Direct observation of dipolar chains in ferrofluids in zero field using cryogenic electron microscopy
Direct observation of dipolar chains in ferrofluids in zero field using cryogenic electron microscopy
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DOI：
10.1088/0953-8984/15/15/310
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发表时间：
2003-04-23
影响因子：
2.7
通讯作者：
Philipse, AP
中科院分区：
文献类型：
--
作者：
Butter, K;Bomans, PH;Philipse, AP
用低温电子显微镜在铁和磁铁矿分散体的玻璃化膜上原位研究了铁磁流体的颗粒结构。通过合成具有可控粒径和不同类型表面活性剂的铁胶体，偶极颗粒相互作用可以在很宽的范围内变化，这显著影响铁磁流体颗粒结构。我们的铁分散体（与磁铁矿分散体相比）的实验首次证明，在零场的铁磁流体中，随着颗粒尺寸的增加，从单独的颗粒到线性颗粒链的过渡（Butter K，Bomans P H，Frederik P M，Vroege G J和Philipse A P 2003 Nature Mater 2 89）。这些链已经由de Gennes和Pincus在理论上预测（de Gennes PG和Pincus PA 1970 Phys.Kondens. mater. 11，189），非常类似于在偶极流体的模拟中发现的波动链（Weis J J 1998 Mol. 93 36 1，Chantrell R W，Bradbury A，Popplewell J和Charles S W 1982 J.Appl.Phys.53 2742）。通过采用较薄的表面活性剂层减少颗粒之间的空间排斥的范围被发现改变颗粒结构以及。的偶极性质的聚集证实了现有的链和单个颗粒在磁场方向上的取向后，在饱和的，磁场中的分散体的玻璃化。频率依赖的磁化率测量表明，在真正的三维铁磁流体的颗粒结构是定性类似的液体薄膜。
The particle structure of ferrofluids is studied in situ, by cryogenic electron microscopy, on vitrified films of iron and magnetite dispersions. By means of synthesis of iron colloids with controlled particle size and different types of surfactant, dipolar particle interactions can be varied over a broad range, which significantly influences the ferrofluid particle structure. Our experiments on iron dispersions (in contrast to magnetite dispersions) for the first time demonstrate, in ferrofluids in zero field, a transition with increasing particle size from separate particles to linear chains of particles (Butter K, Bomans P H, Frederik P M, Vroege G J and Philipse A P 2003 Nature Mater 2 89). These chains, already predicted theoretically by de Gennes and Pincus (de Gennes P G and Pincus P A 1970 Phys. Kondens. Mater. 11, 189), very much resemble the fluctuating chains found in simulations of dipolar fluids (Weis J J 1998 Mol. Phys. 93 36 1, Chantrell R W, Bradbury A, Popplewell J and Charles S W 1982 J. Appl. Phys. 53 2742). Decreasing the range of steric repulsion between particles by employing a thinner surfactant layer is found to change particle structures as well. The dipolar nature of the aggregation is confirmed by the alignment of existing chains and individual particles in the field direction upon vitrification of dispersions in a saturating, magnetic field. Frequency-dependent susceptibility measurements indicate that particle structures in truly three-dimensional ferrofluids are qualitatively similar to those in liquid films.