Study On Deformation And Motion Of Ferrofluid Jointly Controlled By Magnetic Field And Optical Field

Optical control of droplet movement and optical control of liquid flow have been widely explored in microfluidic systems.With its rapid development,optical control microfluidic system as a very promising control method has been widely applied in physical,chemical,biological,medical and other fields.Although fluid mixing and pumping has been realized,most of these fluid mixing and pumping is concentrated on the micro domain,and many complex macro-operations have not been realized.In this work,the optical field and the magnetic field are integrated organically and jointly to regulate the motion of the ferrofluid,which realizes the periodic motion manipulation of the ferrofluid droplet,the self-circulation driving of the long-range ferrofluid,and the large-scale rotation of the ferrofluid.And by using the circulation of long-range ferrofluid drive,this work has developed two application instances: a ferrofluid self-circulating cool system and a droplet transport system.(1)This study demonstrates the periodic motion manipulation of ferrofluid droplet.When the laser is irradiated to the droplet and the power is low,the droplet gradually shrinks and slides due to the attenuation of magnetic field force.When the laser exceeds a certain threshold,the droplet will appear alternatively.(2)For the self-circulating drive of the long-range ferrofluid,the ferrofluid flows out from the laser irradiation position and recirculates back from the cool position due to the surface tension gradient and thermal demagnetization under the coupling of the Marangoni effect and thermalmagnetic convection.In addition,the magnetic field can enhance the Marangoni convection.The experiment confirmed that the high-speed and long-range Marangoni convection occurs under the magnetic field,and the enhancement of the magnetic field is further supported by the computational fluid dynamics simulation.(3)The ferrofluid is distributed in a dome shape by using a circular magnetic field,and the ferrofluid is placed in a vertical position.The ferrofluid is rotated as a whole,and the rotational direction of the ferrofluid is controllable and the rotational speed is adjustable.As two examples of long-range ferrofluid self-circulation actuation applications.Firstly,a self-driven ductless liquid conveyor belt is demonstrated,which can effectively transfer heat from the source to the end without external power supplies,thereby achieving the purpose of heat dissipation;secondly,this self-driven liquid conveyor belt also can be used to transport droplets.