随机多孔介质中离子流体的汽液phase diagram
Vapour-liquid phase diagram for an ionic fluid in a random porous medium
摘要：
本文研究了由不带电的硬球粒子构成的无规多孔基质中离子流体的汽液相行为。离子流体被建模为带相反电荷的等尺寸硬球的等摩尔二元混合物，即所谓的受限原始模型（RPM）。考虑到矩阵流体系统作为一个部分淬火模型，我们开发了一个理论方法，结合集体变量的方法与扩展的标度粒子理论（SPT）的硬球流体限制在无序硬球矩阵。该方法使我们能够制定微扰理论使用SPT的热力学描述的参考系。RPM在不同孔隙率的矩阵和不同的矩阵和流体颗粒的尺寸比的相图计算在随机相位近似，也当考虑到离子之间的高阶相关性的影响。这两种近似法都正确地再现了多孔介质对汽液相图的基本影响，即，随着孔隙度的减小，临界点向低流体密度和低温度方向移动，共存区变窄。对于固定的基体孔隙率，随着基体颗粒尺寸的增大，临界温度和临界密度均增大，并趋于体积RPM的临界值。
英文摘要：
We study the vapour-liquid phase behaviour of an ionic fluid confined in a random porous matrix formed by uncharged hard sphere particles. The ionic fluid is modelled as an equimolar binary mixture of oppositely charged equisized hard spheres, the so-called restricted primitive model (RPM). Considering the matrix-fluid system as a partly-quenched model, we develop a theoretical approach which combines the method of collective variables with the extension of the scaled-particle theory (SPT) for a hard-sphere fluid confined in a disordered hard-sphere matrix. The approach allows us to formulate the perturbation theory using the SPT for the description of the thermodynamics of the reference system. The phase diagrams of the RPM in matrices of different porosities and for different size ratios of matrix and fluid particles are calculated in the random-phase approximation and also when the effects of higher-order correlations between ions are taken into account. Both approximations correctly reproduce the basic effects of porous media on the vapour-liquid phase diagram, i.e., with a decrease of porosity the critical point shifts toward lower fluid densities and lower temperatures and the coexistence region is getting narrower. For the fixed matrix porosity, both the critical temperature and the critical density increase with an increase of size of matrix particles and tend to the critical values of the bulk RPM.
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