Counterion-correlation-induced attraction and necklace formation in polyelectrolyte solutions: Theory and simulations
Counterion-correlation-induced attraction and necklace formation in polyelectrolyte solutions: Theory and simulations
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DOI：
10.1021/ma052086s
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发表时间：
2006-03-07
期刊：
影响因子：
5.5
通讯作者：
Rubinstein, M
中科院分区：
文献类型：
--
作者：
Liao, Q;Dobrynin, AV;Rubinstein, M
我们已经开发了一个项链模型的疏水聚电解质，其中的项链结构组成的聚合物小球（珠）连接的链（串的单体）的延长部分出现作为结果的反离子缩合，是由相关诱导的吸引力的平衡凝聚的反离子带电单体和静电之间的排斥未补偿的电荷。珠粒的尺寸随聚合物浓度增加而增加，而每条链的珠粒数量减少。我们预测在任何聚合物浓度下，聚合物主链上具有不同数量的珠的项链共存。为了测试这个项链模型，我们进行了分子动力学模拟的聚合度N从25到373变化，并与带电单体的分数f =（3）\（1），（2）\（1），和1在不良溶剂条件下的聚合物主链的双链。所观察到的珠粒尺寸的浓度依赖性支持项链结构的对流冷凝起源的假设。对于弱电荷链（f =（3）\（1）），重叠浓度几乎与聚合度无关。对于强电荷链与f = 1的重叠浓度遵循正常的N依赖性观察到的在圆减和良好的溶剂制度的聚合物主链的dichloromethane解决方案。在半稀溶液中，完全带电链的相关长度与聚合物浓度的平方根成反比。在差溶剂条件下的聚合物主链的聚电解质的溶液的渗透系数表现出非单调的浓度依赖性与两区模型的预测。在稀溶液中，它随着聚合物浓度的增加而减小，而在半稀溶液中，它是聚合物浓度的递增函数。链形状因子的Kratky图与中子散射实验非常吻合。
We have developed a necklace model of hydrophobic polyelectrolytes in which the necklace structure consisting of polymeric globules (beads) connected by extended sections of the chain (strings of monomers) appears as a result of the counterion condensation and is caused by the balance of the correlation-induced attraction of condensed counterions to charged monomers and electrostatic repulsion between uncompensated charges. The size of the beads increases with polymer concentration while their number per chain decreases. We predict coexistence of necklaces with different number of beads on a polymer backbone at any polymer concentration. To test this necklace model, we performed molecular dynamics simulations of polyelectrolyte chains with degree of polymerization N varying from 25 to 373 and with fraction of charged monomers f = (3)\(1), (2)\(1), and 1 in poor solvent conditions for polymer backbone. The observed concentration dependence of the bead size supports the assumption of the counterion condensation origin of the necklace structure. The overlap concentration is almost independent of the degree of polymerization for weakly charged chains (f = (3)\(1)). For strongly charged chains with f = 1 the overlap concentration follows the normal N dependence observed for polyelectrolyte solutions in circle minus and good solvent regimes for polymer backbone. In semidilute solutions the correlation length of fully charged chains is inversely proportional to the square root of polymer concentration. The osmotic coefficient of the solutions of polyelectrolytes in poor solvent conditions for polymer backbone exhibits nonmonotonic concentration dependence in agreement with two-zone model predictions. It decreases with increasing polymer concentration in dilute solutions, while it is an increasing function of polymer concentration in the semidilute regime. The Kratky plot of the chain form factor is in excellent agreement with the neutron scattering experiments.