Entropy of electrolytes with off-centre charge cations. Monte Carlo studies

Monte Carlo techniques including Inverse Grand Canonical Monte Carlo simulations are utilized to calculate the entropy of a restricted primitive model electrolyte with the caveat that the cation charge centre is displaced from the geographical centre of the cation sphere towards the surface of the sphere. Calculations have been performed for symmetric valency (1:1) and asymmetric valency (2:1) electrolytes at 298.15 K for a range of electrolyte concentrations. The cation charge centre displacement accompanied by an increase of temperature leads to an increase of entropy. For the 2:1 valency system the entropy as a function of the square root of concentration reveals a broad inflexion region that separates the domains of deformation due to the electrostatic and steric interactions. When the central ion is an anion, and the charge centres of the surrounding cations are oriented towards the anion then the electrostatic interac-tions are stronger than in the standard restricted primitive model and the entropy decreases, while a cen-tral cation deforms the ionic atmosphere surrounding it and the entropy increases. In the low concentration regime good agreement is seen between the results from the Debye-Huckel limiting law and the corresponding simulations. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Inverse Grand Canonical Monte Carlo simulations were used to calculate the entropy of a restricted primitive model electrolyte, considering the displacement of the cation charge centre. The results showed that the charge centre displacement and temperature increase led to an increase in entropy. The entropy as a function of concentration exhibited a turning point for different valency systems, indicating the presence of deformation caused by electrostatic and steric interactions. The type of ion also influenced the entropy change.