Research On Preparation Of Ag/Fe₃O₄ Magnetic Fluid And Tunability Of Its Refractive Index

As a kind of soft condensed matter of the particle composite system,the magnetic property of magnetic fluid is mainly provided by magnetic particles which will be arranged in chain or column structures along the direction of an external magnetic field.This can produce some optical phenomena,such as the Faraday effect,the dichroism,the magneto-induced birefringence,the polarization and so on.Among these optical properties,the refractive index tunability of magnetic fluid is the basis of many optical applications,which has high academic value and research significance.From the perspective of good adjustability and low synthetic cost,this paper proposes a magnetic fluid doped with precious metal particles.Water-based Fe₃O₄magnetic fluid and Ag/Fe₃O₄ magnetic fluid are prepared by an improved co-precipitation method combined with the redox reaction of Ag.The refractive index tunability of the two magnetic fluids with different concentrations and different magnetic fields are also investigated.In the first stage of this research,water-based Fe₃O₄ magnetic fluid is prepared by co-precipitation method.Group experiments are performed by controlling the reactant concentration ratio,the reaction temperature,the reaction p H and the stirring speed and the morphology of nanoparticles is observed.The experimental results show that the stirring speed has little effect on the morphology of Fe₃O₄ particles while the concentration ratio of the reactants,the reaction temperature and the reaction p H value can affect the morphology of magnetic nanoparticles to some extent.The optimized preparation conditions of these experimental variables are:the reactant concentration ratio 1:1.6,the reaction temperature 60?,the reaction p H 9 and the stirring speed 300rad/min.In this chapter,the effect of sodium dodecyl sulfate,oleic acid and polyethylene glycol used as surfactants is focused on the morphology of nanoparticles and the properties of magnetic fluid.Experimental results indicate that the dispersion of nanoparticles prepared by polyethylene glycol as the surfactant is better than the other two surfactants.Besides,this magnetic fluid has lower viscosity and reaches a stable state in a short time at a certain shear rate.Next,based on the optimized preparation process of Fe₃O₄ magnetic fluid,Ag/Fe₃O₄magnetic fluid is prepared with the redox reaction of silver.Meanwhile,the magnetic property of Ag/Fe₃O₄ nanoparticles is also studied by controlling the concentration of silver nitrate solution and using different reducing agents.VSM is carried out to characterize the samples of these group experiments.Results show that the nanoparticles prepared by 0.15 mol/L silver nitrate solution and formaldehyde solution as the reducing agent retain lower saturation magnetization,which demonstrates that more Ag particles have been reduced.Various characterization methods are used to characterize the Ag/Fe₃O₄ magnetic fluid prepared by the optimized process.Results show that some Fe₃O₄ nanoparticles are attached to the surface of Ag particles while others are free in the carrier liquid.The saturation magnetization of Ag/Fe₃O₄ nanoparticles is 57.85 emu/g,reducing by about 10 emu/g compared with bare Fe₃O₄ nanoparticles.Finally,the experimental device is designed to explore the refractive index tunability of Ag/Fe₃O₄ magnetic fluid.In this research,the optical fiber sensing device based on the long period grating is used to obtain the refractive index of magnetic fluid through the change of the output spectral loss peak.The experimental results indicate that refractive indexes of both water-based Fe₃O₄ magnetic fluid and Ag/Fe₃O₄ magnetic fluid increase with the increasing concentration.What's more,in the same concentration,the refractive index of Ag/Fe₃O₄ magnetic fluid is lower than that of Fe₃O₄ magnetic fluid.This can be explained by the reason that the Ag particles in the solution provide good nonlinear optical responses,which can affect the refractive ability of incident light in the solution,leading to the lower refractive index of Ag/Fe₃O₄ magnetic fluid.In addition,with the increasing strength of the external magnetic field,the refractive indexes of these two magnetic fluids increase.This can be explained by the action of magnetic fluid in the external magnetic field.The nanoparticles in the solution are oriented along the direction of external magnetic field to form chain/column structures,which affects the propagation speed and the refractive ability of the incident light,resulting in an increase in the refractive index of the solution.