What factors control the structure of silica aerogels
Conference
·
OSTI ID:6791432
By manipulating polymerization conditions in solution precursors, it is possible to control the structure of silica aerogels. Porosity varies from grain-like to polymer-like. When produced from alkoxides, pH is the dominant factor that determines structure. Under strongly basic conditions (pH > 12) compact colloidal particles are observed. In the range pH = 8--12, particles of varying surface roughness result. In the neutral range, polymerization is self-limiting, producing polymers with the geometry of percolation clusters at threshold. Under acidic conditions, highly ramified branched polymers are realized. Using the concept of fractal geometry, different growth processes are identified that account for the observed structure. These processes include Eden growth (reaction-limited monomer-cluster aggregation) under basic conditions and the cluster-cluster analogue under acidic conditions. Kinetic percolation is postulated for the neutral regime. 23 refs., 5 figs.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 6791432
- Report Number(s):
- SAND-88-1636C; CONF-8809131-2; ON: DE89005599
- Country of Publication:
- United States
- Language:
- English
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