Kim Jin Young, Osterloh Frank E, Hiramatsu Hiroki, Dumas R K, Liu Kai
Departments of Chemistry and Physics, University of California-Davis, Davis, California 95616, USA.
J Phys Chem B. 2005 Jun 9;109(22):11151-7. doi: 10.1021/jp050348m.
Superparamagnetic colloidal plates were synthesized from tetrabutylammonium stabilized Ca(2)Nb(3)O(10) nanosheets and oleic acid-stabilized Fe(3)O(4) nanoparticles. Modification with 3-aminopropyltrimethoxysilane produces amine-terminated Ca(2)Nb(3)O(10) with an amine concentration of 0.43 +/- 0.06 groups per Ca(2)Nb(3)O(10) unit as follows from spectroscopic quantification with trinitrobenzenesulfonic acid as a dye. Treatment of the modified sheets in THF/ethanol with 5.3 nm oleic acid-stabilized magnetite nanoparticles yields pseudo-2D assemblies that consist of 2 nm thick nanosheets decorated on both sides with a dense collection (9.3 +/- 0.5 x 10(3) particles per square micrometer per side) of magnetite particles. In noncoordinating or weakly coordinating solvents, these composite particles further aggregate into stacked aggregates with a mean edge length of 1.6 +/- 0.7 microm and a thickness of 79 +/- 30 nm. The colloidal plates were characterized by elemental analysis, X-ray powder diffraction, and infrared and UV/vis spectroscopy. SQUID measurements show that films of the aligned particles are superparamagnetic at room temperature. The magnetic hysteresis that is observed at 5 K reveals that the plates have a magnetic anisotropy with the easy axis in the plane of the plates and the hard axis perpendicular to it. Calculations show that the magnetic anisotropy is a direct consequence of the two-dimensional distribution of the magnetic nanoparticles on the sheets. Optical microscopy reveals that when suspended in ethanol or THF, the colloidal plates can be rotated in real time with a variable external magnetic field (200 Oe). Magnetic alignment of the particles in suspensions also produces asymmetric light scattering patterns and magnetic birefringence. These effects and the observed magneto-orientational properties make the biaxial colloids interesting as components in displays and as magnetic actuators.
超顺磁性胶体板由四丁基铵稳定的Ca₂Nb₃O₁₀纳米片和油酸稳定的Fe₃O₄纳米颗粒合成。用3-氨丙基三甲氧基硅烷改性可得到胺封端的Ca₂Nb₃O₁₀，通过用三硝基苯磺酸作为染料进行光谱定量分析可知，每个Ca₂Nb₃O₁₀单元的胺浓度为0.43±0.06个基团。在四氢呋喃/乙醇中用5.3纳米的油酸稳定的磁铁矿纳米颗粒处理改性后的薄片，可得到准二维组装体，该组装体由2纳米厚的纳米片组成，纳米片两侧装饰有密集的磁铁矿颗粒集合（每侧每平方微米9.3±0.5×10³个颗粒）。在非配位或弱配位溶剂中，这些复合颗粒进一步聚集成堆叠聚集体，平均边长为1.6±0.7微米，厚度为79±30纳米。通过元素分析、X射线粉末衍射以及红外和紫外/可见光谱对胶体板进行了表征。超导量子干涉仪测量表明，排列的颗粒薄膜在室温下具有超顺磁性。在5K下观察到的磁滞现象表明，这些板具有磁各向异性，易轴在板平面内，难轴垂直于板平面。计算表明，磁各向异性是磁性纳米颗粒在薄片上二维分布的直接结果。光学显微镜显示，当悬浮在乙醇或四氢呋喃中时，胶体板可以在可变外部磁场（200奥斯特）作用下实时旋转。悬浮液中颗粒的磁排列还会产生不对称光散射图案和磁双折射。这些效应以及观察到的磁取向特性使得双轴胶体作为显示器组件和磁致动器具有吸引力。
