Colloids, polymers, and needles: demixing phase behavior.

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 colloid-poor phases is found. For hard needle-polymer interactions, we predict rich phase diagrams, exhibiting three-phase coexistence, and reentrant demixing behavior.