The dynamic structure factor of fractal colloidal gels is shown to exhibit a stretched exponential decay to a finite plateau with an exponent of about 0.7. The value of the plateau depends on both initial particle volume fraction ${\phi }_0$ and scattering wave vector. We show that this behavior results from the contribution of internal elastic modes of many length scales, and present a model which accounts for the data. From the observed plateau we determine that the very small elastic modulus scales as $G\sim {\phi }_0^{3.9}$, in agreement with predictions, and with direct mechanical measurements.

• Received 22 May 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.778