INTERNAL DYNAMICS AND ELASTICITY OF FRACTAL COLLOIDAL GELS

The dynamic structure factor of fractal colloidal gels is shown to exh ibit a stretched exponential decay to a finite plateau with an exponen t of about 0.7. The value of the plateau depends on both initial parti cle volume fraction phi(0) and scattering wave vector. We show that th is 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 mod ulus scales as G similar to phi(0)(3.9), in agreement with predictions , and with direct mechanical measurements.