The development of multifunctional and robust swimming microrobots working at the free air–liquid interface has encountered challenge as new manipulation strategies are needed to overcome the complicated interfacial restrictions. Here, flexible but reliable mechanisms are shown that achieve a remote‐control bubble microrobot with multiple working modes and high maneuverability by the assistance of a soft air–liquid interface. This bubble microrobot is developed from a hollow Janus microsphere (JM) regulated by a magnetic field, which can implement switchable working modes like pusher, gripper, anchor, and sweeper. The collapse of the microbubble and the accompanying directional jet flow play a key role for functioning in these working modes, which is analogous to a “bubble tentacle.” Using a simple gamepad, the orientation and the navigation of the bubble microrobot can be easily manipulated. In particular, a speed modulation method is found for the bubble microrobot, which uses vertical magnetic field to control the orientation of the JM and the direction of the bubble‐induced jet flow without changing the fuel concentration. The findings demonstrate a substantial advance of the bubble microrobot specifically working at the air–liquid interface and depict some nonintuitive mechanisms that can help develop more complicated microswimmers.
Purpose The purpose of this study is to use a weak light source with spatial distribution to realize light-driven fluid by adding high-absorbing nanoparticles to the droplets, thereby replacing a highly focused strong linear light source acting on pure droplets. Design/methodology/approach First, Fe3O4 nanoparticles with high light response characteristics were added to the droplets to prepare nanofluid droplets, and through the Gaussian light-driven flow experiment, the Marangoni effect inside a nanofluid droplet was studied, which can produce the surface tension gradient on the air/liquid interface and induce the vortex motion inside a droplet. Then, the numerical simulation method of multiphysics field coupling was used to study the effects of droplet height and Gaussian light distribution on the flow characteristics inside a droplet. Findings Nanoparticles can significantly enhance the light absorption, so that the Gaussian light is enough to drive the flow, and the formation of vortex can be regulated by light distribution. The multiphysics field coupling model can accurately describe this problem. Originality/value This study is helpful to understand the flow behavior and heat transfer phenomenon in optical microfluidic systems, and provides a feasible way to construct the rapid flow inside a tiny droplet by light.
The development of multifunctional and robust swimming microrobots working at the free air-liquid interface has encountered challenge as new manipulation strategy are needed to overcome the complicated interfacial restrictions. Here, we show flexible but reliable mechanisms to achieve a remote-control bubble microrobot with multiple working modes and high maneuverability by the assistance of a soft air-liquid interface. This bubble microrobot is developed from a hollow Janus microsphere regulated by a magnetic field, which can implement switchable working modes like pusher, gripper, anchor and sweeper. The cavitation of the microbubble and the accompanying directional jet flow play a key role for functioning in these working modes, which is analogues to "bubble tentacle". In particular, we find a novel speed modulation method for the bubble microrobot that does not need to change the fuel concentration. Our findings demonstrate a substantial advance of the bubble microrobot specifically working at the air-liquid interface. And the results depict the nonintuitive mechanisms, such as bubble dynamics confined by a free surface, hydrodynamic jetting and surface capillary wave induced by bubble collapse, and bubble particle interaction, which offer helpful insights for developing swimming microrobots working in complicated environments.
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