  We consider a ternary mixture of hard colloidal spheres, ideal polymer
spheres, and rigid vanishingly thin needles, which model stretched polymers or
colloidal rods. For this model we develop a geometry-based density functional
theory, apply it to bulk fluid phases, and predict demixing phase behavior. In
the case of no polymer-needle interactions, two-phase coexistence between
colloid-rich and -poor phases is found. For hard needle-polymer interactions we
predict rich phase diagrams, exhibiting three-phase coexistence, and reentrant
demixing behavior.
