Micromotor Swarms Controlled By Multiple Light Fields

Active matter system which continuously consumes energy to produce displacement or motion in a thermodynamically non-equilibrium state,has exhibited promising prospects in a number of fields because of its unique non-equilibrium behavior.Micro/nanomotor,a micro-nano device converting energy in other forms into mechanical energy,has become a popular choice for artificial active matter systems because of its programmable structure,motion behavior and interaction.Because of the necessary unbalanced driving force on the micro/nanomotor,it requires the intrinsic asymmetry caused by the intrinsic structure or composition of the motor,or the induced asymmetry of the motor induced by the external field.The previous works of micro/nanomotor swarms are mostly based on the intrinsically asymmetric motors,therefore limited by the invariance of the intrinsic asymmetry,only simple collective behaviors emerge,while few researches involve the swarm consisting of motors with induced asymmetry.Presumably the induced asymmetry can exhibit great advantage in active matter systems with various behavior modes because of its variable or adjustable characteristics.Two swarms consisting of different micromotors with photo-induced asymmetry have been researched,one of which consists of AgBr micromotors while the other consists of Anatase-TiO₂ microsphere motors modified by Pt nanoparticles?“TiO₂@Pt”for short?.The irreversible photo-induced asymmetry of AgBr micromotor is solidified on the micron motor,which is only variable but not adjustable.The AgBr micromotor can be driven by UV or visible light in water.The micromotor swarm can prolong the motion life of the individual,and realize simple and reversible self-assembly by light control.The reversible photo-induced asymmetry of TiO₂@Pt micromotor is in situ and instantaneous,therefore variable and adjustable.The response of the TiO₂@Pt micromotor swarm to light stimulation is anisotropic,and the individual interaction can be reversed from attraction to repulsion by the change of light direction.The TiO₂@Pt micromotor swarm controlled by multiple UV light field composed of UV light with different incident directions can realize the directional migration and controllable melting of colloidal crystal,reversible phase transition,in situ"machining"of assembly shape,etc.,which exhibits great application potential in crystal phase transition study,micro-machining,micro-device and micro-pattern.On the other hand,a new finite element analysis method is proposed for electrolyte diffusiophoresis motors to study multiple systems including multiple motors,fluids,and substrates,in which the double layers are incorporated into the analysis through Gouy-Chapman-Stern?GCS?model.The double layers and the effect of electroosmotic flow are well incorporated into the calculation,as well as the diffusiophoresis phenomena of multiple objects,and the driving mechanism can be judged by calculating the contribution of each force.Therefore the method has references for the finite element analysis of the near-wall motion of motors and motor swarms.In summary the active matter system consisting of micro/nanomotors with reversible induced asymmetry exhibits great advantage in active matter systems with multiple behavior modes,which has references for the study of active matter systems.