Permittivity Of Solutions Research Articles

Electrokinetic instabilities of non-dilute colloidal suspensions

An experimental investigation of electrokinetic instabilities (EKIs) of non-dilute colloidal suspensions in microchannels is presented. The addition of charged colloidal particles to a solution can alter the solution's electrical conductivity and permittivity as well as the average particle electrophoretic mobility. In this work, a colloidal (500 nm polystyrene) volume fraction gradient is achieved at the intersection of a Y-shaped polydimethylsiloxane (PDMS) microchannel. The flow becomes unstable when the electroviscous stretching and folding of the conductivity and permittivity interfaces exceed the dissipative effects of viscous forces and particle diffusion. The suspension conductivity as a function of the particle volume fraction is presented. The critical conditions required for flow instability are measured along with a scaling analysis which shows that the flow becomes unstable due to a coupling of applied electric fields and the electrical conductivity and permittivity gradients in the flow. The flow becomes unstable at a critical electric Rayleigh number ofRae= 1.8 × 105for a wide range of applied electric fields spanning three orders of magnitude and colloid volume fractions varying two orders of magnitude. EKIs of non-dilute colloidal suspensions may be important for applications such as the electrophoretic deposition of micropatterned colloidal assemblies, electrorheological devices and on-chip electrokinetic (EK) manipulation of colloids.

A model of the supramolecular structure, aggregation phenomena, and permittivity of solutions containing star-like aggregates

The quasi-chemical model of nonideal associated solutions was for the first time used to construct a model of solutions of polar substances whose supramolecular structure contained chain and star-like aggregates with an arbitrary number of beams as the main fragments. Analytic methods for calculating the concentrations of aggregates and integral (the mean aggregation numbers) and differential (aggregate distribution functions according to topological types, composition, size, etc.) characteristics of the supramolecular organization of solutions were developed. Equations for the dipole moments of aggregates and dipole correlation factors of solution components were obtained. These equations were used to establish interrelations between the permittivity of a solution and its excess thermodynamic functions on the one hand and the thermodynamic and structural parameters of its supramolecular organization on the other.

A Contactless Impedance Probe for Simple and Rapid Determination of the Ratio of Liquids with Different Permittivities in Binary Mixtures

AbstractSimple contactless cells with planar or tubular electrodes have been designed for measurement of the permittivity of solutions. The cells, connected to an integrated circuit of astable multivibrator, respond primarily to the capacitance component of the cell impedance, the multivibrator frequency depends in a defined manner on the solution permittivity and is readily used as the analytical signal in determinations of the ratios of components in binary liquid mixtures; water solution of methanol, ethanol and dioxane have been tested. The response of the cell with planar electrodes satisfies well the simple theoretical model and both the cells provide results with a sufficient sensitivity, a low LOD value (units of %vol) and a good precision (around 1%rel). The cell simplicity, small dimensions, long‐term stability and the possibility of powering them from a battery make them suitable for hand‐held meters. As an example of application in practice, the content of ethanol was determined in the car fuel petrol.

Effect of Volume Fraction and Temperature on Dielectric Relaxation Spectroscopy of Suspensions of PS/PANI Composite Microspheres

In this work, we aim to contribute new data on the dielectric relaxation behavior of suspensions of nonconducting/conducting composite microspheres (polystyrene/ polyaniline, PS/PANI). Then, the dielectric investigation over the frequency range of 40 Hz to 110 MHz has been carried out to display the characteristic of dielectric relaxation spectroscopy of suspensions with PS/PANI composite microspheres from two contributions which are the dependences of dielectric relaxation spectroscopy of suspensions on the volume fraction of particles (ϕ) and temperature (T), individually. Two relaxations can be identified in dielectric spectroscopy of suspensions: the so-called α- relaxation (typically at kHz) due to the polarization of counter-ions, and the Maxwell−Wagner−O’Konski (M−W−O) relaxation (typically at MHz) ascribed to a consequence of an accumulation of polarized charges on the boundary surfaces of the dispersed particles. The dependences of dielectric parameters by fitting data with Cole−Cole equations on ϕ and T have been discussed in detail, respectively. According to the dielectric analysis, several interesting phenomena arise in the range of investigation: First, special dielectric increments, where ∂εl = (εl − εm)/ϕ and ∂εh = (εm − εh)/ϕ denoting the low- and high-frequency relaxation amplitude of suspensions of PS/PANI particles per unit volume, respectively, are increasing with the enhancement of volume fraction ϕ. Second, all high-frequency permittivities (εh) are higher or much higher than the permittivity of aqueous solution (80.05 at 18 ± 1 °C). On the basis of the comparisons between PS/PANI and PS, PS/PPY, PS/ZnO particles, we extract some proposals to responsible for such interesting phenomena, namely, except for the two distinct relaxations, α-relaxation and M−W−O relaxation, suspension exhibits an additional dielectric relaxation over the megahertz frequency range, due to the polarization of internal double layer of the thin layer of conducting polymer PANI when an external field is employed. Meanwhile, the different dependences of εh on ϕ for suspensions of PS/PANI (PS/PPY) and PS/ZnO particles are ascribed to the different conducting mechanism and surface morphology of conducting polymer PANI (PPY) and ZnO shells. Finally, after the detailed analysis we obtained the activation energy Ea of the low- and high-frequency relaxations of suspensions of PS/PANI microspheres which is experimentally determined by the dielectric data, individually.

Characterisation of sugar content in yoghurt by means of microwave spectroscopy

Abstract Measurements of the complex dielectric permittivity of sugar solutions in yoghurt were taken in the 1–20 GHz microwave frequency range. Quantitative relationships between parameters that define both the real and the imaginary part of the Debye relations and the weight fraction of sugar content in yoghurt were obtained. These data were used to model the dielectric behaviour of the sugar content in the microwave region.

Comparison of Carbon-Based Nano Materials as Conductive Fillers for Single Layer Microwave Absorber

In this paper, we have studied the permittivities of E-glass fabric/epoxy composite laminates containing three different types of carbon-based nano conductive fillers such as carbon black (CB), carbon nano fiber (CNF) and multi-wall carbon nano tube (MWNT). The measurements were performed for permittivities at the frequency band of 0.5 GHz ~ 18.0 GHz using a vector network analyzer with a 7 mm coaxial air line. The experimental results show that the complex permittivities of the composites depend strongly on the natures and concentrations of the conductive fillers. The real and imaginary parts of the complex permittivities of the composites were proportional to the filler concentrations. But, depending on the types of fillers and frequency band, the increasing rates of the real and imaginary parts with respect to the filler concentrations were all different. At the frequency of 10 GHz, the rates in the CNF filled composite and the MWNT filled composite were much larger then those of the CB filled composite. Between the CNF filled composite and MWNT filled composite, however, the former showed a little higher increasing rates than the other. These different rates can have great effect on the thickness in designing the single layer microwave absorbers. The effect of the different rates was examined by using Cole-Cole plots; the plot is composed of a single layer absorber solution line and permittivity lines of these three types of composites.

Complex permittivity of sodium chloride solutions at microwave frequencies

The complex permittivity of aqueous solutions at 20 degrees C has been measured at concentrations between 0.001 and 5 mol/L and over a frequency range 0.13-20 GHz. The results were combined with literature values to derive empirical equations to predict the dielectric behavior of sodium chloride solutions between 0 and 5 mol/L and 5 degrees C-35 degrees C.

Corrosion of Nitrided Stainless Steel (SUS316L) in Super Critical Water Environments

Supercritical water (SCW) is obtained at pressures above 22.1 MPa and temperatures above 648 K and is advantageous because of its great solubility in organic liquids. Waste treatment of toxic substances, such as the decomposition of polychlorinated biphenyle (PCBs) and their application to the recycling of plastics using SCW is very effective and has less negative influence on environmental destruction. However, SWC was found to corrode a reactive container remarkably, and as a result, the shortened longevity of the container obstructed its industrial use. Moreover, a large-scale reactive container is necessary for the recycling of waste plastics and resources. Therefore, the use of an expensive Ni based alloy in the container is difficult from an economical standpoint. Application of austenitic stainless steel, comparatively economical in Ni based alloy, is has been tried for the container material, but provides insufficient corrosion resistance under the conditions of SCW. In this study, improvement of the corrosion resistance by the nitride process of SUS316L alloy under the supercritical state is considered. (1) Under the influence of a nitrided process, SUS316L alloy endures during usage as a container material in the vicinity of 640K due to the decrease in the corrosion rate by transpassive corrosion. (2) There is a correlation between the corrosion speed and the permittivity for the nitrided SUS316L alloy. Thus, the longevity of a reactive container correlates to a value of the permittivity of solution. (3) Above the value of 25 permittivity, it is unsuitable for use as a reactive container because of the flaking off of the nitride layer of the SUS316L alloy surface.

Experimental Anion Affinities for the Air/Water Interface

Anion affinities, gammaX-, for the aerial interface of aqueous (Br- + NO3- + I- + SCN- + BF4- + ClO4-) solutions are determined by electrospray ionization mass spectrometry. The composition of the ions ejected from the surface of fissioning nanodroplets shows that gammaX- increase (decrease) exponentially with anionic radii, aX-(dehydration free energies, dGX-), and selectively respond to the presence of surfactants. BF4-, the least hydrated and polarizable anion of the set, has one of the largest gammaX- values. Non-ionic surfactants decrease gammaI- and gammaSCN- but increase gammaBF4-. Cetyltrimethyl ammonium markedly enhances the gammaX- of smaller anions. A similar but weaker effect is observed upon lowering the pH of the bulk solutions from 8.2 to 3.0. Dodecyl sulfate has a negligible effect on gammaX-. Considering that (i) universal many-body electrodynamic interactions will progressively stabilize the interfacial layer as its dielectric permittivity falls relative to that of the bulk solution and (ii) water permittivity is uniformly depressed by increasing concentrations of these anions, we infer that the observed Hofmeister correlation, ln gammaX- infinity - dGX-, is consistent with the optimal depression of the permittivity of the drier interfacial layer by the least hydrated ions. Interfacial ion-ion interactions can significantly influence gammaX- in environmental aqueous media.

Dipole moments and electron distribution of conjugated molecules; para derivatives of benzene

Dipole moments of 24 1,4-bis derivatives of benzene with conjugated substituents were calculated at two levels of the DFT theory, B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p) and B3LYP/AUG-cc-pVTZ//B3LYP/6-311+G(d,p). The results at the two levels were slightly different but very tightly correlated and were also proportional to the experimental apparent dipole moments determined from the permittivity of benzene solutions. The interaction dipole moments μ int were obtained by subtracting the moments of the two pertinent mono derivatives and were interpreted in terms of resonance structures. This interpretation was supported by the values of bond lengths C2–C3 and by the energies of interaction obtained by subtracting the energies of mono derivatives. Interpretation by resonance seems to be correct and in agreement with the classical concept in typical examples: conjugation of the acceptors NO 2, CN, B(CH 3) 2, CF 3 with the donors NH 2 or N(CH 3) 2. It is also acceptable in the case of donors OH and OCH 3, although the direction of the dipole moment is less certain. In the case of weak donors F or Cl, the values of μ int are near to zero and resonance cannot be proven.

Modeling of Supramolecular Ordering and Physicochemical Properties in Cyclohexane−Ethanol Mixtures

The quasichemical model of the nonideal associated solution (QCNAS) was used to analyze the excess thermodynamic functions and permittivity of cyclohexane-ethanol mixtures in the entire range of compositions and in a wide temperature range. A new model of supramolecular organization was substantiated, taking into account chain and cyclic aggregation of alcohol with the formation of chain aggregates of arbitrary size, which describes a set of physicochemical properties of this mixture with complicated behavior of both thermodynamic and dielectric properties. Equilibrium constants and thermodynamic parameters of H bonding having cooperative character and integral and differential characteristics of aggregation and the structural parameters of aggregates were determined. It was established that the role of nonpolar cyclic structures increases as alcohol concentration decreases. The model describes the permittivity of solutions in the entire range of compositions and reproduces a minimum of the dipolar correlation factor in the range of dilute alcohol solutions. The new data obtained on the supramolecular ordering characterized by the long-range molecular correlations due to H bonding are discussed in detail.

The effective dipole moments of isobutyric acid in the liquid state and dilute solutions in methanol

The dipole moments of isobutyric acid (I) were determined in the liquid state (μ1) and dilute solutions in methanol (μ1) at 20–50°C. The permittivity of I in the liquid state was found to increase as the temperature grew, and the permittivity of solutions of I was lower than that of pure methanol; it decreased as the concentration of I and the temperature of solutions increased. The effective dipole moments of I were calculated using the Onsager polarization theory for the pure liquid and the Buckingham statistical polarization theory for solutions with various acid concentrations in methanol. The small μ1 (∼0.8 D) and higher μ2 (∼3.0 D) values compared with the dipole moment of I in the gas phase μ0 (1.9 D) were analyzed as determined by the character of acid-acid, acid-solvent, and solvent-solvent intermolecular interactions, a key role in which was played by H-bonds. An analysis of the dipole moments of I in methanolic solutions led us to conclude that the μ1 and μ2 values corresponded to the dipole moments of associates and solvates comprising like and unlike molecules linked by intermolecular H-bonds. Their stoichiometry changed as the temperature increased.

Solvent effect on the heat of solution and partial molar volume of some non‐electrolytes and lithium perchlorate

AbstractFor several non‐electrolytes and for lithium perchlorate the solvent effect on the heat of solution and partial molar volumes was studied. In the absence of the donor–acceptor and electrostatic interactions, clear proportionality can be seen only in the alkane solutions and these changes are defined by the non‐alkane component. For solutions of π‐acceptor (tetracyanoethylene) and ν‐acceptor (gallium chloride) in the presence of π,π‐, π,ν‐ and n,ν‐complexes, the relation between the changes of interaction energy and the values of the partial molar volumes can be seen. The maximum change in the value of partial molar volumes (up to 50 cm3 mol−1) was noted for lithium perchlorate in ten solvents. The volume change is proportional to the compressibility coefficients of the solvents and correlates less with the values of heat of solution and solvent permittivity. Copyright © 2006 John Wiley & Sons, Ltd.

Lanthanide Salts Solutions: Representation of Osmotic Coefficients within the Binding Mean Spherical Approximation

Osmotic coefficients of aqueous solutions of lanthanide salts are described using the binding mean spherical approximation (BIMSA) model based on the Wertheim formalism for association. The lanthanide(III) cation and the co-ion are allowed to form a 1-1 ion pair. Hydration is taken into account by introducing concentration-dependent cation size and solution permittivity. An expression for the osmotic coefficient, derived within the BIMSA, is used to fit data for a wide variety of lanthanide pure salt aqueous solutions at 25 degrees C. A total of 38 lanthanide salts have been treated, including perchlorates, nitrates, and chlorides. For most solutions, good fits could be obtained up to high ionic strengths. The relevance of the fitted parameters has been discussed, and a comparison with literature values has been made (especially the association constants) when available.

Interaction cetyltrimethylammonium bromide–DNA investigated by dielectric spectroscopy

Abstract The complex dielectric permittivity of aqueous solutions of low-molecular weight DNA (0.5–1 kbp) in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) has been measured in the frequency range from 0.1 to 100 MHz, at the temperature of 25 °C. The DNA concentration was 0.64 × 10 −3 M in terms of phosphates and the CTAB concentration was varied from 1.3 × 10 −5 to 9 × 10 −4 M. The dielectric data have been analyzed in terms of a single dielectric dispersion and discussed on the basis of a model involving the fluctuation of counter-ions along short segments of the DNA chains. Viscosity and surface tension measurements on DNA/CTAB solutions are also reported. The results show that CTAB binds as a single monomer to the DNA phosphate sites and that there is a release of one Na + ion per CTAB bound to a phosphate site. Appreciable modification of the DNA conformation subsequent to the formation of the complex is also evidenced.

Static permittivity of water revisited: ε in the electric field above 108V m−1and in the temperature range 273 ≤ T ≤ 373 K

Calculations are presented of the permittivity of water residing in conditions encountered in hydration shells. The present approach is applicable to water in high electric fields and in the whole range of temperature where it is liquid. Possible applications to various systems are mentioned. Static permittivity of aqueous solutions of exemplary salts is calculated and its comparison with experiment discussed in some detail.

Correlation between Deposition Parameters and Structures of the SiNx Films Deposited at Extremely High Rates by Atmospheric Pressure Plasma CVD

Using the atmospheric pressure plasma chemical vapor deposition (CVD) technique, further investigations were performed to improve the density of silicon nitride (SiNx) films deposited at extremely high deposition rate. The films were prepared on Si(001) wafers at atmospheric pressure in a very high frequency (150MHz) plasma of gas mixtures containing He, H2, SiH4 and NH3. Si-N, Si-H and N-H bond densities of the SiNx films were studied as functions of NH3/SiH4 ratio and the H2 concentration by Fourier transformation infrared (FTIR) absorption spectroscopy. Etching rate with buffered HF (BHF) solution, refractive index and relative permittivity of the SiNx films were also studied as a function of Si-N bond density of those films. It is found that by decreasing NH3/SiH4 ratio or increasing H2 concentration, Si-N and Si-H bond densities increase, while N-H bond density decreases. It is also noticed that N-H bond density is larger than Si-H bond density within the present deposition conditions, indicating that the SiNx films are N-rich. These facts suggest that elimination of excessive hydrogen atoms bonded with N atoms at the film-growing surface is an important factor to form SiNx film with a dense Si-N network. The highest Si-N bond density and then the lowest hydrogen content are obtained for the film deposited with the H2 concentration of 20% and the input power of 1000W.

Measurement/computation of effective permittivity of dilute solution in saponification reaction

For better application of microwaves in chemistry, the interaction between microwaves and the chemical reaction needs further study. Since the reactants form a complicated mixture, which changes with time, an effective permittivity can be used to describe the molecular polarization of the mixture in the reaction. The effective permittivity is expected to change with microwave frequency, temperature and reaction time. However, in many cases, the change of effective permittivity in a saponification reaction is too small to be detected using traditional methods. In this paper, we present a hybrid experimental/computational method for determining the effective permittivity in a saponification reaction. We use a resonant coaxial sensor to measure the reflection coefficients. To predict its performance, the electromagnetic-field distribution near the sensor and the reflection coefficient are calculated employing a frequency-dependent finite-difference time-domain method. Next, we develop a genetic-algorithm-based inverse-calculation technique and employ it to determine the complex permittivity of pure water from the measured reflection coefficient and compare the results with those obtained from Debye's equation. Finally, the hybrid experimental/computational method is employed to determine the effective permittivity of a dilute solution in a typical saponification reaction. Results are presented and discussed.

Polarization Deficiency and Excess Free Energy of Ion Hydration in Electric Fields

Polarization deficiency and excess ion hydration free energy at an electric field E (ion hydration free energy at the field E subtracted by the ion hydration free energy at zero field) of hydrated calcium, sodium, and chloride ions have been determined by Monte Carlo simulations. A spherical cell containing either one ion and molecular water or only molecular water subjected to an external electrical field was used. The permittivity of pure water decreases as E is increased, in quantitative agreement with previous simulation studies and the Booth theory. The excess ion hydration free energy depends quadratically on E up to ca. 2.5·108 V/m, whereas it becomes linear in E at higher field due to dielectric saturation. The values of the excess ion hydration free energies are in quantitative agreement with measured dependencies of the relative permittivity of electrolyte solution upon the ion concentration. A primitive polarization model of electrolyte solution near charged interfaces is proposed. The use of this model leads to an additional effective repulsive force acting on hydrated ions near charged surfaces and significantly affects the distribution of calcium ions near such surfaces.

Description of Vapor−Liquid Equilibria for CO2 in Electrolyte Solutions Using the Mean Spherical Approximation

The mean spherical approximation is used to describe the vapor pressure over aqueous solutions containing an electrolyte and carbon dioxide. Three electrolytes have been studied: NaOH, NaCl, and acetic acid. A good representation is obtained with a reduced number of parameters as compared to previous models. These parameters account for the concentration and temperature dependence of the solute sizes and the relative permittivity of solution. The numerical values of these physically interpretable parameters are in a reasonable range.