DYNAMICS OF DENSITY-FLUCTUATIONS IN COLLOIDAL GELS

We use dynamic light scattering to measure the dynamic structure facto r of density fluctuations occurring in colloidal suspensions that have attained a quiescent state long after aggregation. We find a stretche d-exponential decay to a finite plateau. Our interpretation of the arr ested decay is that these systems are gels, i.e., systems possessing a finite elastic modulus G. We develop a theory for the internal elasti c modes of a fractal cluster and use it to derive G and the arrested, stretched-exponential behavior of colloidal gel dynamics. Good agreeme nt between experiment and theory is obtained.