PHYSICAL-PROPERTIES OF SILICA-GELS AND AEROGELS PREPARED WITH NEW POLYMERIC PRECURSORS

Silica aerogels were made by sol-gel techniques using industrial silic on derivatives (polyethoxydisiloxanes, PEDS-P-x) obtained by the react ion of tetraethoxysilane (TEOS) and water (water to TEOS molar fractio n, n, ranging between 0.8 and 1.8) in the presence of sulfuric acid. F or each type of precursor, sol-gel reactions were performed under acid ic, neutral or basic conditions, in alcohols (methanol or ethanol) or acetone. The gels were dried under hypercritical conditions with respe ct to alcohol or CO2 leading to monolithic organic-dried aerogels and CO2-dried aerogels. Gels were characterized by the gelling time, t(g), and the shrinkage during aging, tau(s), and the aerogels by their app arent density, d(a), their global shrinkage, tau(g), and their specifi c surface area, S-BET. It was shown that these values are strongly cor related. In most cases, t(g) decreases whereas tau(s) increases when n varies between 0.8 and 1.8. This study shows that the use of these ne w precursors allows synthesis of a very large variety of monolithic tr ansparent aerogels.