Wien effect

The Wien effect describes a behavior of dissolved ions in the electrolyte at high electric field strengths. The effect is named after Max Wien.


Ions in an electrolytic solution are surrounded by oppositely charged ions, such cations of several anions which are in turn surrounded by a plurality of cations. This environment around the central ion is also known as ion cloud or ion atmosphere.

The ion atmosphere is when no electric field is applied, approximately spherically symmetric, so that coincide the charge centers. With an electric field, the charge distribution is deformed, the ions are attracted to the oppositely charged electrode. So the charge centers are no longer together, and that thereby resulting electric field decelerates the ion motion, the charge transport and thus the current flow.

: Molar conductivity at the field strength E.

: Molar conductivity at the zero field.

: Molar conductivity at infinitely high field strength.

The First Wien's effect states that the conductivity of an electrolyte solution again increases sharply at high field strengths and different from an infinite dilute solution any more.

The reason suggested is that the braking effects of ion atmosphere are eliminated by the ion is accelerated to such an extent that the ion atmosphere can not form until complete or the relaxation of the ion atmosphere is too big to them during the electrolysis process adjust. Typical field strengths for this are above 10,000 V / cm; here the ion velocity is 10 cm / s

Must be noted here that are generated at high voltages to the electrodes to high speeds of the ions, so that the friction of Stokes' law to be modified, which is included in the calculation.

In a strong field occur in weak acids and salts ( electrolytes ) Effects of about five to ten times the size in comparison to strong acids. The strength of an acid is related to the acidity constant, and the associated value. These effects can not be explained by ion cloud effects. There occurs the effect of the increased dissociation of weak acids and salts in strong fields. The effect is due to the increase of the number of ions, that is a resultant increase in ion concentration.

It is either an ionization of the electrolyte molecules by ion impact or the strong field causes a separation of the ions in the molecules that are already due to the thermal motion in a loosened connection.

Both Wien's effects are not observed separately, they appear to be rather time. The prevailing in weaker fields First Wien's effect goes on in stronger fields in the predominantly Second Wien's effect.