水基自形成CoFe_2O_4磁性液体的零磁场粘滞特性

The Properties of Viscosity of the Aqueous CoFe_2O_4 Magnetic Fluid of Self-formed in Zero Magnetic Field

在零磁场下 ,水基自形成CoFe2 O4磁性液体粘度 η与CoFe2 O4纳米微粒体积分数Φ显示出特异的关系 ,然而 ,球形刚性粒子填料悬浮液粘度理论不能很好解释 .通过对水基自形成CoFe2 O4磁性液体中的微粒相互作用分析发现 ,此磁性液体的沉降和在磁场中的成链需有以预团聚体为核的大粒子存在 .在这一基础上 ,建立了团聚涨落模型 .于是 ,平均粒径、Einsten系数和粒径分布偏差均成为微粒体积分数的函数 ,也即对Popplewell粘度公式的修正 .最后得到与实验很好吻合的 η～Φ曲线及关系式 .

The plot of viscosity versus particle volume fraction for the water carrier of self-formed CoFe_2O_4 magnetic fluid is abnormal in zero magnetic field. However, the viscosity theory of the suspension with the global rigid particle filling cannot explain the experiment well. That is because the nanoparticles have aggregated before preparation of magnetic fluid. The fact is found that the sedimentation without magnetic field and the becoming chains in magnetic field of this type of magnetic fluid need the big particles which core are pre-aggregates by researching the interaction of particles of magnetic fluid. Around the big particles, nanoparticles are absorbed with the type of dynamic state. It is on that idea that the model of fluctuant aggregation is made. So, the average diameter, Einstein ratio and particles size distributive deviation of free suspended bodies in zero magnetic fluid are the functions of the particles volume fraction. And then, Popplewell’s formula of the viscosity is modified with this model. As a result, a well-fitted curve is obtained.