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Fractal Structure and Fractal Time in Silica Sol-Gels

Published online by Cambridge University Press:  28 February 2011

James E. Martin  and
Jess Wilcoxon
James E. Martin
Affiliation:
Sandia National Laboratories,Albuquerque,NM 87185
Jess Wilcoxon
Affiliation:
Sandia National Laboratories,Albuquerque,NM 87185
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Abstract

Near the gel point, light scattering studies of silica sol-gels reveal fractal clusters whose size diverges as a power law, in accord with the predictions of percolation theory. More surprising is the appearance of a fractal time description of the dynamics of these clusters. This novel dynamics has recently been revealed by quasielastic light scattering from the density fluctuations that occur at the sol-gel transition. Since the relaxation of fluctuations in these branched polymer systems is self-similar, decay processes occur on all time scales (fractal time), and average decay times diverge. An interpretation of this observation will be presented that relies on a length-scale-dependent viscosity and the geometrical self-similarity of the sol-gel transition. The scattering theory is extended to the calculation of time- and frequency-dependent viscoelastic properties, as well as mechanical properties such as the shear modulus, steady state creep compliance, and viscosity. The viscoelastic predictions are found to be in good agreement with experimental data.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 180: Symposium A – Better Ceramics Through Chemistry IV , 1990 , 199
Copyright
Copyright © Materials Research Society 1990

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References

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