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Dipolar origin of the gas-liquid coexistence of the hard-core 1:1 electrolyte model

J. M. Romero-Enrique·L. F. Rull·A. Z. Panagiotopoulos
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Abstract

We present a systematic study of the effect of the ion pairing on the gas-liquid phase transition of hard-core 1:1 electrolyte models. We study a class of dipolar dimer models that depend on a parameter R_c, the maximum separation between the ions that compose the dimer. This parameter can vary from sigma_{+/-} that corresponds to the tightly tethered dipolar dimer model, to R_c --> infinity, that corresponds to the Stillinger-Lovett description of the free ion system. The coexistence curve and critical point parameters are obtained as a function of R_c by grand canonical Monte Carlo techniques. Our results show that this dependence is smooth but non-monotonic and converges asymptotically towards the free ion case for relatively small values of R_c. This fact allows us to describe the gas-liquid transition in the free ion model as a transition between two dimerized fluid phases. The role of the unpaired ions can be considered as a perturbation of this picture.

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J. M. Romero-Enrique, L. F. Rull, A. Z. Panagiotopoulos. 2002-08-05. Dipolar origin of the gas-liquid coexistence of the hard-core 1:1 electrolyte model. https://doi.org/10.1103/physreve.66.041204

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