DYNAMIC VISCOELASTIC CHARACTERIZATION OF SOL-GEL REACTIONS

The evolution of viscoelasticity in a tetraethoxysilane gel system has been measured starting immediately following mixing and proceeding through the macroscopic gel point. The storage and loss dynamic shear moduli, Gʹ(ω) and Gʺ(ω), were determined with the multiple-lumped resonator instrument as a function of time for frequencies in the range 104-6200 Hz. The water to silane monomer ratio maintained at 6:1, while the concentration of HCl acid catalyst was varied in separate measurements. The scaling exponent for the variation of Gʹ and Gʺ with frequency at the gel point is Δ = 0.72 ± 0.02. Reaction time dependent shift factors for the frequency and modulus are determined which allow creation of a modulus-frequency master curve. The scaling of these shift factors with the extent of reaction yields critical exponents for zero shear viscosity, elastic modulus, and cluster radius. © 1990, American Chemical Society. All rights reserved.