Joining and Welding Research Institute, Osaka University, Osaka 567-0047, Japan.
National Institute for Materials Science, Ibaraki 305-0047, Japan.
Int J Mol Sci. 2019 Jul 24;20(15):3617. doi: 10.3390/ijms20153617.
Magnetic microspheres in a concentrated suspension can be self-assembled to form chain structures under a magnetic field, resulting in an enhanced viscosity and elasticity of the suspension (i.e., the magnetorheological (MR) effect). Recently, interest has been raised about the relationship between nonspherical particles, such as octahedral particles and the MR effect. However, experimental studies have not made much progress toward clarifying this issue due to the difficulty associated with synthesizing microparticles with well-defined shapes and sizes. Here, we presented a method for the shape-controlled synthesis of magnetite (FeO) microparticles and investigated the MR effects of two suspensions prepared from the two shape-controlled samples of FeO microparticles. Our method, which was based on the polyol method, enabled the preparation of spherical and octahedral FeO microparticles with similar sizes and magnetic properties, through a reduction of α-FeOOH in a mixed solvent of ethylene glycol (a polyol) and water. The water played an important role in both the phase transition (α-FeOOH to FeO) and the shape control. No substantial difference in the MR effect was observed between an octahedral-particle-based suspension and a spherical-particle-based one. Therefore, in this study, the shape of the microparticles did not strongly influence the MR effect, i.e., the properties of the chain structures.
在浓悬浮液中的磁性微球在磁场下可以自组装形成链状结构，从而增加悬浮液的粘度和弹性（即磁流变效应）。最近，人们对非球形颗粒（如八面体颗粒）与磁流变效应之间的关系产生了兴趣。然而，由于难以合成具有明确形状和尺寸的微颗粒，实验研究在澄清这一问题方面没有取得太大进展。在这里，我们提出了一种控制合成磁铁矿（FeO）微颗粒的形状的方法，并研究了由两种形状控制的 FeO 微颗粒样品制备的两种悬浮液的磁流变效应。我们的方法基于多元醇法，通过在乙二醇（多元醇）和水的混合溶剂中还原α-FeOOH，可以制备出具有相似尺寸和磁性的球形和八面体 FeO 微颗粒。水在相转变（α-FeOOH 到 FeO）和形状控制中都起着重要作用。基于八面体颗粒的悬浮液和基于球形颗粒的悬浮液之间的磁流变效应没有明显差异。因此，在这项研究中，微颗粒的形状并没有强烈影响磁流变效应，即链状结构的性质。
