Publications (8)24.45 Total impact
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Article: Synthesis of thermosensitive microgels with a tunable magnetic core.
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ABSTRACT: In this work, we describe a new methodology for the preparation of monodisperse and thermosensitive microgels with magnetic core. In order to produce such a material, hydrophobic magnetic Fe(3)O(4) nanoparticles were prepared by two methods: thermal decomposition and coprecipitation. The surface of these nanoparticles was modified by addition of 3-butenoic acid, and after that these nanoparticles were dispersed in water and submitted to free radical polymerization at 70 °C in the presence of N-isopropylacrylamide (NIPAM) and bisacrylamide. The result of this reaction was monodisperse microgels with a magnetic core. By varying the amount of 3-butenoic acid, it was possible to obtain hybrid microgels with different magnetic core sizes and different architectures.Langmuir 08/2011; 27(17):10484-91. · 4.19 Impact Factor -
Article: Tuning the Size, the Shape, and the Magnetic Properties of Iron Oxide Nanoparticles
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ABSTRACT: The influence of a variety of parameters on the synthesis of iron oxide nanoparticles (magnetite/maghemite Fe3O4/γ-Fe2O3) by thermal decomposition of a metal−organic iron precursor in an organic medium is reported. We study the role of both the surfactant and the reducing agent on the shape, the size distribution, and the magnetic properties. We aim at synthesizing magnetic nanoparticles with high crystal quality and good magnetic response. A narrow size distribution of pseudospherical and faceted particles (4−20 nm) with a high saturation magnetization (Ms ≈ 80−85 emu/g at 5 K) is obtained when using oleic acid as a surfactant. In contrast, decanoic acid yields much larger pseudocubic particles (45 nm) with a wider size distribution and a larger saturation magnetization (Ms = 92 emu/g at 5 K), close to the expected value for bulk magnetite. Besides, the use of a variety of reducing agents monitors the magnetic behavior. In the case of 1,2-hexadecanediol, magnetic characterization suggests that the nanoparticles have uniform oxidation. However, those particles prepared without the use of any reducing agent also show uniform oxidation just with a slightly smaller value of the saturation magnetization (Ms = 76 emu/g at 5 K). In contrast, hydrazine seems to promote a nonuniform oxidation that results in the appearance of the exchange bias phenomenon and in a smaller saturation magnetization (Ms = 67 emu/g at 5 K). New ways to tune the shape, the size, and the magnetic properties are discussed.12/2010; -
Article: Heating rate influence on the synthesis of iron oxide nanoparticles: the case of decanoic acid.
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ABSTRACT: Iron oxide nanoparticles with uniform sizes between 13 nm and 180 nm can be selectively prepared through the "heating up" thermal decomposition method by using decanoic acid and carefully tuning the heating rate.Chemical Communications 09/2010; 46(33):6108-10. · 6.17 Impact Factor -
Article: Controlled synthesis of iron oxide nanoparticles over a wide size range.
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ABSTRACT: We report on the effect of using decanoic acid as capping ligand on the synthesis of iron oxide nanoparticles by thermal decomposition of an organic iron precursor in organic medium. This procedure allowed us to control the particle size within 5 nm and about 30 nm by modifying the precursor-to-capping ligand ratio in a systematic fashion and to further expand the particle size range up to about 50 nm by adjusting the final synthesis temperature. The nanoparticles also showed high saturation magnetization of about 80-83 emu/g at low temperature, almost size-independent and close to the value for the bulk counterpart. Decanoic acid-coated nanoparticles were transferred to water by using tetramethylammonium hydroxide, which allowed further coating with silica in a tetraethyl orthosilicate solution. Consequently, these iron oxide nanoparticles are tunable in size and highly magnetic, and they could become suitable candidates for various biomedical applications such as contrast agents for magnetic resonance imaging and magnetic carriers for drug delivery.Langmuir 12/2009; 26(8):5843-7. · 4.19 Impact Factor -
Article: Reaction regimes on the synthesis of hollow particles by the Kirkendall effect.
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ABSTRACT: The formation of hollow vs solid particles by means of the oxidation reaction of solid metal particles depends on the differential self-diffusivities of the reactants through the composite shell, the reaction probabilities at each interface, and the concentration and diffusivity of the element in solution. By means of a kinetic model of the oxidation process, we determine the phase diagrams for the geometry of the oxidized particles and propose four shell growth regimes. We experimentally illustrate the different growth scenarios by changing the conditions of oxidation of cadmium spherical crystals using different chalcogen precursors.Journal of the American Chemical Society 08/2009; 131(32):11326-8. · 9.91 Impact Factor -
Article: Surface anisotropy broadening of the energy barrier distribution in magnetic nanoparticles
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ABSTRACT: The effect of surface anisotropy on the distribution of energy barriers in magnetic fine particles of nanometer size is discussed within the framework of the $T\ln(t/\tau_0)$ scaling approach. The comparison between the distributions of the anisotropy energy of the particle cores, calculated by multiplying the volume distribution by the core anisotropy, and of the total anisotropy energy, deduced by deriving the master curve of the magnetic relaxation with respect to the scaling variable $T\ln(t/\tau_0)$, enables the determination of the surface anisotropy as a function of the particle size. We show that the contribution of the particle surface to the total anisotropy energy can be well described by a size--independent value of the surface energy per unit area which permits the superimposition of the distributions corresponding to the particle core and effective anisotropy energies. The method is applied to a ferrofluid composed of non-interacting Fe$_{3-x}$O$_{4}$ particles of 4.9 nm in average size and $x$ about 0.07. Even though the size distribution is quite narrow in this system, a relatively small value of the effective surface anisotropy constant $K_{s}=2.9\times 10^{-2}$ erg cm$^{-2}$ gives rise to a dramatic broadening of the total energy distribution. The reliability of the average value of the effective anisotropy constant, deduced from magnetic relaxation data, is verified by comparing it to that obtained from the analysis of the shift of the ac susceptibility peaks as a function of the frequency.10/2008; -
Article: Correction to Growth Kinetics of Asymmetric Bi(2)S(3) Nanocrystals: Size Distribution Focusing in Nanorods (vol 115, pg 7947, 2011)
JOURNAL OF PHYSICAL CHEMISTRY C. 115(23):11888. -
Article: Growth Kinetics of Asymmetric Bi(2)S(3) Nanocrystals: Size Distribution Focusing in Nanorods
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ABSTRACT: The growth kinetics of colloidal Bi(2)S(3) nanorods was investigated. After nucleation, the length distribution of the growing Bi(2)S(3) nanorods narrows with the reaction time until a bimodal length distribution appears. From this critical reaction time on, the smallest nanorods of the ensemble dissolve, feeding with monomer the growth of the largest ones. A comprehensive characterization of the size-distribution evolution of Bi(2)S(3) nanorods is used here to illustrate the dependences of the anisotropic growth rates of cylindrical nanoparticles on the nanoparticle dimensions and the monomer concentration in solution. With this goal in mind, a diffusion-reaction model is presented to explain the origin of the experimentally obtained out length distribution focusing mechanism. The model is able to reproduce the decrease of the growth rate in the nanorod axial direction with both its thickness and length. On the other hand, low lateral reaction rates prevent the nanorod thickness distribution to be focused. In both crystallographic growth directions, a concentration-dependent critical thickness exists, which discriminates between nanorods with positive growth rates and those dissolving in the reaction solution.JOURNAL OF PHYSICAL CHEMISTRY C. 115(16):7947-7955.
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2010
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University of Barcelona
Barcelona, Catalonia, Spain
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