We present a density functional theory for mixtures of (hard sphere) colloidal particles and ideal polymers. For this extreme nonadditive system we employ a fundamental measures approach to construct a functional which incorporates the correct dimensional crossover and the exact low density limit. In bulk fluid mixtures the functional yields the same free energy and, therefore, the same gas-liquid (demixing) transition as given by free-volume theory. It generates consistent pair correlation functions; the partial structure factors $S^{\mathrm{ij}}\left(k\right)$ diverge, as $k\to 0$, at the critical point obtained from the free energy. Our results for the structure agree well with those from simulation and Percus-Yevick theory.

• Received 17 April 2000

DOI:https://doi.org/10.1103/PhysRevLett.85.1934