AMPHIPHILIC ASSOCIATION STRUCTURES AND THE MICROEMULSION GEL METHOD FOR CERAMICS - INFLUENCE ON ORIGINAL PHASE REGIONS BY HYDROLYSIS AND CONDENSATION OF SILICON TETRAETHOXIDE

Silicon tetraethoxide was reacted with water in inverse micellar solution, lyotropic liquid crystals, and aqueous micellar solutions in the system water, sodium dodecyl sulfate, and pentanol to compare the silica gel formation in microemulsions or lyotropic liquid crystals with that in alcohol solutions. The reaction resulted in transparent gels in a limited region of the total phase diagram. The extension of the area that formed transparent gels after the reaction depended on the original silicon tetraethoxide (TEOS) concentration in such a manner that higher TEOS concentration gave a smaller region. The lyotropic liquid crystals were changed to isotropic gels in which the long-range order was lost. The reason for this structural change was the disordering influence of the ethanol formed during the hydrolysis reaction. The system changed from a pentanol solution to a water-in-oil (W/O) microemulsion with addition of surfactant, and a comparison could be made between conditions for gel formation in an alcoholic solution (pentanol + water) and in the W/O microemulsions (pentanol + surfactant + water). One essential difference was that the minimum water content to form a transparent gel was decisively lower in the microemulsion than in the solution. In fact gel formation in the microemulsions required no excess water to that necessary for the hydrolysis and condensation to take place.