Reserch On The Leader-follower Hierarchical Micro/Nanomotor Swarms And The Light-controlled Behaviors

Micro/nanomotors are micro/nanodevices that can convert energy from surrounding chemical fuels or external fields into their own mechanical energy.There is a growing interest in developing micro/nanomotors in low Reynolds number fuild due to their promising potential application in biosensing,biomedicine,manipulation and environment protection.In the past decade,research focus has been changed from the propulsion mechanisms,motion control strategies,applications of single micro/nanomotor to the construction,control and applications of micro/nanoswarms.Very recently,considering research works have been devoted to homogeneous micro/nanoswarms composed of similar individual.However,the reported microswarms only have a single-level group structure because the individuals play a similar role in the group,which restricts their application in an ambiguous environment.Hence,the micro/nanomotor systems with complicated structures and multifunctions in a more user-friendly approach deserves to be investigated.Among many construction methods,the approaches used by external electric and light signals have an edge in terms of parameter manipulation,response speed and adaptability.In view of the above situation,we have put forward on a new strategy to construct hierarchical microswarms:First,we chose micromotors with size differences to construct leader?follower hierarchical microswarms propelled by electric-field-induced electrohydrodynamic flows.The symmetric of the surrounding electrohydrodynamic flows was broken due to its asymmetric leader?follower structure and thus propelled the swarms.The speed of leader?follower microswarm can be regulated by adjusting electric voltage E or frequency f.The average speed of the microswarms scaled linearly with E²,and could be increased up to 8.6?m s^-1 when E reach to 17 V.Furthermore,the speed v of the microswarms increases at first and then decrease in a frequency range from 200 Hz to5 k Hz,and has an optimum f of 1 k Hz to the maximize speed v of 6.3?m s^-1.The speed of the leader?follower microswarm also showed a strong dependence on the number N of followers and the optimum number N value of 10.Second,the leader?follower microswarm,like many planktonic algae in nature,show switchable phototactic behaviors in the UV signals.The L-TiO₂/S-TiO₂ leader?follower microswarms showed an intensity-dependent switchable phototaxis.At low light intensity,the L-TiO₂/S-TiO₂ leader?follower microswarms showed negative phototaxis because the speed of the leader is much faster than the follower cluster.And at high light intensity,the L-TiO₂/S-TiO₂ leader?follower microswarms showed positive phototaxis because the speed of the leader is much faster than the follower cluster.With the input of the vertical UV signal in the Z-axis,the L-TiO₂/S-TiO₂ leader?follower microswarms displayed light-controlled go-and-stop motion behaviors.Third,this strategy was expected to possess the adaptability because the velocity of electrohydrodynamic flows are strongly dependent on the sizes,shapes and dielectric properties.It was demonstrated that both L-SiO₂/S-TiO₂ and L-TiO₂/S-SiO₂ leader?follower microswarms displayed phototactic behaviors with the input of sidewise UV signals.This strategy of leader?follower hierarchical microswarms is expected to promote the development of microsystems with high-efficiency,multiresponsiveness,multifunction and intelligence and have significant design spaces in the application of cargo delivery,biomedical delivery,manipulation and pollution protection.