  Experiments with polymer latex solutions show the coexistence of
order-disorder structures of macroions. Because of the large macroions' sizes,
this order-disorder phase coexistence imply the existence of very long-range
attractive and repulsive forces, which can not be explained in terms of
conventional direct interaction potentials, which are short-range. Here we
apply an integral equations theory to a simple model for colloidal dispersions,
at finite concentrations, calculate the particles distribution functions and
the involved effective forces. We find very long-range attractive and repulsive
forces among the like-charged macroions. The distribution functions are in
qualitative agreement with experimental results. The origin of these forces are
discussed in terms of an energy-entropy balance.
