Surface functionalization for tailoring the aggregation and magnetic behaviour of silica-coated iron oxide nanostructures

10 páginas, 8 figuras, 1 tabla.-- et al.We report here a detailed structural and magnetic study of different silica nanocapsules containing uniform and highly crystalline maghemite nanoparticles. The magnetic phase consists of 5 nm triethylene glycol (TREG)- or dimercaptosuccinic acid (DMSA)-coated maghemite particles. TREG-coated nanoparticles were synthesized by thermal decomposition. In a second step, TREG ligands were exchanged by DMSA. After the ligand exchange, the ζ potential of the particles changed from − 10 to − 40 mV, whereas the hydrodynamic size remained constant at around 15 nm. Particles coated by TREG and DMSA were encapsulated in silica following a sol–gel procedure. The encapsulation of TREG-coated nanoparticles led to large magnetic aggregates, which were embedded in coalesced silica structures. However, DMSA-coated nanoparticles led to small magnetic clusters inserted in silica spheres of around 100 nm. The final nanostructures can be described as the result of several competing factors at play. Magnetic measurements indicate that in the TREG-coated nanoparticles the interparticle magnetic interaction scenario has not dramatically changed after the silica encapsulation, whereas in the DMSA-coated nanoparticles, the magnetic interactions were screened due to the function of the silica template. Moreover, the analysis of the AC susceptibility suggests that our systems essentially behave as cluster spin glass systems.The authors thank the financial support of the Spanish Ministry of Science and Innovation (MICINN) through Instituto de Salud Carlos III under the development of CIBER-BBN. AGR and CP acknowledge financial support of the MICINN and the Spanish Council of Scientific Research (CSIC) through MAT2008-01319/NAN, MAT2008-06542- C04-01 and 200980I05 research projects.Peer reviewe