  We model charged colloidal suspensions using an analogy with foams. We study
the solid--solid phase transitions of these systems as a function of particle
volume-fraction and ionic strength. The screened Coulomb interaction is
replaced by an interaction between walls of the Voronoi cells around each
particle. We fit the surface charge to reproduce the phase diagram for the
charged suspension studied by Sirota, et al. [Phys. Rev. Lett. 62, 1524
(1989)]. With this fit parameter we are able to calculate the elastic moduli of
the system and find good agreement with the available data.
