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

Abstract

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.

Assembling of Magnetic Iron Oxide Nanoparticles Controlled by Self- Assembled Monolayers of Functional Coordinating or Chelating Trialkoxysilanes

“…After immersion in the NPs suspension, the SAM-THY is featured by a higher roughness (2.2 ± 0.1 nm) than the corresponding SAMs before immersion (0.5 ± 0.1 nm). These results are very similar to those obtained from SAMs prepared on gold substrates [10,11]. It appears that the higher roughness of gold substrates compared with silicon wafer does not influence the assembling of NPs.…”

“…Coordinating amine groups induce weaker interactions than chelating thymine groups. Therefore, as we observed previously with hydroxyl and carboxylic acid terminal groups at the SAM surface, the density of assembled NPs is modified by the kinetics of the reaction [10]. Moreover, the immobilization of NPs from the solution to the substrate occurs randomly in domains.…”

“…Iron oxide nanoparticles were synthesized by the thermal decomposition of an iron oleate precursor at 310 °C in a high boiling point solvent such as octylether. At the end of the reaction it is very important to wash out the sample by centrifugation and dialysis to remove the side-products of the reaction as well as the excess of surfactant molecules which influence the kinetic of the assembling on SAMs [10]. A size selection precipitation (SSP) procedure was also applied to narrow the size distribution of nanoparticles.…”

“…This equilibrium depends on the NPs/oleic acid molecules ratio as well as the solvent. The high density of coordinating or chelating groups at the SAM surface also significantly modifies the equilibrium [10]. Here, the reaction condition favors the free molecules in solution and therefore the NPs surface is partially uncovered and amine or thymine groups interact directly with NPs.…”

“…On the other hand the direct immobilization of PbSe, PbS, Co or Fe 3 O 4 NPs onto SAMs lead to non homogeneous films where the density in NPs and the orientation of molecules of the SAM influence the magnetic microstructure of the assemblies [6][7][8][9]. Very recently, we reported on the chemical assisted assembling of iron oxide NPs controlled by specific functional head groups at the SAM surface [10]. The deposition of NPs was demonstrated to strongly depend on the chelating and coordinating abilities of these terminal groups.…”