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arXiv 1708.08397cond-mat.stat-mech
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无序基质中离子流体尺寸非对称模型的汽液相行为:基于集体变量的方法

Vapor-liquid phase behavior of a size-asymmetric model of ionic fluids confined in a disordered matrix: the collective variables-based approach

O. V. Patsahan, T. M. Patsahan, M. F. Holovko

摘要:

我们发展了一个基于集体变量方法的理论来研究无序多孔介质中非对称离子流体的汽液平衡。该方法使我们能够制定微扰理论使用扩展的缩放粒子理论的描述的参考系作为一个两个组件的硬球流体限制在硬球矩阵。将离子流体视为尺寸和电荷不对称的原始模型(PM),我们推导出一个明确的表达式,该表达式考虑到离子之间的三阶相关性的受限离子系统的相关化学势。使用这个表达式,相图的大小不对称PM计算不同的矩阵孔隙率以及不同尺寸的矩阵和流体颗粒。观察到共存曲线与基质孔隙率的总体趋势与无序约束下的简单流体的趋势相似,即,随着孔隙率的降低,共存区域变窄,同时降低的临界温度$T_{c}^{*}$和临界密度$ρ_{i,c}^{*}$变低。同时,我们的研究结果表明,相反电荷的离子的尺寸不对称性的增加显着影响的气液图导致$T_{c}^{*}$和$ρ_{i,c}^{*}$,甚至消失的相变,特别是对于小基质颗粒的情况下,更快地减少。

英文摘要:

We develop a theory based on the method of collective variables to study the vapor-liquid equilibrium of asymmetric ionic fluids confined in a disordered porous matrix. The approach allows us to formulate the perturbation theory using an extension of the scaled particle theory for a description of a reference system presented as a two-component hard-sphere fluid confined in a hard-sphere matrix. Treating an ionic fluid as a size- and charge-asymmetric primitive model (PM) we derive an explicit expression for the relevant chemical potential of a confined ionic system which takes into account the third-order correlations between ions. Using this expression, the phase diagrams for a size-asymmetric PM are calculated for different matrix porosities as well as for different sizes of matrix and fluid particles. It is observed that general trends of the coexistence curves with the matrix porosity are similar to those of simple fluids under disordered confinement, i.e., the coexistence region gets narrower with a decrease of porosity, and simultaneously the reduced critical temperature $T_{c}^{*}$ and the critical density $ρ_{i,c}^{*}$ become lower. At the same time, our results suggest that an increase in size asymmetry of oppositely charged ions considerably affects the vapor-liquid diagrams leading to a faster decrease of $T_{c}^{*}$ and $ρ_{i,c}^{*}$ and even to a disappearance of the phase transition, especially for the case of small matrix particles.

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