Sol–Gel Synthesis and Characterization of Microporous Silica Membranes I: SAXS Study on the Growth of Polymeric Structures

series (11) will present the synthesis chemistry of silica sols Silica-based microporous membranes can be successfully proto make unsupported membranes with predictable pore size/ cessed by sol–gel techniques. However tailor making of such memporosity. This article aims to give a detailed account of small branes is still not possible because of the unavailability of systemangle X-ray scattering of silica sols and further calculations atic studies on membrane oriented sol processing and characterizaof fractal dimensions and monomer/polymer sizes. Fractal tion. The present series of papers aims to give a systematic dimensions are compared with typical simulated aggregates understanding of silica polymeric growth, synthesis chemistry, and from literature (12, 13). finally membrane characterization. Polymeric silica sols were preSynthesis of silica polymers by the sol–gel process inpared by hydrolysis and condensation of alkoxide. The fractal volve the hydrolysis and condensation reactions of starting growth of the polymers during sol–gel transition is monitored with the help of small angle X-ray scattering. Fractal dimensions and alkoxides. radii of gyration of sols and gels with different synthesis chemistry are compared. The type of aggregation mechanism prevailing in these systems is identified as cluster–cluster aggregation with reachydrolysis r GSi{OR / H2O S GSi{OH / ROH R esterification [1] tion limitations during synthesis and reaction and diffusion limitations during aging. q 1996 Academic Press, Inc.