Magneto-orientational properties of ionically stabilized aqueous dispersions of Ni(OH)2 nanoplatelets.

Magnetic and orientational behavior of nickel hydroxide nanoplatelets ionically stabilized in a liquid matrix is studied. Under an applied field the platelets orient their faces normal to its direction. For characterization of the individual behavior of dispersed and non-interacting particles three techniques are used: SAXS, SQUID and magneto-optics. Analysis reveals that nickel hydroxide in a platelet phase is paramagnetic with a pronounced anisotropy of the intrinsic susceptibility, the major component of which (in the direction normal to platelet face) exceeds the minor one by about 25%.

From bulk materials to nanoparticles using a one-step electrochemical method.

This paper describes an electrochemical method which permits us to transform solid metals (cobalt, iron or nickel) into nanoparticles. An electrolysis cell is made, the anode being a metal bar and the cathode a mercury layer. Magnetic nanoparticles are obtained in one step by electroreduction of mercury. Electrolysis is performed in an aqueous medium at pH above 6 in order to avoid the reduction of protons. The magnetic nanoparticles obtained are kept in mercury and can be recovered in an organic solvent.

Synthesis and dispersion of Ni(OH)2 platelet-like nanoparticles in water.

Synthesis of nanometric platelet-like Ni(OH)2 particles is described. The role of several experimental parameters on the particle size is investigated. A colloidal dispersion of particles is produced by adsorbing ionizable organic ligands (trisodium citrate) on the particle surface. The stability of this colloidal dispersion and the particle charge density are determined for different citrate ions concentrations.

Tuning the interactions of a magnetic colloidal suspension.

We present a versatile experimental system of magnetic charged nanospheres dispersed in water that belongs to both dipolar and electrostatic systems. In this system, the interactions can be continuously tuned by varying the ionic strength I. At low I, the potential is a strongly repulsive Yukawa potential that leads to a phase diagram similar to the one of repulsive spheres (fluid and solid phases). At high I, the potential is a globally attractive Lennard-Jones potential that leads to a phase diagram similar to the one of atomic systems (gas, liquid, fluid, and solid phases).

Magnetic phospholipid tubes connected to magnetoliposomes: Pearling instability induced by a magnetic field.

We propose here a method to modify the membrane tension of phospholipid tubes with an applied magnetic field. The tubes are connected to giant liposomes capping the tubes at both ends. Tubes and liposomes are all filled with a magnetic fluid. The tension of the tube membrane is tuned by the deformation of the ending liposomes under the applied field. We modelize the magnetoliposome deformation and we are then able to describe the tube evolution. At low magnetic fields, the tube remains at equilibrium with a cylindrical shape and a uniform radius. It responds to an increase of membrane tension by a diameter reduction. Above a magnetic-field threshold, the cylindrical shape becomes unstable with respect to a pearling deformation. The tube shape then selected by the system is an unduloid, with a constant mean curvature equal to C 0, the spontaneous curvature of the membrane.

Shape transitions of giant liposomes induced by an anisotropic spontaneous curvature.

We explore how a magnetic field breaks the symmetry of an initially spherical giant liposome filled with a magnetic colloid. The condition of rotational symmetry along the field axis leads either to a prolate or to an oblate ellipsoid. We demonstrate that an electrostatic interaction between the nanoparticles and the membrane triggers the shape transition.

Silica Coating on Colloidal Maghemite Particles.

Maghemite colloidal particles are coated with a silica layer using a silicon alkoxide as silica precursor. The coating process is studied by electrophoresis, quasi-elastic light scattering, nitrogen adsorption, and infrared spectrometry analyses. The conditions of complete coverage of the iron oxide particles by silica and the nature of the maghemite-silica interface are discussed. Copyright 1999 Academic Press.

Incorporation of Magnetic Nanoparticles in New Hybrid Networks Based on Heteropolyanions and Polyacrylamide.

The copolymerization of acrylamide with the tetrafunctionalized polyanion [gamma-SiW(10)O(36)(RSiO)(4)](4-) (R=C(3)H(6)OC(O)C(Me)=CH(2)), which acts as a cross-linker, is performed in an aqueous dispersion of maghemite (gamma-Fe(2)O(3)) nanoparticles. It results in a magnetic hybrid hydrogel with superabsorption properties (see scheme). The magnetic properties of the nanoparticles enables their mobility inside the network to be estimated and their release during the swelling of the hydrogel to be observed.