Influence of ionic strength on poly(diallyldimethylammonium chloride) macromolecule conformations in electrolyte solutions
Influence of ionic strength on poly(diallyldimethylammonium chloride) macromolecule conformations in electrolyte solutions
复制标题
DOI：
10.1016/j.jcis.2014.07.037
复制
发表时间：
2014-12-01
影响因子：
9.9
通讯作者：
Michna, Aneta
中科院分区：
文献类型：
--
作者：
Adamczyk, Zbigniew;Jamrozy, Krzysztof;Michna, Aneta
用动态光散射、微电泳和粘度测量等方法研究了聚二甲基二烯丙基氯化铵（PDADMAC）分子在电解质溶液中的构象。系统地研究了离子强度在10 ~（-4）和2 M范围内变化的作用。对于5 × 10（-4）至10（-2）M的离子强度范围，聚合物分子的扩散系数等于1.3 × 10（-7）cm（2）s（-1），对于更高的离子强度略微降低。这对应于38.5nm的流体动力学直径。使用的扩散系数和电泳迁移率的数据，PDADMAC分子上的电动电荷计算作为离子强度的函数。它是正的，在84和51个基本电荷之间变化。这使得大分子的有效电离度分别等于5 × 10（-4）和0.15 M离子强度的13%和8%。有关大分子构象的其他信息来自稀释PDADMAC溶液的粘度测量。从这些测量得到的特性粘度随着离子强度从10（-4）M的3400突然降低到2 M NaCl溶液的100。通过外推流体动力学直径和特性粘数数据到零离子强度，预测了分子的轮廓长度为240 nm，主链直径为0.85 nm。另一方面，在较高的离子强度的特性粘度的下降是由于在大分子构象的变化，更多的崩溃。通过考虑离子强度效应和有效电离度的PDADMAC分子链构象的分子动力学模型对实验结果进行了解释。在较低的离子强度范围内达到了定量一致，证明了组合的DLS和粘度测量提供了有关电解质溶液中大分子构象的可靠信息。(C)2014 Elsevier Inc. All rights reserved.
Conformations of poly(diallyldimethylammonium chloride), PDADMAC, molecules in electrolyte solutions were experimentally evaluated by dynamic light scattering (DLS), micro-electrophoretic and viscosity measurements. The role of ionic strength varied within 10(-4) and 2 M was systematically studied. The diffusion coefficient of the polymer molecules was equal to 1.3 x 10(-7) cm(2) s(-1) for the ionic strength range 5 x 10(-4) to 10(-2) M decreasing slightly for higher ionic strength. This corresponds to the hydrodynamic diameter of 38.5 nm. Using the diffusion coefficient and the electrophoretic mobility data, the electrokinetic charge on PDADMAC molecules was calculated as a function of ionic strength. It was positive and varied between 84 and 51 elementary charges. This gives the effective ionization degree of the macromolecule equal to 13% and 8% for ionic strength of 5 x 10(-4) and 0.15 M, respectively. Additional information about macromolecule conformation was derived from the viscosity measurements of dilute PDADMAC solutions. The intrinsic viscosity derived from these measurements decreased abruptly with ionic strength from 3400 for 10(-4) M to 100 for 2 M, NaCl solutions. By extrapolating the hydrodynamic diameter and intrinsic viscosity data to zero ionic strength the polyelectrolyte molecule contour length of 240 nm and the backbone diameter of 0.85 nm were predicted. On the other hand, the decrease in the intrinsic viscosity for higher ionic strength was attributed to changes in macromolecule conformations to more collapsed ones. The experimental results were interpreted by molecular dynamics modeling of PDADMAC chain conformations in electrolyte solutions where the ionic strength effect and the effective ionization degree were considered. A quantitative agreement was attained for lower ionic strength range proving that the combined DLS and viscosity measurements furnish reliable information about macromolecule conformations in electrolyte solution. (C) 2014 Elsevier Inc. All rights reserved.