SPECTROFLUOROMETRIC STUDIES OF WATER-CONTENT IN SOL-GEL PROCESSING OFTMOS

Measurements of water during acid-catalyzed sol-gel processing TMOS ha ve been carried out, The compositions of the initial sols correspond t o TMOS:H2O:MeOH = 1:n:3, where n = 1, 2, 4, 6, 8, 15 and 25. Pyranine, a sensitive water photoprobe enables monitoring fast water content ch anges. Initial decrease of water content due to hydrolysis of TMOS was fast for sols corresponding to(n greater than or equal to 15). A mini mum was reached in about I mill, For Ir less than or equal to 2 these changes were much slower, Subsequent increase of water was caused by c ondensation reactions. Changes of water content and mass which occur m ore rapidly after pin-holing the seals of cuvettes containing sols-gel s are caused by evaporation of pore liquid. The results of the numeric al fits of these changes suggest that this liquid consists mainly of H 2O and MeOH. (C) 1997 Elsevier Science B.V.