Insight into the structure of polymer-silica nano-composites prepared by vapor-phase

Using a new synthesis technique, in which mesoporous Amberlite XAD7HP resin beads swollen with TEOS were exposed to vapors of either (H2O+HCl) or (H2O+NH3), we obtained smooth, porous, mechanically stable silica gel spheres after burning out the sacrificial organic template. Combined N2 sorption, SEM, TEM, (29)Si NMR, and Raman measurements were used to characterize the physical properties and molecular structures of the intermediate and final gels. Our atomically resolved TEM pictures provide the first visual demonstration of the presence of 3 to 6 member siloxane rings predicted by our Raman studies and other indirect methods. It is demonstrated that the physical appearance, morphology and porosity of the acid and base set gels are different from each other and also from those silica gels that were earlier polymerized from TEOS or Na-silicate saturated Amberlite XAD7HP with aqueous NH4OH or HCl solutions in liquid phase. We show that the different physical properties of the vapor-phase set gels are associated with different gelling rates at acidic and basic conditions, which generates molecular differences both in the intermediate and the final products.