Silica monodispersed

Figure C2.17.3. Close-packed array of sub-micrometre silica nanoparticles. Wlren nanoparticles are very monodisperse, they will spontaneously arrange into hexagonal close-packed stmcture. This scanning electron micrograph shows an example of this for very monodisperse silica nanoparticles of -250 nm diameter, prepared in a thin-film fonnat following the teclmiques outlined in [236].

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

Interestingly, it was found that gold particles were not produced with monodisperse amorphous Si02 particles prepared by the method of Stober et al. [26]. Flence, silica... 

Stober, W Fink, A. and Bohn, E. (1968) Controlled growth of monodispersed silica spheres in the micron size range. Journal of... 

The use of silica particles in bioapplications began with the publication by Stober et al. in 1968 on the preparation of monodisperse nanoparticles and microparticles from a silica alkoxide monomer (e.g., tetraethyl orthosilicate or TEOS). Subsequently, in the 1970s, silane modification techniques provided silica surface treatments that eliminated the nonspecific binding potential of raw silica for biomolecules (Regnier and Noel, 1976). Derivatization of silica with hydrophilic, hydroxylic silane compounds thoroughly passivated the surface and made possible the use of both porous and nonporous silica particles in all areas of bioapplications (Schiel et al., 2006). 

Nyffenegger, R., Quellet, C., and Rieka, J. (1993) Synthesis of fluorescent, monodisperse, colloidal silica particles./. Colloid Interface Sci. 159, 150-157. 

It was apparent that the dense adsorption layer of HPC which was formed on the silica particles at the LCST plays a part in the preparation of new composite polymer latices, i.e. polystyrene latices with silica particles in the core. Figures 10 and 11 show the electron micrographs of the final silica-polystyrene composite which resulted from seeded emulsion polymerization using as seed bare silica particles, and HPC-coated silica particles,respectively. As may be seen from Fig.10, when the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of silica particles, and indeed new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were generated. This indicated that the dense adsorption layer of HPC formed at the LCST plays a role as a binder between the silica surface and the styrene molecules. 

Yamada, Y. Nakamura, T. Ishi, M. Yano, K., Reversible control of light reflection of a colloidal crystal film fabricated from monodisperse mesoporous silica spheres, Langmuir. 2006, 22, 2444 2446... 

Figure 3.6 Silica spheres with monodisperse particle size are expensive analytical gels of top performance. Silica spheres with determined particle size ranges are ideally suited for preparative chromatography. (Photo courtesy of SiliCycle.)...

Figure 1.27 Double-walled silica nanotubes with monodisperse diameters self-orga-nize into highly ordered centimetre-sized fibres, using a synthetic octa-peptide as a template. The growth mechanism is proposed to be the fundamental mechanism for growth processes in biological systems. (Reproduced from ref. 53, with permission.)...

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

In Zerrouki s experiments, the preparation of aqueous phases of identical clusters is performed in six steps. First, colloidal particles of silica, 1.2 pm in diameter, are synthesized. Next, the surface of the particles is made hydrophobic by chemical grafting. Then, an oil-in-water premix emulsion is made by adding an octane suspension of the colloids in an aqueous solution. Controlled shear of the premix in a Couette-type apparatus is subsequently performed to obtain a quasi-monodisperse... 

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