Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Singapore.
J Chem Phys. 2012 Mar 28;136(12):124109. doi: 10.1063/1.3697865.
The formation of agglomerates by salt-induced double layer compression of magnetic nanoparticles in the absence and presence of an external magnetic field was investigated experimentally as well as computationally in this study. The structures of the agglomerates were analyzed through scanning electron microscopy and proved to be highly porous and composed of large spaces among the branches of a convoluted network. In the absence of an external magnetic field, the branches of such a network were observed to be oriented in no particular direction. In contrast, when the agglomeration process was allowed to occur in the presence of an external magnetic field, these branches appeared to be oriented predominantly in one direction. A modified Discrete Element Method was applied to simulate the agglomeration process of magnetic nanoparticles both in the absence and presence of an external magnetic field. The simulations show that agglomeration occurred by the formation of random clusters of nanoparticles which then joined to form a network. In the presence of anisotropic magnetic forces, these clusters were rotated to align along the direction of the magnetic field and the final network formed consisted largely of elongated branches of magnetic nanoparticles.
本研究通过实验和计算研究了在外磁场存在和不存在的情况下，盐诱导的磁性纳米粒子双层压缩形成聚集体。通过扫描电子显微镜分析了聚集体的结构，证实其具有高度多孔性，由分支卷曲网络之间的大空间组成。在外磁场不存在的情况下，观察到这种网络的分支没有特定的方向。相比之下，当允许在外磁场存在的情况下发生团聚过程时，这些分支似乎主要朝一个方向取向。应用改进的离散单元法模拟了在外磁场存在和不存在的情况下磁性纳米颗粒的团聚过程。模拟表明，团聚是通过纳米颗粒随机簇的形成而发生的，然后这些簇连接形成网络。在外磁场的各向异性磁力作用下，这些簇被旋转以沿磁场方向对齐，最终形成的网络主要由拉长的磁性纳米颗粒分支组成。
