Preparation And Performance Study Of Silicon Oil-based Magnetic Liquid Doped With Carbon Nanotubes

Silicone oil-based magnetic liquid is a kind of magnetic liquid that uses silicone oil as the carrier liquid.It has the advantages of high temperature resistance,low vapor pressure,and small viscosity change with temperature.It can be used in civilian,military and other fields.The preparation of silicone oil-based magnetic liquids with excellent performance breaks through the monopoly of foreign technology.Using oleic acid or silane coupling agent as the surfactant,we prepare the Fe₃O₄@MWNT magnetic particles by in-situ chemical precipitation method,and it is dispersed in silicone oil through ball milling or ultrasound,etc.The Fe₃O₄@MWNT particles were characterized by TEM,XRD,IR,VSM characterization methods.The stability of the magnetic liquid can be judged by detecting the particle concentration in different positions of the magnetic liquid through the L-C oscillating circuit made by laboratory.The application of magnetic fluid is inseparable from its rheological properties.Therefore,it is necessary to systematically study the rheological properties of magnetic fluids.The rheological properties of magnetic fluids were tested by Anton Paar rheometer.Combining experimental results,such as viscosity-temperature curves,magnetic-viscosity curves,flow curves,and shear stress-strain curves,a system understanding of the the complex rheology of silicone oil-based magnetic fluids has been obtained.The research content and main results of this article are as follows:（1）Fe₃O₄ magnetic particles have high saturation magnetization,stable chemical properties,and easy of preparation,so they are often used to prepare magnetic liquids.At the same time,its density（5.8 g/cm³）is too different from silicone oil（0.863 g/cm³）,it is very easy to agglomerate and settle.In this paper,carbon nanotubes（MWNT）with a density of 1.8 g/cm³ and a hollow structure are used to prepare Fe₃O₄@MWNT composite magnetic particles to reduce the density of magnetic particles,thereby improving the stability of the magnetic liquid.Using oleic acid as the surfactant,Fe₃O₄@MWNT particles were prepared by in-situ chemical precipitation method.The influence of temperature and reaction time on the size and morphology of magnetic particles was discussed.It is concluded that the change of temperature has no obvious effect on the size and morphology of the particles,and a shorter reaction time is beneficial to obtain Fe₃O₄particles with a smaller size.MWNT provides sites for the nucleation and growth of Fe₃O₄during the reaction,and most Fe₃O₄ grows on MWNT.Through IR results we can know that oleic acid has been successfully coated on Fe₃O₄ particles and MWNT has also been successfully doped.In addition,a long milling time will reduce the stability of the magnetic fluid,and adding MWNT can improve the stability of the magnetic fluid.（2）Using N-aminoethyl-γ-aminopropyltrimethoxysilane（792）as a surfactant,Fe₃O₄@MWNT magnetic particles are spherical,with a particle size of about 8.5 nm,and most of Fe₃O₄ grows on MWNT.The size and morphology of Fe₃O₄ magnetic particles do not changed while the difference of silane coupling agents.Most Fe₃O₄ grows on MWNT.The silane coupling agent has been successfully coated on Fe₃O₄ particles,and MWNT has also been successfully doped.At the same time,doping with MWNT will cause the saturation magnetization of the magnetic particles to decrease,from 122 emu/g to 106 emu/g.（3）Through the L-C oscillating circuit,the influence of the types of surfactants,the ratio of magnetic particles to the base carrier liquid,the dispersion method of magnetic particles,and the content of carbon nanotubes on the stability of the magnetic liquid are discussed.Adding MWNT can improve the stability of the magnetic liquid.The dispersion method has the greatest influence on the stability of the magnetic liquid.The stability of the magnetic liquid dispersed by ball milling shows two extremes.Long ball milling time will destroy the structure of the material and reduce the stability of the magnetic liquid,but at the same time the concentration distribution of magnetic liquid particles obtained by ball milling is more uniform.（4）The effects of the types of surfactants,the ratio of magnetic particles and base carrier liquid,the dispersion method of magnetic particles and the content of carbon nanotubes on the rheological properties of carbon nanotube-doped silicone oil-based magnetic liquids were studied.In the research of rheological properties,the viscosity of the magnetic liquid decreases with the increase of temperature,and the substitution amount of MWNT of the size is beneficial to improve the viscosity-temperature performance.Different reaction conditions will affect the viscosity-temperature properties of the final prepared magnetic liquid.The viscosity of the magnetic liquid increases with the increase of the magnetic field strength,and decreases with the increase of the shear rate.Silicone oil-based magnetic liquids doped with carbon nanotubes exhibit Newtonian behavior in the absence of a magnetic field.In the presence of a magnetic field,the magnetic fluid is closer to the pseudoplastic Bingham body.In addition,the viscosity change of silicone oil-based carrier fluid is not affected by magnetic field strength and shear rate.（5）In terms of research on rheological properties,an Anton Paar rheometer was used.Under the action of a magnetic field,the magnetic moment shifts and the formation of a chain structure of the magnetic liquid causes the viscosity of the magnetic liquid to increase.Shearing will destroy the internal structure of the magnetic fluid,which manifests as a decrease in viscosity.According to the Shiloims relative rotation formula,the maximum viscosity change caused by the internal magnetic moment of a single magnetic particle under the action of a magnetic field is calculated to determine the internal structure of the magnetic particle under the action of external force.At the same time,the results show that the magnetic liquid exhibits Newtonian behavior in the absence of a magnetic field,and is closer to a pseudoplastic Bingham model in the presence of a magnetic field.（6）Finally,the graphene-doped silicone oil-based magnetic liquids were systematically studied.TEM shows that most of the magnetic particles are grown on the MWNT,and a small amount of agglomeration of magnetic particles occurs.While only a small amount can be seen at the edge of grapheme（with a large size 800 nm）.Magnetic particles.It is difficult for magnetic particles to show nucleation and growth in graphene.In addition,MWNT and graphene are easily entangled together during the doping process,forming a large agglomerate structure,which is why carbon nanotubes and graphene-doped silicone oil-based magnetic fluid shows the worst stability among all magnetic fluids.There are 76 pictures,34 tables,and 153 references.