Preparation Of Magnetic Micro/nano-particles And Its Application In Microfluidic Manipulation

Micro/nano-particles(MNPs)are widely used in many fields,such as biomedicine,materials,water treatment,flow field display,etc.Due to the small size of MNPs,the precise control of MNPs has become the current research difficulty in the field of MNPs.As a kind of controllable MNPs,magnetic MNPs have unique advantages.For example,in the case of non-contact with particles,the magnetic field can guide the movement of particles,which has the characteristics of simple generation method and convenient control,It has important applications in medical treatment and environmental pollutant treatment.Therefore,many researchers pay attention to the research of magnetic MNPs.In this paper,firstly,the manipulation of MNPs and the research background of magnetic MNPs were introduced.Uniform Fe₃O₄ magnetic nanoparticles and non-uniform Pt-Ni-Si O₂ magnetic microparticles were prepared by electron plating method and solvothermal method respectively.Based on the advantages of magnetic field controlling MNPs,a magnetic field controlling platform was designed,which was composed of signal generator,power amplifier,Helmholtz coil and other devices.On this basis,the following two aspects of research were carried out.(1)The behavior of magnetic particles in cluster magnetic field was studied by using homogeneous magnetic particles.After applying an oscillating uniform magnetic field in the Z-axis direction,the magnetic particles formed vertical chain.Through the analysis and study of the formation mechanism of magnetic chains,the chain forming model of magnetic micro-nano particles was given,and the effects of frequency,voltage,particle concentration and other factors on the magnetic chain formation were studied experimentally.The results showed that when other conditions are fixed,with the increase of frequency,it is more difficult to form magnetic chains,because compared with the relaxation time,the direction of magnetic field changes too fast,which is not conducive to the mutual attraction of magnetic particles;meanwhile,increasing the voltage in a certain range,that is,increasing the magnetic field intensity,makes the chain formation easier.the phase diagram of frequency voltage was given and the best magnetic chain formation area was divided in this paper.Meanwhile,with the increase of particle concentration,the distance between particles became closer and the speed of magnetic chain formation became faster.In order to solve the problems existing in the flow field display of microscale bubble collapse,such as difficult selection of tracer particles and limited frame rate,a new flow field display method was explored in this paper.The magnetic chain was used to replace tracer particles,and the change of adjacent vertical magnetic chain was used to reflect the change of flow field,which overcame some difficulties in the original flow field display method of bubble collapse.(2)The non-uniform Pt-Ni-Si O₂ magnetic particles prepared by electron plating method on the one hand,can drive the movement of particles through bubbles.On the other hand,the advantage is that the magnetic field controls the direction of movement.The directional movement path experiment was completed in H₂O₂ solution,and the precise control of MNPs movement at microscale was realized.The results showed that Pt-Ni-Si O₂ magnetic particles can generate bubbles through chemical reaction in H₂O₂solution,and the bubble growth and collapse process provided the driving force for the particles to move forward.At this time,the driving direction was random,but the magnetic particles can move along the directional path through the change of magnetic field.The application of magnetic particles controlled by magnetic field in particle loading was preliminarily explored.In summary,this paper designed a precise magnetic field control platform and prepares two different types of magnetic particles.The magnetic chain forming mechanism of uniform magnetic particles in magnetic field was studied,and the magnetic chain forming model is given.The influence of different factors on the magnetic chain forming was studied through experiments.A new method of flow field display was explored,and the flow field of bubble collapse was displayed by magnetic chain.In addition,the non-uniform magnetic particles were precisely controlled by the way of bubble driven magnetic navigation to realize the directional navigation motion of magnetic MNPs at the microscale,and the application of microscale manipulation of loading magnetic particles was preliminarily studied.