A Molecular Explanation for Anomalous Diffusion in Supramolecular Polymer Networks
A Molecular Explanation for Anomalous Diffusion in Supramolecular Polymer Networks
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DOI：
10.1021/acs.macromol.7b02465
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发表时间：
2018-04-10
期刊：
影响因子：
5.5
通讯作者：
Olsen, Bradley D.
中科院分区：
文献类型：
--
作者：
Ramirez, Jorge;Dursch, Thomas J.;Olsen, Bradley D.
最近的实验表明，具有不同结构（线性和支化）和不同性质的关联相互作用（关联蛋白质结构域和金属配体键）的各种缔合聚合物表现出无法解释的超扩散行为。在这里，布朗动力学模拟未纠缠的粗粒关联星星形聚合物被用来建立一个分子链动力学的图片，解释这种行为。聚合物被概念化为具有有效劳斯扩散系数的颗粒，其通过在代表聚合物的臂的无质量弹簧的末端处的贴纸的附件与平均场背景相互作用。模拟揭示了三种机制的分子扩散的长度尺度远大于回转半径：受阻扩散，步行扩散，和分子跳跃，所有这些都强烈依赖于聚合物浓度，臂长，和缔合/解离速率常数。分子模型建立了超扩散缩放的结果主要来自分子跳跃，这只发生在附着的动力学慢于悬挂链的弛豫时间。标度关系可用于确定预期该行为的速率常数范围。网络中回路的形成通过减少为了发生跳跃步骤而必须分离的臂的总数来促进这种超扩散缩放。
Recent experiments have revealed that a variety of associative polymers with different architecture (linear and branched) and different nature of the associating interaction (associative protein domains and metal-ligand bonds) exhibit unexplained superdiffusive behavior. Here, Brownian dynamics simulations of unentangled coarse-grained associating star shaped polymers are used to establish a molecular picture of chain dynamics that explains this behavior. Polymers are conceptualized as particles with effective Rouse diffusivities that interact with a mean field background through attachments by stickers at the end of massless springs that represent the arms of the polymer. The simulations reveal three mechanisms of molecular diffusion at length scales much larger than the radius of gyration: hindered diffusion, walking diffusion, and molecular hopping, all of which depend strongly on polymer concentration, arm length, and the association/dissociation rate constants. The molecular model establishes that superdiffusive scaling results primarily from molecular hopping, which only occurs when the kinetics of attachment are slower than the relaxation time of dangling strands. Scaling relationships can be used to identify the range of rate constants over which this behavior is expected. The formation of loops in the networks promotes this superdiffusive scaling by reducing the total number of arms that must detach in order for a hopping step to occur.