| Magnetic polymer microparticle combines the property of magnetic particle with that of macromolecule particle. It not only can be separated from the medium easily, but also can be surface-modified in order that the surface of magnetic microparticle was endued with functional groups. So it has broad application in the fields of biomedicine, cytology and biology engineering, etc. The microparticle must possess high magnetic responsibility and specific surface area, so that magnetic separation is quick and convenient. In this paper ferrite was doped with rare earth elements of great magnetic moment and rare earth ferrite/polyacrylamide magnetic composite microparticles were prepared by one-step method in a single inverse microemulsion. The typical composite microparticles were charactered by FTIR, XRD, TEM and TG-DTA. The influencing factors, such as pH value, the charging mode of sodium hydroxide, temperature, were discussed respectively. Magnetic properties of composite microparticles were studied by Gouy magnetic balance. At the same time magnetic motion method, turbidimetric method, magnetic balance method were used to determine and study the magnetic responsibility of rare earth ferrite/polyacrylamide composite microparticles. Then the effect of the species and consumption of rare earth on magnetic responsibility were discussed. At last, the composite microparticles were used for preparation of magnetorheological fluid and research of viscosity property.Dysprosium ferrite / PAM composite microparticles with an average particle size about 25nm were prepared by inverse microemulsion system of polyethylene glycol octylphenyl ether, n-hexyl alcohol, cyclohexane and water phase, using acrylamide as monomer and AIBN as initiator. In the process of the preparation of DyxFe3-xO4/PAM composite microparticles, we find that DyxFe3-xO4/PAM nano-composite microparticles could be obtained with the condition of adding NaOH solution quickly at once into reaction system, changing pH to 11 and aging for 1h at 80 °C. We also find that deoxidize and preventing oxidizing is important to this reaction.The results of testing magnetic property of composite particles indicate that composite particles can be magnetized under exterior magnetic field and composite particles are ferrimagnetism material. Bulk magnetic susceptibility of DyxFe3.xO4/PAM is higher than that of FeaO/j/PAM, which indicates that the addition of dysprosium can improve magnetic property of ferrite. At the same time, magnetic properties of water-based dysprosium ferrite/PAM magnetic fluid was investigated. In the downfield the magnetic fluid is paramagnetism material. The magnetic fluid reaches the state of magnetization saturation in the high magnetic field and saturation magnetization were measured.Research of magnetic responsibility of rare earth ferrite/polyacrylamide indicates that the magnetic motion method and turbidimetric method aren't applicable to the determination of magnetic responsibility of composite particles prepared in this paper. Magnetic balance method is more suitable to the particles with smaller diameters and low magnetic content, which can be used to measure magnetic responsibility of composite microparticles prepared in this paper. Magnetic responsibility of composite microparticles doped Dy, Er, Tb or Gd rises up. The changing tendency of magnetic responsibility is similar to that of magnetic moment of rare earth ions. Magnetic responsibility of dysprosium ferrite/PAM composite microparticles increases at first and decreases later with growth of dysprosium content. The microparticles show the strongest magnetic responsibility when the molar ratio of Dy3+/iron is 0.20.DyxFe3.xO4/PAM magnetic composite microparticles were dispersed in silicon oil and magnetorheological fluid (MRF) was prepared. Viscosity behavior of magnetorheological fluid under exterior magnetic field was investigated and the influencing factors, such as rotate speed, magnetic field strength, content of magnetic particles and temperature, were also discussed respectively. T... |
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