Monodisperse magnetic nanoparticles: Preparation and dispersion in water and oils
- PDF / 310,343 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 11 Downloads / 276 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Monodisperse magnetic nanoparticles: Preparation and dispersion in water and oils S. Lefebure, E. Dubois, V. Cabuil,a) S. Neveu, and R. Massart Laboratoire Liquides Ioniques et Interfaces Charg´ees,b) Equipe “Collo¨ıdes Magn´etiques,” Universit´e Pierre et Marie Curie, Paris, France (Received 13 December 1996; accepted 3 April 1998)
Nanometric maghemite and cobalt ferrite particles are chemically synthesized. The process produces particles polydisperse in size. The positive charges of their surface allow one to disperse them in aqueous acidic solutions and to obtain dispersions stabilized through electrostatic repulsions. Increasing acid concentration (in the range 0.1 to 0.5 mol.L21 ), interparticles repulsions are screened and phase transitions are induced. Using this phenomenon, we describe a two-step size sorting process, in order to get significant amounts of nanometric monosized particles (with diameters monitored between typically 6 and 13 nm). As the surface of the latter is not modified by the size sorting process, usual procedures are used to disperse them in several aqueous or oily media.
I. INTRODUCTION
Production of monodisperse magnetic particles in the nanometric range is an important problem to solve because magnetic properties of fine particles are strongly size dependent.1–3 More generally, average properties of collections of particles are influenced by the polydispersity of the samples, each average being specific of the property or characterization technique under consideration.4 Some solutions have been proposed: small monosized magnetite or cobalt ferrite particles have been synthesized inside micelles or vesicles,5,6 and size sorting methods have been proposed using centrifugation or magnetic separation.7 But on a practical point of view, such synthesis procedures are not so easy to carry out when large amounts of particles are needed. We propose here a procedure which allows one to get large quantities of magnetic monodomain particles with a very narrow size distribution. This method allows further dispersion of the particles in several media (oils, organic or aqueous solvents, . . . ). Magnetic ferric oxide particles in the nanometric range may be obtained by several methods. An easy procedure is a chemical one, which has been well known for a long time,8 but was reactualized by one of us in order to synthesize ionic magnetic fluids,9 which means dispersions of nanosized magnetic particles in water, stabilized without surfactant.10 Varying experimental conditions of the chemical process allows one to control the average diameter of particles between 3 and 20 nm, but does not allow one to reduce the
a)
Author to whom correspondence should be sent. Associated with the CNRS.
b)
J. Mater. Res., Vol. 13, No. 10, Oct 1998
http://journals.cambridge.org
Downloaded: 11 Jul 2014
polydispersity of the system.11 The procedure we present here is not a modification of the experimental conditions for the synthesis of particles, but a size sorting pro
Data Loading...
