Consistence of the Mean Field Description of Charged Colloidal Crystal Properties

Abstract

The Debye-Hückel-Potential in combination with an effective or renormalized charge is a widely and often successfully used concept to describe the interaction in charged colloidal model systems and the resulting suspension properties. In particular the phase behaviour can be described in dependence of the parameters particle number density, salt concentration and effective charge. We performed simultaneous measurements of the phase behaviour, the shear modulus and the low frequency conductivity of deionised aqueous suspensions of highly charged colloidal spheres. From the shear modulus the interaction potential at the nearest neighbour distance in terms of a Debye-Hückel potential can be determined with an effective charge Z*_G as free parameter. Conductivity measures the number of freely moving small ions Z*_σ and thus relates to the ion condensation process in the electric double layer under conditions of finite macroion concentrations. We present the first experimental access of the pair energy of interaction in charged colloidal suspensions which describes both the elastic properties and the fluid crystalline phase behaviour. This means that a consistent description of the suspension properties is obtained, when Z*_G is taken from the elasticity measurement.