Anomalous dynamic light scattering from solutions of light absorbing polymers

Dynamic light scattering data from highly absorbing solutions exhibit inten sity-intensity correlation functions characterized by a sum of exponential decays superposed with an oscillatory term. Anew analytical treatment is pr oposed, which explains this behavior as arising from the heterodyning of sc attered light from two distinct species in convective motion. Similar data were obtained both for solutions of polyaniline (PANI) as well as for a com plex of cytochrome c and cytochrome c peroxidase in phosphate buffer. This suggests the generality of the phenomenon for polymers that both absorb lig ht and aggregate, such as proteins and conducting polymers. Effects of lase r power on convection, thermal lensing, and coning of the beam and concentr ation of absorbing species have been considered. The presence or absence of the oscillations is shown to be a sensitive indication of aggregation.