Rescaled density expansions and demixing in hard-sphere binary mixtures.

The demixing transition of a binary fluid mixture of additive hard spheres is analyzed for different size asymmetries by starting from the exact low-density expansion of the pressure. Already within the second virial approximation the fluid separates into two phases of different composition with a lower consolute critical point. By successively incorporating the third, fourth, and fifth virial coefficients, the critical consolute point moves to higher values of the pressure and to lower values of the partial number fraction of the large spheres. When the exact low-density expansion of the pressure is rescaled to higher densities as in the Percus-Yevick theory, by adding more exact virial coefficients a different qualitative movement of the critical consolute point in the phase diagram is found. It is argued that the Percus-Yevick factor appearing in many empirical equations of state for the mixture has a deep influence on the location of the critical consolute point, so that the resulting phase diagram for a prescribed equation has to be taken with caution.

[1]  A. Vlasov,et al.  Binary mixtures of hard spheres: how far can one go with the virial equation of state? , 2003 .

[2]  J. Solana,et al.  Contact pair correlation functions of binary mixtures of additive hard spheres from the virial expansion , 2003 .

[3]  A. Vlasov,et al.  Monte-Carlo integration for virial coefficients re-visited: hard convex bodies, spheres with a square-well potential and mixtures of hard spheres , 2002 .

[4]  S. B. Yuste,et al.  Contact values of the radial distribution functions of additive hard-sphere mixtures in d dimensions: A new proposal , 2002, cond-mat/0203182.

[5]  S. Amokrane,et al.  On some empirical expressions for the contact values of the pair distribution functions and fluid—fluid phase separation in hard sphere mixtures , 2001 .

[6]  Wenchuan Wang,et al.  Monte Carlo data of dilute solutions of large spheres in binary hard sphere mixtures , 2000 .

[7]  S. B. Yuste,et al.  Demixing in binary mixtures of hard hyperspheres , 2000, cond-mat/0002354.

[8]  J. Veverka,et al.  New equations of state for pure and binary hard-sphere fluids , 1999 .

[9]  M. Baus,et al.  Demixing vs freezing of binary hard-sphere mixtures , 1998 .

[10]  N. G. Almarza,et al.  Virial coefficients of hard-sphere mixtures , 1998 .

[11]  N. G. Almarza,et al.  Low density equation of state of asymmetric hard sphere mixtures , 1997 .

[12]  William R. Smith,et al.  COMPUTER SIMULATION OF THE CHEMICAL POTENTIALS OF BINARY HARD-SPHERE MIXTURES , 1996 .

[13]  E. Hamad.  Consistent contact pair correlation functions and equations of state for hard‐sphere mixture , 1995 .

[14]  Hansen,et al.  Phase separation of asymmetric binary hard-sphere fluids. , 1991, Physical review letters.

[15]  T. Kihara,et al.  Geometry of three convex bodies applicable to three-molecule clusters in polyatomic gases , 1975 .

[16]  K. E. Starling,et al.  Equilibrium Thermodynamic Properties of the Mixture of Hard Spheres , 1971 .

[17]  Joel L. Lebowitz,et al.  Exact Solution of Generalized Percus-Yevick Equation for a Mixture of Hard Spheres , 1964 .

[18]  J. Lebowitz,et al.  Thermodynamic Properties of Mixtures of Hard Spheres , 1964 .