The poor stability of magnetic fluid is a key problem which limits its application. To understand the impact of surfactants on stability, we prepare kerosene-based magnetic fluid with Fe₃O₄ magnetic nanoparticles (MNPs) using different surfactants i.e. linoleic acid, oleic acid and stearic acid. The distribution of nanoparticles in magnetic fluid is obtained by transmission electron microscope (TEM) and granularity analyzer. We find that MNPs coated with stearic acid agglomerate and the size is the largest. In contrast, the MNPs coated with linoleic acid or oleic acid are well dispersed with smaller size, which reveals that the type of surfactant will affect the stability of the magnetic fluid. To understand this, the adhesion energy of surfactant on particles and the solvation energy of surfactant in carrier fluid are calculated by ab initio and molecular dynamics. Based on the calculation results, we propose a formula for estimating the stability of magnetic fluid by combining the repulsive energy between Fe₃O₄ nanoparticles covered by surfactant and the calculated solvation energy of surfactants and carrier fluid, which can well interpret our experimental results. Our study reveals the mechanism of magnetic fluid stability and provides theoretical guidance for the preparation of stable magnetic fluid.

中文翻译：

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用 Fe3O4 模拟表面活性剂（亚油酸/油酸/硬脂酸）对煤油基磁流体稳定性的影响

磁性流体稳定性差是限制其应用的关键问题。_{为了了解表面活性剂对稳定性的影响，我们用 Fe 3} O ₄制备了煤油基磁流体磁性纳米粒子 (MNP) 使用不同的表面活性剂，即亚油酸、油酸和硬脂酸。磁性流体中纳米粒子的分布是通过透射电子显微镜（TEM）和粒度分析仪获得的。我们发现涂有硬脂酸的MNPs团聚并且尺寸最大。相比之下，亚油酸或油酸包覆的MNPs分散良好，尺寸较小，这表明表面活性剂的类型会影响磁流体的稳定性。为了理解这一点，表面活性剂在颗粒上的粘附能和表面活性剂在载液中的溶剂化能由下式计算：从头算和分子动力学。基于计算结果，我们提出了将表面活性剂覆盖的Fe ₃ O ₄纳米颗粒之间的排斥能与计算出的表面活性剂和载液的溶剂化能相结合来估计磁性流体稳定性的公式，可以很好地解释我们的实验结果。我们的研究揭示了磁流体稳定的机理，为稳定磁流体的制备提供了理论指导。