Dou Yong, Tzelios Peter M, Livitz Dimitri, Bishop Kyle J M
Department of Chemical Engineering, Columbia University, New York, NY, USA.
Soft Matter. 2021 Feb 19;17(6):1538-1547. doi: 10.1039/d0sm01443e.
We describe how spatially uniform, time-periodic magnetic fields can be designed to power and direct the migration of ferromagnetic spheres up (or down) local gradients in the topography of a solid substrate. Our results are based on a dynamical model that considers the time-varying magnetic torques on the particle and its motion through the fluid at low Reynolds number. We use both analytical theory and numerical simulation to design magnetic fields that maximize the migration velocity up (or down) an inclined plane. We show how "topotaxis" of spherical particles relies on differences in the hydrodynamic resistance to rotation about axes parallel and perpendicular to the plane. Importantly, the designed fields can drive multiple independent particles to move simultaneously in different directions as determined by gradients in their respective environments. Experiments on ferromagnetic spheres provide evidence for topotactic motions up inclined substrates. The ability to program the autonomous navigation of driven particles within anisotropic environments is relevant to the design of colloidal robots.
我们描述了如何设计空间均匀、时间周期的磁场，以驱动铁磁球体沿固体基底形貌中的局部梯度向上（或向下）迁移并引导其方向。我们的结果基于一个动力学模型，该模型考虑了粒子上随时间变化的磁转矩及其在低雷诺数下通过流体的运动。我们使用解析理论和数值模拟来设计磁场，以使沿倾斜平面向上（或向下）的迁移速度最大化。我们展示了球形粒子的“拓扑趋性”如何依赖于绕平行和垂直于平面的轴旋转时流体动力阻力的差异。重要的是，所设计的磁场可以驱动多个独立粒子在各自环境中的梯度所决定的不同方向上同时移动。对铁磁球体的实验为沿倾斜基底的拓扑趋性运动提供了证据。在各向异性环境中对驱动粒子的自主导航进行编程的能力与胶体机器人的设计相关。
