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arXiv 1202.5979cond-mat.soft
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离子对受限近临界二元水溶液的影响

Effect of ions on confined near-critical binary aqueous mixture

Faezeh Pousaneh, Alina Ciach, Anna Maciolek

摘要:

近临界二元混合物中含有离子和两个带电和选择性表面之间的限制进行了研究扩展到包括静电相互作用的朗道-金兹伯格理论。电荷密度分布和有效的限制表面之间的相互作用的情况下,计算的溶剂组分之一的离子的化学偏好。在接近二元溶剂的共溶点时,离子的优先溶解性导致电荷密度分布相对于从Debye-Hückel理论获得的电荷密度分布的修改。因此,静电对带电表面之间的有效电势的贡献可以表现出吸引阱。我们的计算是基于有效的近似方案,如果一种溶剂的体积相关长度远大于德拜屏蔽长度;在这个临界状态下,电荷对溶剂浓度分布的影响是次显性的。这些条件在最近对作用于基底和浸入近临界水-二甲基吡啶混合物中的球形胶体颗粒之间的有效力的测量中得到满足[Nature V.451,172(2008)]。我们的分析结果与实验结果在定量上是一致的。

英文摘要:

Near-critical binary mixtures containing ions and confined between two charged and selective surfaces are studied within a Landau-Ginzburg theory extended to include electrostatic interactions. Charge density profiles and the effective interactions between the confining surfaces are calculated in the case of chemical preference of ions for one of the solvent components. Close to the consolute point of the binary solvent, the preferential solubility of ions leads to the modification of the charge density profiles in respect to the ones obtained from the Debye-Hückel theory. As a result, the electrostatic contribution to the effective potential between the charged surface can exhibit an attractive well. Our calculations are based on the approximation scheme valid if the bulk correlation length of a solvent is much larger than the Debye screening length; in this critical regime the effect of charge on the concentration profiles of the solvent is subdominant. Such conditions are met in the recent measurements of the effective forces acting between a substrate and a spherical colloidal particle immersed in the near-critical water-lutidine mixture [Nature V. 451, 172 (2008)]. Our analytical results are in a quantitative agreement with the experimental ones.

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