Complete Exchange of the Hydrophobic Dispersant Shell\non Monodisperse Superparamagnetic Iron Oxide Nanoparticles

Abstract

High-temperature synthesized monodisperse\nsuperparamagnetic iron\noxide nanoparticles are obtained with a strongly bound ligand shell\nof oleic acid and its decomposition products. Most applications require\na stable presentation of a defined surface chemistry; therefore, the\nnative shell has to be completely exchanged for dispersants with irreversible\naffinity to the nanoparticle surface. We evaluate by attenuated total\nreflectance−Fourier transform infrared spectroscopy (ATR−FTIR)\nand thermogravimetric analysis/differential scanning calorimetry (TGA/DSC)\nthe limitations of commonly used approaches. A mechanism and multiple\nexchange scheme that attains the goal of complete and irreversible\nligand replacement on monodisperse nanoparticles of various sizes\nis presented. The obtained hydrophobic nanoparticles are ideally suited\nfor magnetically controlled drug delivery and membrane applications\nand for the investigation of fundamental interfacial properties of\nultrasmall core–shell architectures.