The development of functional micro- and nanoscale robotics calls for new strategies to design locomotion that facilitates navigation through crowded environments. However, this task has proved challenging due to the significant gravitational and thermal forces that are operational at reduced scales, which tend to confine the motion of self-propelled particles to two dimensions. Now, Lee and colleagues show how to realize and program helical motion using patchy microspheres powered by an electric field in solution.
Polystyrene microspheres are coated with triangular metal patches characterized by a single plane of mirror symmetry. On application of an a.c. field, an asymmetric fluidic flow is generated around each particle due to the induced-charge electrophoresis effect, driving the particle to perform steady helical motions. The speed and radius of the trajectories are programmable by controlling the geometry of the metal patches and the strength of the a.c. field. The particles following helical trajectories are shown to have an enhanced transport efficiency through a crosslinked cellulose membrane with porous structure, compared with those moving along linear trajectories. This approach can help design future micro- and nanorobots capable of moving in three-dimensional complex environments in an efficient and controllable way.
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Advanced Intelligent Systems (2020)