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Density functional theory for a model colloid-polymer mixture: bulk fluid phases M. Schmidt, H. Löwen, J. M. Brader, and R. Evans, J. Phys.: Condens. Matter 14, 9353 (2002). Locate in [bare] [illustrated] list. Get [full paper] as pdf. Abstract. We describe a density functional theory for mixtures of hard sphere (HS) colloids and ideal polymers, the Asakura-Oosawa model. The geometry-based fundamental measures approach which is used to construct the functional ensures the correct behaviour in the limit of low density of both species and in the zero-dimensional limit of a cavity which can contain at most one HS. Dimensional crossover is discussed in detail. Emphasis is placed on the properties of homogeneous (bulk) fluid phases. We show that the present functional yields the same free energy and, therefore, the same fluid-fluid demixing transition as that given by a different approach, namely the free-volume theory. The pair direct correlation functions c(2)ij(r) of the bulk mixture are given analytically. We investigate the partial structure factors Sij(k) and the asymptotic decay, r -> infinity, of the total pair correlation functions hij(r) obtained from the Ornstein-Zernike route. The locus in the phase diagram of the crossover from monotonic to oscillatory decay of correlations is calculated for several size ratios q = Rp/Rc, where Rp is the radius of the polymer sphere and Rc that of the colloid. We determine the (mean-field) behaviour of the partial structure factors on approaching the fluid-fluid critical (consolute) point. [figures] Read the [full paper] as pdf. |