  In this paper we propose a framework allowing to compute the effective
interactions between two anisotropic macromolecules, thereby generalizing the
DLVO theory to non spherical finite size colloids. We show in particular that
the effective interaction potential remains anisotropic at all distances and
provide an expression for the anisotropy factor. We then apply this framework
to the case of finite rod-like polyelectrolytes. The calculation of the
interaction energy requires the numerical computation of the surface charge
profiles, which result here from a constant surface potential on the rod-like
colloids. However, a simplified analytical description is proposed, leading to
an excellent agreement with the full numerical solution. Conclusions on the
phase properties of rod-like colloids are proposed in this context.
