Crossover from Rouse to Reptation Dynamics in Salt-Free Polyelectrolyte Complex Coacervates
Crossover from Rouse to Reptation Dynamics in Salt-Free Polyelectrolyte Complex Coacervates
复制标题
无盐聚电解质复合凝聚层中从唤醒到蠕动动力学的交叉
DOI：
10.1021/acsmacrolett.0c00522
复制
发表时间：
2020
影响因子：
7.015
通讯作者：
de Pablo, Juan J.
中科院分区：
文献类型：
--
作者：
Yu, Boyuan;Rauscher, Phillip M.;Jackson, Nicholas E.;Rumyantsev, Artem M.;de Pablo, Juan J.
聚电解质络合物凝聚体的动力学和流变性受到其作为粘度调节剂的工业应用的极大兴趣。一个核心问题是经典的劳斯和重复模型在多大程度上可以应用于静电相互作用在热力学中起关键作用的系统。通过分子模拟，我们直接分析了无盐络合物凝聚体中从劳斯到重复动力学的交叉作为链长度的函数。当静电相互作用变得更强时，这种交叉转移到更短的链长，这对应于更密集凝聚的形成。为了区分库仑相互作用和密度的作用，我们将凝聚的动力学与相同密度下的中性半稀溶液的动力学进行了比较。这两种体系在连通性占主导地位（亚扩散和正常扩散）的情况下都表现出普遍的动力学行为，但凝聚中的单体弛豫时间要长得多，并且随着Bjerrum长度的增加而增加。这类似于在玻璃形成聚合物中观察到的笼形效应，但局部动态减速是由相反电荷单体之间的强库仑吸引（离子配对）引起的。我们的发现为定量理解凝聚动力学和流变学提供了一个微观框架。
Considerable interest in the dynamics and rheology of polyelectrolyte complex coacervates has been motivated by their industrial application as viscosity modifiers. A central question is the extent to which classical Rouse and reptation models can be applied to systems where electrostatic interactions play a critical role on the thermodynamics. By relying on molecular simulations, we present a direct analysis of the crossover from Rouse to reptation dynamics in salt-free complex coacervates as a function of chain length. This crossover shifts to shorter chain lengths as electrostatic interactions become stronger, which corresponds to the formation of denser coacervates. To distinguish the roles of Coulomb interactions and density, we compare the dynamics of coacervates to those of neutral, semidilute solutions at the same density. Both systems exhibit a universal dynamical behavior in the connectivity-dominated (subdiffusion and normal diffusion) regimes, but the monomer relaxation time in coacervates is much longer and increases with increasing Bjerrum length. This is similar to the cage effect observed in glass-forming polymers, but the local dynamical slowdown is caused here by strong Coulomb attractions (ion pairing) between oppositely charged monomers. Our findings provide a microscopic framework for the quantitative understanding of coacervate dynamics and rheology.