Dielectric response of charged spheres: interpolation formulae linking the low and high zeta potential expressions

In a previous article (C. Chassagne, D. Bedeaux, G.J.M. Koper, Physica A, to be published) an analytical expression for the dipolar coefficient of a charged sphere in an electrolyte was derived as a function of the frequency which is valid for all double layer thicknesses both for low and for high zeta potentials. In order to access the whole range of zeta potentials an interpolation formula is derived and tested. It is concluded that for the systems for which experimental information is available the expression for high zeta-potentials is sufficient.