非平衡态磁性微转子高有序结构调控机制研究

Mechanisms of highly ordered structures in nonequilibrium magnetic microrotor systems

  • 摘要: 针对气–液界面磁性颗粒体系中高有序结构稳定性不足及形成过程可重复性受限机制不清晰的问题,在二维均匀磁场条件下,本研究对旋转磁场与振荡磁场驱动下磁性颗粒集群的结构演化进行了系统对比研究。以直径约300 μm的磁性颗粒为对象,通过调节驱动频率与颗粒面密度(Ф),结合高速显微成像与六方序参量表征方法,对两种驱动方式下的界面流场特征及有序结构形成机制进行了对比分析。结果表明,旋转磁场驱动下六方有序结构仅在有限参数区间内形成,且稳定性随面密度增加明显降低;振荡磁场通过周期性力矩反转抑制整体迁移,在更宽参数范围内获得稳定的六方排列,并且当Ф < 0.08且4.5 < ReΩ < 8.2时,时六方序参量提高约16%。当旋转雷诺数(ReΩ)为5.65时,局域扰动实验显示,已形成结构可在约2~3 s内自发恢复;并且在循环驱动条件下,结构形成时间缩短约75%,表现出稳定的结构记忆特性。本工作为界面颗粒的有序组装提供了新的技术手段和理论基础。

     

    Abstract: To address the limited stability of highly ordered structures and the unclear mechanisms underlying the reproducibility of structure formation in magnetic micro-rotor systems at air–liquid interfaces, a systematic comparative study was conducted on the structural evolution of magnetic micro-rotor clusters driven by rotating and oscillating magnetic fields under two-dimensional uniform magnetic fields. Nickel-coated (Ni) micro-rotors with a diameter of approximately 300 μm were employed. By varying the driving frequency and particle area density, and combining high-speed microscopic imaging with hexagonal order parameter analysis, the interfacial flow organization and the mechanisms of ordered structure formation under the two driving modes were quantitatively compared. The results show that under a rotating magnetic field, hexagonally ordered structures emerge only within a limited parameter window, and their stability decreases markedly with increasing area density. In contrast, the oscillating magnetic field suppresses global cluster migration through periodic torque reversal, enabling the formation of stable hexagonal arrangements over a much broader parameter range, with an approximately 16% increase in the hexagonal order parameter. Local perturbation experiments reveal that the formed structures can spontaneously recover within approximately 2–3 s. Under cyclic driving conditions, the structure formation time is reduced by about 75%, indicating robust structural memory effects. This work provides new experimental strategies and physical insights for the ordered assembly of interfacial particle systems.

     

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