OSCILLATING TIME-CORRELATION FUNCTIONS FROM DYNAMIC LIGHT-SCATTERING OF GOLD-LABELED TRACERS

Nanoparticles containing small gold clusters as labels have been used to study tracer diffusion in concentrated colloidal dispersions by dyn amic light scattering. Our samples consisted of a small amount of gold tracers in a concentrated dispersion of nonlabeled matrix particles o f similar size. Unexpectedly, the intensity time correlation functions showed oscillations. The unusual signal has been attributed to convec tion which may be caused by light absorption of the tracer particles, creating a thermal gradient within the sample. However, the origin of the oscillations in our homodyne light scattering experiment is still not perfectly understood. Here, we present a qualitative discussion co ncerning the dependency of oscillations both on laser light power and the concentration of matrix particles. (C) 1998 American Institute of Physics.