带活性末端的化学-机械胶体链的集体动力学

中文摘要 AI 辅助

我们报道了一项关于二维悬浮液中涌现动力学的研究，该悬浮液中的半柔性链末端具有化学活性，可产生泳动场。通过改变链长（每条链的单体数$N_{pc}$）、面积分数$ϕ$以及泳动耦合的符号$J_0$，我们绘制出了存在泳动相互作用时丰富的非平衡相图。对于链之间的排斥性泳动相互作用（$J_0 > 0$），我们发现短链（$N_{pc} = 2$）会形成瞬态混沌流态，该状态在长时间后会转变为全局极性 flock，具有超扩散均方位移和长程速度关联。令人惊讶的是，我们发现该状态的密度涨落受到抑制，表明超均匀性的涌现。在中等链长（$N_{pc} \text{约} 4$-$8$）下，排斥性化学场驱动混沌介观流——这是一种无需流体动力学相互作用或空间位阻排列相互作用的活性湍流干途径。对于吸引性泳动相互作用（$J_0 < 0$），链会自组织成类似刺猬的胶束聚集体，头部形成核心，柔性尾部向外辐射，其结构与两亲分子胶束化类似，但完全由非平衡自驱动驱动。一种关于末端发射活性棒的粗粒化理论预测了二聚体 flock 的形成，不过高估了更长链的极性有序程度。我们的研究结果表明，泳动末端活性是一种最小化、可通过实验实现的机制，可产生此前被归因于流体动力学相互作用或空间位阻排列的一系列集体态。

英文摘要

We report a study of the emergent dynamics arising in two-dimensional suspensions of semi-flexible chains whose tip is chemically active, generating a phoretic field. By varying the chain length (number of monomers per chain $N_{pc}$), the area fraction $ϕ$, and the sign of the phoretic coupling $J_0$, we map out a rich non-equilibrium phase diagram in the presence of phoretic interactions. For repulsive phoretic interactions ($J_0 > 0$) between the chains, we find that short chains ($N_{pc} = 2$) develop a transient chaotic flow state that crosses over at long times to a global polar flock with super-diffusive mean-squared displacement and long-ranged velocity correlations. Surprisingly, we find this state to have suppressed density fluctuations, indicating the emergence of hyperuniformity. At intermediate chain lengths ($N_{pc} \sim 4$-$8$), the repulsive chemical field drives chaotic mesoscale flows -- a dry route to active turbulence -- without the need for hydrodynamic interactions or steric alignment interactions. For attractive phoretic interactions ($J_0 < 0$), chains self-organise into hedgehog-like micellar aggregates with heads forming the core and flexible tails radiating outward, in structural analogy with amphiphile micellisation but driven entirely by non-equilibrium self-propulsion. A coarse-grained theory of a tip-emitting active rod predicts the onset of the flocking of dimers, though overestimates the presence of polar order for longer chains. Our results establish phoretic tip activity as a minimal, experimentally realisable mechanism for a spectrum of collective states hitherto attributed to hydrodynamic interactions or steric alignment.

发表机构

• Indian Institute of Technology Madras（印度马德拉斯理工学院）

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