Electrolytes, dielectric properties

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

There are several factors through which anions can influence the pathway and O2 reduction kinetics. The main factors are competition with O2 for surface sites changes in the activity coefficients of the reactants, intermediates, and transition states and the acidity and dielectric properties of the electrolyte side of the interface [Adzic, 1998]. For example, perfluoro acids have higher O2 solubility and lower adsorbability than... 

Each breakdown is accompanied by some sound effect and is followed by a steady degradation of properties.284 It can also lead to a complete destruction of the oxide with visible fissures and cracks.286 The particular behavior observed depends on a large number of factors (electrolyte concentration,287 defect concentration in the oxide,288 etc.). The breakdown of thin-film systems (M-O-M and M-O-S structures) as a rule leads to irreversible damage of oxide dielectric properties.289... 

In dilute solutions it is possible to relate the activity coefficients of ionic species to the composition of the solution, its dielectric properties, the temperature, and certain fundamental constants. Theoretical approaches to the development of such relations trace their origins to the classic papers by Debye and Hiickel (6-8). For detailpd treatments of this subject, refer to standard physical chemistry texts or to treatises on electrolyte solutions [e.g., that by Harned... 

Another example is the influence of the electrical resistance of PVC cable insulation. This is caused not by the organic pigment itself but by ethoxylated surfactants, which are added as auxiliaries in the manufacture of these pigments, especially azo pigments. Contrary to a repeatedly expressed view, a possible electrolyte content, which laked azo pigments for example can have, has no effect on the dielectric properties of PVC [34]. Some pigment manufacturers offer special product ranges with verified dielectric properties for this purpose. 

The dielectric properties of electrolytes are almost identical to those of water with the addition of a a term in Eq. (1) due to the ionic conductance of the dissolved ion species. The static dielectric permittivity of electrolytes of usual physiological strength (0.15 N) is about two units lower than that of pure water (4), a negligible change. 

The situation becomes more interesting if we consider particles which are surrounded by a shell having different dielectric properties. Such a three-phase system can be treated in an analogous way as the above two-phase system. Assuming the shell to be a practically non-conductive membrane and the external and internal medium to be an aqueous electrolyte, a dielectric dispersion can be derived which explains nicely the large effect observed in the MHz range with membrane-covered biological cells. It can be qualitatively interpreted by a membrane... 

Electro-insulation materials. The retention of dielectric properties in a high-temperature environment, coupled with good corrosion resistance in contact with certain reactive chemicals, suggests excellent possibilities of polybenzimidazole use in electrical insulation and other dielectric applications at high operating temperatures and/or in aggressive chemical environments. Typical applications, hence, can be foimd in special cable and wire insulation, in the manufacture of circuit boards and radomes for supersonic aircraft, as battery and electrolytic cell separators, and as fuel cell frame structural materials. Some recent publications in the patent and technical report literature may serve to illustrate such applications. 

Nernst applied the electrical bridge invented by Wheatstone to the measurement of the dielectric constants for aqueous electrolytes and different organic fluids. Nemst s approach was soon employed by others for measurement of dielectric properties and the resistance of galvanic cells. Finkelstein applied the technique to the analysis of the dielectric response of oxides. Warburg developed expressions for the impedance response associated with the laws of diffusion, developed almost 50 years earlier by Fick, and introduced the electrical circuit analogue for electrolytic systems in which the capacitance and resistance were functions of frequency. The concept of diffusion impedance was applied by Kruger to the capacitive response of mercury electrodes. ... 

In this chapter some aspects of the present state of the concept of ion association in the theory of electrolyte solutions will be reviewed. For simplification our consideration will be restricted to a symmetrical electrolyte. It will be demonstrated that the concept of ion association is useful not only to describe such properties as osmotic and activity coefficients, electroconductivity and dielectric constant of nonaqueous electrolyte solutions, which traditionally are explained using the ion association ideas, but also for the treatment of electrolyte contributions to the intramolecular electron transfer in weakly polar solvents [21, 22] and for the interpretation of specific anomalous properties of electrical double layer in low temperature region [23, 24], The majority of these properties can be described within the McMillan-Mayer or ion approach when the solvent is considered as a dielectric continuum and only ions are treated explicitly. However, the description of dielectric properties also requires the solvent molecules being explicitly taken into account which can be done at the Born-Oppenheimer or ion-molecular approach. This approach also leads to the correct description of different solvation effects. We should also note that effects of ion association require a different treatment of the thermodynamic and electrical properties. For the thermodynamic properties such as the osmotic and activity coefficients or the adsorption coefficient of electrical double layer, the ion pairs give a direct contribution and these properties are described correctly in the framework of AMSA theory. Since the ion pairs have no free electric charges, they give polarization effects only for such electrical properties as electroconductivity, dielectric constant or capacitance of electrical double layer. Hence, to describe the electrical properties, it is more convenient to modify MSA-MAL approach by including the ion pairs as new polar entities. 

Effect of ion association on the dielectric properties of electrolyte solution... 

The free ions and ion pairs play a distinct role in the dielectric properties of electrolyte solutions. Due to the saturation of the dipole orientation near free ions, the dielectric constant of the system decreases with the increase of free ion concentration. Ion pairs possess the dipole moments and produce an additional contribution to the dielectric properties. Due to the new polarization effect, the dielectric constant of the entire system increases with the increase of the ion pair concentration. It is generally accepted to distinguish the solvent dielectric constant, es, and the solution dielectric constant, e [3], The dielectric constant of the solvent describes the polarization effect of the solvent molecules in the presence of ions es decreases with the increase of ion concentration. The dielectric constant of the solution also includes the polarization effect from the ion pairs that can increase or decrease with the increase of ion concentration. Due to this, e > es, and only for a completely dissociated electrolyte, (a = 1) e = es. 

Gestblom, B., and Songstad, J. Solvent properties of dichloromethane. VI. Dielectric properties of electrolytes in dichloromethane. Acta Chem. Scand. Ser. B, 1987,41, p. 396-400. 

Michaelis reviews the application of valve metals in electronics based on the dielectric properties of ultra-thin films. Following presentation of fundamental principles and experimental details, the discussion of valve metal systems includes thin film oxide behavior of Ti, Zr, Hf, Nb, Ta, and Al. The application of these valve metal systems in electrolytic capacitor manufacturing is discussed with emphasis on current development trends and research issues. In addition, special emphasis on Si02 dielectric films is provided for integrated circuit applications associated with dynamic random access memory chip fabrication. 

Dimensional analysis shows that k has units of reciprocal length, and it is called the Debye-Huckel reciprocal distance. It depends on the ionic strength of the solution, the dielectric properties of the solvent, and temperature. For an aqueous solution containing a 1-1 electrolyte at a concentration of 1 M (1000 mol m ) at 25°C, K is equal to 3.288 nm h As will be seen below, 1/k corresponds to the effective thickness of the ionic atmosphere, which would be 304 pm for a 1 M solution. 

Barthel, J. Buchner, R. Miinsterer, M. Electrolyte Data Collection, Part 2 Dielectric Properties of Water and Aqueous Electrolyte Solutions Dechema Frankfurt/Main, 1995. 

Initially, some relevant thermodynamic and molecular properties of polar solvents are considered. Then, their dielectric properties are considered in detail. Ion solvation in these solvents is also discussed with emphasis on some non-thermo-dynamic methods of dividing experimentally measured data for electrolytes into contributions for the cation and anion. Finally, the important characteristics of the solvent in its direct interaction with the solute, namely, its acidity and basicity, are also described. 

Concerning the two-layer model, the thickness and properties of each layer depend on the nature of the electrolyte and the anodisation conditions. For the application, a permanent control of thickness and electrical properties is necessary. In the present chapter, electrochemical impedance spectroscopy (EIS) was used to study the film properties. The EIS measurements can provide accurate information on the dielectric properties and the thickness of the barrier layer [13-14]. The porous layer cannot be studied by impedance measurements because of the high conductivity of the electrolyte in the pores [15]. The total thickness of the aluminium oxide films was determined by scanning electron microscopy. The thickness of the single layers was then calculated. The information on the film properties was confirmed by electrical characterisation performed on metal/insulator/metal (MIM) structures. 

The above results showed that an aluminium oxide film with the best dielectric properties was prepared in neutral electrolyte of 0.01 M tartaric acid at low current densities and formation voltages < 30 V. 

Minakata A, Imai N, Oosawa F. Dielectric properties of poly electrolytes. II. A theory of dielectric increment due to ion fluctuation by a matrix method. Biopolymers 1972 11 347-359. 

Mandel M, Odijk T. Dielectric properties of poly electrolyte solutions. Ann Rev... 

Warashina A, Minakata A. Dielectric properties of poly electrolytes. IV. Calculation of dielectric dispersion by a stochastic model. J Chem Phys 1973 58 4743-4751. 

The amount of charge at the interface depends on the field strength and the dielectric properties (conductivity and permittivity) of the particle and the electrolyte. However, there is a slight asymmetry in the charge density on the particle which gives rise to an effective or induced dipole across the particle. Note that if the field is removed the dipole disappears, it is induced . The magnitude of the dipole moment depends on the amount of charge and the size of the particle. For a spherical particle in an electrolyte subject to a uniform applied electric field, three cases can be considered ... 

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