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.

中文翻译：

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无盐聚电解质复合凝聚层中从劳斯到蠕动动力学的交叉

聚电解质复合凝聚层的动力学和流变学引起了人们对它们作为粘度调节剂的工业应用的极大兴趣。一个中心问题是经典 Rouse 和Reptation 模型在多大程度上可以应用于静电相互作用对热力学起关键作用的系统。通过依靠分子模拟，我们直接分析了无盐复合凝聚层中从 Rouse 到蠕动动力学的交叉与链长的函数关系。随着静电相互作用变得更强，这种交叉转移到更短的链长度，这对应于更密集的凝聚层的形成。为了区分库仑相互作用和密度的作用，我们将凝聚层的动力学与相同密度的中性半稀溶液的动力学进行了比较。两个系统在连通性主导（次扩散和正常扩散）状态下都表现出普遍的动力学行为，但凝聚层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。这类似于在形成玻璃的聚合物中观察到的笼效应，但这里的局部动态减速是由带相反电荷的单体之间的强库仑吸引力（离子配对）引起的。我们的研究结果为定量理解凝聚层动力学和流变学提供了一个微观框架。但是这里的局部动态减速是由带相反电荷的单体之间的强库仑吸引力（离子配对）引起的。我们的研究结果为定量理解凝聚层动力学和流变学提供了一个微观框架。但是这里的局部动态减速是由带相反电荷的单体之间的强库仑吸引力（离子配对）引起的。我们的研究结果为定量理解凝聚层动力学和流变学提供了一个微观框架。