Silica concentration, aggregation kinetics

Influence of Total Silica Concentration on Aggregation Kinetics, Dilution of the silicate solution would be expected to give rise to a crossover in the type of aggregation behavior of the primary silicate particles. For relatively concentrated systems ([Si02] 5 wt %), a... 

Influence oe Total Silica Concentration ON Aggregation Kinetics... 

Rheological experiments were used by Wittmar et al. (2012) for the stability analysis of functionalised nanoparticles in ionic liquid. The authors examined viscosity curves (i.e. viscosity vs. shear rate) as well as viscoelastic properties for suspensions of varying particle concentration but identical preparation history. The qualitative criterion for destabilisation was whether the suspensions did gel, i.e. whether the storage modulus G was smaller the loss modulus G". A different approach was proposed by Vogelsberger et al. (2000), who studied the nucleation and aggregation kinetics of silica, synthesised via TEOS (tetraethyl-orthosilicate) condensation and precipitation. For that purpose, the viscosity and the viscoelastic moduli were continuously monitored. The latter data were i. a. used to derive the rate of aggregation. 

Addad, J.P.C., Dujourdy, L. Silica concentration dependence of the kinetics of polydimethylsiloxane adsorption on aggregates. Polym. Bull. 41, 253 (1998)... 

Frolov, Shabanova, and co-workers (37-39) studied the transition of a sol into a gel and the aggregate stability of colloidal silica. Their aim was to develop a technology for the production of highly-concentrated silica sols and to use them as binders, catalyst supports, polymer fillers, adsorbents, and so forth. Kinetic studies were made of polycondensation and gel formation in aqueous solutions of silicic acids. At the stage of particle growth, poly condensation proceeds in the diffusion-kinetic region. With changes in pH, temperature, concentration, and the nature of electrolytes,... 

The aluminum present in ionic form in natural water can normally be expected to occur for the most part as complexes of fluoride or hydroxide, or of sulfate in some waters of low pH. These are possibly overshadowed in waters whose pH is below neutrality by polymerized hydroxide aggregates of colloidal or subcolloidal size. The occurrence of polymerized hydroxide will depend on the past history of the water and on kinetic rather than equilibrium considerations. Some standard procedures for determination of aluminum are insensitive to the hydroxide polymer and many existing analyses probably reflect this fact. The behavior of aluminum in natural water is probably also related to concentrations of dissolved silica. This aspect of aluminum chemistry is being studied in our laboratory. 

A cosolvent is usually present in fairly large amount and miscible with the main solution solvent. A cosolvent will alter micellar behavior and the reactivity of the inorganic components. A cosolvent could lead to increase surfactant solubility and modification of the critical micellar concentration (increased in most cases). The cosolvent is normally not located within the micellar aggregates. However, specific interaction with the polar head groups is possible. Furthermore, the kinetics of hydrolysis and condensation of inorganic precursors (e.g. alkoxysilane) may be affected. Methanol and ethanol are typical examples, acting as cosolvent in aqueous syntheses of mesoporous silica. 

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