Magnetite (Fe₃O₄) nanoplates with a hexagonal platelet shape were synthesized by two steps: hydrothermal synthesis of iron(III) oxide (α-Fe₂O₃) nanoplates followed by wet chemical reduction of the α-Fe₂O₃ nanoplates. Then, poly(methyl methacrylate) (PMMA) chains were grafted onto the surface of the hexagonal Fe₃O₄ nanoplates (F) via surface-initiated atom transfer radical polymerization (SI-ATRP), which ensures dispersion stability in organic solvents and ionic liquids. After mixing with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Emim⁺][NTf₂⁻]), a representative ionic liquid, the resulting PMMA-modified F were found to show good lyotropic liquid-crystalline (LC) behaviour in [Emim⁺][NTf₂⁻] and to exhibit a fast response to the application of an external magnetic field. Ultrasmall-angle synchrotron X-ray scattering (USAXS) measurements verified that the PMMA chain length, the weight ratio of the ionic liquid and the external magnetic field could significantly influence the interparticle distance (I_D) of the PMMA-modified F in [Emim⁺][NTf₂⁻]. In particular, the lyotropic LC phase could be assigned as a nematic phase with a columnar alignment. In addition, the PMMA-modified F maintained a uniaxially aligned nematic columnar structure along the magnetic field direction. Our study also determined the mechanism for the special alignment of the PMMA-modified F under an external magnetic field by analysing the growth axis, the easy magnetic axes, and the interparticle distance of F. The results suggested that the special alignment of the PMMA-modified F was affected by the interparticle interaction caused by the PMMA long chains on F under the magnetic field. Furthermore, the present study revealed that PMMA-modified F exhibited a new magnetic field responsive behaviour that led not only to the formation of a uniaxial alignment structure but also to control of I_D with the help of the PMMA soft corona under the application of a magnetic field. These features could prove to be a promising advance towards novel applications of magnetic nanoparticles (NPs), such as functional magnetic fluids, rewritable magnetic switching devices, and smart magneto-electrochemical nanosensors.

中文翻译：

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具有可控颗粒间相互作用的易溶液晶 PMMA 接枝 Fe3O4 纳米板的磁场诱导单轴排列

通过两个步骤合成具有六边形片晶形状的磁铁矿 (Fe ₃ O ₄ ) 纳米片：水热合成氧化铁 ( III ) (α-Fe ₂ O ₃ ) 纳米片，然后湿化学还原 α-Fe ₂ O ₃纳米片. 然后，将聚（甲基丙烯酸甲酯）（PMMA）链接枝到六方Fe ₃ O ₄纳米板（F）的表面，通过表面引发的原子转移自由基聚合（SI-ATRP），可确保在有机溶剂和离子液体中的分散稳定性。与代表性离子液体1-乙基-3-甲基咪唑双(三氟甲磺酰基)亚胺 ([Emim ⁺ ][NTf ₂ ^- ]) 混合后，发现所得 PMMA 改性F具有良好的易溶液晶 (LC) [Emim ⁺ ][NTf ₂ ^-] 并表现出对外部磁场应用的快速响应。_{超小角同步加速器X}射线散射 (USAXS) 测量验证了 PMMA 链长、离子液体的重量比和外部磁场可以显着影响PMMA改性F在 [Emim ⁺ ][NTf ₂ ^- ]。特别是，溶致 LC 相可以指定为具有柱状排列的向列相。此外，PMMA修饰的F沿磁场方向保持单轴排列的向列柱状结构。我们的研究还确定了 PMMA 修饰的F的特殊对齐机制通过分析F的生长轴、易磁轴和粒子间距。结果表明，PMMA修饰的F的特殊排列受到磁场下F上PMMA长链引起的颗粒间相互作用的影响。此外，本研究表明，PMMA 修饰的F表现出新的磁场响应行为，不仅导致形成单轴排列结构，而且控制I _D在磁场应用下的 PMMA 软电晕的帮助下。这些特征可能被证明是磁性纳米粒子 (NPs) 新应用的一个有希望的进步，例如功能性磁流体、可重写磁开关装置和智能磁电化学纳米传感器。