The aggregation process in tetraethoxysilane-derived sonogels as an analogy to the critical phenomenon
Nenhuma Miniatura disponível
Data
2008-06-25
Autores
Vollet, D. R. [UNESP]
Donatti, D. A. [UNESP]
Ruiz, Alberto Ibanez [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Iop Publishing Ltd
Resumo
The structural evolution in silica sols prepared from tetraethoxysilane (TEOS) sonohydrolysis was studied 'in situ' using small-angle x-ray scattering (SAXS). The structure of the gelling system can be reasonably well described by a correlation function given by gamma(r) similar to (1/R(2))(1/r) exp(- r/xi), where xi is the structure correlation length and R is a chain persistence length, as an analogy to the Ornstein-Zernike theory in describing critical phenomenon. This approach is also expected for the scattering from some linear and branched molecules as polydisperse coils of linear chains and random f-functional branched polycondensates. The characteristic length. grows following an approximate power law with time t as xi similar to t(1) (with the exponent quite close to 1) while R remains undetermined but with a constant value, except at the beginning of the process in which the growth of. is slower and R increases by only about 15% with respect to the value of the initial sol. The structural evolution with time is compatible with an aggregation process by a phase separation by coarsening. The mechanism of growth seems to be faster than those typically observed for pure diffusion controlled cluster-cluster aggregation. This suggests that physical forces (hydrothermal forces) could be actuating together with diffusion in the gelling process of this system. The data apparently do not support a spinodal decomposition mechanism, at least when starting from the initial stable acid sol studied here.
Descrição
Palavras-chave
Como citar
Journal of Physics-condensed Matter. Bristol: Iop Publishing Ltd, v. 20, n. 25, p. 5, 2008.