In order to evaluate the full complexity of the systems of interest, it was decided to focus on quaternary systems, as illustrated below:
The salt AB is a combination of an acid (HA) and a base (BOH), that both form ions when dissolved in a high dielectric constant (permittivity) medium as water:
HA = H+ + A-
BOH = B+ + OH-
When a cosolvent is added, the permittivity of the medium decreases, and as a consequence, the relative strength of the acid and the base change. The quaternary system therefore becomes in fact a system with nine components. Changing the concentration of the acid or the base affects the pH of the system, while changing the concentration of the non-aqueous solvent affects the permittivity and thus the ionic strength. The modelling of such system is therefore particularly challenging.
Within EleTher, it is the objective to propose best practices for developing a modeling approach for such a system in view of computing fluid phase equilibria: vapour-liquid or liquid-liquid.