Magnetic nanocomposite multilayers using layer-by-layer assembly in nonpolar and polar solvent

Abstract

Magnetic nanoparticles have recently attracted a great deal of attentions due to a number of potential applications such as MRI contrast agents, magnetic separation, nonvolatile memory devices or magnetic cards as well as a fundamental scientific interest. The effective use of magnetic nanoparticles in a given application is based on two important factors: the inherent properties of nanoparticles (magnetization, size, etc.) and the ability to tailor their adsorbed amount onto the substrates. It has been reported by several research groups that high temperature decomposition of iron precursors in the presence of capping ligands can induce the high quality particles with facile size control, size uniformity and crystalline in comparison with more traditional coprecipitation/dextran methods or the reduction method in aqueous solution. These nanoparticles obtained from thermal decomposition can be well dispersed in nonpolar solvent due to hydrophobic property of the used stabilizers. Additionally, the particles with negatively charged stabilizers can allow the multiple depositions (i.e., layerby-layer assembled deposition) between particles and oppositely charged components and resultantly can enhance the intensity of their inherent properties such as magnetization. However, to the best of our knowledge, the facile and efficient method fully satisfying these two factors has not been introduced up to date. Herein, we introduce the novel and simple method for the fabrication of magnetic nanocomposite multilayers, including the high quality γ-Fe2O3 nanoparticles (MP) by thermal decomposition method and allowing the tailored magnetic properties. 2-bromo-2-methylpropionic acid (BMPA)-stabilized MP in toluene solvent was prepared by exchanging oleic acid with BMPA after initially synthesizing the oleic acid-stabilized MP (OA-MP). The bromo (-Br) groups of BMPA-MP can be covalently bonded with amine (-NH2) groups. Based on this high affinity, it is demonstrated that the magnetic nanocomposite multilayers can be fabricated using BMPA-MP dispersed in toluene and poly(allyamine hydrochloride) (PAH) in water.