Preparation Of Magnetically Driven Janus Motors And Study Of Their Motion Characteristics

In recent years,strides in micro-and nanofabrication technology have enabled researchers to design and develop micro-and nanoscale motors that are versatile and easy to fabricate.Among them,synthetic micro-and nanomotors powered by oscillating magnetic fields have recently gained much attention because of their capability of remote actuation and navigation.In this dissertation,we focus on a new type of magnetic surface walker that is composed of magnetic Janus particles and can perform directed motion propelled by oscillating magnetic fields.First,fully or half-coated magnetic particles were prepared.In an early experiment,iron oxide?Fe₃O₄?magnetic nano particles were synthesized by a co-precipitation method,and were coated on the surface of polystyrene?PS?microspheres by electrostatic attraction to prepare Fe₃O₄@PS fully coated magnetic particles.However,it was found that the Fe₃O₄@PS particles were not able to attract each other to form dimers that could be powered by an oscillating magnetic field.Therefore,the experiment scheme was adjusted,and metal Ni was deposited on the surface of PS particles.Ni@PS magnetic microspheres were then successfully prepared.However,dimers composed of Ni@PS magnetic microspheres were not able to move forward in an oscillating magnetic field.Finally,half coated Ni@SiO₂ magnetic particles were prepared by electron beam evaporation,and it was able to attract each other to form dimer motor s that were able to perform directed motion in an oscillating magnetic field.Following this success,Ni@SiO₂ particles of different Ni thickness and different particle sizes were fabricated,and the effect of various parameters such as the driving frequency,magnetic field strength,and the different liquid environment on the motor movement were studied.It was found that as the driving frequency increased,motor speed increased.When the frequency exceeded a critical frequency,motor speed started to decline.Second,the motor speed increased with the increase of the driving voltage.But when the driving voltage reached a certain value,the motor was not able to move well.In addition,the speed of the motor decreased as the viscosity increased.When the motor was placed in a NaCl solution of different salt concentration,it was found that as the NaCl concentration increased,the dimer motor gradually stuck to the bottom of the chamber,and the speed of the motor gradually decreased.In order to explore the possible application of the dimer motor,we investigated its ability of being controlled and climbing over obstacles.In this dissertation,driving magnetic fields in different directions was constructed,and letters such as "HIT" were written by the motors' trajectory.By adjusting the driving frequency and the driving voltage,precise control of motor speeds was realized.Our study found that the dimer motors could avoid obstacles that were up to three times as its size and could move easily on rough surfaces.In summary,a simple and well controlled magnetic surface walker was developed.We have elucidated its synthesis process and its motion mechanism,and have advanced its prospect in future applications.