| Bicontinuous microemulsions, stabilized with didodecyldimethylammonium bromide, are used as templates for the synthesis of microporous materials. Bicontinuous microemulsions are formed with monomer either in the oleic domain or in the hydrophilic domain. Polymerization of the monomer results in a solid material that retains the original structure of the bicontinuous microemulsion. Extraction of the surfactant and drying of the microporous polymer alter the microstructure of the material.;In a second set of experiments, bicontinuous microemulsions based on methyl methacrylate were polymerized to form white solids, indicating new structures on the order of the wavelength of light. SAXS experiments indicate no change in the characteristic size of the microemulsion (17 A) during polymerization but show the appearance of polymer particles at least an order of magnitude larger (500A). These particles probably form because of phase separation. Subsequent processing retains the larger polymer structure but destroys the microemulsion structure, resulting in microporous materials with moderate surface areas (75 m;For one set of experiments, bicontinuous microemulsions based on partially hydrolyzed tetramethoxysilane sols were polymerized to form transparent silica gels. When vacuum dried, the gels made as microemulsions contain about twice the specific surface area of conventionally prepared vacuum dried gels. Pore size analysis of supercritically dried microemulsion-based gels indicate a binodal distribution of pores. Small 50 A pores, typical of conventional silica gels, coexist with larger 200A pores, generated in the microemulsion. Small angle X-ray scattering (SAXS) data show that the characteristic pore size grows with the square root of time, suggesting diffusion-controlled gelation. |
