Abstract This work reported a carbon layer modified magnetite (Fe3O4) nanospheres (Fe3O4@C) which could be applied in preparing high performance magnetic fluid. The porous Fe3O4@C nanospheres were prepared by calcinating the Fe3O4@Polydopamine (Fe3O4@PDA) precursor in N2 atmosphere. The shear stress of Fe3O4@C-based magnetic fluid was as high as 24.9 Pa at saturated magnetic field, which was about 3.8 times larger than pristine Fe3O4-based magnetic fluid (6.6 Pa). Furthermore, the particle level dynamic simulation was employed to analyze the microstructure evolution and shear stress of Fe3O4@C-based magnetic fluid under applying an external magnetic field. The chain-like model well explained the magnetorheological (MR) mechanism and the simulation results matched perfectly with the experimental data. Since the crystallinity of Fe3O4 was improved during the pyrolysis, Fe3O4@C nanospheres possessed a higher saturation magnetization. The stronger magnetic dipolar forces and chain-chain interactions resulted in a much steadier Fe3O4@C chain-like structure. As a result, it was found that the superior MR performance and high stability of the Fe3O4@C-based magnetic fluid were originated from the core-shell and porous structures of Fe3O4@C. This work proposed a valuable magnetic particle model to prepare high performance magnetic fluid and further understand the origination of MR effects.

中文翻译：

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基于碳改性磁铁矿（Fe3O4）纳米球的高性能磁流体

摘要 本文报道了一种碳层改性磁铁矿（Fe3O4）纳米球（Fe3O4@C），可用于制备高性能磁流体。通过在 N2 气氛中煅烧 Fe3O4@Polydopamine (Fe3O4@PDA) 前驱体制备多孔 Fe3O4@C 纳米球。Fe3O4@C基磁流体在饱和磁场下的剪切应力高达24.9 Pa，比原始Fe3O4基磁流体（6.6 Pa）大3.8倍左右。此外，采用颗粒级动力学模拟分析了外加磁场作用下Fe3O4@C基磁性流体的微观结构演变和剪切应力。链状模型很好地解释了磁流变（MR）机理，模拟结果与实验数据完全吻合。由于在热解过程中 Fe3O4 的结晶度得到改善，Fe3O4@C 纳米球具有更高的饱和磁化强度。更强的磁偶极力和链-链相互作用导致更稳定的 Fe3O4@C 链状结构。结果发现，Fe3O4@C基磁性流体优异的磁阻性能和高稳定性源于Fe3O4@C的核壳结构和多孔结构。这项工作提出了一种有价值的磁粒子模型来制备高性能磁流体并进一步了解 MR 效应的起源。结果表明，Fe3O4@C 基磁性流体优异的磁阻性能和高稳定性源于 Fe3O4@C 的核壳结构和多孔结构。这项工作提出了一种有价值的磁粒子模型来制备高性能磁流体并进一步了解 MR 效应的起源。结果表明，Fe3O4@C 基磁性流体优异的磁阻性能和高稳定性源于 Fe3O4@C 的核壳结构和多孔结构。这项工作提出了一种有价值的磁粒子模型来制备高性能磁流体并进一步了解 MR 效应的起源。