Binding of monovalent ions to PEO in solution: Relevant parameters and structural transitions
Binding of monovalent ions to PEO in solution: Relevant parameters and structural transitions
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DOI：
10.1021/ma0495801
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发表时间：
2004-11-02
期刊：
影响因子：
5.5
通讯作者：
Bockstaller, MR
中科院分区：
文献类型：
--
作者：
Hakem, IF;Lal, J;Bockstaller, MR
我们提出了一个比较小角中子散射和理论研究的聚（环氧乙烷）（PEO）的充电效应在单价离子的存在下作为溶剂特性和阳离子强度的函数，我们证明了经典的“盐溶”条件是由不同的subregimes取决于盐和溶剂的特性。在具有中等介电常数和中等氢键能力的溶剂中，可以区分两种不同的状态：（1）在低离子强度下，盐的加入主要导致聚合物-阳离子缔合物的形成，从而导致聚合物链的带电（约束机制）;（2）在较高的盐浓度下，离子的结合变得越来越不利，导致静电相互作用的屏蔽，并且观察到PEO的中性聚合物样特征（屏蔽机制）。离子结合的程度进行比较的平均场理论的基础上的热力学极限的预测，它表明，在聚合物的构象中的伪-doppler型的变化可以成功地描述的随机相近似。在高介电常数或明显的氢键能力的溶剂中，离子的溶剂化抵消了复合物的形成过程，PEO有效地保持了溶液中的中性聚合物。
We present a comparative small-angle neutron scattering and theoretical study of the charging effects of poly(ethylene oxide) (PEO) in the presence of monovalent ions as a function of the solvent characteristics and cation strength, and we demonstrate that the classical "salting-in" condition is constituted by distinct subregimes depending on salt and solvent characteristics. In solvents with moderate dielectric constant and moderate hydrogen- bonding capacity, two distinct regimes can be distinguished: (1) at low ionic strengths, the addition of salts primarily results in the formation of polymer-cation association complexes and thus in charging of the polymer chain (binding regime); (2) at higher salt concentrations, the binding of ions becomes increasingly unfavorable, resulting in the screening of electrostatic interactions and neutral polymer-like characteristics of PEO are observed (screening regime). The extent of ion-binding is compared to predictions based on mean-field theory in the thermodynamic limit, and it is shown that the pseudo-polyelectrolyte type changes in the polymer's conformation can successfully be described by the random phase approximation. In solvents of high dielectric constant or pronounced hydrogen-bonding capacity, the solvation of ions counteracts the complex formation process, and PEO effectively remains a neutral polymer in solution.