Electroviscous effect explanation

The increasing dilution of flexible polyelectrolytes at low ionic strength, the reduced viscosity may increase first, reach a maximum, and then decrease. Since a similar behavior can also be observed even for solutions of polyelectrolyte lattices at low salt concentration, the primary electroviscous effect was thought as a possible explanation for the maximum, as opposed to conformation change. 

A theoretical explanation for the increase of the viscosity t) could be found in the so-called electroviscous effect. It is well known that an electrolyte solution streaming between two charged walls shows an increase of the apparent shear viscosity. Assuming that the results obtained for plane parallel channels in a steady state by Levine et al. " may be used for the film situation, it was found that a maximum increase of about 20% can be expected for the viscosity of the solution inside the film compared to the bulk value. This electroviscous effect is expected to be important only in equilibrium films where an overlap of the electrical double layers occurs but nevertheless this phenomenon cannot explain the full discrepancy between theory and experiment. 

Thus in principle the electroviscous effect finds a simple explanation. All other facts discussed in the proceeding section may also be explained in an analogous way. 

For an explanation of the self suppression of the electroviscous effect we may then suppose that the macro-molecular electrolyte itself acts as indifferent electrolyte and thus diminishes the interaction between its own charged spots thus leading to a denser coil and a smaller electroviscous effect. 

For hydrophilic colloids recently a diiferent explanation of the electroviscous effect has been suggested, based upon a swelling of the particles under the influence of the electrical repulsion between the charges . 

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