Sarraguça J M G, Pais A A C C
Departamento de Química, Universidade de Coimbra, 3004-535, Coimbra, Portugal.
Phys Chem Chem Phys. 2006 Sep 28;8(36):4233-41. doi: 10.1039/b606087k. Epub 2006 Aug 3.
It has been experimentally observed that trivalent ions are capable of promoting compaction of semi-flexible polyelectrolyte chains. In this work we perform Monte Carlo simulations on single chain model systems with varying chain size and stiffness and evaluate the action of multivalent salt on the chain conformation. It is observed that longer chains tend to achieve relatively more compact conformations than shorter ones, and the dimensions of the collapsed structures do not significantly vary with contour length. The influence of contour length and intrinsic stiffness in the process of ion condensation is studied by analysis of the ion-ion nearest-neighbor distribution. The general trend is an increase of the degree of ion condensation as the chain length increases, in accordance with experimental evidence. A decreased importance of end-effects and, especially, larger volume charge densities are responsible for such behavior. The influence of chain stiffness is nontrivial, and depends on salt concentration. The results emphasize the complex nature of ion-correlation phenomena in flexible or semi-flexible chains and call for the development of more sophisticated analytical theories.
实验观察到三价离子能够促进半柔性聚电解质链的压缩。在这项工作中，我们对具有不同链尺寸和刚度的单链模型系统进行了蒙特卡罗模拟，并评估了多价盐对链构象的作用。观察到较长的链比较短的链倾向于实现相对更紧凑的构象，并且塌缩结构的尺寸不会随轮廓长度显著变化。通过分析离子 - 离子最近邻分布来研究轮廓长度和固有刚度在离子凝聚过程中的影响。总体趋势是随着链长度增加离子凝聚程度增加，这与实验证据一致。末端效应重要性的降低，尤其是更大的体积电荷密度导致了这种行为。链刚度的影响是复杂的，并且取决于盐浓度。结果强调了柔性或半柔性链中离子相关现象的复杂性，并呼吁发展更复杂的分析理论。
