title: Core-shell nano-architectures: the incorporation mechanism of hydrophobic nanoparticles into the aqueous core of a microemulsion.
abstract: This work presents an in-depth investigation of the molecular interactions in the incorporation mechanism of colloidal hydrophobic-capped nanoparticles into the hydrophilic core of reverse microemulsions. (1)H Nuclear Magnetic Resonance (NMR) was employed to obtain molecular level details of the interaction between the nanoparticles capping amphiphiles and the microemulsion surfactants. The model system of choice involved oleic acid (OAC) and oleylamine (OAM) as capping molecules, while igepal-CO520 was the surfactant. The former were studied both in their "free" state and "ligated" one, i.e., bound to nanoparticles. The latter was investigated either in cyclohexane (micellar solution) or in water/cyclohexane microemulsions. The approach was extremely useful to gain a deeper understanding of the equilibria involved in this complex system (oleic acid capped-Bi2S3 in igepal/water/cyclohexane microemulsions). In difference to previously proposed mechanisms, the experimental data showed that the high affinity of the capping ligands for the reverse micelle interior was the drivingforce for the incorporation of the nanoparticles. A simple ligand-exchange mechanism could be ruled out. The collected information about the nanoparticle incorporation mechanism is extremely useful to develop new synthetic routes with an improved/tuned coating efficiency, in order to tailor the core-shell structure preparation.
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari, Monserrato Campus, SS 554 bivio Sestu, I-09042 Monserrato (CA), Italy. scorciapino@unica.it
authors.forename: Mariano A
authors.initials: MA
authors.lastname: Scorciapino
authors.forename: Roberta
authors.initials: R
authors.lastname: Sanna
authors.forename: Andrea
authors.initials: A
authors.lastname: Ardu
authors.forename: Federica
authors.initials: F
authors.lastname: Orrù
authors.forename: Mariano
authors.initials: M
authors.lastname: Casu
authors.forename: Anna
authors.initials: A
authors.lastname: Musinu
authors.forename: Carla
authors.initials: C
authors.lastname: Cannas
keywords: CHX; CMC; DQF-COSY; Intermolecular interactions; Ligand-exchange; Liquid-state NMR; NMR; NOESY; Nanoparticles synthesis; Nuclear Magnetic Resonance; OAC; OAM; Paramagnetic relaxation enhancement; Reverse micelles; SI; Supporting Information; TEM; TEOS; TMS; TOCSY; critical micelle concentration; cyclohexane; double quantum filtered correlation spectroscopy; nuclear overhauser effect spectroscopy; oleic acid; oleylamine; tetraethyl orthosilicate; tetramethyl silane; total correlation spectroscopy; transmission electron microscopy