Dielectric Spectroscopy of Cesium Fluoride in Methanol

Dielectric relaxation spectra have been measured at frequencies up to 20 GHz for CsF solutions in methanol (MeOH) at concentrations up to about 1 mol-L at 25°C. Spectra were also obtained for a few concentrations of the much less soluble KF. The data show that CsF forms a solvent shared ion pair (SSIP) in MeOH solutions. Detailed consideration of the possible geometries and comparison with earlier conductometric data suggest that the ion pair involves an oriented solvent molecule located at a vertex of one of the coordination sites of the cesium, rather than a conventional SSIP. Solvation numbers of the ions, estimated via the modified Cavell equation, are unrealistically large. This suggests, consistent with the large dielectric decrement and the conductivity data, that the ions significantly break down the chain structure of MeOH.     

Dielectric properties of alcohol electrolyte solutions

Dielectric properties of ethanol and 1-hexanol solutions containing LiCl, CaCl₂·2H₂O and Ca(NO₃)₂·4H₂O, respectively, have been determined. It is found that LiCl reduces the static permittivity in ethanol, but CaCl₂·2H₂O and Ca(NO₃)₂·4H₂O both give an initial increase in _s. All the electrolytes studied increase the mean relaxation time of the ethanol solutions. In 1-hexanol the static permittivity is rather invariant for all studied electrolytes at low concentrations, while the same lengthening of the mean relaxation time is observed. When water is added in addition to the hydration water of the electrotyte, the static permittivity in hexanol is almost unaltered while the relaxation time is drastically shortened. The experimental result is discussed in terms of a formation of ion pairs, solvation sheaths, and kinetic depolarization, a partial release of hydration water and a structuring influence on the alcohol structure by the hydrated cation.     

Dielectric relaxation studies of monoalcohol solutions with 1,2-diols

Dielectric relaxation processes in solutions of monoalcohols with ethanediol, 1,2-propanediol, and 1,2-butanediol have been studied using the dielectric time domain spectroscopy technique. The dielectric spectrum has been analyzed in terms of two dispersions. The influence of varying content of diol, and of chainlength of the alcohol, on the static dielectric constant _s and on the main dispersion is reported. For the long-chain alcohols _s is lowered and the main relaxation time successively shortened with the addition of diol to the solution. The results are compared to these found for aqueous alcohol solutions and discussed in terms of a structural model with rupturing of predominantly linear complexes on addition of water, diols, or on increasing the temperature.     

FTIR study of ion solvation and ion-pair formation in alkaline and alkaline earth metal salt solutions in acetonitrile

The IR spectra of alkaline and alkaline earth metal perchlorate and of lithium bromide solutions in acetonitrile, obtained with the help of FTIR measurements in the region of the C-N stretching mode of the solvent, reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO ₄ ^– ions in contact and solvent separated ion pairs. The shift and the attenuation of the C-N stretching band of acetonitrile at 2254 cm^–1 is used for the calculation of cation solvation numbers for Li⁺(4), Na⁺(4), Mg²⁺(6), Ca²⁺(6), and Ba²⁺(6). No solvation is assumed for the contact ion pairs of LiClO₄, LiBr, NaClO₄, Mg(ClO₄)₂, Ca(ClO₄)₂, and Ba(ClO₄)₂. The association constants of the symmetrical electrolytes are compared to those obtained from other methods.     

Dielectric properties of ion-exchange beads of sulfonic acid type dispersed in aqueous solutions — effect of fixed charge density

Ion-exchange beads with different densities of fixed charges were prepared by sulfoethylation of dextran gel beads. The relative permittivities and the electrical conductivities of the ion-exchange beads in a sodium form were evaluated by a dielectric technique consisting of the following two procedures proposed in a previous study (2): (a) Dielectric measurements for densely packed sediments of the ion-exchange beads; (b) Analysis of the observed dielectric relaxations by means of a theoretical equation of interfacial polarization for suspensions of spherical particles. The deduced permittivities of the ionexchange beads in equilibrium with water were about 60, which is lower than those of outer aqueous phases. The deduced conductirities were of the order of 1 to 10 mS cm^–1 and were increased reasonably with the fixed charge density. Closer consideration on these deduced values indicates that no specific interaction exists between the counter ions and the fixed charges irrespective of changes in fixed charge density and temperature.     

Interactions of La(III) with anions in aqueous solutions. A139La NMR study

The interactions of the La(III) cations with three anions (X), nitrate, chloride and perchlorate, in aqueous solutions in the pH range 4.0–6.5, were studied by¹³⁹La NMR spectroscopy. A single model, involving the formation of the contact ion-pair (inner-sphere complex) (LaX)²⁺ was successfully and quantitatively applied to the chemical shift and the transverse relaxation rate data. Both measurements gave values for the thermodynamic equilibrium constants of formation of (LaX)²⁺ (K _th ) in good agreement (average K _th =0.45±0.05; 0.15±0.09; 0.03±0.01, respectively for nitrate, chloride and perchlorate). The complexes are characterized by chemical shifts of –25, 22 and –3.1 ppm and by transverse relaxation rates of 11.2, 5 and 1.65 kHz respectively for nitrate, chloride and perchlorate. The¹³⁹La quadrupolar relaxation rate is not controlled by the reorientational correlation time. This finding is discussed, and it is suggested that the very fast exchange of water molecules in the first coordination sphere of La(III) is responsible for the time fluctuation of the electric field gradient at the¹³⁹La nucleus site.     

Dielectric relaxation spectroscopy of aqueous micellar electrolyte solutions: A novel application to infer Dukhin number and zeta potential of a micelle

The complex permittivities of aqueous SDS solutions, with and without the addition of sodium chloride (NaCl), are measured in the frequency range from 200 MHz to 14 GHz. The SDS concentrations are chosen such that the SDS molecules aggregate to micelles. In this frequency range, the measured spectra allow for the identification of two different relaxation processes. That is, the relaxation of the water molecules at frequencies above 1 GHz and the micellar relaxation at frequencies lower than 1 GHz. It is found that the addition of NaCl to the system mostly affects the micellar relaxation process. In detail, the time constant as well as the amplitude of the relaxation decrease by adding NaCl. These effects are attributed to the change in the solution conductivity that changes the properties of the micelle's electrical double layer. We also extract the Dukhin number of the micelles as a function of surfactant and electrolyte content from the measurements. The Dukhin number is a dimensionless group that describes the influence of the surface conductivity on a phenomena. A regression between Dukhin numbers and free sodium ions is found so that all data collapses on a single curve independent of the surfactant concentration. The surface conductivity is a manifestation of the electrical double layer and we use the Bikerman equation to infer the zeta potential of the micelles. Comparison to literature data shows very good agreement and proves that dielectric relaxation spectroscopy can be engaged to infer the zeta potential of micelles. Abbreviations: CMC critical micelle concentration, DRS dielectric relaxation spectroscopy, EDL electrical double layer     

Dielectric spectroscopy on aqueous solutions of pyridine and its derivatives

The complex (dielectric) permittivity has been measured as a function of frequency between 1 MHz and 40 GHz for aqueous solutions of pyridine, 2- and 3-methylpyridine, as well as 2,4- and 2,6-dimethylpyridine at various temperatures and solute concentrations. Different relaxation spectral functions are used to analytically represent the data, in particular the Cole-Cole function. The solute contribution to the extrapolated static permittivity has been calculated to show that, in correspondence with other aqueous solutions of organic molecules and ions, the permittivity of the solvent seems to be enhanced with respect to the pure water value. Also in accordance with other aqueous systems it is found that the principal dielectric relaxation time for equimolar solutions of stereo isomers at the same temperature may significantly differ from one another. A further result is the finding of an unusually strong temperature dependence in the relaxation time of the 1 molar solution of 2,6-dimethylpyridine.     

Investigations of electrode surfaces in acetonitrile solutions using surface-enhanced Raman spectroscopy

The discovery of surface-enhanced Raman scattering (SERS) has resulted in a new tool for the elucidation of phenomena occurring at the electrode/solution interface. Our long term objective is to use this technology to identify species adsorbed at the electrode surface and to determine the dependence of the Raman intensity from these species on such variables as solvent, concentration, pH, electrode potential and laser exciting wavelength. The phenomenon is described in the introduction, to provide background for those not familiar with this topic. This is followed by a presentation of recent data from our laboratory, with a focus on nonaqueous solvents. Bands of the solvated Li⁺ and Na⁺ cations at the electrode surface are reported. Bands from trace H₂O (D₂O and HOD) and OH^– (OD^–) have been observed. At sufficiently negative potentials CN^– is generated from acetonitrile. Evidence is presented for the occurrence of photoelectrochemical reduction. Some preliminary results are given for propylene carbonate solvent which support this interpretation.Session lecture, IX International Conference on Non-Aqueous Solutions, Pittsburgh, PA, August 1984.     

Dielectric relaxation in water–cholesterol mixture cluster: molecular dynamics simulation

Molecular dynamics (MD) studies of the cluster composed of cholesterol (C₂₇H₄₅OH) and water molecules are presented. We have investigated several dynamical quantities of cholesterol as a function of its concentration in the mixture cluster and the temperature. The main attention was focused on the temperature and concentration dependence of the calculated total dipole moment autocorrelation function and dielectric loss of the cluster.     

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate in dioxane-water mixtures

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate, i-Pen ₄ NNO ₃ . in various dioxane-water mixtures have been studied using dielectric time domain spectroscopy (TDS). The static permittivity of the solutions _s increases for low concentrations of solute but levels off to asymptotic values at higher concentrations. The limiting sloped_s dc, and the asymptotic value depend on the static permittivity of the solvent mixture. The relaxation time due to the solute varies with solute concentration and depends on the solvent mixture. In the solvent mixtures of lowest permittivity the plots of relaxation time vs. concentration go through a maximum, while in the mixtures of highest permittivity the relaxation time initially decreases and then levels off to an asymptotic value. The concentration dependence of the dielectric parameters is discussed in relation to ion association.     

Dielectric relaxation of poly(ester-ether-carbonate) multiblock terpolymers

The dielectric properties of a series of poly(ester-ether-carbonate) multiblock terpolymers have been investigated as a function of ether and carbonate composition in the frequency range of 10³–10⁶ Hz. The degree of polymerization of the samples was determined by viscosimetry measurements. The weight fraction, degree of crystallinity, and melting temperatures were characterized by means of x-ray diffraction and DSC methods. Dielectric behavior has been discussed in terms of Havriliak-Negami formulation. The variation of the dielectric properties with temperature has been associated with two relaxation processes: a) the -relaxation process observed at low temperature, which is associated to local motion of polar groups attached to both the soft and the hard segments, and b) the process assigned to long-range molecular motions above the glass transition temperature.     

1-H and 14-N NMR relaxation studies on solutions of Mn(ClO4)2 in acetonitrile

Proton spin-lattice and spin-spin relaxation times of acetonitrile solutions of Mn(ClO₄)₂ between 298°KT413°K have been measured over a wide frequency range (10 kHzv90 MHz). From these data and corresponding 14-N NMR line width measurements of acetonitrile at varying temperatures, it is possible to extract structural and dynamical parameters such as the number of complexed acetonitrile molecules, their mean lifetime in the first solvation sphere of the manganese ions, and the rotational diffusion constant of the [Mn(CH₃CN)₆]²⁺ complex.     

The behavior of ion pairs in high frequency electric fields exemplified by acetonitrile solutions of Bu4NBr

Permittivity data from 0.9 to 40 GHz for acetonitrile and 0.05 to 1.4 molar acetonitrile solutions of Bu₄NBr at 25°C are used to exemplify the behavior of ion pairs in high frequency electric fields. Measurements were excuted by the method of travelling waves with equipment known to produce data of high precision. Data analysis of the acetonitrile spectrum shows a single relaxation process at relaxation time of 3.5 ps for the solvent reorientation; the spectra of the salt solutions reveal two relaxation processes with relaxation times increasing from 3.5 to 6.8 ps for the solvent and decreasing from 120 to 70 ps for the ion pair [Bu₄NBr]^o at increasing salt concentration. The association constant of Bu₄NBr in acetonitrile determined by permittivity measurements agrees well with that from conductance measurements. The concentration-dependence of the ion-pair relaxation times reveals the rate constants of ion-pair formation and decomposition.Presented at the Symposium on Electrochemistry and Spectroscopy of Solutions, Honoring Johannes Coetzee, University of Pittsburgh, November 30, 1989.     

Dielectric relaxation studies of binary mixtures of N-methylacetamide and N-methylformamide in benzene solutions using microwave absorption data

Using standard microwave X-band technique and by following Gopala Krishna's single frequency (9.90?GHz) concentration variational method, the dielectric relaxation times (τ) and the dipole moments (μ) of dilute solution of N-methylacetamide (NMA), N-methylformamide (NMF) and NMA?+?NMF binary mixtures in benzene solutions have been calculated at different temperatures. The energy parameters for the dielectric relaxation process for NMA?+?NMF binary mixture containing 30?mol% NMF have been calculated at 25, 30, 35 and 40°C and compared with the corresponding viscosity parameters. A good agreement between the free energy of activation from these two sets of values shows that the dielectric relaxation process like the viscous flow process can be treated as the rate process. From relaxation time behavior of NMA and NMF binary mixture in benzene solution, solute–solute types of the molecular association has been proposed.     

Vapor pressure data for non-aqueous electrolyte solutions. Part 5. Tetraalkylammonium salts in acetonitrile

Precise vapor pressure data for solutions of Et₄NBr (concentration range of 0.04–1]<0.4), Pr₄NBr (0.044NBr (0.024NCl (0.044NI (0.054NBr (0.06相似文献   

Investigation of MWS polarization and dc conductivity in polyamide 610 using dielectric relaxation spectroscopy

Dielectric relaxation spectroscopy technique was employed to study the Maxwell–Wagner–Sillars (MWS) polarization and dc conductivity in polyamide 610. The experimental dielectric data were analyzed within the formalisms of complex permittivity and electric modulus. The results were discussed in terms of ac conductivity, MWS polarization, electrode polarization and dc conductivity. In the frequency spectra of polyamide 610, charge carriers movement resulted in high values of the dielectric permittivity. The results revealed that the motion of the polymer chains governs the charge carrier transport. Two different mechanisms for charge carrier movement showed a transition temperature located between 110 and 120 °C. The change of charge carrier movement mechanisms was resulted from the onset of the polymeric chains in the interphase between amorphous and crystalline phases.     

Conductance of 1,1-electrolytes in acetonitrile solutions from −40° to 35°C

Conductance data for perchlorates of Li⁺, K⁺, Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, iodides of K⁺, Me₄N⁺, i-Am₃BuN⁺, and tetraphenylborates of Na⁺, Bu₄N⁺ and i-Am₃BuN⁺ in acetonitrile solution in the temperature range −40° to 35°C are reported. Λ_° (limiting molar conductance) and K_A (association constant) are evaluated for several temperatures using a conductance equation based on the chemical model of electrolyte solutions including short range forces. Limiting molar ion conductances, λ _ΰ ⁱ , at −35°, −25°, −15°, −5°, 5°, 15° and 25°C are evaluated from temperature dependent limiting transference numbers. Enthalpies and entropies of association, obtained from the temperature dependence of the association constants, are also presented. Dedicated to the memory of Professor Raymond M. Fuoss.