CORRELATION AND ANTICORRELATION OF FRACTAL AGGREGATES - A MODEL FOR [[SPINODAL-TYPE]] AGGREGATION

We present a simple phenomenological model, based on mass conservation arguments, in order to describe aggregation in dense solutions. It ha s been previously shown that for diffusion-limited processes scattered intensity distributions exhibit a peak at q not equal 0 which grows i n time and moves to smaller and smaller q vectors. According to the mo del, each aggregate is surrounded by a depletion region whose size dep ends on the aggregation kinetics. The form factor for such a cluster s hould satisfy local mass conservation and hence exhibit a pronounced d epression at q = 0. The initial stages of aggregation, when the cluste rs are far apart, are accounted on the basis of a form factor alone. T he model shows good agreement with the data and also explains the expe rimental evidence that the peak does not appear in reaction-limited co nditions.