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.     

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.     

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.     

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.     

The dielectric relaxation study of 2(2-alkoxyethoxy)ethanol-water mixtures using time domain reflectometry

Complex permittivity spectra of 2(2-alkoxyethoxy)ethanol-water mixtures for the entire concentration range and at 25 °C have been measured using time domain reflectometry technique up to 30 GHz. The relaxation processes have been obtained by fitting the complex permittivity spectra of the binary mixtures in 2-Debye equation. In glycol ether-water mixtures except for pure water and its rich region the double relaxation times, primary process (τ₁) and secondary process (τ₂) have been observed. The primary relaxation process (τ₁) may be due to cooperative relaxation of the H-bond network of mixture constituents and the secondary relaxation process (τ₂) may be due to its flexible parts attached to the carbon chain. The intra and intermolecular hydrogen bonding of 2(2-alkoxyethoxy)ethanol in pure form as well as in binary mixtures of water have been discussed using Kirkwood correlation factor, Excess dielectric properties and the Bruggeman factor.     

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.     

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.     

Dielectric studies on binary polar mixtures of propanoic acid with esters

It is interesting to see the nature of intermolecular interactions between associative and non-associative polar liquids. Binary polar–polar liquid mixtures of ethyl acetate, ethyl benzoate, ethyl acrylate, ethyl butyrate, n-butyl acetate and benzyl benzoate, each with propanoic acid were subjected to dielectric studies at temperatures 25 °C, 35 °C and 45 °C. Static permittivity (ε_o) and dielectric constant at high frequency (ε_∞) were found through dielectric measurements for different concentrations of each system. The Bruggeman dielectric factor, Kirkwood correlation factor and the excess permittivity were determined. Deviations from the linearity of various models suggest molecular association through hydrogen bonding between the polar–polar constituents of the mixtures. The formation of cyclic and linear α-multimers in the above systems were identified. The results and their temperature dependence were interpreted accordingly.     

Dielectric relaxation studies of methyl cellulose with phenol derivatives in non-polar solvents using time domain reflectometry

Dielectric relaxation measurements of methyl cellulose with substituted phenols p-cresol, m-cresol and o-cresol mixture in different non-polar solvents CCl₄, benzene and 1,4-dioxan for different concentrations over the frequency range of 10 MHz–20 GHz at 303 K have been carried out using Time Domain Reflectometry (TDR). Dielectric parameters such as static permittivity (ε₀) and relaxation time (τ) were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The dielectric constant and relaxation time were found to be high for methyl cellulose with p-cresol in CCl₄ compared with the other mixtures.     

Dielectric studies of alkyl acrylates with primary alcohols using time domain reflectometry

Binary polar–polar liquid mixtures of alkyl acrylates (methyl acrylate, ethyl acrylate and butyl acrylate) with primary alcohols (propan-1-ol, butan-1-ol and hexan-1-ol) were subjected to dielectric studies at 303?K for different concentrations using time domain reflectometry (TDR) over the frequency range from 10?MHz to 10?GHz. Static permittivity (ε₀) dielectric constant at high frequency (ε_∞) and relaxation time (τ) were found through dielectric measurements for different concentrations of each system. The Bruggeman dielectric factor, Kirkwood correlation factor and the excess inverse relaxation time were determined and discussed to yield information on the molecular interactions of the systems. Deviations from the linearity of various models suggest molecular association through hydrogen bonding between the ?OH group of alcohols and C=O group of esters. The results also show a dependence of dielectric parameters on the alkyl chain length of both the alcohols and esters.     

Concentration and temperature dependent interaction studies using dielectric and thermodynamic methods on mixtures of anisole with o-toluidine and m-toluidine

Molecular interactions in mixtures of anisole with o-toluidine and anisole and m-toluidine have been studied at three different temperatures using the dielectric method with measurements of the static permittivity and permittivity at optical frequency. From the measured values, the Kirkwood correlation parameter, Bruggeman parameter, excess permittivity and thermodynamic excess free energy were computed for the mixtures. Positive and negative values of excess permittivity were obtained for both mixtures. The excess free energy for the anisole+o-toluidine mixture is positive at all three temperatures, whereas mixed values (positive and negative) are obtained for the anisole+m-toluidine mixture. Alignment of the dipoles in both mixtures was identified by Kirkwood factors. The investigation shows that the interaction between the components changes systematically with concentration and temperature and the change is minimum.     

Dielectric relaxation study of dipropylsulfoxide/water mixtures

The complex dielectric spectra of dipropylsulfoxide (DPSO)/water mixtures in the whole concentration range have been measured as a function of frequency between 100 MHz and 20 GHz at four temperatures between 298.15 K and 328.15 K. The dielectric parameters, static dielectric constant (ε_s), relaxation time (τ) and relaxation strength (Δε) have been obtained by the least squares fit method. The relaxation in these mixtures can be described by two Debye functions, whereas for pure DPSO Cole-Davidson type is valid. The relaxation times of the mixtures show a maximum at about x(DPSO) ≈ 0.3. In the concentration range where a maximum appears, the interaction of DPSO with water is presumably the result of hydrogen bonding between water and the sulfonyl group of the sulfoxide molecule. The concentration and temperature dependent excess dielectric constant and effective Kirkwood correlation factor of the binary mixtures have been determined. The excess permittivity is found to be negative for all concentrations.     

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, X_w. 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 δ? against X_w suggests that there is a changing pattern of dielectric behaviour from below X_w = 0.5 to higher values of X_w. 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.     

Microwave dielectric characterization of binary mixture of formamide with <Emphasis Type="Italic">N,N</Emphasis>-dimethylaminoethanol

Dielectric relaxation measurements of formamide (FMD)-N,N-dimethylaminoethanol (DMAE) solvent mixtures have been carried out over the entire concentration range using time domain reflectometry technique at 25, 35 and 45°C in the frequency range of 10 MHz to 20 GHz. The mixtures exhibit a principle dispersion of the Davidson-Cole relaxation type at microwave frequencies. Bilinear calibration method is used to obtain complex permittivity ɛ*(ω) from complex reflection coefficient ρ*(ω) over the frequency range of 10 MHz to 10 GHz. The excess permittivity (ɛ ^E), excess inverse relaxation time (1/τ)^E, Kirkwood correlation factor (g ^eff), activation energy and Bruggeman factor (f _B) are also calculated to study the solute-solvent interaction.      

Dielectric relaxation studies of four aliphatic esters in benzene at 30°, 40°, 50° and 60°

The complex permittivity at 9.92 GHz, the static permittivity and the high frequency limiting permittivity have been determined for n-butyl-acrylate, allyl-methacrylate, isobutyl-methacrylate and isobutyl-acrylate monomers in benzene at 30°, 40°, 50° and 60°C. The relaxation time values and the dipole moment values calculated from these data employing different methods, are interpreted in terms of the molecular and the intramolecular rotations. Various thermodynamic parameters calculated for the dielectric relaxation as well as the viscous flow processes also suggest the existence of both the intramolecular and the overall orientations in these monomer esters. The comparative study of enthalpies of activation for the dipolar relaxation and the viscous flow suggests the absence of any solid rotator phase in these molecules. Values of the Debye's factor and the Kalman's factor show that the Kalman's equation represents the relation between the dielectric relaxation and the viscosity, more satisfactorily than the Debye's equation.     

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.     

NMR relaxation in binary aqueous mixtures of acetone and tetrahydrofurane

NMR proton relaxation rates of normal and ¹⁷O-enriched water and deuteron relaxation rates of heavy water were measured in mixtures with acetone and tetrahydrofurane at different compositions. The ¹⁷O-induced proton relaxation rate was extracted and from this the rotational correlation time of water was determined. Using these correlation times the composition-dependence of the deuteron quadrupole coupling constant of water was derived. A strong variation was found for the system acetone-water, whereas little variation was observed for tetrahydrofurane-water.     

GROMOS polarisable model for acetone

A polarisable model for acetone, COS/A, is proposed that is based on the charge-on-spring (COS) polarisation model and is compatible with the polarisable COS/D2 and COS/G2 models for liquid water. A series of acetone-water mixtures at different acetone mole fractions was simulated using the new model in conjunction with the mentioned polarisable and the non-polarisable SPC and SPC/E water models. The model was parameterised to reproduce the following liquid acetone properties: density, heat of vaporisation, surface tension, dielectric permittivity, self diffusion and heat capacity and subsequently tested in mixtures with water using different water models. For pure liquid acetone the polarisable COS/A model agrees better with experimental data than the non-polarisable Kirkwood-Buff derived force field (KBFF) model, which was parameterised using experimental data for a 0.5 mole fraction acetone-water mixture. For such mixtures the polarisable models yield better agreement with experiment than the non-polarisable models for the heat of vaporisation and dielectric permittivity, while worse agreement for diffusion. The computational cost of simulating the polarisable acetone-water mixtures is a factor of 3 to 4 higher compared with the non-polarisable models due to the increased number of interaction sites and the multiple iterations required to evaluate self-consistently the positions of the COS sites at every simulation step. The COS/A acetone model can be used in biomolecular simulations in conjunction with the mentioned polarisable water models to solvate biomolecules.     

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 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.