PHASE-SEPARATION IN SILICA SOL-GEL SYSTEM CONTAINING POLYACRYLIC-ACID .3. EFFECT OF CATALYTIC CONDITION

Phase separations of gelling solutions have been investigated in systems containing polyacrylic acid (HPAA) and alkoxysilane over the wide range of acid catalyst concentration. Gels with micrometer-range interconnected pores as previously reported in highly acidic systems have been obtained also in the pH condition higher than the isoelectric point of silica. Decreased acid catalyst concentration leads to both an increase and a decrease in gelation time depending on pH range, and average domain sizes in resultant gels decreased and increased, respectively. The differences in the weight- and number-average molecular weights of silica polymers at gel formation well explained the changes in the relations between reaction conditions and gel morphology with pH of the solution.