Xia Yi-Qi, Shen Zhuang-Lin, Tian Wen-de, Chen Kang
Center for Soft Condensed Matter Physics and Interdisciplinary Research, School of Physical Science and Technology, Soochow University, Suzhou 215006, China.
J Chem Phys. 2019 Apr 21;150(15):154903. doi: 10.1063/1.5095850.
We study the structural and dynamical behavior of an A-B diblock chain in the bath of active Brownian particles (ABPs) by Brownian dynamics simulations in two dimensions. We are interested in the situation that the effective interaction between the A segments is attractive, while that between the B segments is repulsive. Therefore, in thermal (nonactive) equilibrium, the A block "folds" into a compact globule, while the B block is in the expanded coil state. Interestingly, we find that the A block could "unfold" sequentially like unknitting a sweater, driven by the surrounding ABPs when the propelling strength on them is beyond a certain value. This threshold value decreases and then levels off as the length of the B block increases. We also find a simple power-law relation between the unfolding time of the A block and the self-propelling strength and an exponential relation between the unfolding time and the length of the B block. Finally, we probe the translational and rotational diffusion of the chain and find that both of them show "super-diffusivity" in a large time window, especially when the self-propelling strength is small and the A block is in the folded state. Such super-diffusivity is due to the strong asymmetric distribution of ABPs around the chain. Our work provides new insights into the behavior of a polymer chain in the environment of active objects.
我们通过二维布朗动力学模拟研究了A-B二嵌段链在活性布朗粒子（ABP）浴中的结构和动力学行为。我们感兴趣的情况是，A链段之间的有效相互作用是吸引性的，而B链段之间的相互作用是排斥性的。因此，在热（非活性）平衡状态下，A嵌段“折叠”成紧密的球状体，而B嵌段处于伸展的线圈状态。有趣的是，我们发现当周围ABP的推进强度超过一定值时，A嵌段会像解开毛衣一样依次“展开”。随着B嵌段长度的增加，这个阈值先降低然后趋于平稳。我们还发现A嵌段的展开时间与自推进强度之间存在简单的幂律关系，与B嵌段的长度之间存在指数关系。最后，我们研究了链的平动和转动扩散，发现它们在较大的时间窗口内都表现出“超扩散性”，特别是当自推进强度较小时且A嵌段处于折叠状态时。这种超扩散性是由于ABP在链周围的强烈不对称分布所致。我们的工作为聚合物链在活性物体环境中的行为提供了新的见解。
