Panda Suvendu Kumar, Debata Srikanta, Kherani Nomaan Alam, Singh Dhruv Pratap
Department of Physics, IIT Bhilai, Kutelabhata, Durg, Chhattisgarh, 491002, India.
Soft Matter. 2024 May 15;20(19):3971-3979. doi: 10.1039/d4sm00206g.
The ability to move and self-organize in response to external stimuli is a fascinating feature of living active matter. Here, the metallo-dielectric rod-shaped microswimmers are shown to have a similar behavior in the presence of an AC electric field. The silica-copper Janus microrods were fabricated using the physical vapor deposition-based glancing angle deposition technique (GLAD). When the aqueous solution of the microrods was under the influence of an external AC electric field, they were found to exhibit different phases such as clustering, swimming, and vertical standing in response to variation of the applied frequency. The swimming behavior (5-90 kHz) of the rods is attributed to the induced-charge electrophoresis (ICEP) phenomenon, whereas the dynamic clustering (<5 kHz) could be explained in terms of the electrohydrodynamic (EHD) interaction. Interestingly, the rods flip to attain the vertically standing position when responding to the applied electric field above 90 kHz. The reorientation and switching of the major axis of the rod along the field direction is attributed to the electro-orientation phenomenon. This is basically due to the dominance of the electric torque above the upper limit of the characteristic frequency, where the strength of slip flows around the microrods is predicted to be poor. The present study not only offers insight into the fundamental aspects of the dynamics and the phase behavior of rod-shaped microswimmers, but also opens an avenue to design reconfigurable active matter systems with features inspired by biological systems.
响应外部刺激而移动和自我组织的能力是活性生物物质的一个迷人特性。在此，金属 - 电介质棒状微游动体在交流电场存在下表现出类似行为。采用基于物理气相沉积的掠角沉积技术（GLAD）制备了二氧化硅 - 铜双面微棒。当微棒的水溶液处于外部交流电场影响下时，发现它们会根据所施加频率的变化呈现出不同的相，如聚集、游动和垂直站立。棒的游动行为（5 - 90千赫）归因于感应电荷电泳（ICEP）现象，而动态聚集（<5千赫）可以用电流体动力学（EHD）相互作用来解释。有趣的是，当响应高于90千赫的外加电场时，棒会翻转至垂直站立位置。棒的长轴沿场方向的重新定向和切换归因于电取向现象。这主要是由于在特征频率上限以上电转矩占主导，此时预计微棒周围的滑移流强度较差。本研究不仅深入了解了棒状微游动体动力学和相行为的基本方面，还为设计受生物系统启发具有特定功能的可重构活性物质系统开辟了一条途径。
