Modeling the effect of surfactant (linoleic acid/oleic acid/stearic acid) on the stability of kerosene-based magnetic fluid with Fe3O4

Abstract

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.