Low-density expansion for charged particles with hard cores.

Using field-theoretic methods, we obtain the low-density expansion of the free energy of systems where two ionic species with different valences (defined as the absolute value of the charge in units of e, here q[sub 1] and q[sub 2]) and hard-core radii (d[sub l] and d[sub 2]) are present. The resulting expression (calculated up to order 5/2 in the concentration) is exact, and allows one to treat, in a unified way, electrolytes (where q[sub 1] ∼ q[sub 2] and d[sub 1] ∼ d[sub 2]) and charged macro-particles suspensions (as for instance colloidal suspensions, where the size and the charge asymmetry are very large and play a crucial role). [ABSTRACT FROM AUTHOR]