Silica fibrillar

When the slurry ages, the pH rises, and, consequently, the viscosity rapidly elevates, there appears to be a breakdown in the mechanism that binds the solid particles in the silica matrix. With a well-developed sol, this behavior is more controllable. We believe that, at longer aging times, the microgel development proceeds by mechanisms more favorable to a finely textured, fibrillar structure (19). Hence, catalysts bound with this gel are more attrition resistant. We suggest that the dependence of attrition on slurry age/viscosity may be a consequence of an inhibition to forming a strong matrix. The most important conclusion that can be drawn from... 

Fio. 4. Examples of structural motifs exhibited by plant silicas extracted from macrohairs of Phalaris canariensis. (a) Sheetlike, (b) globular, and (c) fibrillar. 

We have observed in various kinds of plant hairs that silica particles are packed around a central axial channel, which at the early stages of development contains cytoplasmic material and a large vacuole, which is the likely pathway for water flow. An explanation for the structural motifs observed could proceed as follows Along the inner edge of this cylinder the silica appears closely packed (fibrillar) and ordering is... 

Silica deposition within the interior of the cusps often showed directional character, with fibrillar elements preferentially oriented both transverse and longitudinal to the axis of the teeth. Some central regions of the cusp comprised random aggregates of fibrillar silicified material. Most internal regions investigated appeared highly porous with extensive voids. 

Fig. 5.2 a-c. Electron micrograph of a fractured silica fibre from the weed Phalaris canariensis showing three regions of differing substructure (x 11,000)"" . Insets a, sheet (x 56,000) b, globular (x 33,000) c, fibrillar (x 24,000) arrangements of deposited silica... 

Most approaches to 1-D PPy nanomaterials have been dependent on the chemical and electrochemical polymerization methods using various templates such as AAO and polymer membranes [165,224-230], mesoporous silica [168,231], inorganic nanofibers [232], surfactants [233], and biomaterials [234,235]. The fibrillar and tubular PPy nanomaterials with controlled diameters were mainly fabricated within the cylindrical pores of AAO or PC membranes [165,225,226]. The 1-D PPy nanomaterials have shown the... 

Figure 3.23. Gels of equal silica concentration. However, smaller particles develop greater coalescence and strength and the structure becomes more fibrillar.

The acid-catalyzed polycondensation of tetraethoxysilane, a silicic acid precursor, results in the formation of an aggregated silica gel (Figure 1). Con aratively, the three-dimensional structure of die aggregated silica gel was similar to the natural morphologies of the silica particles catalyzed by proteins (9) and polypeptides (12J3J7). Furthermore, e use of external force was demonstrated (21) to control the morphology (e.g. arched, fibrillar) of a silica material catalyzed by a biomimetic silaffin peptide (i.e. a non-modified Sil Ip R5... 

It is clearly seen that original silica particles grow with the encapsulation of SPS by the polymerization and that the fuUy grown SPS particles maintain the shape characteristics of the original silica catalyst particles. It is an interesting result because as shown in Rgure 8.7c,d, the SPS particles show a fibrillar... 

A more complex approach to the collagen-silica system has been reported by Niu et al. who infiltrated fibrillar polyallylamine-enriched collagen sponges with... 

Rizkov et al. ° used L-and D- 3-amino alcohols for the enantioseparation of, among others, dansylated (Dns) AAs by CZE in a low-molecular-weight organogel (LMOG)-filled capillary. This LMOG is a fibrillar gel of trans-(15,2S)-l,2-bis-(dodecylamido) cyclohexane in MeOH. Bare fused-silica capillaries with an i.d. of 100 fim and a total length of 60.0 cm (52.0 cm effective length) were used. The BGE contained 10-mM 3-amino alcohol and 5-mM cupric acetate monohydrate in MeOH with pH 5. The selector copper-valinol (2 1) performed best compared... 

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