A general method to coat colloids with silica is described. The amphiphilic, nonionic polymer poly(vinylpyrrolidone) (PVP) was adsorbed to various colloidal particles such as small gold colloids, gold-shell silica-core particles, small and large silver colloids, boehmite rods, gibbsite platelets, and positively or negatively charged polystyrene. After this functionalization the stabilized particles could be transferred to a solution of ammonia in ethanol and directly coated with smooth and homogeneous silica shells of variable thickness by addition of tetraethoxysilane in a seeded growth process. The length of the polymer used strongly influences the stability of the colloids and the homogeneity and smoothness of the initial silica coating. This method is especially useful for colloidal particles that cannot be covered directly with SiO2 by a Stober-like growth process. Compared to methods known from the literature for the coating of such particles, this new method is faster and requires neither the use o...

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A General Method To Coat Colloidal Particles with Silica

Sol-gel based materials for biomedical applications

Formation of highly efficient dye-sensitized solar cells by hierarchical pore generation with nanoporous TiO2spheres

Monodisperse mesoporous anatase titania beads with high surface areas and tunable pore size and grain diameter have been prepared through a combined sol−gel and solvothermal process in the presence of hexadecylamine (HDA) as a structure-directing agent The monodispersity of the resultant titania beads, along with the spherical shape, can be controlled by varying the amount of structure-directing agent involved in the sol−gel process The diameter of the titania beads is tunable from ∼320 to 1150 nm by altering the hydrolysis and condensation rates of the titanium alkoxide The crystallite size, specific surface area (from 89 to 120 m2/g), and pore size distribution (from 14 to 23 nm) of the resultant materials can be varied through a mild solvothermal treatment in the presence of varied amounts of ammonia On the basis of the results of small-angle XRD, high-resolution SEM/TEM, and gas sorption characterization, a mechanism for the formation of the monodisperse precursor beads has been proposed to illust

Synthesis of Monodisperse Mesoporous Titania Beads with Controllable Diameter, High Surface Areas, and Variable Pore Diameters (14−23 nm)

Three-dimensional photonic crystals, or periodic materials, that do not allow the propagation of photons in all directions with a wavelength in the visible region have not been experimentally fabricated, despite there being several potential structures and the interesting applications and physics that this would lead to1. We show using computer simulations that two structures that would enable a bandgap in the visible region, diamond and pyrochlore, can be self-assembled in one crystal structure from a binary colloidal dispersion. In our approach, these two structures are obtained as the large (Mg) and small (Cu) sphere components of the colloidal analogue of the MgCu2 Laves phase2, whose growth can be selected and directed using appropriate wall patterning. The method requires that the particles consist of different materials, so that one of them can be removed selectively after drying (for example, by burning or dissolution). Photonic calculations show that gaps appear at relatively low frequencies indicating that they are robust and open for modest contrast, enabling fabrication from more materials.

Self-assembly route for photonic crystals with a bandgap in the visible region.

Monodisperse spherical titania particles of variable sizes are produced in a sol−gel synthesis from Ti(EtO)4 in ethanol with addition of a salt or a polymer solution. The influence of different salt ions or polymer molecules on the size and the size distribution of the final particles was investigated. The amorphous hydrous titania particles were characterized by electron microscopy, thermogravimetry, 1H-MAS NMR, X-ray absorption spectroscopy, and electrophoresis. Nitrogen absorption measurements revealed that the addition of polymers yields hollow and porous titania colloids.

Synthesis and Characterization of Porous and Nonporous Monodisperse Colloidal TiO2 Particles

Monodisperse spherical ZrO2 particles were prepared by controlled hydrolysis of zirconium tetraalkoxide in alcoholic solution. Ageing the reaction solution at 60 °C for 4 h yields particles with sizes in the range between 200 and 2000 nm. The influence of various ions and surfactants on the final product was investigated. Stable suspensions of coated, monodisperse, zirconia particles were prepared by hydrolysis and subsequent polymerisation of tetraethoxysilane in an alkaline ethanol solution. Thermal analysis revealed that the weight loss of bound water occurred below 400 °C and is about 35 %. The phase transition from amorphous zirconia to the tetragonal phase proceeded at approximately 450 °C, the transition to the monoclinic phase began at about 600 °C and was completed at about 800 °C. The crystallinity of the powders was investigated by X-ray diffraction. Electrophoretic measurements were carried out to determine the charges on the particle surface. Elementary analyses were used for further investigations. On the basis of the results obtained, the mechanism of particle formation was discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis and characterisation of monodisperse zirconia particles

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Johanna Widoniak

Papers

Synthesis and Characterization of Porous and Nonporous Monodisperse Colloidal TiO2 Particles

Synthesis and characterisation of monodisperse zirconia particles

Silver particles tailoring of shapes and sizes

ErratumErratum to “Silver particle: Tailoring shapes and sizes” [Colloids Surf. A: Physicochem. Eng. Aspects 270–271 (2005) 340–344]

Synthesis and Characterization of Porous and Nonporous Monodisperse Colloidal TiO2 Particles.