Direct observation of dipolar chains in iron ferrofluids by cryogenic electron microscopy
Direct observation of dipolar chains in iron ferrofluids by cryogenic electron microscopy
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DOI：
10.1038/nmat811
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发表时间：
2003-02-01
期刊：
影响因子：
41.2
通讯作者：
Philipse, AP
中科院分区：
文献类型：
--
作者：
Butter, K;Bomans, PHH;Philipse, AP
研究铁磁流体（磁性胶体的分散）的一个关键问题是偶极相互作用对其结构和相行为的影响，这不仅对实际应用很重要，而且对一般的偶极流体具有基本的认识。1970年，de Gennes和Pincus预测了一个范德华样相图和零磁场下铁磁流体中粒子线性链的存在。尽管有许多实验研究…没有直接证据表明在没有磁场的情况下偶极子线性链的存在，尽管模拟…清楚地显示了链状结构的存在。在这里，我们展示了零场下铁磁流体中的平行偶极结构，通过电子冷冻显微镜在单分散金属铁颗粒有机分散体的薄玻璃化薄膜上在颗粒水平上可视化。当系统地增加颗粒尺寸时，我们发现从单独的颗粒到随机定向的线性聚集体和支链或网络的突然转变。当在永久磁场中玻璃化时，这些链排列并形成厚的细长结构，表明平行偶极子链之间的横向吸引。这些发现表明，所使用的实验模型非常适合于研究偶极粒子系统的结构特性。
A key issue in research on ferrofluids (dispersions of magnetic colloids) is the effect of dipolar interactions on their structure and phase behaviour,, which is not only important for practical applications but gives fundamental insight in dipolar fluids in general. In 1970, de Gennes and Pincus predicted a Van der Waals-like phase diagram and the presence of linear chains of particles in ferrofluids in zero magnetic field. Despite many experimental studies,,, no direct evidence of the existence of linear chains of dipoles has been reported in the absence of magnetic field, although simulations,,,clearly show the presence of chain-like structures. Here, we showin situlinear dipolar structures in ferrofluids in zero field, visualized on the particle level by electron cryo-microscopy on thin, vitrified films of organic dispersions of monodisperse metallic iron particles. On systematically increasing the particle size, we find an abrupt transition from separate particles to randomly oriented linear aggregates and branched chains or networks. When vitrified in a permanent magnetic field, these chains align and form thick elongated structures, indicating lateral attraction between parallel dipole chains. These findings show that the experimental model used is well suited to study the structural properties of dipolar particle systems.