School of Optoelectronic Information, Chongqing University of Technology, Chongqing 400054, China.
J Phys Chem B. 2010 Oct 28;114(42):13386-92. doi: 10.1021/jp106118q.
The ionic density profiles and corresponding integrated charge distribution close to an aqueous interface carrying charged functional groups of different valences exposed to mixed-salt solutions of 1:1 and 3:1 electrolytes were computed by use of extensive Monte Carlo simulations within the framework of the primitive model. The influence of varying ion sizes on charge inversion was analyzed, along with the crucial role of electrostatic images arising from dielectric discontinuities. For small sizes of charged species, it was found that charge inversion is enhanced by the presence of multivalent interfacial groups. Moreover, dielectric images further intensify the degree of charge inversion despite strong depletion effects. In particular, the onset of charge inversion shifts closer to the nonaqueous phase if the surface charge density is sufficiently low. These observations are opposite to the general belief of image repulsion. When large-sized ions were considered, the degree of charge inversion was found to be independent of the structure of interfacial groups and to remain widely unaffected in the absence and presence of dielectric images. Overall, our results show that interionic excluded-volume interactions are an overwhelming factor in determining counterion condensation. In addition, the inclusion of ionic size asymmetry at weakly charged interface results in surface charge amplification, which becomes more pronounced with increasing valence of the interfacial groups. Our work emphasizes the fact that surface equilibria mainly result from a subtle balance between steric and charge correlations.
我们使用扩展的蒙特卡罗模拟方法，在原始模型的框架内，计算了带有不同价电荷功能基团的水相界面附近的离子密度分布和相应的积分电荷分布，这些界面处于 1:1 和 3:1 电解质混合盐溶液中。我们分析了离子大小变化对电荷反转的影响，以及介电不连续性引起的静电图像的关键作用。对于小尺寸的带电物质，我们发现多价界面基团的存在增强了电荷反转。此外，尽管存在强烈的耗尽效应，但介电图像进一步加剧了电荷反转的程度。特别是，如果表面电荷密度足够低，则电荷反转的起始位置会更接近非水相。这些观察结果与图像排斥的普遍看法相反。当考虑到大尺寸离子时，我们发现电荷反转的程度与界面基团的结构无关，并且在不存在和存在介电图像的情况下基本不受影响。总的来说，我们的结果表明，离子排斥体积相互作用是决定抗衡离子凝聚的压倒性因素。此外，在弱带电界面上包含离子尺寸不对称性会导致表面电荷放大，而随着界面基团价数的增加，这种放大作用会更加明显。我们的工作强调了一个事实，即表面平衡主要是由空间和电荷相关性之间的微妙平衡决定的。
