SPINODAL DYNAMICS IN CLUSTER AGGREGATION

We report small angle static light scattering measurements on colloida l aggregation at high monomer volume fractions. The structure factor S (q) exhibits a pronounced maximum at a finite wave vector q, at any st age during the aggregation reaction. In the later stages the structure factor scales according to a universal law similar to that of spinoda l decomposition dynamics: S(q/q(m)) = q(m)-d) F(q/q(m)). At variance w ith spinodal decomposition, where d = 3, we find d = d(f), the fractal dimension of colloidal clusters. The aggregation stops when the peak position reaches a certain value q which depends on the monomer conce ntration. The terminal stage occurs when all the sample is filled with close packing fractal clusters of size R is-proportional-to 1/q