Dipartimento di Scienze Chimiche, University of Catania, Viale A. Doria 6-95125, Catania, Italy.
J Chem Phys. 2012 Feb 7;136(5):055101. doi: 10.1063/1.3678836.
We develop a semi-quantitative analytical theory to describe adhesion between two identical planar charged surfaces embedded in a polymer-containing electrolyte solution. Polymer chains are uncharged and differ from the solvent by their lower dielectric permittivity. The solution mimics physiological fluids: It contains 0.1 M of monovalent ions and a small number of divalent cations that form tight bonds with the headgroups of charged lipids. The components have heterogeneous spatial distributions. The model was derived self-consistently by combining: (a) a Poisson-Boltzmann like equation for the charge densities, (b) a continuum mean-field theory for the polymer profile, (c) a solvation energy forcing the ions toward the polymer-poor regions, and (d) surface interactions of polymers and electrolytes. We validated the theory via extensive coarse-grained Molecular Dynamics (MD) simulations. The results confirm our analytical model and reveal interesting details not detected by the theory. At high surface charges, polymer chains are mainly excluded from the gap region, while the concentration of ions increases. The model shows a strong coupling between osmotic forces, surface potential and salting-out effects of the slightly polar polymer chains. It highlights some of the key differences in the behaviour of monomeric and polymeric mixed solvents and their responses to Coulomb interactions. Our main findings are: (a) the onset of long-ranged ion-induced polymer depletion force that increases with surface charge density and (b) a polymer-modified repulsive Coulomb force that increases with surface charge density. Overall, the system exhibits homeostatic behaviour, resulting in robustness against variations in the amount of charges. Applications and extensions of the model are briefly discussed.
我们开发了一种半定量分析理论来描述嵌入含有聚合物电解质溶液中的两个相同平面带电表面之间的粘附。聚合物链不带电，其介电常数比溶剂低。该溶液模拟生理流体：它含有 0.1 M 的单价离子和少量与带电脂质的头基形成紧密键的二价阳离子。这些成分具有不均匀的空间分布。该模型通过结合以下内容自洽地推导出来：（a）用于电荷密度的泊松-玻尔兹曼类似方程，（b）用于聚合物轮廓的连续平均场理论，（c）迫使离子进入聚合物贫区域的溶剂化能，以及（d）聚合物和电解质的表面相互作用。我们通过广泛的粗粒分子动力学（MD）模拟验证了该理论。结果证实了我们的分析模型，并揭示了理论无法检测到的有趣细节。在高表面电荷下，聚合物链主要被排除在间隙区域之外，而离子浓度增加。该模型显示出渗透压、表面电势和略带极性的聚合物链的盐析效应之间的强烈耦合。它突出了单体和聚合混合溶剂行为的一些关键差异及其对库仑相互作用的响应。我们的主要发现是：（a）长程离子诱导聚合物耗尽力的出现，该力随表面电荷密度增加而增加，以及（b）聚合物修饰的排斥库仑力随表面电荷密度增加而增加。总的来说，该系统表现出动态平衡行为，对电荷数量的变化具有稳健性。该模型的应用和扩展进行了简要讨论。
