2D Assembling of Magnetic Iron Oxide Nanoparticles Promoted by SAMs Used as Well-Addressed Surfaces

Well-addressed surfaces which consist of self-assembled monolayers (SAMs) of organic molecules have been used to control the assembling of magnetic iron oxide nanoparticles (NPs) coated with oleic acid molecules. The assembling occurs through interactions between the surface of NPs and specific functional terminal groups at the interface of the SAMs and the NP suspension. Polar head groups such as carboxylic acid and hydroxyl promote the assembling of NPs whereas nonpolar groups such as methylene avoid the assembling onto SAMs. The kinetics of the NP assembling is highly dependent on the polarity of terminal groups of the SAMs. Carboxylic acid groups have been shown to promote faster formation of a dense monolayer of NPs than hydroxyl groups. In addition, oleic acid used as a coating agent enables the high stability of the NP suspension and its concentration influences dramatically the kinetics of the assembling. The mechanism proceeds by a ligand exchange process between surfactant on the NP surface and terminal groups at the interface of the SAM with the suspension.