Chain length effect on dynamical structure of poly (vinyl pyrrolidone)-polar solvent mixtures in dilute solution of dioxane studied by microwave dielectric relaxation measurement

Dielectric relaxation study of the binary mixtures of poly(vinyl pyrrolidone) (PVP) (Mw=24000, 40000 and 360000 g mol⁻¹) with ethyl alcohol (EA) and poly(ethylene glycol)s (PEGs) (Mw=200 and 400 g mol⁻¹) in dilute solutions of dioxane were carried out at 10.1 GHz and 35°C. The relaxation time of PVP-EA mixtures was interpreted by the consideration of a wait-and-switch model in the local structure of self-associated ethyl alcohol molecules and also the PVP chain length as a geometric constraint for the reorientational motion of ethyl alcohol molecules. The formation of complexes and effect of PVP chain length on the molecular dynamics, chain flexibility and stretching of PEG molecules in PVP-PEG mixtures were explored from the comparative values of dielectric relaxation time. Further, relaxation time values in dioxane and benzene solvent confirm the viscosity independent molecular dynamics in PVP-EA mixtures but the values vary significantly with the non-polar solvent environment.     

Parameters of viscous flow in dilute solutions of polyalkyl glycol ethers in secondary alcohols

Densities and viscosities were measured for the binary dilute mixtures of triethylene glycol monomethyl ether (TRIEGMME) in 2-alcohols (2-propanol (2-PR), 2-butanol (2-BU), and 2-pentanol (2-PE)) and tetraethylene glycol dimethyl ether (TEGDME) in 2-pentanol, at temperatures from 288.15 K to 318.15 K and in 0 ≤ x₂ ≤ 0.10 mol fraction range of the polyalkyl glycol ethers. The values of the dynamic viscosity in the TRIEGMME + 2-PR systems are more viscous than pure solvent at the work temperatures. The Jones-Dole B coefficients and β_G interaction parameters for viscous flow values were calculated and explain the behavior observed. The partial molar volumes at infinite dilution of solute in 2-alkanols were calculated by the parameters of viscous flow obtained in dilute solutions polyalkyl glycol ethers in 2-alkanols. The values have been compared with the values of partial molar volume at infinite dilution obtained by density measurement for both solutes in the 2-propanol, 2-butanol, and 2-pentanol.     

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.     

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 dispersion studies of mixtures of aniline and benzonitrile in benzene solutions

Dielectric behavior of aniline, benzonitrile and their binary mixtures of different concentrations were studied in benzene at 293, 303, 313 and 323 K. The complex permittivity (∈′, ∈″) at microwave frequencies 7.22, 9.1, 19.61 GHz, static permittivity ∈₀ at 455 KHz and high frequency limiting dielectric constant ∈_∞ = n_D² at optical frequency of these molecules and their binary mixtures were measured. The average relaxation time (τ₀), distribution parameter (α) and thermodynamical parameters were determined. The plot of relaxation time (τ₀) against concentration of benzonitrile in the mixtures is nonlinear indicating complex formation.     

Vibrational relaxation time measurements in CH4 and CH4-rare gas mixtures

With a spectrophone vibrational relaxation times in CH₄ and in mixtures of CH₄ with rare gases were measured. Both the amplitude and the phase method were used. The two infrared active modes of CH₄ (ν₄ and ν₃) were investigated separately. The relaxation times, at one atmosphere, after exciting the lowest mode ν₄, were found to be: τ(CH₄-CH₄) = 1.65 μs; τ(CH₄-He) = 1.97 μs; τ(CH₄-Ne) = 8.6 μs; τ(CH₄-Ar) = 12 μs and τ(CH₄-Kr) ≈ 60 μs. From these values one may in that vibrational-rotational (V-R) energy transfer is the dominant relaxation mechanics. By exciting the higher mode the first step in the deactivation of ν₃ was found to be a V-V transfer to the lowest modes ν₄, ν₂.     

Microwave dielectric response of binary mixture of N,N-dimethylformamide with propylene glycol using TDR method

Dielectric relaxation study of N,N-dimethylformamide (DMF) has been carried out with propylene glycol (PLG) at different temperatures. Time domain reflectometry (TDR) in reflection mode has been used to measure the reflection coefficient in frequency range of 10 MHz to 20 GHz. The dielectric parameters static dielectric permittivity (? ₀) and relaxation time (τ) have been obtained by Fourier transform and least squares fit methods. The experimental results show nonlinear variation in dielectric permittivity and relaxation time with volume fraction of PLG confirm the structural formation due to the intermolecular interaction between N,N-dimethylformamide and PLG. The variation in excess permittivity (ε ^E), excess inverse relaxation times (1/τ)^E, Kirkwood correlation factors (g ^eff, g ^f), activation enthalpy (ΔH) and entropy (ΔS) are also calculated to study the binary mixture interaction.     

Dielectric relaxation study of poly(ethylene glycols) using TDR technique

Temperature dependent dielectric relaxation and thermodynamic properties of polyethylene glycols HO[CH₂CH₂O)_nH with number average molecular weight 200 (n = 4), 300 (n = 7), 400 (n = 9) and 600 (n = 14) g mol^− 1 have been studied using Time Domain Reflectometry (TDR) in the frequency range 10 MHz to 20 GHz. The frequency dependence of the complex dielectric permittivity is analyzed by the Havriliak-Negami expression. The static permittivity ε₀, high frequency limiting static permittivity ε_∞, average relaxation time τ₀ and thermodynamic energy parameters such as free energy, enthalpy of activation and entropy of activation have been determined. The average free energy of activation ΔF_τ for PEG molecules was found to be in the range 4-5 kcal mol^− 1. The values of entropy ΔS_τ for PEG-200, PEG-400 and PEG-600 molecules were found to be positive while entropy ΔS_τ for PEG-300 molecules was found negative, which confirms that the configuration of PEG-300 involved in the dipolar orientation has an activated state, which is more ordered than the normal state compared to PEG-200, PEG-400 and PEG-600 molecules.     

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.     

The role of environment in the nonradiative relaxation of the triplet state of naphthalene derivatives in solid solutions at 77 K

The nonradiative relaxation of the triplet states of oxy-and amino-derivatives of naphthalene and conjugated ions is studied by luminescent and kinetic methods (measurements of the phosphorescence decay and of phosphorescence excitation and phosphorescence spectra) in solid solutions of ethanol-h ₆, ethanol-d ₆, and mixtures of toluene-h ₈ with piperidine-h ₁₁ at 77 K. It is found that, along with intramolecular factors, a microsolvate surrounding a molecule or an ion substantially affects the nonradiative relaxation. The contribution of this factor in ethanol increases in the series cation-polar molecule-anion and in mixtures of toluene with piperidine—with increasing piperidine concentration. The results are interpreted assuming the inductive-resonance dipole-dipole transfer of the triplet energy to the dipole acceptors of intramolecular bonds and bonds with molecules of the environment. The relative arrangement of hydrogen atoms of OH groups of ethanol molecules in microsolvates of cations and anions estimated using the inductive-resonance model agrees with the difference in the structure of solvates of oppositely charged ions, which is caused by the electrostatic charge-dipole interaction and the distribution of the electron density in the ground state of the corresponding emitting center. The inductive-resonance model was used for studying the features of solvation processes involving polar molecules. It is shown that the difference between the structures of microsolvates of 2-oxy-naphthalene molecules in solvents with close dipole moments (ethanol and piperidine) is mainly caused by the different ability of these solvent molecules to form associates. The structure of microsolvates of oxy-derivatives of naphthalene in the associated amphoteric solvent is found to depend on the number and position of substituents. In oxy-derivatives of naphthalene with spatially separated OH groups in ethano-d ₆, deuteroexchange occurs in both substituents, whereas in the naphthalene derivative with adjacent OH groups this occurs only in one of the groups. Comparison of the phosphorescence spectra of hydrogen-bond complexes and proton-transfer complexes in nonpolar solvents at 77 K revealed the existence of molecular naphthol entities in the triplet state that were formed from ionized entities in the singlet state.     

Conformational and dielectric analysis of hydrogen bonded polar binary mixtures of propan-1-ol with propionaldehyde

The dielectric behaviour of polar liquids such as propan-1-ol, propionaldehyde and their equimolar binary mixture in non-polar solvent benzene is studied in the microwave frequency range using the cavity perturbation technique at 6.218 GHz (J band), 9.880 GHz (X band), 16.331 GHz (P band) and 24.951 GHz (K band). Ab initio geometry optimization is performed in the 6-31G (d) basis set using the Gaussian 94W program for both pure and binary systems of propan-1-ol and propionaldehyde. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi's method and compared with the ab initio results. Conformational analysis of the formation of hydrogen bond between the propan-1-ol and propionaldehyde is supported by the FT-IR spectra. The average relaxation times are calculated from their respective Cole–Cole plots.     

Dielectric behaviour and hydrogen bond molecular interaction study of formamide-dipolar solvents binary mixtures

The dielectric constant of binary mixtures of formamide with some common dipolar aprotic and protic solvents has been investigated at sixteen molar concentrations over the entire mixing range at 30 °C. The solvents used for binary mixtures with formamide are water, dimethylsulphoxide, N,N-dimethylformamide, acetone, 1,4-dioxane, mono-, di- and trihydric alcohols, and homologous series of 2-alkoxyethanol, 2-(2-alkoxyethoxy)ethanol, and ethylene glycol oligomers. The concentration dependent plots of excess dielectric constant and Kirkwood correlation factor were used to explore the complexes formed between unlike molecules, the molar ratio of a stable adduct, dipolar ordering, hydrogen-bond molecular connectivities, and their strength in the binary mixtures. Results confirmed that the complexation strength of dipolar aprotic solvents with formamide strongly depends on the value of solvent dielectric constant. The dependence of the hydrogen-bond complexation on number of hydroxyl groups and molecular size of the homologous series of the solvents is recognized from the comparative excess dielectric constant values of the mixed solvents.     

Manifestation of liquid-state and solid-state properties in electron relaxation of paramagnetic ions in solutions: Non-Markovian processes

The linewidth δH and the spin-spin relaxation time T ₂ for Gd³⁺, Mn²⁺, and Cr³⁺ ions in aqueous, water-glycerol, and water-poly(ethylene glycol) solutions at paramagnetic ion concentrations providing the dipole-dipole mechanism of spin relaxation are measured using two independent methods, namely, electron paramagnetic resonance (EPR) and nonresonance paramagnetic absorption in parallel fields. Analysis of the experimental results indicates a gradual crossover from pure liquid-state (diffusion) to quasi-solid-state (rigid lattice) spin relaxation. It is demonstrated that the limiting cases are adequately described by standard, universally accepted formulas for dipole-dipole interactions in the liquid-state (the correlation time of translational motion satisfies the condition τ _c ?τ₂) and solid-state (τ _c ?τ₂) approximations. A complete theoretical treatment of the experimental dependences (including the observed gradual crossover of spin relaxation) is performed in the framework of the non-Markovian theory of spin relaxation in disordered media, which is proposed by one of the authors. Within this approach, the collective memory effects for spin and molecular (lattice) variables are taken into account using the first-order and second-order memory functions for spin-spin and spin-lattice interactions. A correlation between the spin magnitude and the temperature-viscosity conditions corresponding to the crossover to non-Markovian relaxation is revealed, and the situations in which structural transformations occurring in the solutions favor the crossover to solid-state spin relaxation are analyzed.     

Excitation dynamics during the multiphoton absorption in SF6+buffer-gas mixtures

A detailed analysis of the total average number of absorbed photons 〈n〉_total during Infrared multiphoton absorption processes in mixtures of SF₆-Ar, N₂ and CH₄ buffer gases is presented. The results for 〈n〉_total are deduced using pulsed photoacoustic technique in collisional regime. Complete analysis is based on the theoretical generalized coupled two-level model (GCT) and its application to different gas mixtures. Evaluation of partial 〈n〉_coll. values is presented too, obtained using the results from time-resolved optoacoustic (TROA) and time-resolved absorption (TRA) methods for V-T relaxation times (τ_V-T) and the saturable absorber (SA) method for R,R-T relaxation times (τ_rot.-rel.), and applying them directly to the GCT model. All methods (TROA and SA) and the GCT model use the same photoacoustic results from our experiment under identical experimental conditions.     

Microwave spectrum,structure, dipole moment,and internal rotation of the trans isomer of ethyl methyl sulfide

The microwave spectra of the trans isomer of ethyl methyl sulfide and its 10 isotopic species were measured. The r_s structure of this isomer was determined from the observed moments of inertia. The dipole moment and its direction in the molecule were determined by Stark effect measurements of low J transitions for the normal and CH₃CH₂SCD₃ species. The barrier to internal rotation of the SCH₃ group was calculated from the observed A-E splittings of the transitions. The present results were compared with those for the analogous molecules.     

Dielectric relaxation phenomena of rigid polar liquid molecules under giga hertz electric field

The dielectric relaxation phenomena of rigid polar liquid molecules chloral and ethyltrichloroacetate (j) in benzene, n-hexane and n-heptane (i) under 4.2, 9.8 and 24.6 GHz electric fields at 30°C are studied to show the possible existence of double relaxation times τ ₂ and τ ₁ for rotations of the whole and the flexible parts of molecules. The probability of showing double relaxation is more in aliphatic solvents indicating their nonrigidity. The symmetric and asymmetric distribution parameters γ and δ are obtained from X _ij ^′ /X _0ij and X _ij ^″ /X _0ij and w _j →0 where X _ij ^′ and X _ij ^″ are real and imaginary parts of the complex orientational susceptibility X _i ^* and X _0ij is the low frequency susceptibility which is real. X _ij ’s are involved with the measured dielectric relative permittivities ε _ij ^′ , ε _in ^″ , ε _0ij and ε _∞ij of solutions. The theoretical weighted contributions c ₁ and c ₂ towards dielectric dispersions by Fröhlich’s method are compared with the experimental ones obtained from the graphical variation of X _ij ^′ /X _0ij and X _ij ^″ /X _0ij with weight fractions w _j ’s at w _j → 0. The measured dipole moments μ ₂ and μ ₁ of the whole and the flexible part of a polar molecule in terms of the linear coefficients β’s of X _ij ^′ ’s with w _j ’s and the estimated τ ₂ and τ ₁ reveal their associations with aliphatic solvents. The theoretical dipole moments μ _theo’s from the available bond angles and bond moments of the substituent polar groups of the molecules with the estimated μ’s suggest the mesomeric, inductive and electromeric effects in them under GHz electric field.     

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.     

Identification and quantification of diethylene glycol contamination in glycerine raw material

Fourier-transform infrared spectroscopy (FTIR) was successfully used for quantitative determination of diethylene glycol in glycerin raw material. In addition to the pure samples of both diethylene glycol and glycerin, nine binary mixtures of the two components with mixing ratios ranging from (70 to 98)%wt were created and studied as a training set. Glycerine showed, thereby, characteristic infrared bands at 1110, 992, 974, and 922?cm^?1 while those of diethylene glycol appear at 1085, 887, and 881?cm^?1. The quantitative determination of diethylene glycol in binary mixtures with glycerin was achieved upon using the absorbance difference between the 992?cm^?1 and the 881?cm^?1 as well as between 1110 and 1085?cm^?1 bands. With an average %error of 0.60 and 1.74, respectively and a limit of detection down to 0.85%, the created calibration curves from the training set were applied successfully to determine the composition of another eight binary mixtures of the two materials representing a validation set. The method was also applied to aqueous solutions of diethylene glycol and glycerin that contains (25 and 50)%wt water. Once more, training and validation sets of mixtures with different diethylene glycol and glycerin ratios at the two water percentages were prepared and measured. Again, successful determination of diethylene glycol in these aqueous solutions was achieved with an average %error of 0.92 and 0.47, respectively.     

Speeds of sound and isentropic compressibilities of (2-ethoxyethanol + ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol) binary mixtures at 298.15 K

The speed of sound (u) has been obtained at a frequency of 8.3 MHz in {CH₃CH₂OCH₂CH₂OH + HOCH₂CH₂(OCH₂CH₂)_nOH}for n = 0, 1, 2, and 3 over the whole composition range of studied binary liquid mixtures, at T = 298.15 K. The speed of sound values were combined with those of our previous results for densities and viscosities to obtain isentropic compressibility (κ_s), free volume (V_f), and intermolecular free length (L_f). From all these data excess isentropic compressibility (κ_s^E), excess free volume (V_f^E) and excess intermolecular free length (L_f^E) as well as the deviations of the speed of sound (Δu) were obtained. The results are interpreted in terms of molecular interactions occurring in the solutions.