Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin, Madison, Wisconsin 53706, USA.
J Chem Phys. 2010 Feb 21;132(7):074903. doi: 10.1063/1.3319782.
The adsorption of strongly charged polyelectrolyte chains to an oppositely charged planar surface is studied using computer simulation. In addition to an explicit solvent model, two implicit solvent models are considered: one where the solvent induces an implicit Lennard-Jones (ILJ) interaction between polymer sites and one where the solvent induces a many body interaction that depends on the solvent accessible surface area (SASA) of the monomers. Molecular and Brownian dynamics simulations are reported for the explicit and implicit solvent models, respectively. All three models give similar results for the adsorption of the chains in good solvent. The electrostatic attraction between the surface and the polymers is not sufficient to drive the strong adsorption that is seen in experiments. In poor solvents, the models give different results for the adsorption excess and the mechanism for polyelectrolyte adsorption. With explicit solvent, thick adsorbed layers are formed at both charged and neutral surfaces. With the SASA model, adsorbed layers are formed on the charged but not on the neutral surface. With the ILJ model, adsorbed layers are not formed on any surfaces. The results show that the solvent plays a dominant role in the adsorption of polyelectrolytes under poor solvent conditions and that many-body solvent effects have a qualitative effect on the adsorption characteristics and mechanism. In particular, SASA and depletion effects could possibly play an important role; the former can be incorporated in the SASA model, but the latter cannot. The results suggest that accurate computational models for polymer adsorption under poor solvent conditions must incorporate the solvent explicitly.
使用计算机模拟研究了带相反电荷的聚合物链在带相反电荷的平面表面上的吸附。除了显式溶剂模型外，还考虑了两种隐式溶剂模型：一种是溶剂在聚合物位点之间诱导隐式 Lennard-Jones（ILJ）相互作用，另一种是溶剂诱导依赖于单体溶剂可及表面积（SASA）的多体相互作用。分别对显式和隐式溶剂模型进行了分子和布朗动力学模拟。所有三种模型对于良溶剂中链的吸附都给出了相似的结果。表面和聚合物之间的静电吸引不足以驱动实验中观察到的强吸附。在不良溶剂中，模型对于吸附过剩和聚电解质吸附的机制给出了不同的结果。在显式溶剂中，在带电和中性表面上都形成了厚的吸附层。在 SASA 模型中，仅在带电表面上形成吸附层，而在中性表面上则不形成。在 ILJ 模型中，在任何表面上都未形成吸附层。结果表明，在不良溶剂条件下，溶剂在聚电解质吸附中起主导作用，多体溶剂效应对吸附特性和机制具有定性影响。特别是，SASA 和耗尽效应可能起重要作用；前者可以包含在 SASA 模型中，但后者不能。结果表明，在不良溶剂条件下进行聚合物吸附的精确计算模型必须显式包含溶剂。
