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中国物理学会期刊

椭球昆克活性胶体体系中大尺度集体行为

Large-scale collective behavior in systems of ellipsoidal Quincke rollers

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  • 集体运动的涌现是非平衡活性物质中重要的自组织现象。对于杆状粒子体系,当驱动方向垂直于粒子长轴时,相应的对齐机制和集体行为涌现的动力学尚缺乏相关研究。本研究以沿短轴(垂直于长轴)驱动的椭球昆克(Quincke)体系为实验体系。实验发现在高频周期性电场驱动下,活性椭球粒子可以通过翻转与旋转实现对齐,并形成大尺度稳定的宏观涡旋。结果表明,高频电场在维持定向驱动的同时,不仅减弱了粒子的活性,也同时抑制了椭球粒子的手性进动。低活性椭球粒子能够在平行无自旋态和横向自旋态之间进行转换,使得粒子能够通过翻转调整取向。电场驱动力周期性消失,使得椭球粒子间能够通过未完全弛豫的偶极相互作用调整内部极化电偶的取向,实现局部驱动方向的调整和对齐。同时,电场周期性关闭也有效抑制了椭球粒子持续性手性进动,增强了集体运动的稳定性。本研究揭示了横向驱动活性体系的独特对齐机制,并为探索不同驱动模式下向列相中的缺陷动力学提供了理想的实验模型。

     

    The emergence of collective motion is a key self-organization phenomenon in non-equilibrium active matter. For rod-like particles, when the propulsion direction is perpendicular to the long axis, velocity alignment becomes dynamically difficult, and the underlying mechanisms remain largely unexplored. Here, we study an ellipsoidal Quincke roller system propelled along the short axis (perpendicular to the long axis). We show that, under high-frequency periodic electric fields, the particles can align their velocities through flipping and rotation, and form large-scale, stable macroscopic vortices. The high-frequency driving maintains directional propulsion while reducing particle activity and suppressing chiral precession. In this regime, particles can switch between the parallel spinless state and the spinning transversal state, enabling orientation adjustment via flipping. The periodic switching-off of the electric field allows unrelaxed dipolar interactions to reorient particle dipoles, leading to local alignment of propulsion directions. Meanwhile, the interruption of the field suppresses the accumulation of chiral precession, enhancing the stability of collective motion. Our results reveal a distinct alignment mechanism in transversely driven active systems and provide a model system to explore defect dynamics in nematic phases under non-collinear driving.

     

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