Soret coefficient of nanoparticles in ferrofluids in the presence of a magnetic field
Soret coefficient of nanoparticles in ferrofluids in the presence of a magnetic field
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DOI：
10.1063/1.869737
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发表时间：
1998-10
影响因子：
4.6
通讯作者：
E. Blums;S. Odenbach;A. Mezulis;M. Maiorov
中科院分区：
文献类型：
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作者：
E. Blums;S. Odenbach;A. Mezulis;M. Maiorov
在垂直平板热扩散柱中进行了纳米级Mn_（0.5）Zn_（0.5）Fe_（20）O微粒的非稳态分离实验。通过使用一种改进的分离理论，该理论考虑了柱中的一维混合（热和浓度）对流，从分离曲线计算冻干纳米颗粒的Soret系数。结果表明，在零磁场中，粒子是朝着降低温度的方向转移的。热扩散比αT达到值αT <$+20。观察到均匀磁场B对颗粒分离的显著影响。如果B沿着温度梯度T取向，则发生热扩散系数的强烈降低，而横向场B沿温度梯度T取向则导致颗粒热泳传递的增强。这两种效果定性地同意粒子热磁泳运动的流体动力学理论的基础上的理论预测。
Experiments on a nonstationary separation of nanometer-sized Mn0.5Zn0.5Fe2O particles of hydrocarbon-based ferrocolloids in a flat vertical thermal diffusion column are performed. By using a modified separation theory which accounts for a one-dimensional mixed (thermal and concentration) convection in the column, the Soret coefficient of lyophilized nanoparticles from the separation curves are calculated. It is shown that in a zero magnetic field particles are transferring toward decreasing temperatures. The thermal diffusion ratio αT reaches a value αT≈+20. A significant influence of a uniform magnetic field B on particle separation is observed. If B is oriented along the temperature gradient ∇T, a strong decrease in thermal diffusion coefficient takes place whereas the transversal field B⊥∇T causes an intensification of particle thermophoretic transfer. Both effects qualitatively well agree with theoretical predictions based on a hydrodynamic theory of particle thermomagnetophoretic motion.