THE RHEOLOGY OF SILICA SOLS DURING THE GELATION PROCESS

Various silica sols were prepared from a mixture of TEOS, ethanol and water by changing the water content and the types of catalysts. All sols in the closed system showed flow behaviors from Newtonian to thixotropic fluid via pseudoplastic fluid during the sol-gel transition. In the open system, the acidic sol prepared from a solution with a low water content exhibited a highly viscous Newtonian behavior (about 100 Poise) and a spinnability. By contrast, the sol derived from an acidic solution with a high water content behaved as a thixotropic non-Newtonian fluid and showed no spinnability even at a high viscosity. This thixotropic behavior may be due to the formation of network structure of particles. The network structure which is broken under shear flow results in no spinnability. Only the highly viscous sol made from a concentrated acidic solution with a low water content may be suitable to fiber drawing, because it consists of one dimensional polymers.