Wien Effect

Wien Effect

Conductance Under High Potential Gradient

The increase in conductance of an electrolyte at high potential gradients is known as Wien effect. Wien measured the conductance using high voltages of the order of 20,000 volts cm^-1. At such higher voltages the moving ion will be almost free from the effect of the oppositely charged ionic atmosphere. The ion will be moving so fast that there will no time for the ionic atmosphere to be built up. Under these circumstances, the asymmetry and electrophoretic effects may be negligible or even absent. The conductance, therefore, increases and approaches a certain limiting value. This observation had been experimentally verified by Wien much before the development of the theory of strong electrolytes.
The Wien effect is greater when the interionic forces due to ionic atmosphere are large and this exists for concentrated solutions of high- valence ions. The weak acids and bases are dissociated only to a small extent and the Wien effect is several times greater than the expected value. The deviation increases with voltage. The powerful electrical fields produce a temporary dissociation into ions of the molecules of weak acid or base. This phenomenon is called the dissociation field effect.
Debye Falkenhagen effect