Bonini

Slide1 : Silica-Coated Magnetic Nanoparticles: Synthesis and Characterization Massimo Bonini1, Albrecht Wiedenmann2, Piero Baglioni1 1. Department of Chemistry and CSGI, University of Florence, via della Lastruccia 3, I-50019 Sesto Fiorentino (Florence), Italy 2. Hahn-Meitner-Institut, Glienicker Strasse 100, D-14109 Berlin, Germany


Slide2 : FERROFLUIDS Stable Colloidal Suspension of Magnetic Material (Nanoparticles) in a Liquid Carrier Each Nanoparticle Constitutes a Single Magnetic Domain - SuperParaMagnetism - Applications: magnetic seals, lubricants, loudspeakers, dumpers, inks, medicine,…


Slide3 : Aim of this project: Demonstrate that this synthetic strategy really works! Find a synthetic approach that allows a fine control on the thickness of the shell Synthesize ferrofluids constituted by nanoparticles with a magnetic core and a non-magnetic shell (silica: inert, bio-compatible, well established surface chemistry)


Slide4 : Uncoated Cobalt-Ferrite Ferrofluid: Synthesis Cobalt Ferrite Ferrofluids were synthesized introducing some modifications to the Massart’s method1. 1. Massart, R.; U.S. Patent 4329241, 1982.


Slide5 : Uncoated Cobalt-Ferrite Ferrofluid: TEM Characterization TEM micrograph and size distribution of the un-coated cobalt ferrite ferrofluid. The solid line represents the best fit of the data according to a lognormal size distribution.


Slide6 : Silica Coated Cobalt-Ferrite Ferrofluid: Synthesis In order to take advantage from the variation of contrasts, two silica coated nanoparticles batches were synthesized: the first one in water and the other in a H2O/D2O 30/70% vol. mixture. An aliquot of the uncoated nanoparticles was added at room temperature to a mixture of water and 2-propanol. Ammonia water solution and TEOS were consecutively added. This procedure was repeated for a number of times so that the final thickness of the shell was 2 nm (in the hypothesis that all the nanoparticles would be covered by a uniform coating). The core-shell nanoparticles were separated from the reaction medium and then dispersed in water.


Slide7 : TEM micrograph and size distribution of the silica-coated cobalt ferrite ferrofluid. The solid line represents the best fit of the data according to a lognormal size distribution. Particles indicated by the arrows seem to be constituted by more than one magnetic cores. Silica Coated Cobalt-Ferrite Ferrofluid: TEM Characterization


Slide8 : The V4 SANSPOL Instrument at BENSC - Berlin For complete alignment of the moments along H: A(Q)=FN2 and B(Q)=FM2 where FN and FM are the nuclear and magnetic form factors, Q is the scattering vector and  is the angle between H and Q.


Slide9 : SANSPOL: Iso-Intensity Plots


Slide10 : SANSPOL: 2-D Data Averaging I(QH) and I(Q//H) were calculated in two separate ways, obtaining identical results: by adjusting the 2-D pattern to the sin2 dependence; by averaging the 2-D pattern over two sectors (both with a width of 5º). In the case of a dilute system of non-interacting particles with all the moments aligned along H, the SANSPOL intensities perpendicular and parallel to the applied field are given for the two states by:


Slide11 : Uncoated Cobalt-Ferrite Ferrofluid: SANSPOL Characterization Fitting Parameters: Spherical Particles: Np number density of particles Vp volume of the particles N(R) size distribution of particles F(Q,R) form factor


Slide12 : Uncoated Cobalt-Ferrite Ferrofluid: I(QH) SANSPOL intensities perpendicular to the applied field of un-FF: I+(QH) () and I-(QH) (). Solid lines represent the best fittings according to the spherical model. Size distribution (solid line) and volume weighted size distribution (dotted line). Scattering intensities scale over the whole Q range. I(Q//H) data confirm I(QH) results.


Slide13 : Silica Cobalt-Ferrite Ferrofluid: SANSPOL Characterization Fitting Parameters: Silica Coated Ferrofluid (Core-Shell Particles): Np number density of particles Vp volume of the particles N(R) size distribution of particles F(Q,R) form factor R1, R2 core and shell radii Schematic scattering length density profile as obtained from SANSPOL intensity fitting procedure.


Slide14 : Silica Coated Cobalt-Ferrite Ferrofluid: I(QH) Experimental SANSPOL perpendicular to the applied field data obtained for silica coated cobalt-ferrite nanoparticles. Solid lines: fittings according to a core-shell model. a) H2O/D2O mixture [I-(QH)(), I+(QH)()]. b) pure water [I-(QH)(), I+(QH)()].


Slide15 : Silica Coated Cobalt-Ferrite Ferrofluid: I(Q//H) SANSPOL intensities parallel the applied field obtained with co-FF in 30:70 water/heavy water mixture () and pure water (). Solid lines: fittings according to the core-shell model.


Slide16 : Silica Coated Cobalt-Ferrite Ferrofluid: SANSPOL Results Comparison of size distributions of magnetic nanoparticles as obtained by TEM of un-FF, SANSPOL of un-FF and SANSPOL of co-FFs (in this latter case size distribution of the cores is reported). Silica Shell Thickness = 1.8 nm


Slide17 : Conclusions Silica-coated magnetic ferrofluids were successfully synthesized by coating cobalt ferrite magnetic nanoparticles. TEM and SAXS analysis do not allow to correctly evaluate the thickness and the polydispersity of the shell. Both un-coated and silica-coated ferrofluids have been characterized by means of SANSPOL analysis, obtaining a uniform silica shell thickness of 1.8 nm.The synthesis was performed in a way to obtain a thickness of 2 nm.