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Mesoscopic theory for size- and charge- asymmetric ionic systems. I. Case of extreme asymmetry

A. Ciach·W. T. Góźdź·G. Stell
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Abstract

A mesoscopic theory for the primitive model of ionic systems is developed for arbitrary size, $λ=σ_+/σ_-$, and charge, $Z=e_+/|e_-|$, asymmetry. Our theory is an extension of the theory we developed earlier for the restricted primitive model. The case of extreme asymmetries $λ\to\infty$ and $Z \to\infty$ is studied in some detail in a mean-field approximation. The phase diagram and correlation functions are obtained in the asymptotic regime $λ\to\infty$ and $Z \to\infty$, and for infinite dilution of the larger ions (volume fraction $n_p\sim 1/Z$ or less). We find a coexistence between a very dilute 'gas' phase and a crystalline phase in which the macroions form a bcc structure with the lattice constant $\approx 3.6σ_+$. Such coexistence was observed experimentally in deionized aqueous solutions of highly charged colloidal particles.

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A. Ciach, W. T. Góźdź, G. Stell. 2005-11-07. Mesoscopic theory for size- and charge- asymmetric ionic systems. I. Case of extreme asymmetry. https://doi.org/10.1088/0953-8984%2F18%2F5%2F016

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