Abstract
Rheological properties of silica sol-gel materials were determined using dynamic and steady shear flow measurements. During aging, transitions from Newtonian to shear thinning to thixotropic flow behavior were observed. Yield stresses were also observed during the later stages of aging. Measurements of storage and loss moduli indicated that dissipative (viscous) processes dominated during the Newtonian flow period. Elastic interactions became increasingly important during the shear thinning and thixotropic flow periods. These changes in rheological properties during aging reflected the structural evolution from a dilute sol (containing isolated, non-interacting polysilicate species) to the development of polysilicate structures with a three-dimensional network character. As observed by previous workers, silica sols prepared with acid catalyst and low water content exhibited “spinnability” after sufficient aging. Optimum spinnability was observed when the flow behavior was highly shear thinning, but not thixotropic. Freestanding fibers could be formed with sols having high polysilicate species concentration.
Published Version
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