On the properties of methanolic NaCl solution by molecular dynamics simulations

Cruz Sanchez Cruz Sanchez,Pizio Pizio,Dominguez Dominguez

doi:10.5488/cmp.23.23602

Abstract

Isothermal-isobaric molecular dynamics simulations are used to examine the microscopic structure and principal thermodynamic properties of a model solution consisting of NaCl salt dissolved in methanol solvent. Four united atom force fields for methanol are involved. Concerning ion solutes we used the Joung-Cheatham, Smith-Dang models as well as the model from the laboratory of Vrabec. Our principal focus is to evaluate the quality of predictions of different combinations of models for basic properties of these solutions. Specifically, we explored the change of density on molality, the structural properties in terms of various pair distribution functions, the coordination numbers, the number of ion pairs and the average number of hydrogen bonds. In addition, changes of the self-diffusion coefficients of species, the solvent dielectric constant and the evolution of the surface tension with ion concentration are described.

Highlights

From a general perspective, this work is focused on the theoretical description of one simplest example of a class of electrolyte systems that comprise ionic solutes dissolved in water with organic co-solvent
Our first series of simulations are focused in the description of the dependence of density of NaCl methanolic solution on solute molality, m, in mol/kg units
We explored the evolution of density, surface tension, solvent dielectric constant and self-diffusion coefficients of the species with an augmenting amount of NaCl solute in the solution

Summary

Introduction

This work is focused on the theoretical description of one simplest example of a class of electrolyte systems that comprise ionic solutes dissolved in water with organic co-solvent. The most comprehensive investigation of ionic solutions in water-methanol solvents was performed in the laboratory of Hawlicka [4,5,6,7,8,9,10,11,12] These studies were restricted to NaCl and NaI univalent salts, as well as MgCl2 and CaCl2 salts with divalent cations as solutes. Our intention is to provide insights into the dependence of the results on the choice of models for methanol and for ionic solutes This issue has not been investigated so far, in contrast to pure methanol [33, 34]. The isobaric-isothermal molecular dynamics computer simulations represent our tools

Models and simulation details

Density of solutions

10 Cl - O

Self-diffusion coefficients of methanol and ions

Solvent dielectric constant

Surface tension

Summary and conclusions