Title: THERMODYNAMIC PROPERTIES OF POLYDISPERSE FLUID MIXTURES
Authors: S.Leroch, D.Gottwald, G.Kahl (Center for Computational Materials Science and Institut für Theoretische Physik, Technische Universität Wien, Wiedner Hauptstraße 8-10, A-1040 Wien, Austria)

We present a systematic study of the thermodynamic properties of a polydisperse fluid mixture. The size of the particles, σ, is assumed to be distributed according to a continuous distribution function f_Σ(σ), for which we have chosen a Γ-distribution. The interatomic potentials are given by a hard core repulsion plus an adjacent attractive tail in the form of a square-well or a Yukawa potential; for the size-dependence of the attraction strength we have assumed different models. The properties of the mixture are calculated using the optimized random phase approximation (ORPA), a thermodynamic perturbation theory which is known to give reliable results in the case of simple liquids. To take into account polydispersity we combine the ORPA with the orthogonal decomposition technique where all σ-dependent functions (i.e., the correlation functions and the interatomic potentials) are expanded in terms of orthogonal polynomials p_i(σ) associated with the weight function f_Σ(σ).

Key words: fluid mixture, polydispersity, colloids, phase diagram, liquid structure
PACS: 05.70.Ce, 61.20.Gy, 82.70.Dd