Unfolding of a diblock chain and its anomalous diffusion induced by active particles

YQ Xia and ZL Shen and WD Tian and K Chen, JOURNAL OF CHEMICAL PHYSICS, 150, 154903 (2019).

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. Published under license by AIP Publishing.

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