Publisher DOI: 10.1016/j.molliq.2020.115204
Title: On the analogy between the restricted primitive model and capacitor circuits: Semi-empirical alternatives for over- and underscreening in the calculation of mean ionic activity coefficients
Language: English
Authors: González de Castilla, Andrés  
Müller, Simon  
Smirnova, Irina 
Keywords: COSMO-RS;Debye-Hückel;Electrolytes;Mean spherical approximation;Overscreening;Restricted Primitive model;Underscreening
Issue Date: 15-Mar-2021
Source: Journal of Molecular Liquids (326): 115204 (2021-03-15)
Journal or Series Name: Journal of molecular liquids 
Abstract (english): 
The analogy between the restricted primitive model and capacitor circuits, originally described decades ago for the Mean Spherical Approximation, is explored to demonstrate its transferability in linearized electrolyte theories. On this basis, we offer an explanation of why treating the salt diameter as a free adjustable parameter blurs differences between electrolyte theories in the calculation of mean ionic activity coefficients. Furthermore, a capacitor circuit analogy with an approximation of the Dressed Ion Theory is applied to develop a modified closest approach parameter “b” for the Pitzer-Debye-Hückel term. This modification is able to account for the qualitative effects of over- and underscreening in the calculation of mean ionic activity coefficients. This is achieved by defining “b” as a semi-empirical function that allows close resemblance with the multiple decay-length extension of the Debye-Hückel theory for high dielectric constant values and that lies close to recommended literature values of “b” for low dielectric constant values. Finally, as proof of principle, this modified semi-empirical Pitzer-Debye-Hückel term is implemented in the predictive COSMO-RS-ES model, an own reimplementation of the COSMO-RS theory developed for thermodynamic property calculations of electrolyte systems. It is shown that the modified semi-empirical Pitzer-Debye-Hückel term is an effective replacement for the recently published version of COSMO-RS-ES with explicit considerations for ion pairing. This reduces the modelling complexity by implicitly considering ion pairing and improves overall qualitative performance for the prediction of salt solubilities in mixed-solvent systems and even mean ionic activity coefficients in non-aqueous media.
URI: http://hdl.handle.net/11420/8538
ISSN: 0167-7322
Institute: Thermische Verfahrenstechnik V-8 
Document Type: Article
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