  Using a density functional based interface displacement model we determine
the effective interaction potential between two spherical particles which are
immersed in a homogeneous fluid such as the vapor phase of a one-component
substance or the A-rich liquid phase of a binary liquid mixture composed of A
and B particles. If this solvent is thermodynamically close to a first-order
fluid-fluid phase transition, the spheres are covered with wetting films of the
incipient bulk phase, i.e., the liquid phase or the B-rich liquid,
respectively. Below a critical distance between the spheres their wetting films
snap to a bridgelike configuration. We determine phase diagrams for this
morphological transition and analyze its repercussions on the effective
interaction potential. Our results are accessible to force microscopy and may
be relevant to flocculation in colloidal suspensions.
