Colloids silica particles

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

The Stober method is also known as a sol-gel method [44, 45], It was named after Stober who first reported the sol-gel synthesis of colloid silica particles in 1968 [45]. In a typical Stober method, silicon alkoxide precursors such as tetramethylorthosili-cate (TMOS) and tetraethylorthosihcate (TEOS), are hydrolyzed in a mixture of water and ethanol. This hydrolysis can be catalyzed by either an acid or a base. In sol-gel processes, an acidic catalyst is preferred to prepare gel structure and a basic catalyst is widely used to synthesize discrete silica nanoparticles. Usually ammonium hydroxide is used as the catalyst in a Stober synthesis. With vigorous stirring, condensation of hydrolyzed monomers is carried out for a certain reaction time period. The resultant silica particles have a nanometer to micrometer size range. 

Silica gel is synthetic amorphous silica consisting of a compact network of spherical colloidal silica particles. Its surface area is typically between 300 and 850 m2/g. The predominant pore diameters are in the range 22-150 A. Silica gel is produced via the following procedure a sodium silicate solution reacts with a mineral acid, such as sulfuric acid, producing a concentrated dispersion of finely divided particles of hydrated Si02,... 

Polymer beads have also been tagged by treating them after each new diversity-introducing reaction with dye-containing, colloidal silica particles, which can be irreversibly adsorbed on the surface of the beads with the aid of polyelectrolytes such as poly(diallyldimethylammonium chloride) and poly(acrylic acid) [42,43]. Larger portions of support can also be linked to a chip that enables electronic tagging with a radio emitter [44-46]. 

A continuous Fl-FFF channel analogous to a dialysis cell or ultrafiltration cell [247] was described theoretically and later demonstrated in practice for the separation of bovine serum albumin from methylene blue, various viruses, proteins, and colloidal silica particles. 

Silica can exist in many crystalline forms such as quartz, cristobalite, and tridymite. Fumed silica on the contrary tends to be amorphous, which could be attributed to the fabrication process of the abrasive. The amorphous nature is probably caused by the rapid cooling employed in the process [83]. Colloidal silica, which is usually synthesized via wet chemical methods, is highly amorphous as well. In addition, colloidal silica particles are usually spherical and highly hydrated in nature, which makes them far less likely to cause scratches on metal substrate surface. 

FIGURE 7.17 Polymer particles deforming under the pressure providing a cushioning effect. Polymer particles coated with colloidal silica particles (from Ref 101). 

Cab-O-Sil — trademark for colloidal silica particles Viton A — trademark for a synthetic rubber derived from vinylidene fluoride and hexafluoropropylene... 

Figure 35. Schematic representation of the Ru(bpy)3 /a-ZrP/viologen onion structure grown on colloidal silica particles. The sequence of fast (1, 2) and slow (3) electron-transfer steps that follow photoexcitation of Ru(Me-vpy)(bpy)2 " polymer is shown. Reproduced from D.M. Kaschak, S.A. Johnson, C.C. Waraksa, J. Pogue and T.E. Mallouk, Coord. Chem. Rev. 1999, 185-186, 403, with permission from Elsevier Science.

Experimental Implementation. Various operational parameters affecting the formation of the density gradient generated by the electric field action on the charged colloidal silica particles and the focusing effect of larger particles were investigated experimentally under con-... 

The selection of slurry abrasives is one of the most important task in CMP process development. It will determine the removal rate and the level of defects such as particles and scratches. In this study various slurry particles and surfaces to be polished were chosen to measure their electrical properties in aqueous solutions. The harder particles, the greater the removal rates. Table 1 shows the hardness of materials of interest to CMP process. Among particles in Table 1, y-alumina, Ce02, Mn02, fumed and colloidal silica particles were used to measure their zeta potentials as a function of solution pH. 

Cab-O-Sil [Cabot], TM for colloidal silica particles sintered together in chainlike formations. Surface area ranges from 50 to 400 m2/g, depending on grade. 

Silicsol is a commercial product introduced in Europe this past decade. It is described as an activated silica liquor with a calcium-based reagent. As opposed to sodium silicate (colloidal silica particles dispersed in soda), silicsol is claimed to be a true solution. Viscosity and penetrability are similar to sodium silicate, but the reaction is different, resulting in a stronger end product more resistant to creep. There is no syneresis associated with silicsol. 

Kobayashi, M. et al., Aggregation and charging of colloidal silica particles Effect of particle size, Langmuir, 21, 5761, 2005. 

One of Ilers accomplishments was the development of a new structure consisting of porous silica beads built up from colloidal silica particles. Use of this structure in liquid phase chromatography greatly increased speed of operation and provided a first-order advance in the state of the art. 

Figure 5. Schematic representation in two dimensions of a dehydrated but fully hydroxylated colloidal silica particle. The fourth oxygen coordinated with Si is above or below the plane of the paper. The figure is only a diagram, not a model. In an amorphous silica model the Si-O-Si bond angle may vary, but the Si-O distances are constant each oxygen ion is linked to not more than two cations the coordination number of oxygen ions about the control cation is 4 or less oxygen tetrahedra share comers, not edges or faces and at least two comers of each tetrahedron are shared.

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