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arXiv 1105.2489cond-mat.softcond-mat.stat-mech
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含离子近临界二元混合水溶液中疏水壁和亲水壁间吸引力的起源

Origin of attraction between likely charged hydrophobic and hydrophilic walls confining near-critical binary aquaeous mixture with ions

F. Pousaneh, A. Ciach

摘要:

在一个简单的密度泛函理论中考虑了离子溶质对被限制在不同吸附偏好的带电壁之间的近临界二元水溶液混合物的影响。对于含有少量离子的近临界体系,基于关联式$ξ$和德拜屏蔽长度$κ^{-1}$均远大于分子尺寸的假设,导出了Landau型泛函.对于不溶于有机溶剂的离子,得到了相应的近似欧拉-拉格朗日方程。非平凡的浓度分布的溶剂被发现附近的带电疏水壁作为结果之间的竞争的短程吸引力的有机溶剂和水合离子的静电吸引力。对于一定范围的表面电荷和$ξκ$,在疏水表面附近可能存在过量的水。结果,亲水表面和疏水表面之间的有效电势在远离临界点时可以是排斥的,然后是吸引的,并且当接近临界温度时再次是排斥的,这与最近的实验一致[Nellen等人,软物质{ \bf 7},5360(2011)]。

英文摘要:

Effect of ionic solute on a near-critical binary aqueous mixture confined between charged walls with different adsorption preferences is considered within a simple density functional theory. For the near-critical system containing small amount of ions a Landau-type functional is derived based on the assumption that the correlation, $ξ$, and the Debye screening length, $κ^{-1}$, are both much larger than the molecular size. The corresponding approximate Euler-Lagrange equations aresolved analytically for ions insoluble in the organic solvent. Nontrivial concentration profile of the solvent is found near the charged hydrophobic wall as a result of the competition between the short-range attraction of the organic solvent and the electrostatic attraction of the hydrated ions. Excess of water may be present near the hydrophobic surface for some range of the surface charge and $ξκ$. As a result, the effective potential between the hydrophilic and the hydrophobic surface can be repulsive far from the critical point, then attractive and again repulsive when the critical temperature is approached, in agreement with the recent experiment [Nellen at.al., Soft Matter {\bf 7}, 5360 (2011)].

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