Abstract
We have performed Monte Carlo simulations to obtain the thermodynamic properties of fluids with two kinds of hard-core plus attractive-tail or oscillatory potentials. One of them is the square-well potential with small well width. The other is a model potential with oscillatory and decaying tail. Both model potentials are suitable for modeling the effective potential arising in complex fluids and fluid mixtures with extremely-large-size asymmetry, as is the case of the solvent-induced depletion interactions in colloidal dispersions. For the former potential, the compressibility factor, the excess energy, the constant-volume excess heat capacity, and the chemical potential have been obtained. For the second model potential only the first two of these quantities have been obtained. The simulations cover the whole density range for the fluid phase and several temperatures. These simulation data have been used to test the performance of a third-order thermodynamic perturbation theory (TPT) recently developed by one of us [S. Zhou, Phys. Rev. E 74, 031119 (2006)] as compared with the well-known second-order TPT based on the macroscopic compressibility approximation due to Barker and Henderson. It is found that the first of these theories provides much better accuracy than the second one for all thermodynamic properties analyzed for the two effective potential models.
Highlights
Complex fluids, which are present in a variety of fields such as soft-matter physics, biophysics, and colloid science, have received much attention in past decades
The other is a model potential with oscillatory and decaying tail. Both model potentials are suitable for modeling the effective potential arising in complex fluids and fluid mixtures with extremely-largesize asymmetry, as is the case of the solvent-induced depletion interactions in colloidal dispersions
The multicomponent character and the large asymmetry between the particles of the different species in these mixtures make it cumbersome to carry out the statistical thermodynamic treatment considering explicitly each species in the mixture
Summary
Complex fluids, which are present in a variety of fields such as soft-matter physics, biophysics, and colloid science, have received much attention in past decades. The basic feature1͔ of the complex fluids is the extremely large asymmetry in size, charge, number of degrees of freedom, and shape between the constituent particles. The multicomponent character and the large asymmetry between the particles of the different species in these mixtures make it cumbersome to carry out the statistical thermodynamic treatment considering explicitly each species in the mixture. Theoretical investigation about the phase behavior of the complex fluids often has to resort to a so-called effective singlecomponent macrofluid approximation. The large colloidal particles interact with each other through an effective potential consisting of a direct colloid-colloid interaction and a solvent-induced potential. After obtaining the effective potential between colloidal particles in one way or another, the complex fluids can be handled by means of statistical mechanics theory for a single-component “atomic fluid.”
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