  We introduce the Poisson-Boltzmann cell model for spherical colloidal
particles with a heterogeneous surface charge distribution. This model is
obtained by generalizing existing cell models for mixtures of homogeneously
charged colloidal spheres. Our new model has similar features as Onsager's
second-virial theory for liquid crystals, but it predicts no orientational
ordering if there is no positional ordering. This implies that all phases of
heterogeneously charged colloids that are liquid-like with respect to
translational degrees of freedom are also isotropic with respect to particle
orientation.
