Counterion Cloud Research Articles

Ein Näherungsmodell für die Äquivalentleitfähigkeit mizellarer Seifenlösungen

AbstractA half‐quantitative cell model of micellar surfactant solutions is used to give a physical explanation for the increase of the equivalent conductivity, as it is observed at high concentrations in many paraffin‐chain salt solutions. The increase of the equivalent conductivity is found to result from the finite size of the micelles which, with increasing concentration, leads to an overlap of the counterion clouds and thus to an increase of the partial conductivity of the counterion. Spherical micelles with constant aggregation number and constant degree of dissociation are assumed. By fitting the theoretical curves to experimental data of different alkylsulfates, the degree of dissociation of the respective kinetic micelles is estimated.

High-field electrophoresis of insulating particles in insulating liquids. II. A study of the basic transport mechanisms, including a novel space charge limited conduction process

The electrical transient technique described in the previous paper has been used to investigate the basic transport mechanisms of charged insulating particles in a highly insulating liquid, under the influence of electric fields from 10 6 to 3 × 10 7 V m −1. The fields (which were applied by a parallel-plate system) and the charge levels on the particles both extended to much higher levels than those used in previous investigations, and the particle charges were much greater than the equilibrium “electrochemical” levels. Evidence is given that in these circumstances the particles can be considered as unipolar charges with no significant cloud of counterions; the balancing charge resides primarily in the electrodes, much as happens in the case of charge-carriers injected into solids. For charge levels that are not too high, the field-driven particle motion can be described as simple “true” electrophoresis (uniform straight-line motion with mobility independent of field strength and direction); this probably corresponds to a simple balance between the Coulombic driving force and the Stokes frictional resistance. Particles residing on one electrode leave it almost immediately after the field is switched on, and (after a very brief acceleration time) move steadily to the other electrode. For higher levels of charge, we report what appears to be the first investigation of electrophoresis limited by the particle space charge. This space charge limited (scl) conduction still corresponds to a balance between the Coulombic force and the Stokes drag, but the field on the particles is now greatly modified by their own charge. The scl phenomena show a number of unique features; these can be explained on the basis of the limited size of the particle aggregates. This causes the particles to move under scl conditions in the early part of their motion, the later stages of the transit becoming more or less space-charge-free. Finally, the adhesion phenomena exhibited by systems of this type are investigated; these arise from an electrostatic “image-field” force (proportional to the square of the particle charge) and a nonelectrostatic term.