Preparation and properties are discussed of a novel magnetic dispersion, containing surface-modified silica colloids with a core of single-domain magnetite particles. The underlying idea is to tailor the silica shell thickness and surface properties such that the colloids are stable spheres with isotropic interactions, whereas an external magnetic field produces weak dipolar attractions and consequently reversible anisotropic structures. The influence of the shell thickness is analyzed in terms of a dipolar-sphere potential. Preparation of magnetite cores, silica growth, and surface modifications with an alcohol and a silane are described in detail. Particle properties are investigated, among other things, with SAXS, light scattering, and electron microscopy. The major conclusion is that the preparation route yields stable, nonaggregated magnetic silica particles with a shape and internal structure which is mainly determined by small magnetite clusters in the starting ferrofluid.

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We report a single step procedure to prepare monodisperse colloidal poly (

Fairly monodisperse colloidal boehmite fibrils with a high aspect ratio were synthesized by hydrothermal treatment at 150°C of an acidified aqueous alkoxide solution, prepared by adding an aqueous HCl solution to an aluminum alkoxide precursor. The average particle length could be controlled between about 100 and 500 nm by varying the initial amounts of alkoxide and acid. Using two different alkoxides in a 1 : l molar ratio yielded the most needlelike product, having a particle length standard deviation of 40%. The boehmite particles were polycrystalline and contained 0.14 mol of excess H 2 0 per mol of AlOOH, bound to the particle surface. [

We report the emulsion polymerization and seeded growth of negatively charged, monodisperse fluorinated latex spheres in water with radii in the range 50-700 nm. Due to their low refractive index (np ) 1.3660), the spheres can be index matched in aqueous media, without any complications due to (optical) polydispersity or specific solvent adsorption. Such index-matched dispersions of fluorinated latex allow study of the structure and dynamics of strongly interacting charged colloids in water, using light scattering or microscopy. Moreover, we prepared core-shell particles with fluorinated latex shells and optically anisotropic PFA (tetrafluoroethylene copolymerized with perfluoroalkylvinyl ether) cores. We demonstrate with depolarized light scattering that these cores allow for measurement of rotational self-diffusion. The fluorinated latex dispersions are characterized extensively using light scattering, electron microscopy, atomic force microscopy, and electrophoresis. Optical contrast variation is used to determine the particle refractive index and to demonstrate that the particles are optically homogeneous.