Debye-Huckel-Bjerrum theory for charged colloids

We formulate an extension of the Debye-Huckel-Bjerrum theory [M.E. Fisher, Y. Levin, Phys. Rev. Lett. 71 (1993) 3826] to the fluid state of a highly asymmetric charged colloid. Allowing for the formation of clusters consisting of one polyion and n condensed counterions, the total Helmholtz free energy of the colloidal suspension is constructed. The thermodynamic properties, such as the cluster-density distribution and the pressure, are obtained by the minimization of the free energy under the constraints of a fixed number of polyions and counterions. In agreement with the current experimental and Monte Carlo results, no evidence of any phase transition is encountered. (C) 1998 Elsevier Science B.V. All rights reserved.