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Abstract:
The translational mobility of anisometric dissolved polyions depends on their orientation relative to the direction of motion. If such particles are oriented by means of the flow gradient in the gap of a Couette apparatus, for example, the electrical conductivity of the solution becomes anisotropic. Measurements in a suitable direction (perpendicular to the plane of flow) enable rod-shaped and disc-shaped particles to be distinguished from one another, merely by the arithmetical sign of the change in conductivity. The “apparent size” of particles can be calculated from the shape of the anisotropic curves plotted against the orienting forces. This is in general larger than the real size, but approaches it as the particle interaction vanishes. Determinations of shape and size are possible even when the particles undergo flow damage. The theory of conductivity anisotropy is tested on a disc-shaped model (graphitic acid) and a rod-shaped model (polyphosphate), and confirmed. Measurements on concentrated cetyl trimethylammonium bromide and sodium oleate sols indicate the presence of rod-shaped micelles.
