TIME-DEPENDENT POLYDISPERSITY OF GROWING COLLOIDAL AGGREGATES - PREDICTIONS FROM DYNAMIC LIGHT-SCATTERING THEORY

A theory is presented for the variation of the polydispersity index measured in a dynamic light scattering experiment performed on a suspension of aggregating colloidal particles. The analytical forms of this index, calculated by cumulants analysis, are described for various models of colloidal aggregation and numerical data is presented showing the dependence of the index, which contains contributions from the dynamics of internal aggregate motions, on aggregate size and shape for aggregates of different fractal structure. The value of this dynamic optical index as a diagnostic for aggregation pattern is discussed and the analysis is applied to the results of a light scattering study of the heat-induced aggregation of a globular protein.