Low density silica gels and solvent permeability

The aerogel-like properties of rite previously reported lyosils prepared by base catalyzed TMOS were further improved by using partially condensed TMOS followed by curing in TEOS. The cur ed and dried gels showed lower density: < 0.3 g ml(-1), higher BET surface area: 860 m(2) g(-1) and larger pore size. The effectiveness of the curing media were tested by measuring permeability and wettability of the liquid media. The permeability values varied over time with a similar trend for methanol, ethanol and octanol which exhibited decreasing permeability attributable to re-esterification. Similar trends are grouped together for TEOS and water which exhibited increasing permeability up to similar to 10 h due to pore coarsening and decreasing values beyond similar to 10 h attributable to the chemisorption of TEOS and silanol condensation with water. The curability was consistent more with wettability than permeability of the liquids tested. (C) 1997 Elsevier Science Limited.