Effect of Gravity on the Gelation of Silica Sols

Autor:	Gwenael J. A. Chiffoleau, Christine L. Pienaar, Lana R. A. Follens, Johan A. Martens, Theodore A. Steinberg, Christine E. A. Kirschhock
Rok vydání:	2007
Předmět:	Centrifuge Gravity (chemistry) Buoyancy Materials science General Chemical Engineering Intermolecular force General Chemistry engineering.material Silicate chemistry.chemical_compound Chemical engineering chemistry Polymerization Materials Chemistry engineering Organic chemistry Porosity Sol-gel
Zdroj:	Chemistry of Materials. 19:660-664
ISSN:	1520-5002 0897-4756
Popis:	Acid-catalyzed silica polymerization was carried out under gravity conditions varied from 0.01g aboard a reduced gravity aircraft to 70g in a centrifuge. The silicate connectivity of the final xerogels was analyzed using solid state 29Si NMR and the porosity using nitrogen adsorption. Gravity was found to have an important influence on the occurrence of intra- and intermolecular condensation reactions. Under reduced gravity buoyancy driven-free convection is limited and silica polymerization occurs in a diffusion-limited regime. Intramolecular condensations and densifications prevail and extended coils of cages are formed through cyclization reactions in the sol particles. In terrestrial and high-gravity conditions, bimolecular reactions compete more favorably with internal condensations. More open structures composed of chains and rings are formed. These flexible species delay the onset of gelation, leading to an increase in gelation time as the gravity level is increased. During the subsequent drying pr...
Databáze:	OpenAIRE
Externí odkaz:	https://explore.openaire.eu/search/publication?articleId=doi_________::e430239816cd2e6702d530e6ee1e7020 https://doi.org/10.1021/cm0527219 Zobrazit plný text záznamu