Zeta descriptionCan be used to calculate zeta potentials for ka>6 from electrophoretic mobilities measured at the stationary levelZeta is a small, simple, powerful and reliable software that can be used to calculate zeta potentials for ka>6 from electrophoretic mobilities measured at the stationary level, from apparent zeta potentials displayed by zetameter or from apparent mobilities measured at 3 different levels in a rectangular cell.

For electrophoresis at high zeta potentials and thick double layers additional braking forces must be considered. The force exerted on the particle by the excess of counterions moving in opposite direction is called retardation. Moreover, when the particle moves fast enough the centres of the particle charge and countercharge (diffuse layer) do not coincide and thus the effective electric field strength felt by the particle is lower than the external field (relaxation).

Accurate differential equations accounting for these effects have been published by O'Brien and White. These equations do not lead to accurate analytical expressions to calculate mobility from zeta potential. This problem can be solved numerically and desired accuracy can be achieved when the number of iterations is high enough. Commercial (and not open-source) programs Mobility and Winmobil are available from University of Melbourne. The solutions obtained by means of these programs are valid for any value of the zeta potential and kappa*a.

Why do we need Zeta when Mobility and Winmobil are available? For systems with kappa*a <