College of Chemistry, Sichuan University, Chengdu 610064, China.
Phys Chem Chem Phys. 2022 Mar 23;24(12):7415-7429. doi: 10.1039/d2cp00323f.
Macromolecular crowding plays a crucial role in determining the dynamics in a living cell. We adopt Langevin dynamics simulations to investigate the anomalous diffusion dynamics of passive and active particles in a solution of polymer chains with tunable stiffness. The solution's anisotropic feature is modulated by changing both the polymer stiffness and volume fraction, where isotropic-to-nematic phase transition is involved. Our results demonstrate the significant impact of polymer flexibility on the dynamics of both passive and active probes. The distinct diffusion mechanism for an active particle is clarified by the interplay between polymer stiffness, crowdedness and activity. Polymer stiffness leads to a global inhibition effect on passive particle diffusion. The diffusion coefficient exhibits an intriguing non-monotonic variation at increasing polymer stiffness, which is due to the fact that the alignment of polymer chains is beneficial for diffusion along the nematic direction but unfavorable for that in the direction perpendicular to it. In sharp contrast, polymer stiffness plays a dominant role in facilitating active particle diffusion. Self-propulsion of the particle can utilize stiffness-induced elastic interactions more efficiently, which promotes its mobility in both directions. Meanwhile, an active particle might have a stronger ability to take advantage of the polymer alignment, contributing substantially enhanced diffusivity. In addition, the diffusion coefficient of an active particle is subject to a tendency of degeneration against varying volume fraction. This counter-intuitive behavior is due to the contrasting factors that increasing crowdedness induces a lower particle speed but a longer persistent motion time.
大分子拥挤在决定活细胞中的动力学方面起着至关重要的作用。我们采用朗之万动力学模拟来研究在聚合物链溶液中被动和主动粒子的异常扩散动力学，该溶液的各向异性特征可以通过改变聚合物的刚度和体积分数来调节，其中涉及各向同性到向列相的转变。我们的结果表明，聚合物的柔韧性对被动和主动探针的动力学有重大影响。通过聚合物刚度、拥挤度和活性之间的相互作用，阐明了活性粒子的独特扩散机制。聚合物刚度对被动粒子扩散具有全局抑制作用。随着聚合物刚度的增加，扩散系数表现出有趣的非单调变化，这是因为聚合物链的取向有利于沿向列方向扩散，但不利于垂直于该方向的扩散。相比之下，聚合物刚度在促进主动粒子扩散方面起着主导作用。粒子的自推进可以更有效地利用刚度诱导的弹性相互作用，从而提高其在两个方向上的迁移率。同时，主动粒子可能具有更强的能力利用聚合物的取向，从而显著提高扩散率。此外，活性粒子的扩散系数随着体积分数的变化表现出退化的趋势。这种违反直觉的行为是由于增加拥挤度会导致粒子速度降低但持久运动时间延长的相反因素所致。
