Volumetric properties of solutions on the perspective of Voronoi tessellation

Abstract

The intrinsic volume of a molecule in solution can be calculated with the help of Voronoi tessellation. It is suggested to extend it to components of the solution and to use it as a new volumetric property, which we call the Voronoi volume of a component. The known volumetric properties of solution, which are thermodynamic characteristics, can be expressed in terms of this geometric property of the components. In this work the Voronoi volumes are calculated for aqueous solutions of TMAO and TBA at different concentrations. Formulas expressing apparent and partial molar volumes of the components via their Voronoi molar volumes are derived. The nature of the minimum on the curves of the apparent and partial molar volumes of TBA at low concentrations, and its absence on the curves for TMAO, are discussed. It is shown that the intrinsic volumes of TBA and TMAO at low concentrations exceed the values for the apparent and partial molar volumes. This excess is compensated by a negative contribution of water to these volumetric properties.