Swarming and collective migration of micromotors under near infrared light

Abstract It is nowadays of a great challenge to create and navigate artificial micro/nanomotor swarms by external stimuli, which, however, may develop reconfigurable robots or programmable matter for cooperative grasping, collective cargo transportation, microfactories, etc. This work demonstrates a general strategy to create and navigate micromotor swarms by near infrared (NIR) light-induced convection flows. Upon NIR irradiation at a selected area, convection flows are produced inside the liquid medium because of the temperature gradient established across the NIR-exposed area and unexposed area. Under the drag forces from the convection flows, the dispersed micromotor swarm phototactically to the convection center. After swarming, interactions between neighboring micromotors, such as electrostatic attractions or diffusiophoretic repulsions, are activated or enhanced because of the sharply-decreased interparticle distances. By simply moving NIR spot, the micromotors in the swarm can further collectively migrate to designated locations with the moving convection cell. By adjusting the NIR power density, the swarming and collective migration of micromotors, including parameters such as response time, swarming range and speed, can be swiftly and reversibly controlled. More interestingly, the strategy developed in this work can be applied to various micromotors (TiO2/Pt, SiO2/Pt, TiO2, ZnO micromotors) as well as microorganism such as E. coli regardless of their geometrical and material features. This facile and universal strategy may have far-reaching implications for the applications of micro/nanomotor swarms in cooperative cargo transport, micro/nanoengineering and chemical sensing because of its potential to create and manipulate local mixing systems, such as motor/motor, motor/organism, motor/cargo and motor/sensor assemblies and swarms.