Sols, formation

Chow M K and Zukoski C F 1994 Gold sol formation meohanism role of oolloidal stability J. Coll. Int. Sc/. 165 97... 

Condensation of these monomers to form colloidlike oligomers (sol formation). 

Multicomponent sol—gel fibers have been successfuUy developed (1,52). The early stages of sol formation and gelation are cmcial for controlling the fiber microstmcture. Aluminosilicates, zirconates, and aluminates (1,18,52) can be prepared by sol—gel methods. MuUite [55964-99-3] 3AI2 O3 -2Si02, fibers... 

Precipitation is effected in hot solutions, provided the solubility and the stability of the precipitate permit. Either one or both of the solutions should be heated to just below the boiling point or other more favourable temperature. At the higher temperature (a) the solubility is increased with a consequent reduction in the degree of supersaturation, (b) coagulation is assisted and sol formation decreased, and (c) the velocity of crystallisation is increased, thus leading to better-formed crystals. 

In this case, there is no distinct sol formation process but rather simultaneous hydrolysis and condensation reactions proceed to form a gel. 

Fig. 3.1 Ti me dependences of the complex viscosity measured at a frequency of 1 Hz. An aqueous solution was prepared by dissolving 30wt.% of precursor and 0.2wt.% of N-[(trimethox-ysilyl)propyl]-N,N,N-trimethylammonium chloride in 0.01 M sulfuric acid. The stages ofthe sol-gel processes discussed in the text are I - condensation and sol formation, II - sol-gel transition, III - gel maturation. (Unpublished results).

It should be pointed out that the diglyceryl silane is a solid compound [113,138,139] thus sol-gel processing with its participation is performed through dissolution of the precursor in an aqueous solution. This leads, as shown experimentally in Ref. [140], to the hydrolysis and subsequent sol formation in accordance with Equations (2)-(4). The important consequence is that the diglyceryl silane can be involved only in the two-stage immobilization procedure shown schematically in Figure 3.3. 

The one-stage process with THEOS proceeds differently (Figure 3.7B). The difference is in the absence of sol nanoparticles in the initial solution. There are entangled macromolecular chains (stage 1, Figure 3.7B). The silica precursor is introduced in a biopolymer solution as a monomer. The experimental results available to date (see Section 3.4.2) demonstrate that instead of sol formation there... 

Biocompatible silica nanoparticles prepared by analogous sol formation followed by emulsification and doped with the antibiotic... 

Laschtschenko therefore suggested that the amorphous forms may be of colloidal origin and may thus represent stages in the continuous passage from the colloidal to the crystalline state. The mode of preparation of the brown form by reduction of arsenic compounds in solution is favourable to sol formation, and the view that the various forms differed only in degree of dispersion of the particles has already been mentioned (p. 30). X-ray investigations6 show that the precipitated... 

Warm the solutions to 60°C and quickly add the reducing mixture to the gold solution while stirring. The temperature is critical at this stage. Evidence of sol formation is the red color of the mixture. 

Aggregation methods usually lead to the formation of polydispersed sols, mainly because the formation of new nuclei and the growth of established nuclei occur simultaneously, and so the particles finally formed are grown from nuclei formed at different times. In experiments designed to test the validity of theories, however, there are obvious advantages attached to the use of monodispersed systems. The preparation of such systems requires conditions in which nucleation is restricted to a relatively short period at the start of the sol formation. This situation can sometimes be achieved either by seeding a supersaturated solution with very small particles or under conditions which lead to a short burst of homogeneous nucleation. 

Y = gel formed ut room temperature unless noted otherwise N = no evidence of gel formation sol = sol formation ppt = precipitate soln = isotropic-like solution. 

Preparation of metal oxides by the sol—gel route proceeds through three basic steps (/) partial hydrolysis of metal alkoxides to form reactive monomers (2) the polycondensation of these monomers to form coUoid-like oligomers (sol formation) and (i) additional hydrolysis to promote polymerization and cross-linking leading to a three-dimensional matrix (gel formation). Although presented herein sequentially, these reactions occur simultaneously after the initial processing stage. 

High levels of SERS activity can be expected if nanoparticle substrates were prepared by colloidal chemical methods because colloidal particles tend to aggregation, thus forming the narrow interparticle spacings needed for plasmon coupling. A traditional technique for the preparation of silver colloids is the sol formation according to Lee et al. [17]. 

Chow MK, Zukoski CF (1994) Gold sol formation mechanisms role of colloidal stability. J Colloid Interface Sci 165 97-109... 

The sol formation step can be carried out by precipitating a hydroxide with ammonia, which is then washed and dispersed as a sol by peptizing the slurry while controlling the pH. A 3.5 M zirconia sol, prepared by dispersing zirconium hydroxide in a dilute acid and then adding calcium or yttrium salt solutions, produces Y203-stabilized... 

We will discuss first the reaction kinetics by which the turbidity increases. As shown by Ottewill and Watanabe (15) in the case of sol formation, a complex series of consecutive and simultaneous reactions occur. These can be schematically presented as follows (15) ... 

P. Chanaud, A. Julbe, P. Vaija, M. Persin and L. Cot, Study of lanthanum-based colloidal sols formation. /. Mater. Sci., 29 (1994) 4244. 

Alkali metal hydroxides, dissolution rate effect, 521-523f Alkoxides, formation of uniform precipitates, 451-464 Aluminum, silicic acid effect on adsorption in food, 612/ 613 Aluminum in biological systems, 604, 605f, 606 Aluminum-modified silica sol, formation, 62, 63/ Aluminum-silicon interactions in biology,... 

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