Boymelgreen Alicia, Kunti Golak, García-Sánchez Pablo, Yossifon Gilad
Department of Mechanical and Materials Engineering, Florida International University, Miami, Florida, 33174, USA.
Faculty of Mechanical Engineering, Indian Institute of Technology Delhi, New Delhi, 110016, India.
Soft Matter. 2024 May 22;20(20):4143-4151. doi: 10.1039/d3sm01640d.
Theoretical and numerical models of active Janus particles commonly assume that the metallo-dielectric interface is parallel to the driving applied electric field. However, our experimental observations indicate that the equilibrium angle of orientation of electrokinetically driven Janus particles varies as a function of the frequency and voltage of the applied electric field. Here, we quantify the variation of the orientation with respect to the electric field and demonstrate that the equilibrium position represents the interplay between gravitational, electrostatic and electrohydrodynamic torques. The latter two categories are functions of the applied field (frequency, voltage) as well as the height of the particle above the substrate. Maximum departure from the alignment with the electric field occurs at low frequencies characteristic of induced-charge electrophoresis and at low voltages where gravity dominates the electrostatic and electrohydrodynamic torques. The departure of the interface from alignment with the electric field is shown to decrease particle mobility through comparison of freely suspended Janus particles subject only to electrical forcing and magnetized Janus particles in which magnetic torque is used to align the interface with the electric field. Consideration of the role of gravitational torque and particle-wall interactions could account for some discrepancies between theory, numerics and experiment in active matter systems.
活性Janus粒子的理论和数值模型通常假定金属 - 电介质界面与所施加的驱动电场平行。然而，我们的实验观察表明，电动驱动的Janus粒子的平衡取向角会随着所施加电场的频率和电压而变化。在此，我们量化了取向相对于电场的变化，并证明平衡位置代表了重力、静电和电流体动力矩之间的相互作用。后两类是所施加场（频率、电压）以及粒子在基底上方高度的函数。在感应电荷电泳的低频特性以及重力主导静电和电流体动力矩的低电压下，与电场的对齐出现最大偏差。通过比较仅受电驱动力的自由悬浮Janus粒子和使用磁力矩使界面与电场对齐的磁化Janus粒子，表明界面与电场对齐的偏差会降低粒子迁移率。考虑重力矩和粒子 - 壁相互作用的作用可以解释活性物质系统中理论、数值计算和实验之间的一些差异。
