Macroscopic and Microscopic Structural Analyses of Needle-Shaped Condensed Phases in Magnetic Fluids under External Magnetic Fields
Macroscopic and Microscopic Structural Analyses of Needle-Shaped Condensed Phases in Magnetic Fluids under External Magnetic Fields
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外磁场下磁流体中针状凝聚相的宏观和微观结构分析
DOI：
10.1021/acs.jpcc.0c08648
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Balachandran Jeyadevan
中科院分区：
文献类型：
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作者：
Mamiya Hiroaki;Sudo Hironori;Cuya Huaman Jhon L.;Suzuki Kazumasa;Miyamura Hiroshi;Balachandran Jeyadevan
为了确保磁性流体在各种工程设备和生物医学应用中的最佳利用，人们对磁性流体中的层次结构进行了研究。本研究通过在煤油中分散粒径分别为10.0、11.7和17.4 nm的单分散磁铁矿颗粒制备磁性液体。暗场光学显微镜和小角X射线散射(SAXS)实验表明，在没有磁场的情况下，胶体分散不稳定。在磁场作用下，可以在宏观水平上观察到针状微米级凝聚相的形成，而与颗粒平均直径的差异无关。磁场下的SAXS谱分析表明，在含有17.4 nm颗粒的磁性流体中形成了松散的纳米颗粒束链，而其他磁性流体缺乏纳米颗粒的局部空间有序性。因此，结果表明，纳米颗粒在宏观结构内的微观排列随着尺寸的变化而变化，尽管它们的外部形状表现出相似之处。从静磁能和粒子间偶极相互作用两个方面对结果进行了讨论。这些不同的分层结构条件是充分利用每种应用特性的关键；例如，磁流体热疗的优秀设计既包括单独提供分散良好的纳米颗粒作为热种子，也包括在磁场暴露下合作产生链状纳米颗粒的磁热。
Hierarchal structures in magnetic fluids have been studied to ensure the optimal utilization of these fluids, which exhibit both magnetism and fluidity, in various engineering devices and biomedical applications. In this study, magnetic fluids were prepared by dispersing monodispersed magnetite particles with sizes of 10.0, 11.7, and 17.4 nm in kerosene. Dark-field optical microscopy and small-angle X-ray scattering (SAXS) experiments showed no results indicating destabilization of colloidal dispersion in the absence of magnetic fields. Under magnetic fields, the formation of a needle-shaped micrometer-scale condensed phase was observed on the macroscopic level, irrespective of the differences in the average diameter of the particles. Analyses of SAXS profiles under magnetic fields revealed that loosely bundled chains of nanoparticles were formed in the magnetic fluid containing particles with a size of 17.4 nm, whereas other magnetic fluids lacked local spatial ordering of nanoparticles. Thus, the results indicate that the microscopic arrangements of nanoparticles inside a macroscopic structure vary with size, despite the similarity exhibited in their outward form. The results are discussed based on magnetostatic energy and interparticle dipolar interactions. These different hierarchal structuring conditions are key to fully exploiting the properties for each application; for instance, an excellent design for magnetic fluid hyperthermia treatments involves both the individual delivery of well-dispersed nanoparticles as thermal seeds and cooperative magnetic heat generation of chained nanoparticles under exposure to magnetic fields.