Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
J Chem Phys. 2010 Jul 28;133(4):044906. doi: 10.1063/1.3463426.
Electrostatic interactions may promote or abate polyelectrolyte adsorption onto a charged surface depending on a number of interrelated factors including the surface and polymer charge densities, the salt concentration, and nonelectrostatic interactions such as van der Waals and hydrophobic forces. Even without the nonelectrostatic interactions, the electrostatic behavior of polyelectrolyte systems is often counterintuitive and cannot be explained with conventional theories of polymers or simple electrolytes. In this work, a nonlocal density functional theory (NLDFT) and Monte Carlo simulations are used together to investigate polyelectrolyte adsorption at both oppositely charged and like-charged surfaces (one due to the direct electrostatic attraction and the other due to counterion correlations). The simulation results provide a stringent test of the numerical performance of the NLDFT, in particular for systems containing multivalent counterions where electrostatic correlations are important. A systematic study of the effects of ion valence, salt concentration, and polyion chain length reveals that polyelectrolyte attraction to an oppositely charged surface is nearly a neutralization effect, little influenced by the polyion chain length and counterion valence. Neither the surface mean electrostatic potential nor the integrated local charge density shows no significant sign of charge inversion. Both theory and simulation predict polyelectrolyte adsorption onto a like-charged surface when the system contains multivalent counterions. In that case, the surface excess is sensitive to the surface charge density, the counterion valence, and the salt concentration. The surface mean electrostatic potential shows a clear evidence of charge inversion when two layers of like charges are mediated by multivalent counterions. The theoretical investigations indicate that most likely, the electrostatic correlation mediated by multivalent counterions is responsible for the layer-by-layer assembly of oppositely charged polyelectrolyte films.
静电相互作用可以促进或抑制聚电解质在带电表面上的吸附，这取决于许多相互关联的因素，包括表面和聚合物的电荷密度、盐浓度以及范德华力和疏水相互作用等非静电相互作用。即使没有非静电相互作用，聚电解质体系的静电行为通常也违背直觉，无法用传统的聚合物或简单电解质理论来解释。在这项工作中，我们使用非局部密度泛函理论（NLDFT）和蒙特卡罗模拟一起研究了带相反电荷和相同电荷表面上的聚电解质吸附（一种是由于直接静电吸引，另一种是由于抗衡离子相关）。模拟结果对 NLDFT 的数值性能进行了严格的测试，特别是对于含有多价抗衡离子的系统，其中静电相关性很重要。对离子价、盐浓度和聚离子链长的影响进行了系统的研究，结果表明，聚电解质对带相反电荷表面的吸引力几乎是中和效应，受聚离子链长和抗衡离子价的影响很小。表面平均静电势和积分局部电荷密度都没有明显的电荷反转迹象。理论和模拟都预测了当系统含有多价抗衡离子时，聚电解质会吸附在带相同电荷的表面上。在这种情况下，表面过剩对表面电荷密度、抗衡离子价和盐浓度敏感。当两层相同电荷由多价抗衡离子介导时，表面平均静电势显示出明显的电荷反转证据。理论研究表明，最有可能的是，多价抗衡离子介导的静电相关性是导致带相反电荷的聚电解质薄膜逐层组装的原因。
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