study of Ethylene Glycol-Water Mixtures

Using the picosecond time domain reflectometry method, dielectric relaxation measurements for 13 ethylene glycol (EG)-water mixtures have been studied from 0 to 40°C. The dielectric relaxations in the mixtures show a Debye-type behavior, whereas the relaxation in pure EG can be described by the Cole-Cole model. The static dielectric constant ɛ0, the relaxation time τ and the dielectric constant at high frequency ɛ∞ have also been determined at various temperatures. The dielectric relaxation data suggests that there is no tendency to form hydrogen bonds with the addition of water to EG unlike other alcoholic systems but this tendency becomes increasingly important with decreasing temperature. The activation energy decreases with increased water content in the mixture as expected.

Dielectric relaxation spectra for N,N-Dimethylacetamide-water mixures using picosecond time domain reflectometry

Abstract Using time domain reflectometry technique dielectric study has been carried out in the thirteen different mixtures of aqueous solutions of N,N-Dimethylacetamide (DMA). The static dielectric constant (ϵo), dielectric constant at high frequency (ϵ∞) and relaxaion time (τ) have been obtained at various temperature. The relaxation in these systems can be described by the Davidson-Cole model. The Thermodynamic properties and Arrhenius behaviour of the system are also reported. The values of excess dielectric properties as a function of concentration of water suggest the disapperance of dimers or trimers and leaving behind monomers by addition of water in DMA.

Dielectric relaxation and structural study of aniline–methanol mixture using picosecond time domain reflectometry

Complex permittivity of aniline–methanol mixture for various temperatures have been measured as a function of frequency between 10 MHz and 10 GHz using time domain reflectometry technique (TDR). Dielectric parameters viz. static dielectric constant es, relaxation time τ were obtained from complex permittivity spectra using nonlinear least‐square fit method. With these parameters, excess dielectric properties, Kirkwood correlation factor and thermodynamic parameters were determined and discussed to yield the information on the molecular structure and dynamics of the mixture. At low methanol concentration, strong interaction between the solute–solvent molecules was observed through hydrogen bonding. The values of ΔH* and Kirkwood correlation factors support the same. The dielectric constant of the mixture fits well with the modified Bruggman equation.

Dielectric study of dimethyl sulfoxide–water mixtures using the time-domain technique

Complex dielectric spectra, Iµ*(ω)=Iµ′– iIµ″, in the frequency range 10 MHz–10 GHz have been determined using the time-domain reflectometry (TDR) technique at various temperatures for dimethyl sulfoxide–water mixtures. The dielectric spectra can be described by the Davidson–Cole relaxation model. The thermodynamic properties of the mixture have also been evaluated. The behaviour of the principal relaxation time of the mixture shows a maximum at a value corresponding to a mixture with 30% of water. An attempt has been made to explain the dielectric behaviour of binary mixtures by the hydrogen-bonding model as suggested by Luzar. The static relative permittivity of the mixtures can be explained if one assumes that the dipole moments of water and DMSO in the mixture are 14% and 10% larger than the corresponding values in the gas phase.

Structural behavior of alcohol-1,4-dioxane mixtures through dielectric properties using TDR.

The values of complex permittivity for alcohol-1,4-dioxane (DX) mixtures with various concentrations have been determined in the frequency range 10 MHz to 20 GHz using the time domain reflectometry (TDR) method. Numbers of hydrogen bonds between alcohol-alcohol and alcohol-dioxane pairs are estimated from the values of the static dielectric constant by using the Luzar model. The model provides a satisfactory explanation of the experimental results related to the static dielectric constant. The binding energies for alcohol-alcohol (pair 11) and alcohol-DX (pair 12) are estimated to be -13.98 and -16.25 kJ/mol, respectively. The results have also been compared with previous results of the ethyleneglycol-DX system.