Measurement of heteroaggregation rate constants by simultaneous static and dynamic light scattering.

The early stages of the heteroaggregation (or heterocoagulation) of latex particles were probed by time resolved simultaneous static and dynamic light scattering (SSDLS). We show that the heteroaggregation rate constant and the apparent hydrodynamic radius of the dimer can be obtained by analyzing the SSDLS data without the need to invoke the optical form factors for the doublets. A similar approach was proposed earlier for homoaggregation. The validity of the present approach was tested by investigating heteroaggregation between sulfate and amidine latex particles of different size, and similar data for smaller particles, which were previously analyzed in terms of the Rayleigh-Debye-Gans (RDG) theory. In this case, the presently obtained rate constants were found to be in excellent agreement with the results based on RDG. The present technique is particularly interesting for larger particles, where RDG cannot be applied, or to particles of more complex shapes, where the optical form factor cannot be easily evaluated.