Homodyne dynamic light scattering in supramolecular polymer solutions: anomalous oscillations in intensity correlation function

Dilute solutions of electronically active molecules capable of irradiation-driven supramolecular self-assembly are studied by dynamic light scattering. We detect unusual well-defined oscillations in the long time range of the homodyne intensity correlation function for all solutions that were irradiated with white light prior to the measurements. The oscillation effect is attributed to the local laser-induced heating of the samples due to strongly enhanced absorption manifested by the supramolecular filaments. It is found that the oscillation frequency depends on the irradiation time, solution concentration, and the incident laser power, but is independent of the scattering angle. These observations are explained with a semi-quantitative theory relating the oscillation effect to thermo-gravitational convection flows generated by laser beam. The results suggest that the presence of such homodyne oscillations could be a sensitive probe for aggregation in many complex systems.