Unusual crowding-induced chain looping kinetics in hard-sphere fluids: a contrastive study with polymer solutions.
Unusual crowding-induced chain looping kinetics in hard-sphere fluids: a contrastive study with polymer solutions.
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DOI：
10.1039/c9sm00400a
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发表时间：
2019-06
期刊：
影响因子：
3.4
通讯作者：
Yukun Bian;Ran Yan;Peng Li;N. Zhao
中科院分区：
文献类型：
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作者：
Yukun Bian;Ran Yan;Peng Li;N. Zhao
基于广义Smoluchowski扩散反应方程，建立了一个研究硬球（HS）流体中链成环动力学的理论框架。与聚合物溶液进行了对比研究。适当地考虑了拥挤相关的有效粘度和坍塌效应，它们在HS和聚合物流体中遵循不同的标度关系。我们研究的依赖循环时间的浓度和规模的拥挤，展示了不寻常的和明显的差异，在两个拥挤的媒体。首先，在大聚合物溶液中，成环速率随聚合物浓度单调增长。另一方面，在大HS的解决方案中，可以观察到一个笼子制度，其中的循环时间往往在没有拥挤的值。其次，中等尺寸的聚合物通常由于粘度增加而阻碍链成环。然而，在HS流体中，循环时间随着HS尺寸的增加而呈现出相当复杂的变化。我们展示了一种可能的机制，其中在探测链中具有相对较强压实的小拥挤的情况下，可以促进成环动力学。随着拥挤的大小增加，崩溃的效果减少，成环是由粘度引起的抑制为主。同时，我们的理论合理化的另一种可能性的机制观察到最近的模拟工作。我们的结论是，在特定的系统中的循环动力学实际上应该由两个拥挤因子之间的关键竞争。通过给出有效粘度和坍塌的合理测量，我们的理论框架可以提供一个统一的策略，以系统的方式分析拥挤对成环率的影响。
A theoretical framework is developed to investigate the looping kinetics of a chain in hard-sphere (HS) fluids, based on a generalized Smoluchowski diffusion-reaction equation. A contrastive study with polymer solutions is performed. The crowding-associated effective viscosity and collapse effects are properly taken into account, which obey different scaling relations in HS and polymer fluids. We examine the dependence of the looping time on both concentration and size of crowders, demonstrating unusual and distinct discrepancies in the two crowded media. Firstly, in the solution of large polymers, the looping rate grows monotonically with polymer concentration. On the other hand, in the solution of large HSs, a caging regime can be observed, where the looping time tends to the value in the absence of crowders. Secondly, polymers in moderate size generally impede chain looping due to the enhanced viscosity. However, in HS fluids, the looping time exhibits a rather complicated variation with increasing HS size. We show a possible mechanism where in the case of small crowders with a relatively strong compaction in the probed chain, the looping kinetics can be facilitated. As the crowder size increases, the collapse effect is reduced and looping is dominated by viscosity-induced inhibition. Simultaneously, our theory rationalizes another possibility of the mechanism observed by recent simulation work. We conclude that the looping kinetics in specific systems actually should be governed by the critical competition between the two crowding factors. By giving reasonable measurements of effective viscosity and collapse, our theoretical framework can provide a unified strategy to analyze crowding effects on the looping rate in a systematic manner.