Density anomaly of charged hard spheres of different diameters in a mixture with core-softened model solvent. Monte Carlo simulation results

Abstract

Very recently the effect of equisized charged hard sphere solutes in a mixture with core-softened fluid model on the structural and thermodynamic anomalies of the system has been explored in detail by using Monte Carlo simulations and integral equations theory [J. Chem. Phys., 2012, 137, 244502]. Our objective of the present short work is to complement this study by considering univalent ions of unequal diameters in a mixture with the same soft-core fluid model. Specifically, we are interested in the analysis of changes of the temperature of maximum density (TMD) lines with ion concentration for three model salt solutes, namely sodium chloride, potassium chloride and rubidium chloride models. We resort to Monte Carlo simulations for this purpose. Our discussion also involves the dependences of the pair contribution to excess entropy and of constant volume heat capacity on the temperature of maximum density line. Some examples of the microscopic structure of mixtures in question in terms of pair distribution functions are given in addition.

Phase behaviour of a continuous shouldered well model fluid. A grand canonical Monte Carlo study

“…The TMD line has been obtained by performing separately a large set of canonical MC simulations at constant density while changing temperature step by step. The procedure is similar to what was reported by us recently [42, 43]. …”

“…The hydrophobic effect plays an important role in a wide variety of phenomena such as the collapse of polymers (and proteins) in water, and in the formation of micelles [40, 41]. Mixtures of ions with core-softened fluids and the effects of structural and thermodynamic anomalies in these mixtures were investigated by us [42, 43]. Partly-quenched systems involving the soft-core annealed fluid were as well studied by one of us [34, 44, 45].…”