The Role of Solvent Viscosity, Ionic Radii, and Solvation

3 The Role of Solvent Viscosity, Ionic Radii, and Solvation 

For simple salts the influence of parameters (1)—(3) can be studied separately by the investigation of series of salts with a common anion or cation in a solvent of high dielectric permittivity. Flowever, high solvent permittivity is only a necessary, but not a sufficient, condition for complete dissociation. High permittivity of the solvents does not prevent ions from associating, if these ions interact specifically 

The results of an investigation performed upon various salts in PC [207] or MeOH [15] can be summarized as follows. Both the maximum conductivity and the appertaining concentration 41 are determined by the viscosity and ionic radii (nonsolvated ions) or Stokes radii (solvated ions), meaning that electrolytes show a Stokes-Walden behavior, entailing 

Analysis of the activation energies of charge transport as a function of temperature and concentration shows that a type of corresponding state is attained at concentration 41 characterized by constant critical energies of activation for a given temperature. Electrolytes based on salts with small nonsolvated ions or small Stokes radii attain high 41 and /rmax values, whereas those based on large ions attain only small 41 and /fmax values. 

Many recent examples show the importance of ionic radii and solvation in the conductivity of concentrated solutions. Suffice it to refer to three examples from the literature. 

Bu4NBr in AN/PC in the temperature range 75 C -35°C a linear correla-lO Lmol which are of the order of tion is found [209], independ- 

Many recent examples show the importance of ionic radii and solvation for the conductivity of concentrated solutions. Suffice it to refer three examples from the literature. Binary mixtures of dipolar aprotic solvents of sufficiently high permittivity such as butylene carbonate (BC),PC,EC, and AN show Stokes-Walden behavior [412, 413]. For Bu4NBr in AN/PC in the temperature range 75°C —35 °C a linear correlation /Cmax(At) is found [413], independent of temperature and solvent composition. The use of high-permittivity solvents belonging to the same class suppresses the effects due to strong selective solvation or effects due to changing association. 

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