Dynamic Light Scattering of gold-filled polyorganosiloxane-μ-gel tracers in concentrated colloidal dispersions

Polyorganosiloxane microgels of average diameter 40 nm containing tiny gold clusters have been prepared as tracers to study single particle dynamics in concentrated colloidal dispersions by Dynamic Light Scattering (DLS). Those particles show light absorption at 525 nm, leading to an effective enhancement of Rayleigh scattering intensity in this wavelength regime. Unexpectedly, intensity time correlation functions with regular oscillation have been found in some DLS experiments. These oscillations are attributed to regular convective flux of tracer and host particles caused by light absorption of the tracer particles. In this paper, the oscillation phenomenon is discussed in dependence of scattering angle, laser power and laser wavelength. Using laser light of wavelength 647 nm far from the absorption maximum of the gold tracers at low light intensity, exponentially decaying correlation functions without oscillations have been found. Therefore, the self diffusion coefficient of the tracer particles could ...