Fluid--fluid phase separations in nonadditive hard sphere mixtures

Journal Article · Sun Jan 15 00:00:00 EST 1995 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.468921· OSTI ID:7082733

Jung, J; Jhon, M S ^[1]; Ree, F H ^[2]

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1. Center for Molecular Science and Department of Chemistry, Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)
2. University of California, Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

We investigated the phase stability of a system of nonadditive hard sphere (NAHS) mixtures with equal diameters, [ital d], between like species and an unequal collision diameter, [ital d](1+[alpha]), between unlike species. It is based on an analytic equation of state (EOS) which refines an earlier expression [J. Chem. Phys. [bold 100], 9064 (1994)] within the mixed fluid phase range. The new EOS gives a reliable representation of Monte Carlo EOS data over a wide range of density, composition, and nonadditivity parameters ([alpha]). Comparisons with available computer simulations show that the new EOS predicts satisfactory phase boundaries and the critical density line. It is superior to results derived from integral equations (the Percus--Yevick, the Martynov--Sarkisov, and the modified Martynov--Sarkisov) and analytic theories (the MIX1 model, the van der Waals one-fluid model, and the scaled particle theory). The present study shows that, unless [alpha] exceeds 0.026, the fluid phase will remain fully miscible up to the freezing point of pure hard spheres. We have also investigated structural aspects of the phase stability by Monte Carlo computations. The radial distribution functions, the local mole fraction, and coordination numbers for like and unlike pairs of hard spheres exhibit significant number dependencies close to the fluid phase boundary. They provide precursory signals to an impending phase change. Finite systems used in the Monte Carlo sampling limit fluctuations in sizes and shapes of heterogeneous clusters. The observed number dependence simply reflects this fact.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 7082733
• Journal Information: Journal of Chemical Physics; (United States), Vol. 102:3; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
FLUIDS
PHASE STUDIES
AGGLOMERATION
BINARY MIXTURES
CHEMICAL COMPOSITION
DENSITY
DISTRIBUTION FUNCTIONS
EQUATIONS OF STATE
FLUCTUATIONS
HARD-SPHERE MODEL
INTEGRAL EQUATIONS
MOLECULE COLLISIONS
MONTE CARLO METHOD
PERCUS-YEVICK EQUATION
SAMPLING
SHAPE
SIZE
VAN DER WAALS FORCES
CALCULATION METHODS
COLLISIONS
DISPERSIONS
EQUATIONS
FUNCTIONS
MIXTURES
PHYSICAL PROPERTIES
VARIATIONS
360602* - Other Materials- Structure & Phase Studies