Silicate oligomers structure

Approximately 85% of the of the peak area shown in Figure 1 can be assigned to 19 specific silicate structures 14.51. A schematic of these structures is presented in Table I, together with the chemical shift for each distinct silicon atom. It is evident from this table that silicate oligomers tend to occur as single and multiple ring structures, rather than as linear chains. 

In the following section the structure of the silicate oligomers will be considered in more detail. 

Because the structure of silicates oligomers tend to be as condensed as possible, structures with long linear chains and large cyclic rings are less plausible. On the basis of this statement, structures containing three-membered rings and threefold substituted Si sites appear the most likely candidates. Therefore, the most probable structure of the analysed species is 7e. In combination with two other samples... 

STRUCTURE of the SILICATE OLIGOMERS The experimentally identified species (9.10.11) are comprised of a rather small number of silicon tetrahedra (t < 12). They are for instance linear (t = 1 to 4). cyclic (t = 3 and 4). bicyclic oligomers (t = 6,8 and 12) consisting of 2 identical rings. There are, in addition, more complex species related to the cyclic trimer and tetramer and other polycyclic forms (t 7 and 8). 

Silicate oligomers in basic media have been demonstrated to form preorganized inorganic-organic structures in the presence of TPA+ ions which have short order, and have a configuration similar to that of the final crystal structure [56]... 

The classic description of the structure and mechanisms of formation of silica sols by the hydrolysis and condensation of silicates in aqueous media was given by Iler in 1979 (I). According to Iler, polymerization may occur in essentially three stages (1) the polymerization of monomers to oligomers and then to primary particles, (2) growth of particles, and (3) particle aggregation to form networks that eventually give rise to a gel... 

Biosilica extracts from Equisetum arvense have been found to accelerate the rate of formation of small oligomers of silicic acid, and more silica was produced that exhibited a narrower distribution of particle sizes than for silica formed in the absence of the biomolecule extracts (Figure 37.3), with the particle size distribution closely mirroring that found for the biogenic silica from which the biosilica extract was taken. Layered, crystalline materials were also produced that could have arisen from the epitaxial matching of initially formed oligomers on a p-sheet type material, the silica structure continuing to develop from the initial biopolymer-controlled nucleation event. 

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