Dielectric relaxation studies of some aliphatic alcohols and their mixtures in benzene solutions

Dielectric absorption of four aliphatic alcohols, viz., methyl alcohol, ethyl alcohol, n-propyl alcohol, tert-butyl alcohol and their binary mixtures, mixtures of these alcohols with dimethyl formamide and 2-fluoroaniline has been studied in the 3 cm microwave region at a temperature of 30°C in benzene. In alcohols and their mixtures the tan σ - concentration curve shows a marked increase in the concentration range 0.02 – 0.05 weight fraction. This behaviour has been explained as due to the formation of complex via self and hetero-association. The alcohols + DMF systems show complex formation at a very low concentration range. The study of systems alcohols + 2 - fluoroaniline indicate that the 2-fluoroaniline produces dissociating effects in these alcohols.     

Dielectric relaxation of mixtures of non-rigid polar molecules in benzene

The dielectric absorption of three compositions of Isobutyl-methacrylate and Allyl-methacrylate, both consisting of non-rigid molecules, has been studied at 9.92 GHz over a range of temperatures in the dilute solutions of benzene. The various relaxation times τ_o, τ(1) and τ(2), the distribution parameter, α and the thermodynamic parameters for the activated states, both for relaxation and the viscous flow processes have been determined using the measured dielectric data. The results indicate that the properties of the single component systems, such as existence of intramolecular and overall rotations, and absence of solid rotator phase, are retained in the two component system. The values of molar entropy of activation for the relaxation process indicate that the cooperative orientation of the molecules in the single component system changes into non-cooperative orientation in the binary system. A comparison of the experimental values of the most probable relaxation time τ₀ with those calculated on the basis of simple and reciprocal mixing rules and also by a procedure suggested by M.P. Madan [5] reveals that none of these procedures can successfully predict the experimental data.     

Dielectric studies in dilute solutions

Dielectric studies in dilute solutions of cyclohexane and benzene have been carried out in the temperature range 294–318°K. The observed data have been utilized to evaluate the relaxation times and thermodynamic parameters of these molecules. The high values ofα for 2-acetyl pyridine indicate the occurrence of more than one relaxation time. In the remaining systems, the observed lowα values indicate their rigid behaviour. The variation in the dielectric relaxation time is mostly correlated with the change in the heterocyclic configuration of the system.     

Dielectric dispersion studies of aromatic ketones in non-polar solvents

Measurements of dielectric constant (ε′) and loss (ε″) have been made at five different microwave frequencies from 1000 MHz to 67.7 GHz for acetophenone, benzophenone and propiophenone in four different non-polar solvents namely benzene, cyclohexane, 1-4-dioxane and n-heptane. Results are reported at five different temperatures from 25°C to 60°C. The dielectric data of these ketones in different solvents are analysed in terms of the Cole-Cole arc plots and superposition of two Debye-type absorptions. Values of mean relaxation times (τ_o), dipolement (μ), overall relaxation time (τ₁) and group relaxation time (τ₂) have been obtained and presented here. The values of relaxation time and dipolemoment are in reasonable good agreement, at the temperatures, at which there are available known data.     

Dielectric relaxation time and dipole moment of isometric butanols in benzene solutions.

Measurements of static permittivity at 100 KHz, refractive index (for Sodium D line) and complex permittivity at 7.73 GHz have been made for Butane 1-01, Iso-butyl alcohol, Sec. butyl alcohol and Tert. butyl alcohol at 35°C. in dilute solutions of benzene. Dielectric relaxation time (τ) have been determined following the three methods, viz., method of Higasi et al, Gopal Krishna's method and Higasi's method. The value of τ and the distribution parameter (α) show evidence for existence of morethan one relaxation mechanism. This has been interpreted in terms of intramolecular orientation of O-H. group occuring simultaneously with the end over end molecular orientation. The > values for all these compounds have been found much larger than the corresponding compounds of similar structure. This behaviour has been explained as due to the formation of dimers by association and solute solvent interaction. This is also confirmed from the tan δ concentration curves. The values of the dipole moments determined from the Higasi's method, Gopal Krishna's method and Guggenheim's method are found to be in good agreement.     

Dielectric dispersion in ferrites

Experimental data are given for the low-frequency dependences of effective resistivity, permittivity and dielectric losses in ferrites. Discussion is based on a generalized barrier model.We wish to thank A. P. Ges for kindly donating the monocrystalline ferrite specimens.     

Dielectric relaxation, thermodynamic and theoretical studies on hydrogen bonded polar binary mixtures of N-methyl aniline with propan-1-ol and isopropyl alcohol

The dielectric relaxation studies on polar binary mixtures of N-methyl aniline with, alcohols, propan-1-ol and isopropyl alcohol have been carried out, at different temperatures and mole fractions, using — LF impedance analyzer, Plunger method and Abbe’s refractometer in radio, microwave and optic frequency regions respectively. Kirkwood effective correlation factor, corrective Kirkwood correlation factor, Bruggeman parameter, relaxation time and thermodynamical parameters are calculated using the experimental data. Conformational analysis of the formation of hydrogen bond in the equi molar binary mixture systems of N-methyl aniline with propan-1-ol and isopropyl alcohol is supported by experimental and theoretical FT-IR values.     

Correlation studies on dielectric and thermodynamic parameters in the binary mixtures of N-methyl aniline and alcohols

The dielectric and thermodynamic studies on polar binary mixtures of N- methyl aniline with alcohols — propan-1-ol and propan-2-ol have been carried out, at different temperatures and mole fractions. LF impedance analyzer, Microwave bench and Abbe’s refractometer are used respectively in radio, microwave (X-Band) and high frequency regions to determine the dielectric data. The experimental data is used to correlate the dielectric and thermodynamic parameters — static permittivity, high frequency permittivity, Kirkwood effective correlation factor, corrective Kirkwood correlation factor, excess permittivity, excess Helmholtz free energy, dipole moment, excessive dipole moment, relaxation time, excess inverse relaxation time and the excess thermodynamic parameters. These parameters are used to interpret the molecular interactions between the molecular species of the liquid mixtures.     

Dielectric studies of some binary liquid mixtures using microwave cavity techniques

The excess parameter studies in the microwave frequency region (X-band) on complex dielectric permittivity for the binary mixtures are reported. The methods employed are fixed cavity perturbation technique and adjustable plunger cavity technique. Also Gopalakrishna method is used to calculate the relaxation time of the polar solute in a non-polar solvent. The samples under study are acetonitrile, chlorobenzene, dimethyl formamide, carbon tetrachloride and benzene.     

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.     

Ultrasonic studies in binary liquid mixtures of benzene and coconut oil near the critical region

Velocity and attenuation of ultrasonic waves have been measured in complex binary mixtures of benzene and multicomponent coconut oil near the critical temperature in the low MHz region. The experimental results are analysed in terms of theories developed by Kawasaki and Mistura. The characteristic frequency and amplitude parameter determined by fitting the data in the relations proposed by Kawasaki-Mistura are scaled at reduced temperature and these agree with scaling exponents. A small velocity dispersion is also observed.     

Intermolecular photoinduced electron-transfer processes between C60 and aniline derivatives in benzonitrile

The quenching behavior of the triplets of C₆₀ by various aniline derivatives (1a-d and 2a-e) was investigated by means of laser flash photolysis in benzonitrile at 293 K. Electron transfer process was proposed to be the main mechanism because of the direct detection of radical ions of aniline derivatives and C₆₀ in time-resolved transient absorption spectra. The quenching rate constants (k_q) of by different substrates determined at 740 nm approach or reach the diffusion-controlled limit. DFT method was employed to calculate the unknown oxidation potentials of substrates in solution. With these E_ox values, free energy changes (ΔG) were obtained through Rehm-Weller equation. Dependence of observed quenching rate constants on the free energy changes further indicates the photoinduced reactions between ³C₆₀^* and substrates proceed through an electron transfer mechanism. Obtained k_q values for the aniline derivatives are impacted obviously by ground-state configurations and the kinds substituents quantified by Hammett σ constant. Good correlation between log k_q and σ values conforms to the empirical Hammett equation. A more negative ρ value (−3.356) was gained for anilines (2a-e) than that of N,N-dimethylanilines (1a-d) (−1.382), which suggests a more susceptible reactivity for the former substrates. Charge density distribution of reaction center “N” originated from quantum calculation supports this suggestion. In addition, a relationship between quenching rate constants and solvent viscosity was gained from C₆₀/dimethyl-p-toluidine system in altered mixtures of acetonitrile and toluene.     

Dielectric losses in statistical mixtures

The specific features of the dielectric spectra of statistical mixtures in the form of heterogeneous systems with spherical particles chaotically arranged in the space have been investigated. The distribution function of relaxation times f(τ) has been restored. It has been established that the relaxation times are continuously distributed within a wide interval [τ₁, τ₂]. Different methods for broadening the relaxation time distribution interval and approximating the relaxation time distribution function f(τ) have been analyzed. It has been demonstrated that f(τ) is a nonmonotonic function with two maxima at the boundaries and a minimum in the vicinity of the midpoint of the interval [τ₁, τ₂]. These features of the relaxation time distribution function are responsible for the large difference between the average relaxation frequencies of the permittivity and the dielectric loss (electrical conductivity).     

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 relaxation and related studies of 4-ethylphenol-methanol mixtures using time domain reflectometry

The dielectric relaxation studies of 4-ethylphenol-methanol mixtures have been carried out at various temperatures ranging from 10°C to 40°C using time domain reflectometry in the frequency range 10 MHz to 10 GHz. The relaxation mechanism in these systems is explained by Cole-Davidson model. The excess dielectric parameters, Kirkwood correlation factor and activation energy have been calculated and discussed with respect to molecular arrangements, and microdynamics of the binary mixture composed of both the associative type of liquids.     

Dielectric dispersion in d-ADP

Complex electric permittivity in paraelectric phase close to T_c of d-ADP over the frequency range 0.8–38 GHz has been measured. Molecular relaxation time τ₀ at 239 K equals to 2.2 or 4.0 ps depending on the internal field model and is very close to that found for d-KDP.     

Dielectric dispersion in KCl: OH

Dielectric measurements at 9.4 GHz in KCl doped with a concentration of 0.2 at. % OH are reported. The dielectric constant exhibits a relaxational anomaly at temperatures far above that observed in the kilohertz frequency range for the same OH concentration. The results indicate that electric dipole freezing in KCl:OH is governed by a relaxational mechanism.