On the "zeta potential" of biological cells.

The zeta potential (i.e., the potential at the slipping plane) of colloidal particles has been used as a parameter describing the electric properties of their surfaces. However, the electrophoretic mobility of particles with surface charge layers is found to be insensitive to the position of the slipping plane, implying that the zeta potential loses its meaning. We have shown that the mobility of such particles is mainly determined by a liquid flow in the mid-region of the surface charge layer, which is not subject to the shielding effect of electrolyte ions. This electrophoresis mechanism is not considered in Smoluchowski's theory.