Translational and rotational dynamics in suspensions of magnetic nanorods
Translational and rotational dynamics in suspensions of magnetic nanorods
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DOI：
10.1039/c3sm51549d
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发表时间：
2013-01-01
期刊：
影响因子：
3.4
通讯作者：
Klapp, Sabine H. L.
中科院分区：
文献类型：
--
作者：
Alvarez, Carlos E.;Klapp, Sabine H. L.
使用计算机模拟，我们研究了有和没有（均匀）外部磁场的情况下磁性纳米棒稀悬浮液的平移和旋转扩散。磁棒被表示为球柱体，其中心具有纵向点偶极子且长宽比L/D=3或L/D=9。在没有场的情况下，杆倾向于形成具有反平行排序的紧凑簇，因此其行为与偶极球（L/D=0）非常不同，偶极球倾向于形成头尾链。此外，对于棒状颗粒来说，外部场往往会不稳定，而不是支持团簇的形成。我们表明，聚集行为的这些差异不仅对场致磁化强度和零频率磁化率等静态材料特性产生深远的影响，而且对动力学也产生深远的影响。特别是，对于磁棒，平行于场的平移扩散常数大于垂直于场的平移扩散常数，这与磁球观察到的行为相反。此外，棒状特征极大地影响了单粒子和集体偶极-偶极时间相关函数及其在频域中的对应函数的形状和密度依赖性。
Using computer simulations we investigate the translational and rotational diffusion of dilute suspensions of magnetic nanorods with and without a (homogeneous) external magnetic field. The magnetic rods are represented as spherocylinders with a longitudinal point dipole at their center and length-to-breadth ratios L/D=3 or L/D=9. In the absence of a field, the rods tend to form compact clusters with antiparallel ordering and thus behave very differently to dipolar spheres (L/D=0), which tend to form head-to-tail chains. Furthermore, for rod-like particles the external field tends to destabilize rather than to support cluster formation. We show that these differences in the aggregation behavior have profound consequences not only in static material properties such as the field-induced magnetization and the zero-frequency susceptibility, but also in the dynamics. In particular, for magnetic rods the translational diffusion constant parallel to the field is larger than the perpendicular one, in contrast to the behavior observed for magnetic spheres. Moreover, the rod-like character greatly affects the shape and the density dependence of the single-particle and collective dipole-dipole time correlation functions and their counterparts in the frequency domain.