Gelation of Superparamagnetic Nanoparticles: Experimental and Computational Studies

The formation of gels by salt-induced double layer compression of superparamagnetic nanoparticles in the absence and presence of an external magnetic field was investigated experimentally as well as computationally in this study. Gels formed appear to exhibit low porosities based on visual inspection of their external morphologies. However, the interior structures were observed 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 gelation 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 gelation process of magnetic nanoparticles both in the absence and presence of an external magnetic field. The simulations show that gelation occurred by the formation of random aggregates of nanoparticles which then joined to form a network. In the presence of anisotropic magnetic forces, these aggregates were rotated to align along the direction of the magnetic field and the final network formed consisted largely of elongated branches of magnetic nanoparticles.