Fractal structure and fractal time in silica sol-gels

Conference · Mon Jan 01 04:00:00 EST 1990

DOI:https://doi.org/10.1557/PROC-180-199· OSTI ID:6786109

Martin, J E; Wilcoxon, J

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. 28 refs., 1 fig.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA)
• Sponsoring Organization: DOE/DP
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6786109
• Report Number(s): SAND-89-2795C; CONF-900466--68; ON: DE90013197
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360203 -- Ceramics
Cermets
& Refractories-- Mechanical Properties
CHALCOGENIDES
COLLOIDS
DISPERSIONS
ELASTICITY
FRACTALS
GELS
MECHANICAL PROPERTIES
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
POLYMERS
SHEAR PROPERTIES
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SOL-GEL PROCESS
SOLID CLUSTERS
TENSILE PROPERTIES
VISCOSITY